Tonnage-app-IMCO/main.go

package main

import (
	"bytes"
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"log"
	"math"
	"net/http"
	"os"
	"os/signal"
	"path/filepath"
	"reflect"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"syscall"
	"time"

	mqtt "github.com/eclipse/paho.mqtt.golang"
	"github.com/fsnotify/fsnotify"
	_ "github.com/mattn/go-sqlite3"
	"github.com/robinson/gos7"
	"gopkg.in/yaml.v3"
)

const version = "1.0.0"

// ---------------------------------------------------------------------------
// Config structs
// ---------------------------------------------------------------------------

type Config struct {
	Server     ServerConfig     `yaml:"server"`
	PLC        PLCConfig        `yaml:"plc"`
	Thresholds ThresholdsConfig `yaml:"thresholds"`
	Trend      TrendConfig      `yaml:"trend"`
	Press      PressConfig      `yaml:"press"`
	UI         UIConfig         `yaml:"ui"`
	Modules    ModulesConfig    `yaml:"modules"`
	DB         DBConfig         `yaml:"db"`
	MQTT       MQTTConfig       `yaml:"mqtt"`
	License    LicenseConfig    `yaml:"license"`
}

type ServerConfig struct {
	ListenAddr string `yaml:"listen_addr"`
}

type PLCConfig struct {
	IP                string `yaml:"ip"`
	DBNum             int    `yaml:"db_num"`
	Rack              int    `yaml:"rack"`
	Slot              int    `yaml:"slot"`
	PollMs            int    `yaml:"poll_ms"`
	ConnectTimeoutSec int    `yaml:"connect_timeout_sec"`
	IdleTimeoutSec    int    `yaml:"idle_timeout_sec"`
	ReconnectDelaySec int    `yaml:"reconnect_delay_sec"`
}

type ThresholdsConfig struct {
	WarningPercent           float64 `yaml:"warning_percent"`
	CriticalPercent          float64 `yaml:"critical_percent"`
	GaugeMaxPercent          float64 `yaml:"gauge_max_percent"`
	ImbalanceWarningPercent  float64 `yaml:"imbalance_warning_percent"`
	ImbalanceCriticalPercent float64 `yaml:"imbalance_critical_percent"`

	LegacyWarningKn  float64 `yaml:"warning_kn,omitempty"`
	LegacyCriticalKn float64 `yaml:"critical_kn,omitempty"`
	LegacyMaxKn      float64 `yaml:"max_kn,omitempty"`
}

type TrendConfig struct {
	Minutes int `yaml:"minutes"`
}

type PressConfig struct {
	MaxTonnage       float64 `yaml:"MAX_TONNAGE"`
	LegacyMaxTonnage float64 `yaml:"max_tonnage,omitempty"`
}

type UIConfig struct {
	Title      string `yaml:"title"`
	Subtitle   string `yaml:"subtitle"`
	LeftLabel  string `yaml:"left_label"`
	RightLabel string `yaml:"right_label"`
	UnitForce  string `yaml:"unit_force"`
	UnitPct    string `yaml:"unit_percent"`
}

type ModulesConfig struct {
	ShowHeaderControls *bool `yaml:"show_header_controls,omitempty"`
	ShowVerdict        *bool `yaml:"show_verdict,omitempty"`
	ShowSummaryBar     *bool `yaml:"show_summary_bar,omitempty"`
	ShowOverview       *bool `yaml:"show_overview,omitempty"`
	ShowIntelligence   *bool `yaml:"show_intelligence,omitempty"`
	ShowAlarmTimeline  *bool `yaml:"show_alarm_timeline,omitempty"`
	ShowGauges         *bool `yaml:"show_gauges,omitempty"`
	ShowGaugeDigital   *bool `yaml:"show_gauge_digital,omitempty"`
	ShowTrendChart     *bool `yaml:"show_trend_chart,omitempty"`
}

type DBConfig struct {
	Path              string `yaml:"path"`
	BusyTimeoutMs     int    `yaml:"busy_timeout_ms"`
	BatchSize         int    `yaml:"batch_size"`
	FlushIntervalMs   int    `yaml:"flush_interval_ms"`
	RetentionDays     int    `yaml:"retention_days"`
	MaxChartPoints    int    `yaml:"max_chart_points"`
	WriterQueueSize   int    `yaml:"writer_queue_size"`
	AlarmQueueSize    int    `yaml:"alarm_queue_size"`
	CheckpointPages   int    `yaml:"checkpoint_pages"`
	CleanupIntervalHr int    `yaml:"cleanup_interval_hours"`
}

type MQTTConfig struct {
	Enabled           bool   `yaml:"enabled"`
	Broker            string `yaml:"broker"`
	ClientID          string `yaml:"client_id"`
	Username          string `yaml:"username"`
	Password          string `yaml:"password"`
	TopicPrefix       string `yaml:"topic_prefix"`
	QoS               int    `yaml:"qos"`
	Retain            bool   `yaml:"retain"`
	AutoPublish       bool   `yaml:"auto_publish"`
	PublishIntervalMs int    `yaml:"publish_interval_ms"`
	ConnectTimeoutSec int    `yaml:"connect_timeout_sec"`
	ReconnectDelaySec int    `yaml:"reconnect_delay_sec"`
}

// ---------------------------------------------------------------------------
// Config helpers
// ---------------------------------------------------------------------------

func boolPtr(v bool) *bool { return &v }

func boolValue(v *bool, def bool) bool {
	if v == nil {
		return def
	}
	return *v
}

func defaultConfig() Config {
	return Config{
		Server: ServerConfig{ListenAddr: ":8080"},
		PLC: PLCConfig{
			IP:                "192.168.0.1",
			DBNum:             1001,
			Rack:              0,
			Slot:              1,
			PollMs:            500,
			ConnectTimeoutSec: 5,
			IdleTimeoutSec:    5,
			ReconnectDelaySec: 5,
		},
		Thresholds: ThresholdsConfig{
			WarningPercent:           80,
			CriticalPercent:          95,
			GaugeMaxPercent:          130,
			ImbalanceWarningPercent:  10,
			ImbalanceCriticalPercent: 20,
		},
		Trend: TrendConfig{Minutes: 5},
		Press: PressConfig{MaxTonnage: 64},
		UI: UIConfig{
			Title:      "Force Monitor",
			Subtitle:   "Siemens S7-1215C • Piezo peak/stroke input • PLC values in % • kN calculated from MAX_TONNAGE",
			LeftLabel:  "LEVI STEBER",
			RightLabel: "DESNI STEBER",
			UnitForce:  "kN",
			UnitPct:    "%",
		},
		Modules: ModulesConfig{
			ShowHeaderControls: boolPtr(true),
			ShowVerdict:        boolPtr(true),
			ShowSummaryBar:     boolPtr(true),
			ShowOverview:       boolPtr(true),
			ShowIntelligence:   boolPtr(true),
			ShowAlarmTimeline:  boolPtr(true),
			ShowGauges:         boolPtr(true),
			ShowGaugeDigital:   boolPtr(false),
			ShowTrendChart:     boolPtr(true),
		},
		DB: DBConfig{
			Path:              "force_monitor.db",
			BusyTimeoutMs:     5000,
			BatchSize:         32,
			FlushIntervalMs:   1000,
			RetentionDays:     30,
			MaxChartPoints:    2000,
			WriterQueueSize:   4096,
			AlarmQueueSize:    512,
			CheckpointPages:   1000,
			CleanupIntervalHr: 6,
		},
		MQTT: MQTTConfig{
			Enabled:           false,
			Broker:            "tcp://localhost:1883",
			ClientID:          "force_monitor",
			TopicPrefix:       "force_monitor",
			QoS:               1,
			Retain:            false,
			AutoPublish:       true,
			PublishIntervalMs: 1000,
			ConnectTimeoutSec: 10,
			ReconnectDelaySec: 5,
		},
		License: LicenseConfig{
			Enabled:           true,
			TrialDays:         7,
			RequireAfterTrial: true,
			DataDir:           "license",
			PublicKeyBase64:   "",
			ProductCode:       "force_monitor",
		},
	}
}

func setIfZeroF(dst *float64, def float64) {
	if *dst <= 0 {
		*dst = def
	}
}

func setIfZeroI(dst *int, def int) {
	if *dst <= 0 {
		*dst = def
	}
}

func setIfEmpty(dst *string, def string) {
	if strings.TrimSpace(*dst) == "" {
		*dst = def
	}
}

func setIfNilBool(dst **bool, def bool) {
	if *dst == nil {
		v := def
		*dst = &v
	}
}

func normalizeConfig(cfg *Config) {
	def := defaultConfig()

	setIfEmpty(&cfg.Server.ListenAddr, def.Server.ListenAddr)

	setIfEmpty(&cfg.PLC.IP, def.PLC.IP)
	setIfZeroI(&cfg.PLC.DBNum, def.PLC.DBNum)
	setIfZeroI(&cfg.PLC.Rack, def.PLC.Rack)
	setIfZeroI(&cfg.PLC.Slot, def.PLC.Slot)
	setIfZeroI(&cfg.PLC.PollMs, def.PLC.PollMs)
	setIfZeroI(&cfg.PLC.ConnectTimeoutSec, def.PLC.ConnectTimeoutSec)
	setIfZeroI(&cfg.PLC.IdleTimeoutSec, def.PLC.IdleTimeoutSec)
	setIfZeroI(&cfg.PLC.ReconnectDelaySec, def.PLC.ReconnectDelaySec)

	if cfg.Thresholds.WarningPercent <= 0 && cfg.Thresholds.LegacyWarningKn > 0 {
		cfg.Thresholds.WarningPercent = cfg.Thresholds.LegacyWarningKn
	}
	if cfg.Thresholds.CriticalPercent <= 0 && cfg.Thresholds.LegacyCriticalKn > 0 {
		cfg.Thresholds.CriticalPercent = cfg.Thresholds.LegacyCriticalKn
	}
	if cfg.Thresholds.GaugeMaxPercent <= 0 && cfg.Thresholds.LegacyMaxKn > 0 {
		cfg.Thresholds.GaugeMaxPercent = cfg.Thresholds.LegacyMaxKn
	}

	setIfZeroF(&cfg.Thresholds.WarningPercent, def.Thresholds.WarningPercent)
	setIfZeroF(&cfg.Thresholds.CriticalPercent, def.Thresholds.CriticalPercent)
	setIfZeroF(&cfg.Thresholds.GaugeMaxPercent, def.Thresholds.GaugeMaxPercent)
	setIfZeroF(&cfg.Thresholds.ImbalanceWarningPercent, def.Thresholds.ImbalanceWarningPercent)
	setIfZeroF(&cfg.Thresholds.ImbalanceCriticalPercent, def.Thresholds.ImbalanceCriticalPercent)

	if cfg.Thresholds.ImbalanceCriticalPercent < cfg.Thresholds.ImbalanceWarningPercent {
		cfg.Thresholds.ImbalanceCriticalPercent = cfg.Thresholds.ImbalanceWarningPercent
	}

	setIfZeroI(&cfg.Trend.Minutes, def.Trend.Minutes)

	if cfg.Press.MaxTonnage <= 0 && cfg.Press.LegacyMaxTonnage > 0 {
		cfg.Press.MaxTonnage = cfg.Press.LegacyMaxTonnage
	}
	setIfZeroF(&cfg.Press.MaxTonnage, def.Press.MaxTonnage)

	setIfEmpty(&cfg.UI.Title, def.UI.Title)
	setIfEmpty(&cfg.UI.Subtitle, def.UI.Subtitle)
	setIfEmpty(&cfg.UI.LeftLabel, def.UI.LeftLabel)
	setIfEmpty(&cfg.UI.RightLabel, def.UI.RightLabel)
	setIfEmpty(&cfg.UI.UnitForce, def.UI.UnitForce)
	setIfEmpty(&cfg.UI.UnitPct, def.UI.UnitPct)

	setIfNilBool(&cfg.Modules.ShowHeaderControls, boolValue(def.Modules.ShowHeaderControls, true))
	setIfNilBool(&cfg.Modules.ShowVerdict, boolValue(def.Modules.ShowVerdict, true))
	setIfNilBool(&cfg.Modules.ShowSummaryBar, boolValue(def.Modules.ShowSummaryBar, true))
	setIfNilBool(&cfg.Modules.ShowOverview, boolValue(def.Modules.ShowOverview, true))
	setIfNilBool(&cfg.Modules.ShowIntelligence, boolValue(def.Modules.ShowIntelligence, true))
	setIfNilBool(&cfg.Modules.ShowAlarmTimeline, boolValue(def.Modules.ShowAlarmTimeline, true))
	setIfNilBool(&cfg.Modules.ShowGauges, boolValue(def.Modules.ShowGauges, true))
	setIfNilBool(&cfg.Modules.ShowGaugeDigital, boolValue(def.Modules.ShowGaugeDigital, false))
	setIfNilBool(&cfg.Modules.ShowTrendChart, boolValue(def.Modules.ShowTrendChart, true))

	setIfEmpty(&cfg.DB.Path, def.DB.Path)
	setIfZeroI(&cfg.DB.BusyTimeoutMs, def.DB.BusyTimeoutMs)
	setIfZeroI(&cfg.DB.BatchSize, def.DB.BatchSize)
	setIfZeroI(&cfg.DB.FlushIntervalMs, def.DB.FlushIntervalMs)
	setIfZeroI(&cfg.DB.RetentionDays, def.DB.RetentionDays)
	setIfZeroI(&cfg.DB.MaxChartPoints, def.DB.MaxChartPoints)
	setIfZeroI(&cfg.DB.WriterQueueSize, def.DB.WriterQueueSize)
	setIfZeroI(&cfg.DB.AlarmQueueSize, def.DB.AlarmQueueSize)
	setIfZeroI(&cfg.DB.CheckpointPages, def.DB.CheckpointPages)
	setIfZeroI(&cfg.DB.CleanupIntervalHr, def.DB.CleanupIntervalHr)

	if cfg.MQTT.Enabled {
		setIfEmpty(&cfg.MQTT.Broker, def.MQTT.Broker)
		setIfEmpty(&cfg.MQTT.ClientID, def.MQTT.ClientID)
		setIfEmpty(&cfg.MQTT.TopicPrefix, def.MQTT.TopicPrefix)
		if cfg.MQTT.QoS < 0 || cfg.MQTT.QoS > 2 {
			cfg.MQTT.QoS = def.MQTT.QoS
		}
		setIfZeroI(&cfg.MQTT.PublishIntervalMs, def.MQTT.PublishIntervalMs)
		setIfZeroI(&cfg.MQTT.ConnectTimeoutSec, def.MQTT.ConnectTimeoutSec)
		setIfZeroI(&cfg.MQTT.ReconnectDelaySec, def.MQTT.ReconnectDelaySec)
	}

	if !cfg.License.Enabled {
		// keep defaults when disabled, but still normalize product code if provided
	}
	setIfZeroI(&cfg.License.TrialDays, def.License.TrialDays)
	setIfEmpty(&cfg.License.DataDir, def.License.DataDir)
	setIfEmpty(&cfg.License.ProductCode, def.License.ProductCode)
}

func loadConfigStrict(configPath string) (Config, error) {
	cfg := defaultConfig()

	data, err := os.ReadFile(configPath)
	if err != nil {
		return cfg, fmt.Errorf("failed to read config file: %w", err)
	}

	dec := yaml.NewDecoder(bytes.NewReader(data))
	dec.KnownFields(true)
	if err := dec.Decode(&cfg); err != nil {
		return cfg, fmt.Errorf("failed to parse config file: %w", err)
	}

	normalizeConfig(&cfg)
	return cfg, nil
}

func loadOrCreateConfig(configPath string) (Config, error) {
	cfg := defaultConfig()

	_, err := os.Stat(configPath)
	if errors.Is(err, os.ErrNotExist) {
		data, marshalErr := yaml.Marshal(&cfg)
		if marshalErr != nil {
			return cfg, fmt.Errorf("failed to marshal default config: %w", marshalErr)
		}
		if writeErr := os.WriteFile(configPath, data, 0644); writeErr != nil {
			return cfg, fmt.Errorf("failed to create config file: %w", writeErr)
		}
		log.Printf("config file not found, created default config: %s", configPath)
		return cfg, nil
	}
	if err != nil {
		return cfg, fmt.Errorf("failed to stat config file: %w", err)
	}

	return loadConfigStrict(configPath)
}

func validateConfig(cfg Config) error {
	if cfg.Thresholds.WarningPercent <= 0 {
		return fmt.Errorf("thresholds.warning_percent must be > 0")
	}
	if cfg.Thresholds.CriticalPercent < cfg.Thresholds.WarningPercent {
		return fmt.Errorf("thresholds.critical_percent must be >= thresholds.warning_percent")
	}
	if cfg.Thresholds.GaugeMaxPercent < cfg.Thresholds.CriticalPercent {
		return fmt.Errorf("thresholds.gauge_max_percent must be >= thresholds.critical_percent")
	}
	if cfg.Thresholds.ImbalanceWarningPercent <= 0 {
		return fmt.Errorf("thresholds.imbalance_warning_percent must be > 0")
	}
	if cfg.Thresholds.ImbalanceCriticalPercent < cfg.Thresholds.ImbalanceWarningPercent {
		return fmt.Errorf("thresholds.imbalance_critical_percent must be >= thresholds.imbalance_warning_percent")
	}
	if cfg.Trend.Minutes <= 0 {
		return fmt.Errorf("trend.minutes must be > 0")
	}
	if cfg.Press.MaxTonnage <= 0 {
		return fmt.Errorf("press.MAX_TONNAGE must be > 0")
	}
	if cfg.MQTT.Enabled && strings.TrimSpace(cfg.MQTT.Broker) == "" {
		return fmt.Errorf("mqtt.broker must be set when mqtt.enabled is true")
	}
	if cfg.MQTT.Enabled && strings.TrimSpace(cfg.MQTT.ClientID) == "" {
		return fmt.Errorf("mqtt.client_id must be set when mqtt.enabled is true")
	}
	return nil
}

// ---------------------------------------------------------------------------
// Domain types
// ---------------------------------------------------------------------------

type Sample struct {
	TS               time.Time
	SilaLPct         float32
	SilaRPct         float32
	SilaLKN          float32
	SilaRKN          float32
	SumPercent       float32
	SumKN            float32
	ImbalancePercent float32
	BiasPercent      float32
}

type AlarmEvent struct {
	TS       time.Time
	Severity string
	Source   string
	Code     string
	State    string
	Message  string
	Value    float64
	Limit    float64
}

type AppState struct {
	sync.RWMutex
	Connected        bool
	SilaL            float32
	SilaR            float32
	SilaLkN          float32
	SilaRkN          float32
	SumPercent       float32
	SumkN            float32
	ImbalancePercent float32
	BiasPercent      float32
	LastUpdate       time.Time
	DroppedSamples   uint64
	DroppedEvents    uint64
}

type APIState struct {
	Connected        bool    `json:"connected"`
	SilaL            float32 `json:"sila_l"`
	SilaR            float32 `json:"sila_r"`
	SilaLkN          float32 `json:"sila_l_kn"`
	SilaRkN          float32 `json:"sila_r_kn"`
	SumPercent       float32 `json:"sum_percent"`
	SumkN            float32 `json:"sum_kn"`
	ImbalancePercent float32 `json:"imbalance_percent"`
	BiasPercent      float32 `json:"bias_percent"`
	LastUpdate       string  `json:"last_update"`
	DroppedSamples   uint64  `json:"dropped_samples"`
	DroppedEvents    uint64  `json:"dropped_events"`
}

type HistoryPoint struct {
	Time  string  `json:"time"`
	SilaL float32 `json:"sila_l"`
	SilaR float32 `json:"sila_r"`
}

type HistoryResponse struct {
	Window string         `json:"window"`
	Points []HistoryPoint `json:"points"`
}

type TrendResponse struct {
	Window             string  `json:"window"`
	AvgPeak5m          float32 `json:"avg_peak_5m"`
	AvgPeak1h          float32 `json:"avg_peak_1h"`
	AvgImbalance5m     float32 `json:"avg_imbalance_5m"`
	AvgImbalance1h     float32 `json:"avg_imbalance_1h"`
	ForceDeltaPct      float32 `json:"force_delta_pct"`
	ImbalanceDeltaPct  float32 `json:"imbalance_delta_pct"`
	ForceDirection     string  `json:"force_direction"`
	ImbalanceDirection string  `json:"imbalance_direction"`
	ProcessStability   string  `json:"process_stability"`
	StabilityReason    string  `json:"stability_reason"`
	ForceStdDev        float32 `json:"force_stddev"`
	ImbalanceStdDev    float32 `json:"imbalance_stddev"`
	SampleCount        int     `json:"sample_count"`
	OldHalfCount       int     `json:"old_half_count"`
	NewHalfCount       int     `json:"new_half_count"`
}

type AlarmEventAPI struct {
	Time     string  `json:"time"`
	Severity string  `json:"severity"`
	Source   string  `json:"source"`
	State    string  `json:"state"`
	Message  string  `json:"message"`
	Value    float64 `json:"value"`
	Limit    float64 `json:"limit"`
}

type AlarmResponse struct {
	Events []AlarmEventAPI `json:"events"`
}

type PublicConfigResponse struct {
	Version     string           `json:"version"`
	UIRevision  uint64           `json:"ui_revision"`
	UI          UIConfig         `json:"ui"`
	Thresholds  ThresholdsConfig `json:"thresholds"`
	Trend       TrendConfig      `json:"trend"`
	Press       PressConfig      `json:"press"`
	Modules     ModulesConfig    `json:"modules"`
	LicenseHint LicenseHint      `json:"license"`
}

type LicenseHint struct {
	Enabled   bool `json:"enabled"`
	TrialDays int  `json:"trial_days"`
}

type NumericStats struct {
	Avg   float64
	AvgSq float64
	Min   float64
	Max   float64
	Count int
}

func (s NumericStats) StdDev() float64 {
	if s.Count <= 1 {
		return 0
	}
	v := s.AvgSq - (s.Avg * s.Avg)
	if v < 0 {
		v = 0
	}
	return math.Sqrt(v)
}

type AlarmTracker struct {
	sync.Mutex
	PLCKnown     bool
	PLCConnected bool
	LeftZone     string
	RightZone    string
	ImbZone      string
	LastChange   map[string]time.Time
}

// ---------------------------------------------------------------------------
// MQTT types
// ---------------------------------------------------------------------------

type MQTTReceivedMsg struct {
	Topic    string `json:"topic"`
	Payload  string `json:"payload"`
	Retained bool   `json:"retained"`
	Time     string `json:"time"`
}

type MQTTPublishRequest struct {
	Topic   string `json:"topic"`
	Payload string `json:"payload"`
	QoS     int    `json:"qos"`
	Retain  bool   `json:"retain"`
}

type MQTTSubscribeRequest struct {
	Topic string `json:"topic"`
	QoS   int    `json:"qos"`
}

type MQTTStatusResponse struct {
	Enabled     bool     `json:"enabled"`
	Connected   bool     `json:"connected"`
	Broker      string   `json:"broker"`
	ClientID    string   `json:"client_id"`
	TopicPrefix string   `json:"topic_prefix"`
	Subscribed  []string `json:"subscribed"`
	LastError   string   `json:"last_error,omitempty"`
}

type mqttManager struct {
	mu         sync.RWMutex
	client     mqtt.Client
	connected  bool
	lastErr    string
	broker     string
	clientID   string
	prefix     string
	msgHistory []MQTTReceivedMsg
	msgMax     int
	subs       map[string]byte
}

// ---------------------------------------------------------------------------
// Package-level singletons
// ---------------------------------------------------------------------------

var (
	cfg      Config
	cfgMu    sync.RWMutex
	state    AppState
	db       *sql.DB
	sampleCh chan Sample
	alarmCh  chan AlarmEvent

	alarmTracker AlarmTracker
	uiRevision   uint64 = 1

	mqttMgr     *mqttManager
	mqttAlarmCh chan AlarmEvent

	licenseMgr *LicenseManager
)

// ---------------------------------------------------------------------------
// MQTT manager
// ---------------------------------------------------------------------------

func newMQTTManager(mcfg MQTTConfig) *mqttManager {
	m := &mqttManager{
		broker:   mcfg.Broker,
		clientID: mcfg.ClientID,
		prefix:   mcfg.TopicPrefix,
		msgMax:   500,
		subs:     make(map[string]byte),
	}

	opts := mqtt.NewClientOptions()
	opts.AddBroker(mcfg.Broker)
	opts.SetClientID(mcfg.ClientID)
	if mcfg.Username != "" {
		opts.SetUsername(mcfg.Username)
		opts.SetPassword(mcfg.Password)
	}
	opts.SetAutoReconnect(true)
	opts.SetMaxReconnectInterval(time.Duration(mcfg.ReconnectDelaySec*6) * time.Second)
	opts.SetConnectTimeout(time.Duration(mcfg.ConnectTimeoutSec) * time.Second)
	opts.SetCleanSession(true)
	opts.SetKeepAlive(30 * time.Second)

	opts.SetOnConnectHandler(func(c mqtt.Client) {
		m.mu.Lock()
		m.connected = true
		m.lastErr = ""
		resub := make(map[string]byte, len(m.subs))
		for k, v := range m.subs {
			resub[k] = v
		}
		m.mu.Unlock()

		log.Printf("MQTT connected to %s", mcfg.Broker)
		for topic, qos := range resub {
			tok := c.Subscribe(topic, qos, m.messageHandler)
			if tok.Wait() && tok.Error() != nil {
				log.Printf("MQTT re-subscribe %s failed: %v", topic, tok.Error())
			}
		}
	})

	opts.SetConnectionLostHandler(func(_ mqtt.Client, err error) {
		m.mu.Lock()
		m.connected = false
		if err != nil {
			m.lastErr = err.Error()
		}
		m.mu.Unlock()
		log.Printf("MQTT connection lost: %v", err)
	})

	m.client = mqtt.NewClient(opts)
	return m
}

func (m *mqttManager) connect() error {
	tok := m.client.Connect()
	if !tok.WaitTimeout(30 * time.Second) {
		return fmt.Errorf("MQTT connect timeout after 30s")
	}
	if err := tok.Error(); err != nil {
		m.mu.Lock()
		m.lastErr = err.Error()
		m.mu.Unlock()
		return err
	}
	return nil
}

func (m *mqttManager) disconnect() {
	if m.client != nil {
		m.client.Disconnect(500)
	}
}

func (m *mqttManager) messageHandler(_ mqtt.Client, msg mqtt.Message) {
	entry := MQTTReceivedMsg{
		Topic:    msg.Topic(),
		Payload:  string(msg.Payload()),
		Retained: msg.Retained(),
		Time:     time.Now().UTC().Format(time.RFC3339Nano),
	}
	m.mu.Lock()
	m.msgHistory = append(m.msgHistory, entry)
	if len(m.msgHistory) > m.msgMax {
		half := m.msgMax / 2
		copy(m.msgHistory, m.msgHistory[half:])
		m.msgHistory = m.msgHistory[:m.msgMax-half]
	}
	m.mu.Unlock()
}

func (m *mqttManager) publish(topic, payload string, qos byte, retain bool) error {
	if topic == "" {
		return fmt.Errorf("topic must not be empty")
	}
	if qos > 2 {
		qos = 2
	}
	m.mu.RLock()
	ok := m.connected
	m.mu.RUnlock()
	if !ok {
		return fmt.Errorf("MQTT not connected")
	}
	tok := m.client.Publish(topic, qos, retain, payload)
	if qos > 0 {
		if !tok.WaitTimeout(5 * time.Second) {
			return fmt.Errorf("MQTT publish timeout")
		}
		return tok.Error()
	}
	return nil
}

func (m *mqttManager) subscribe(topic string, qos byte) error {
	if topic == "" {
		return fmt.Errorf("topic must not be empty")
	}
	if qos > 2 {
		qos = 2
	}
	m.mu.Lock()
	m.subs[topic] = qos
	m.mu.Unlock()

	m.mu.RLock()
	ok := m.connected
	m.mu.RUnlock()
	if !ok {
		return nil
	}

	tok := m.client.Subscribe(topic, qos, m.messageHandler)
	if tok.Wait() && tok.Error() != nil {
		return tok.Error()
	}
	return nil
}

func (m *mqttManager) unsubscribe(topic string) error {
	m.mu.Lock()
	delete(m.subs, topic)
	m.mu.Unlock()

	m.mu.RLock()
	ok := m.connected
	m.mu.RUnlock()
	if !ok {
		return nil
	}
	tok := m.client.Unsubscribe(topic)
	if tok.Wait() && tok.Error() != nil {
		return tok.Error()
	}
	return nil
}

func (m *mqttManager) status() MQTTStatusResponse {
	m.mu.RLock()
	defer m.mu.RUnlock()

	subs := make([]string, 0, len(m.subs))
	for t := range m.subs {
		subs = append(subs, t)
	}
	return MQTTStatusResponse{
		Enabled:     true,
		Connected:   m.connected,
		Broker:      m.broker,
		ClientID:    m.clientID,
		TopicPrefix: m.prefix,
		Subscribed:  subs,
		LastError:   m.lastErr,
	}
}

func (m *mqttManager) getMessages(limit int) []MQTTReceivedMsg {
	if limit <= 0 {
		limit = 50
	}
	if limit > 500 {
		limit = 500
	}
	m.mu.RLock()
	defer m.mu.RUnlock()

	total := len(m.msgHistory)
	if total == 0 {
		return []MQTTReceivedMsg{}
	}
	start := 0
	if total > limit {
		start = total - limit
	}
	out := make([]MQTTReceivedMsg, total-start)
	copy(out, m.msgHistory[start:])
	return out
}

func startMQTTPublisher(ctx context.Context) {
	if mqttMgr == nil {
		return
	}
	mcfg := getConfigSnapshot().MQTT
	if !mcfg.AutoPublish {
		return
	}

	interval := time.Duration(mcfg.PublishIntervalMs) * time.Millisecond
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	prefix := mcfg.TopicPrefix
	qos := byte(mcfg.QoS)
	retain := mcfg.Retain

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			s := snapshotState()

			full, err := json.Marshal(s)
			if err == nil {
				_ = mqttMgr.publish(prefix+"/data", string(full), qos, retain)
			}

			_ = mqttMgr.publish(prefix+"/force/left", fmt.Sprintf("%.2f", s.SilaL), qos, retain)
			_ = mqttMgr.publish(prefix+"/force/right", fmt.Sprintf("%.2f", s.SilaR), qos, retain)
			_ = mqttMgr.publish(prefix+"/force/sum_kn", fmt.Sprintf("%.2f", s.SumkN), qos, retain)
			_ = mqttMgr.publish(prefix+"/force/imbalance", fmt.Sprintf("%.2f", s.ImbalancePercent), qos, retain)

			connStr := "false"
			if s.Connected {
				connStr = "true"
			}
			_ = mqttMgr.publish(prefix+"/connected", connStr, qos, retain)
		}
	}
}

func mqttAlarmWorker() {
	for a := range mqttAlarmCh {
		mqttPublishAlarm(a)
	}
}

func mqttPublishAlarm(a AlarmEvent) {
	if mqttMgr == nil {
		return
	}
	mcfg := getConfigSnapshot().MQTT
	if !mcfg.Enabled {
		return
	}

	payload, err := json.Marshal(map[string]interface{}{
		"time":     a.TS.UTC().Format(time.RFC3339),
		"severity": a.Severity,
		"source":   a.Source,
		"code":     a.Code,
		"state":    a.State,
		"message":  a.Message,
		"value":    a.Value,
		"limit":    a.Limit,
	})
	if err != nil {
		return
	}
	_ = mqttMgr.publish(mcfg.TopicPrefix+"/alarm", string(payload), byte(mcfg.QoS), false)
}

// ---------------------------------------------------------------------------
// Force calculation
// ---------------------------------------------------------------------------

func calculateForces(leftPercent, rightPercent float32, maxTonnage float64) (leftKN, rightKN, sumPercent, sumKN float32) {
	lp := float64(leftPercent)
	rp := float64(rightPercent)

	sumPct := (lp + rp) / 2.0
	left := (lp / 100.0) * (maxTonnage / 2.0)
	right := (rp / 100.0) * (maxTonnage / 2.0)
	total := (sumPct / 100.0) * maxTonnage

	return float32(left), float32(right), float32(sumPct), float32(total)
}

func getConfigSnapshot() Config {
	cfgMu.RLock()
	defer cfgMu.RUnlock()
	return cfg
}

func hotReloadSectionsLocked(dst *Config, src Config) {
	dst.Thresholds = src.Thresholds
	dst.Trend = src.Trend
	dst.Press = src.Press
	dst.UI = src.UI
	dst.Modules = src.Modules
}

func configSectionChanges(oldCfg, newCfg Config) (hotSections []string, restartSections []string) {
	if !reflect.DeepEqual(oldCfg.Thresholds, newCfg.Thresholds) {
		hotSections = append(hotSections, "thresholds")
	}
	if !reflect.DeepEqual(oldCfg.Trend, newCfg.Trend) {
		hotSections = append(hotSections, "trend")
	}
	if !reflect.DeepEqual(oldCfg.Press, newCfg.Press) {
		hotSections = append(hotSections, "press")
	}
	if !reflect.DeepEqual(oldCfg.UI, newCfg.UI) {
		hotSections = append(hotSections, "ui")
	}
	if !reflect.DeepEqual(oldCfg.Modules, newCfg.Modules) {
		hotSections = append(hotSections, "modules")
	}
	if !reflect.DeepEqual(oldCfg.Server, newCfg.Server) {
		restartSections = append(restartSections, "server")
	}
	if !reflect.DeepEqual(oldCfg.PLC, newCfg.PLC) {
		restartSections = append(restartSections, "plc")
	}
	if !reflect.DeepEqual(oldCfg.DB, newCfg.DB) {
		restartSections = append(restartSections, "db")
	}
	if !reflect.DeepEqual(oldCfg.MQTT, newCfg.MQTT) {
		restartSections = append(restartSections, "mqtt")
	}
	if !reflect.DeepEqual(oldCfg.License, newCfg.License) {
		restartSections = append(restartSections, "license")
	}
	return hotSections, restartSections
}

func reloadConfigSafely(configPath string) {
	newCfg, err := loadConfigStrict(configPath)
	if err != nil {
		log.Printf("config reload rejected: %v", err)
		return
	}
	if err := validateConfig(newCfg); err != nil {
		log.Printf("config reload rejected: %v", err)
		return
	}

	oldCfg := getConfigSnapshot()
	hotSections, restartSections := configSectionChanges(oldCfg, newCfg)

	if len(hotSections) > 0 {
		cfgMu.Lock()
		updated := cfg
		hotReloadSectionsLocked(&updated, newCfg)
		cfg = updated
		cfgMu.Unlock()
		atomic.AddUint64(&uiRevision, 1)
	}

	if len(hotSections) == 0 && len(restartSections) == 0 {
		log.Printf("config reload checked: no effective changes")
		return
	}
	if len(hotSections) > 0 {
		log.Printf("config hot-reloaded safely: %s", strings.Join(hotSections, ", "))
	}
	if len(restartSections) > 0 {
		log.Printf("config changes detected in %s; restart required before they take effect", strings.Join(restartSections, ", "))
	}
}

func startConfigWatcher(ctx context.Context, configPath string) error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return err
	}

	dir := filepath.Dir(configPath)
	target := filepath.Clean(configPath)
	if !filepath.IsAbs(target) {
		target = filepath.Join(dir, target)
	}
	target = filepath.Clean(target)

	if err := watcher.Add(dir); err != nil {
		_ = watcher.Close()
		return err
	}

	go func() {
		defer watcher.Close()

		var (
			debounceTimer *time.Timer
			debounceC     <-chan time.Time
		)

		resetDebounce := func() {
			if debounceTimer == nil {
				debounceTimer = time.NewTimer(350 * time.Millisecond)
			} else {
				if !debounceTimer.Stop() {
					select {
					case <-debounceTimer.C:
					default:
					}
				}
				debounceTimer.Reset(350 * time.Millisecond)
			}
			debounceC = debounceTimer.C
		}

		for {
			select {
			case <-ctx.Done():
				if debounceTimer != nil {
					debounceTimer.Stop()
				}
				return
			case event, ok := <-watcher.Events:
				if !ok {
					return
				}
				name := event.Name
				if !filepath.IsAbs(name) {
					name = filepath.Join(dir, name)
				}
				if filepath.Clean(name) != target {
					continue
				}
				if event.Has(fsnotify.Chmod) {
					continue
				}
				if event.Has(fsnotify.Write) || event.Has(fsnotify.Create) || event.Has(fsnotify.Rename) {
					resetDebounce()
				}
			case <-debounceC:
				debounceC = nil
				reloadConfigSafely(configPath)
			case err, ok := <-watcher.Errors:
				if !ok {
					return
				}
				log.Printf("config watcher error: %v", err)
			}
		}
	}()

	return nil
}

// ---------------------------------------------------------------------------
// State helpers
// ---------------------------------------------------------------------------

func snapshotState() APIState {
	state.RLock()
	defer state.RUnlock()

	lastUpdate := ""
	if !state.LastUpdate.IsZero() {
		lastUpdate = state.LastUpdate.Format(time.RFC3339Nano)
	}
	return APIState{
		Connected:        state.Connected,
		SilaL:            state.SilaL,
		SilaR:            state.SilaR,
		SilaLkN:          state.SilaLkN,
		SilaRkN:          state.SilaRkN,
		SumPercent:       state.SumPercent,
		SumkN:            state.SumkN,
		ImbalancePercent: state.ImbalancePercent,
		BiasPercent:      state.BiasPercent,
		LastUpdate:       lastUpdate,
		DroppedSamples:   state.DroppedSamples,
		DroppedEvents:    state.DroppedEvents,
	}
}

func markDisconnected(reason string) {
	state.Lock()
	state.Connected = false
	state.Unlock()
	maybeLogPLCDisconnected(reason)
}

func enqueueSample(s Sample) {
	select {
	case sampleCh <- s:
	default:
		state.Lock()
		state.DroppedSamples++
		state.Unlock()
	}
}

func enqueueAlarm(a AlarmEvent) {
	select {
	case alarmCh <- a:
	default:
		state.Lock()
		state.DroppedEvents++
		state.Unlock()
	}
	if mqttAlarmCh != nil {
		select {
		case mqttAlarmCh <- a:
		default:
		}
	}
}

// ---------------------------------------------------------------------------
// Database initialisation
// ---------------------------------------------------------------------------

func ensureColumn(database *sql.DB, tableName, columnName, definition string) error {
	rows, err := database.Query(fmt.Sprintf("PRAGMA table_info(%s)", tableName))
	if err != nil {
		return err
	}
	defer rows.Close()

	found := false
	for rows.Next() {
		var cid int
		var name, ctype string
		var notNull int
		var dfltValue sql.NullString
		var pk int
		if err := rows.Scan(&cid, &name, &ctype, &notNull, &dfltValue, &pk); err != nil {
			return err
		}
		if name == columnName {
			found = true
			break
		}
	}
	if err := rows.Err(); err != nil {
		return err
	}
	if found {
		return nil
	}
	_, err = database.Exec(fmt.Sprintf("ALTER TABLE %s ADD COLUMN %s %s", tableName, columnName, definition))
	return err
}

func initDatabase(dbPath string, dbCfg DBConfig) (*sql.DB, error) {
	dsn := fmt.Sprintf("file:%s?_busy_timeout=%d&_foreign_keys=on", filepath.ToSlash(dbPath), dbCfg.BusyTimeoutMs)
	database, err := sql.Open("sqlite3", dsn)
	if err != nil {
		return nil, fmt.Errorf("open sqlite: %w", err)
	}

	database.SetMaxOpenConns(4)
	database.SetMaxIdleConns(2)
	database.SetConnMaxLifetime(time.Hour)

	pragmas := []string{
		"PRAGMA journal_mode=WAL;",
		"PRAGMA synchronous=NORMAL;",
		fmt.Sprintf("PRAGMA wal_autocheckpoint=%d;", dbCfg.CheckpointPages),
		fmt.Sprintf("PRAGMA busy_timeout=%d;", dbCfg.BusyTimeoutMs),
		"PRAGMA temp_store=MEMORY;",
	}
	for _, q := range pragmas {
		if _, err := database.Exec(q); err != nil {
			_ = database.Close()
			return nil, fmt.Errorf("sqlite pragma failed (%s): %w", q, err)
		}
	}

	schema := `
CREATE TABLE IF NOT EXISTS samples (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    ts DATETIME NOT NULL,
    ts_unix_ns INTEGER NOT NULL DEFAULT 0,
    sila_l_pct REAL NOT NULL,
    sila_r_pct REAL NOT NULL,
    sila_l_kn REAL NOT NULL,
    sila_r_kn REAL NOT NULL,
    sum_pct REAL NOT NULL,
    sum_kn REAL NOT NULL,
    imbalance_pct REAL NOT NULL DEFAULT 0,
    bias_pct REAL NOT NULL DEFAULT 0
);
CREATE INDEX IF NOT EXISTS idx_samples_ts ON samples(ts);
CREATE INDEX IF NOT EXISTS idx_samples_ts_unix_ns ON samples(ts_unix_ns);

CREATE TABLE IF NOT EXISTS alarm_events (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    ts DATETIME NOT NULL,
    ts_unix_ns INTEGER NOT NULL DEFAULT 0,
    severity TEXT NOT NULL,
    source TEXT NOT NULL,
    code TEXT NOT NULL,
    state TEXT NOT NULL,
    message TEXT NOT NULL,
    value REAL NOT NULL DEFAULT 0,
    limit_value REAL NOT NULL DEFAULT 0
);
CREATE INDEX IF NOT EXISTS idx_alarm_events_ts_unix_ns ON alarm_events(ts_unix_ns DESC);
`
	if _, err := database.Exec(schema); err != nil {
		_ = database.Close()
		return nil, fmt.Errorf("create schema: %w", err)
	}

	if _, err := database.Exec(`CREATE INDEX IF NOT EXISTS idx_samples_trend ON samples(ts_unix_ns, sum_pct, imbalance_pct);`); err != nil {
		_ = database.Close()
		return nil, fmt.Errorf("create trend index: %w", err)
	}

	migrations := []struct{ table, col, def string }{
		{"samples", "ts_unix_ns", "INTEGER NOT NULL DEFAULT 0"},
		{"samples", "imbalance_pct", "REAL NOT NULL DEFAULT 0"},
		{"samples", "bias_pct", "REAL NOT NULL DEFAULT 0"},
		{"alarm_events", "ts_unix_ns", "INTEGER NOT NULL DEFAULT 0"},
	}
	for _, m := range migrations {
		if err := ensureColumn(database, m.table, m.col, m.def); err != nil {
			_ = database.Close()
			return nil, fmt.Errorf("migration (%s.%s): %w", m.table, m.col, err)
		}
	}

	if _, err := database.Exec(`CREATE INDEX IF NOT EXISTS idx_samples_ts_unix_ns ON samples(ts_unix_ns)`); err != nil {
		_ = database.Close()
		return nil, fmt.Errorf("create ts_unix_ns index: %w", err)
	}

	for _, tbl := range []string{"samples", "alarm_events"} {
		q := fmt.Sprintf(`UPDATE %s SET ts_unix_ns = CAST(strftime('%%s', ts) AS INTEGER) * 1000000000 WHERE ts_unix_ns = 0 AND ts IS NOT NULL`, tbl)
		if _, err := database.Exec(q); err != nil {
			log.Printf("warning: ts_unix_ns backfill for %s failed: %v", tbl, err)
		}
	}

	if _, err := database.Exec("ANALYZE"); err != nil {
		log.Printf("warning: sqlite analyze failed: %v", err)
	}

	return database, nil
}

// ---------------------------------------------------------------------------
// DB writer goroutines
// ---------------------------------------------------------------------------

func startDBWriter(ctx context.Context, database *sql.DB, batchSize, flushMs int) {
	ticker := time.NewTicker(time.Duration(flushMs) * time.Millisecond)
	defer ticker.Stop()

	stmt, err := database.Prepare(`
		INSERT INTO samples (
			ts, ts_unix_ns, sila_l_pct, sila_r_pct, sila_l_kn, sila_r_kn,
			sum_pct, sum_kn, imbalance_pct, bias_pct
		) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
	`)
	if err != nil {
		log.Printf("db writer prepare failed: %v", err)
		return
	}
	defer stmt.Close()

	batch := make([]Sample, 0, batchSize)
	flushErrCount := 0

	flush := func() {
		if len(batch) == 0 {
			return
		}
		tx, err := database.Begin()
		if err != nil {
			log.Printf("db begin failed: %v", err)
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("db writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		txStmt := tx.Stmt(stmt)
		defer txStmt.Close()
		ok := true
		for _, s := range batch {
			if _, err := txStmt.Exec(
				s.TS.UTC().Format(time.RFC3339Nano), s.TS.UTC().UnixNano(),
				s.SilaLPct, s.SilaRPct, s.SilaLKN, s.SilaRKN,
				s.SumPercent, s.SumKN, s.ImbalancePercent, s.BiasPercent,
			); err != nil {
				ok = false
				log.Printf("db insert failed: %v", err)
				break
			}
		}
		if !ok {
			_ = tx.Rollback()
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("db writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		if err := tx.Commit(); err != nil {
			log.Printf("db commit failed: %v", err)
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("db writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		batch = batch[:0]
		flushErrCount = 0
	}

	for {
		select {
		case <-ctx.Done():
			drained := 0
			for {
				select {
				case s := <-sampleCh:
					batch = append(batch, s)
					drained++
					if drained > 10000 {
						log.Printf("db writer: drain limit reached, dropping remaining")
						flush()
						return
					}
				default:
					flush()
					return
				}
			}
		case s := <-sampleCh:
			batch = append(batch, s)
			if len(batch) >= batchSize {
				flush()
			}
		case <-ticker.C:
			flush()
		}
	}
}

func startAlarmWriter(ctx context.Context, database *sql.DB, batchSize, flushMs int) {
	ticker := time.NewTicker(time.Duration(flushMs) * time.Millisecond)
	defer ticker.Stop()

	stmt, err := database.Prepare(`
		INSERT INTO alarm_events (
			ts, ts_unix_ns, severity, source, code, state, message, value, limit_value
		) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
	`)
	if err != nil {
		log.Printf("alarm db writer prepare failed: %v", err)
		return
	}
	defer stmt.Close()

	batch := make([]AlarmEvent, 0, batchSize)
	flushErrCount := 0

	flush := func() {
		if len(batch) == 0 {
			return
		}
		tx, err := database.Begin()
		if err != nil {
			log.Printf("alarm db begin failed: %v", err)
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("alarm writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		txStmt := tx.Stmt(stmt)
		defer txStmt.Close()
		ok := true
		for _, a := range batch {
			if _, err := txStmt.Exec(
				a.TS.UTC().Format(time.RFC3339Nano), a.TS.UTC().UnixNano(),
				a.Severity, a.Source, a.Code, a.State, a.Message, a.Value, a.Limit,
			); err != nil {
				ok = false
				log.Printf("alarm db insert failed: %v", err)
				break
			}
		}
		if !ok {
			_ = tx.Rollback()
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("alarm writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		if err := tx.Commit(); err != nil {
			log.Printf("alarm db commit failed: %v", err)
			flushErrCount++
			if flushErrCount >= 3 {
				log.Printf("alarm writer: dropping batch of %d after %d failures", len(batch), flushErrCount)
				batch = batch[:0]
				flushErrCount = 0
			}
			return
		}
		batch = batch[:0]
		flushErrCount = 0
	}

	for {
		select {
		case <-ctx.Done():
			drained := 0
			for {
				select {
				case a := <-alarmCh:
					batch = append(batch, a)
					drained++
					if drained > 10000 {
						log.Printf("alarm writer: drain limit reached, dropping remaining")
						flush()
						return
					}
				default:
					flush()
					return
				}
			}
		case a := <-alarmCh:
			batch = append(batch, a)
			if len(batch) >= batchSize {
				flush()
			}
		case <-ticker.C:
			flush()
		}
	}
}

func startDBCleanup(ctx context.Context, database *sql.DB, retentionDays, intervalHr int) {
	if retentionDays <= 0 {
		return
	}

	ticker := time.NewTicker(time.Duration(intervalHr) * time.Hour)
	defer ticker.Stop()

	cleanup := func() {
		cutoffNs := time.Now().AddDate(0, 0, -retentionDays).UTC().UnixNano()
		for _, tbl := range []string{"samples", "alarm_events"} {
			for {
				rows, err := database.QueryContext(ctx,
					fmt.Sprintf(`SELECT rowid FROM %s WHERE ts_unix_ns > 0 AND ts_unix_ns < ? LIMIT 5000`, tbl),
					cutoffNs,
				)
				if err != nil {
					log.Printf("db cleanup %s select failed: %v", tbl, err)
					break
				}
				var rowids []int64
				for rows.Next() {
					var rid int64
					if err := rows.Scan(&rid); err != nil {
						log.Printf("db cleanup %s scan failed: %v", tbl, err)
						break
					}
					rowids = append(rowids, rid)
				}
				rows.Close()
				if len(rowids) == 0 {
					break
				}
				placeholders := make([]string, len(rowids))
				args := make([]any, len(rowids))
				for i, rid := range rowids {
					placeholders[i] = "?"
					args[i] = rid
				}
				query := fmt.Sprintf(`DELETE FROM %s WHERE rowid IN (%s)`, tbl, strings.Join(placeholders, ","))
				if _, err := database.ExecContext(ctx, query, args...); err != nil {
					log.Printf("db cleanup %s delete failed: %v", tbl, err)
					break
				}
			}
		}
	}

	cleanup()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			cleanup()
		}
	}
}

// ---------------------------------------------------------------------------
// Alarm zone helpers
// ---------------------------------------------------------------------------

func zoneFromValue(value, warn, crit float64) string {
	if value >= crit {
		return "critical"
	}
	if value >= warn {
		return "warning"
	}
	return "ok"
}

func sourceName(source string) string {
	switch source {
	case "force_left":
		return "Left force"
	case "force_right":
		return "Right force"
	case "imbalance":
		return "Imbalance"
	case "plc":
		return "PLC"
	default:
		return source
	}
}

func sourceLimit(source, zone string) float64 {
	config := getConfigSnapshot()
	switch source {
	case "imbalance":
		if zone == "critical" {
			return config.Thresholds.ImbalanceCriticalPercent
		}
		if zone == "warning" {
			return config.Thresholds.ImbalanceWarningPercent
		}
	default:
		if zone == "critical" {
			return config.Thresholds.CriticalPercent
		}
		if zone == "warning" {
			return config.Thresholds.WarningPercent
		}
	}
	return 0
}

func maybeLogZoneChange(source, prev, curr string, value float64) {
	if prev == curr {
		return
	}
	name := sourceName(source)
	now := time.Now()
	if prev == "" && curr == "ok" {
		return
	}

	alarmTracker.Lock()
	if alarmTracker.LastChange == nil {
		alarmTracker.LastChange = make(map[string]time.Time)
	}
	if last, ok := alarmTracker.LastChange[source]; ok && now.Sub(last) < 5*time.Second {
		alarmTracker.Unlock()
		return
	}
	alarmTracker.LastChange[source] = now
	alarmTracker.Unlock()

	switch curr {
	case "ok":
		enqueueAlarm(AlarmEvent{
			TS:       now,
			Severity: "info",
			Source:   source,
			Code:     source + "_clear",
			State:    "clear",
			Message:  fmt.Sprintf("%s returned to OK", name),
			Value:    value,
			Limit:    0,
		})
	case "warning":
		msg := fmt.Sprintf("%s entered WARNING zone", name)
		if prev == "critical" {
			msg = fmt.Sprintf("%s downgraded from CRITICAL to WARNING", name)
		}
		enqueueAlarm(AlarmEvent{
			TS:       now,
			Severity: "warning",
			Source:   source,
			Code:     source + "_warning",
			State:    "active",
			Message:  msg,
			Value:    value,
			Limit:    sourceLimit(source, "warning"),
		})
	case "critical":
		msg := fmt.Sprintf("%s entered CRITICAL zone", name)
		if prev == "warning" {
			msg = fmt.Sprintf("%s escalated from WARNING to CRITICAL", name)
		}
		enqueueAlarm(AlarmEvent{
			TS:       now,
			Severity: "critical",
			Source:   source,
			Code:     source + "_critical",
			State:    "active",
			Message:  msg,
			Value:    value,
			Limit:    sourceLimit(source, "critical"),
		})
	}
}

func evaluateProcessAlarms(s Sample) {
	config := getConfigSnapshot()
	warn := config.Thresholds.WarningPercent
	crit := config.Thresholds.CriticalPercent
	imbWarn := config.Thresholds.ImbalanceWarningPercent
	imbCrit := config.Thresholds.ImbalanceCriticalPercent

	leftZone := zoneFromValue(float64(s.SilaLPct), warn, crit)
	rightZone := zoneFromValue(float64(s.SilaRPct), warn, crit)
	imbZone := zoneFromValue(float64(s.ImbalancePercent), imbWarn, imbCrit)

	alarmTracker.Lock()
	prevLeft := alarmTracker.LeftZone
	prevRight := alarmTracker.RightZone
	prevImb := alarmTracker.ImbZone
	alarmTracker.LeftZone = leftZone
	alarmTracker.RightZone = rightZone
	alarmTracker.ImbZone = imbZone
	alarmTracker.Unlock()

	maybeLogZoneChange("force_left", prevLeft, leftZone, float64(s.SilaLPct))
	maybeLogZoneChange("force_right", prevRight, rightZone, float64(s.SilaRPct))
	maybeLogZoneChange("imbalance", prevImb, imbZone, float64(s.ImbalancePercent))
}

func maybeLogPLCConnected() {
	alarmTracker.Lock()
	defer alarmTracker.Unlock()
	if !alarmTracker.PLCKnown {
		alarmTracker.PLCKnown = true
		alarmTracker.PLCConnected = true
		enqueueAlarm(AlarmEvent{
			TS: time.Now(), Severity: "info", Source: "plc",
			Code: "plc_connected", State: "info",
			Message: "PLC connection established", Value: 1,
		})
		return
	}
	if !alarmTracker.PLCConnected {
		alarmTracker.PLCConnected = true
		enqueueAlarm(AlarmEvent{
			TS: time.Now(), Severity: "info", Source: "plc",
			Code: "plc_restored", State: "info",
			Message: "PLC connection restored", Value: 1,
		})
	}
}

func maybeLogPLCDisconnected(reason string) {
	alarmTracker.Lock()
	defer alarmTracker.Unlock()
	if !alarmTracker.PLCKnown || !alarmTracker.PLCConnected {
		return
	}
	alarmTracker.PLCConnected = false
	alarmTracker.LeftZone = ""
	alarmTracker.RightZone = ""
	alarmTracker.ImbZone = ""
	enqueueAlarm(AlarmEvent{
		TS: time.Now(), Severity: "critical", Source: "plc",
		Code: "plc_disconnected", State: "active",
		Message: "PLC connection lost: " + reason, Value: 0,
	})
}

// ---------------------------------------------------------------------------
// PLC poller
// ---------------------------------------------------------------------------

func startPLCPoller(ctx context.Context) {
	bootCfg := getConfigSnapshot()
	pollInterval := time.Duration(bootCfg.PLC.PollMs) * time.Millisecond
	reconnectDelay := time.Duration(bootCfg.PLC.ReconnectDelaySec) * time.Second
	dbNum := bootCfg.PLC.DBNum

	for {
		select {
		case <-ctx.Done():
			return
		default:
		}

		handler := gos7.NewTCPClientHandler(bootCfg.PLC.IP, bootCfg.PLC.Rack, bootCfg.PLC.Slot)
		handler.Timeout = time.Duration(bootCfg.PLC.ConnectTimeoutSec) * time.Second
		handler.IdleTimeout = time.Duration(bootCfg.PLC.IdleTimeoutSec) * time.Second

		if err := handler.Connect(); err != nil {
			markDisconnected(err.Error())
			log.Printf("PLC connect failed: %v - retrying in %ds...", err, bootCfg.PLC.ReconnectDelaySec)
			select {
			case <-ctx.Done():
				return
			case <-time.After(reconnectDelay):
			}
			continue
		}

		maybeLogPLCConnected()

		client := gos7.NewClient(handler)
		log.Println("PLC connected successfully")

		buf := make([]byte, 8)
		readErrCount := 0

		for {
			select {
			case <-ctx.Done():
				_ = handler.Close()
				return
			default:
			}

			if err := client.AGReadDB(dbNum, 0, 8, buf); err != nil {
				readErrCount++
				if readErrCount < 3 {
					log.Printf("PLC read error (attempt %d/3): %v", readErrCount, err)
					select {
					case <-ctx.Done():
						_ = handler.Close()
						return
					case <-time.After(pollInterval):
					}
					continue
				}
				log.Printf("PLC read error: %v - reconnecting...", err)
				markDisconnected(err.Error())
				_ = handler.Close()
				break
			}
			readErrCount = 0

			var helper gos7.Helper
			silaL := helper.GetRealAt(buf, 0)
			silaR := helper.GetRealAt(buf, 4)

			cfgSnap := getConfigSnapshot()
			leftKN, rightKN, sumPercent, sumKN := calculateForces(silaL, silaR, cfgSnap.Press.MaxTonnage)
			imbalance := float32(math.Abs(float64(silaL - silaR)))
			bias := silaL - silaR
			now := time.Now()

			state.Lock()
			state.Connected = true
			state.SilaL = silaL
			state.SilaR = silaR
			state.SilaLkN = leftKN
			state.SilaRkN = rightKN
			state.SumPercent = sumPercent
			state.SumkN = sumKN
			state.ImbalancePercent = imbalance
			state.BiasPercent = bias
			state.LastUpdate = now
			state.Unlock()

			sample := Sample{
				TS: now, SilaLPct: silaL, SilaRPct: silaR,
				SilaLKN: leftKN, SilaRKN: rightKN,
				SumPercent: sumPercent, SumKN: sumKN,
				ImbalancePercent: imbalance, BiasPercent: bias,
			}

			evaluateProcessAlarms(sample)
			enqueueSample(sample)

			select {
			case <-ctx.Done():
				_ = handler.Close()
				return
			case <-time.After(pollInterval):
			}
		}
	}
}

// ---------------------------------------------------------------------------
// Query helpers
// ---------------------------------------------------------------------------

func parseWindow(raw string) (time.Duration, string, error) {
	s := strings.TrimSpace(strings.ToLower(raw))
	if s == "" {
		s = fmt.Sprintf("%dm", getConfigSnapshot().Trend.Minutes)
	}
	if strings.HasSuffix(s, "d") {
		n, err := strconv.Atoi(strings.TrimSuffix(s, "d"))
		if err != nil || n <= 0 {
			return 0, "", fmt.Errorf("invalid day window")
		}
		return time.Duration(n) * 24 * time.Hour, s, nil
	}
	d, err := time.ParseDuration(s)
	if err != nil || d <= 0 {
		return 0, "", fmt.Errorf("invalid window")
	}
	return d, s, nil
}

func formatHistoryLabel(t time.Time, window time.Duration) string {
	local := t.Local()
	if window >= 12*time.Hour {
		return local.Format("02.01 15:04")
	}
	return local.Format("15:04:05.000")
}

func queryHistory(ctx context.Context, window time.Duration) ([]HistoryPoint, error) {
	cutoffNs := time.Now().Add(-window).UTC().UnixNano()

	rows, err := db.QueryContext(ctx,
		`SELECT ts_unix_ns, sila_l_pct, sila_r_pct FROM samples WHERE ts_unix_ns >= ? ORDER BY ts_unix_ns ASC`,
		cutoffNs)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	points := make([]HistoryPoint, 0, 1024)
	for rows.Next() {
		var tsUnix int64
		var l, r float64
		if err := rows.Scan(&tsUnix, &l, &r); err != nil {
			return nil, err
		}
		t := time.Unix(0, tsUnix).Local()
		points = append(points, HistoryPoint{
			Time:  formatHistoryLabel(t, window),
			SilaL: float32(l),
			SilaR: float32(r),
		})
	}
	if err := rows.Err(); err != nil {
		return nil, err
	}

	maxPts := getConfigSnapshot().DB.MaxChartPoints
	if len(points) <= maxPts {
		return points, nil
	}
	return downsamplePoints(points, maxPts), nil
}

func downsamplePoints(points []HistoryPoint, max int) []HistoryPoint {
	if len(points) <= max || max < 3 {
		return points
	}
	out := make([]HistoryPoint, max)
	step := float64(len(points)-1) / float64(max-1)
	for i := 0; i < max; i++ {
		idx := int(float64(i) * step)
		if idx >= len(points) {
			idx = len(points) - 1
		}
		out[i] = points[idx]
	}
	out[max-1] = points[len(points)-1]
	return out
}

func validField(field string) (string, error) {
	switch field {
	case "sum_pct":
		return "sum_pct", nil
	case "imbalance_pct":
		return "imbalance_pct", nil
	default:
		return "", fmt.Errorf("invalid field")
	}
}

func queryNumericStats(ctx context.Context, field string, fromNs, toNs int64) (NumericStats, error) {
	safeField, err := validField(field)
	if err != nil {
		return NumericStats{}, err
	}
	query := fmt.Sprintf(`
		SELECT
			COALESCE(AVG(%[1]s), 0),
			COALESCE(AVG(%[1]s * %[1]s), 0),
			COALESCE(MIN(%[1]s), 0),
			COALESCE(MAX(%[1]s), 0),
			COUNT(*)
		FROM samples
		WHERE ts_unix_ns >= ? AND ts_unix_ns < ?
	`, safeField)

	var stats NumericStats
	err = db.QueryRowContext(ctx, query, fromNs, toNs).Scan(&stats.Avg, &stats.AvgSq, &stats.Min, &stats.Max, &stats.Count)
	if err != nil {
		return NumericStats{}, err
	}
	return stats, nil
}

// ---------------------------------------------------------------------------
// Trend / stability classification
// ---------------------------------------------------------------------------

func classifyDirection(delta float64, oldCount, newCount int, stableThreshold float64, posLabel, negLabel string) string {
	if oldCount < 3 || newCount < 3 {
		return "insufficient_data"
	}
	if math.Abs(delta) < stableThreshold {
		return "stable"
	}
	if delta > 0 {
		return posLabel
	}
	return negLabel
}

func classifyProcessStability(forceStd, imbStd, forceDelta, avgImb5m float64, sampleCount int) (string, string) {
	if sampleCount < 8 {
		return "insufficient_data", "Too few samples in selected trend window"
	}
	config := getConfigSnapshot()

	if forceStd >= 6.0 || math.Abs(forceDelta) >= 8.0 || avgImb5m >= config.Thresholds.ImbalanceCriticalPercent || imbStd >= 4.0 {
		if avgImb5m >= config.Thresholds.ImbalanceCriticalPercent {
			return "unstable", "High average imbalance in last 5 minutes"
		}
		if math.Abs(forceDelta) >= 8.0 {
			return "unstable", "Average peak force is drifting fast"
		}
		if forceStd >= 6.0 {
			return "unstable", "Force variation is too high"
		}
		return "unstable", "Imbalance variation is too high"
	}
	if forceStd >= 3.0 || math.Abs(forceDelta) >= 3.0 || avgImb5m >= config.Thresholds.ImbalanceWarningPercent || imbStd >= 2.0 {
		if avgImb5m >= config.Thresholds.ImbalanceWarningPercent {
			return "caution", "Imbalance is trending above warning region"
		}
		if math.Abs(forceDelta) >= 3.0 {
			return "caution", "Average force is drifting"
		}
		if forceStd >= 3.0 {
			return "caution", "Force is less repeatable than normal"
		}
		return "caution", "Imbalance repeatability is degrading"
	}
	return "stable", "Process variation is low"
}

var (
	trendCache     atomic.Value
	trendCacheTime int64
)

type trendCacheEntry struct {
	Window time.Duration
	Resp   TrendResponse
}

func buildTrendResponse(ctx context.Context, window time.Duration, label string) (TrendResponse, error) {
	now := time.Now().UnixMilli()
	if cached, ok := trendCache.Load().(*trendCacheEntry); ok {
		if cached.Window == window && now-atomic.LoadInt64(&trendCacheTime) < 1000 {
			return cached.Resp, nil
		}
	}

	nowNs := time.Now().UTC().UnixNano()
	windowNs := window.Nanoseconds()
	startNs := nowNs - windowNs
	midNs := startNs + (windowNs / 2)

	force5m, err := queryNumericStats(ctx, "sum_pct", nowNs-(5*time.Minute).Nanoseconds(), nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	force1h, err := queryNumericStats(ctx, "sum_pct", nowNs-(1*time.Hour).Nanoseconds(), nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	imb5m, err := queryNumericStats(ctx, "imbalance_pct", nowNs-(5*time.Minute).Nanoseconds(), nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	imb1h, err := queryNumericStats(ctx, "imbalance_pct", nowNs-(1*time.Hour).Nanoseconds(), nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	forceOld, err := queryNumericStats(ctx, "sum_pct", startNs, midNs)
	if err != nil {
		return TrendResponse{}, err
	}
	forceNew, err := queryNumericStats(ctx, "sum_pct", midNs, nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	imbOld, err := queryNumericStats(ctx, "imbalance_pct", startNs, midNs)
	if err != nil {
		return TrendResponse{}, err
	}
	imbNew, err := queryNumericStats(ctx, "imbalance_pct", midNs, nowNs)
	if err != nil {
		return TrendResponse{}, err
	}

	forceDelta := forceNew.Avg - forceOld.Avg
	imbDelta := imbNew.Avg - imbOld.Avg

	forceDirection := classifyDirection(forceDelta, forceOld.Count, forceNew.Count, 1.0, "rising", "falling")
	imbDirection := classifyDirection(imbDelta, imbOld.Count, imbNew.Count, 0.5, "worsening", "improving")

	fullWindowForce, err := queryNumericStats(ctx, "sum_pct", startNs, nowNs)
	if err != nil {
		return TrendResponse{}, err
	}
	fullWindowImb, err := queryNumericStats(ctx, "imbalance_pct", startNs, nowNs)
	if err != nil {
		return TrendResponse{}, err
	}

	stability, reason := classifyProcessStability(
		fullWindowForce.StdDev(), fullWindowImb.StdDev(),
		forceDelta, imb5m.Avg, fullWindowForce.Count,
	)

	resp := TrendResponse{
		Window:             label,
		AvgPeak5m:          float32(force5m.Avg),
		AvgPeak1h:          float32(force1h.Avg),
		AvgImbalance5m:     float32(imb5m.Avg),
		AvgImbalance1h:     float32(imb1h.Avg),
		ForceDeltaPct:      float32(forceDelta),
		ImbalanceDeltaPct:  float32(imbDelta),
		ForceDirection:     forceDirection,
		ImbalanceDirection: imbDirection,
		ProcessStability:   stability,
		StabilityReason:    reason,
		ForceStdDev:        float32(fullWindowForce.StdDev()),
		ImbalanceStdDev:    float32(fullWindowImb.StdDev()),
		SampleCount:        fullWindowForce.Count,
		OldHalfCount:       forceOld.Count,
		NewHalfCount:       forceNew.Count,
	}

	trendCache.Store(&trendCacheEntry{Window: window, Resp: resp})
	atomic.StoreInt64(&trendCacheTime, now)
	return resp, nil
}

func queryAlarmEvents(ctx context.Context, limit int) ([]AlarmEventAPI, error) {
	if limit <= 0 {
		limit = 20
	}
	if limit > 100 {
		limit = 100
	}
	rows, err := db.QueryContext(ctx, `
		SELECT ts_unix_ns, severity, source, state, message, value, limit_value
		FROM alarm_events
		ORDER BY ts_unix_ns DESC
		LIMIT ?
	`, limit)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	events := make([]AlarmEventAPI, 0, limit)
	for rows.Next() {
		var tsUnix int64
		var severity, source, state, message string
		var value, limitValue float64
		if err := rows.Scan(&tsUnix, &severity, &source, &state, &message, &value, &limitValue); err != nil {
			return nil, err
		}
		displayTime := time.Unix(0, tsUnix).Local().Format("02.01.2006 15:04:05")
		events = append(events, AlarmEventAPI{
			Time: displayTime, Severity: severity, Source: source,
			State: state, Message: message, Value: value, Limit: limitValue,
		})
	}
	return events, rows.Err()
}

// ---------------------------------------------------------------------------
// HTTP helpers
// ---------------------------------------------------------------------------

func writeJSON(w http.ResponseWriter, status int, v any) {
	h := w.Header()
	h.Set("Content-Type", "application/json")
	h.Set("Cache-Control", "no-store")
	h.Set("Access-Control-Allow-Origin", "*")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func allowMethod(w http.ResponseWriter, r *http.Request, method string) bool {
	if r.Method == http.MethodOptions {
		h := w.Header()
		h.Set("Access-Control-Allow-Origin", "*")
		h.Set("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS")
		h.Set("Access-Control-Allow-Headers", "Content-Type")
		w.WriteHeader(http.StatusNoContent)
		return false
	}
	if r.Method != method {
		http.Error(w, `{"error":"method not allowed"}`, http.StatusMethodNotAllowed)
		return false
	}
	return true
}

func requireActiveLicense(w http.ResponseWriter, r *http.Request) bool {
	if licenseMgr == nil {
		return true
	}
	status := licenseMgr.Status()
	if !status.Locked {
		_ = licenseMgr.Touch()
		return true
	}
	writeJSON(w, http.StatusForbidden, map[string]any{
		"error":   "license required",
		"license": status,
	})
	return false
}

// ---------------------------------------------------------------------------
// HTTP handlers — core
// ---------------------------------------------------------------------------

func apiData(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	writeJSON(w, http.StatusOK, snapshotState())
}

func apiUIRevision(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	writeJSON(w, http.StatusOK, map[string]uint64{"revision": atomic.LoadUint64(&uiRevision)})
}

func apiPublicConfig(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	c := getConfigSnapshot()
	resp := PublicConfigResponse{
		Version:    version,
		UIRevision: atomic.LoadUint64(&uiRevision),
		UI:         c.UI,
		Thresholds: c.Thresholds,
		Trend:      c.Trend,
		Press:      c.Press,
		Modules:    c.Modules,
		LicenseHint: LicenseHint{
			Enabled:   c.License.Enabled,
			TrialDays: c.License.TrialDays,
		},
	}
	writeJSON(w, http.StatusOK, resp)
}

func apiHistory(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	window, label, err := parseWindow(r.URL.Query().Get("window"))
	if err != nil {
		http.Error(w, `{"error":"invalid window"}`, http.StatusBadRequest)
		return
	}
	points, err := queryHistory(r.Context(), window)
	if err != nil {
		log.Printf("history query failed: %v", err)
		http.Error(w, `{"error":"history query failed"}`, http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, HistoryResponse{Window: label, Points: points})
}

func apiTrend(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	window, label, err := parseWindow(r.URL.Query().Get("window"))
	if err != nil {
		http.Error(w, `{"error":"invalid trend window"}`, http.StatusBadRequest)
		return
	}
	resp, err := buildTrendResponse(r.Context(), window, label)
	if err != nil {
		log.Printf("trend query failed: %v", err)
		http.Error(w, `{"error":"trend query failed"}`, http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, resp)
}

func apiAlarms(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	limit := 20
	if raw := strings.TrimSpace(r.URL.Query().Get("limit")); raw != "" {
		if n, err := strconv.Atoi(raw); err == nil && n > 0 {
			limit = n
		}
	}
	events, err := queryAlarmEvents(r.Context(), limit)
	if err != nil {
		log.Printf("alarm query failed: %v", err)
		http.Error(w, `{"error":"alarm query failed"}`, http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, AlarmResponse{Events: events})
}

func serveUI(w http.ResponseWriter, r *http.Request) {
	if r.URL.Path == "/" {
		// Parse and execute template with config data
		tmpl, err := template.ParseFiles(filepath.Join("static", "index.html"))
		if err != nil {
			log.Printf("template parse error: %v", err)
			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
			return
		}

		c := getConfigSnapshot()
		data := struct {
			Title, Subtitle, LeftLabel, RightLabel, UnitForce, UnitPct string
			WarningPercent, CriticalPercent, GaugeMaxPercent           float64
			ImbalanceWarningPercent, ImbalanceCriticalPercent          float64
			MaxTonnage                                                 float64
			PollMs                                                     int
			DefaultWindow, DefaultTrendWindow                          string
			UIRevision                                                 uint64
			ShowHeaderControls, ShowVerdict, ShowSummaryBar            bool
			ShowOverview, ShowIntelligence, ShowAlarmTimeline          bool
			ShowGauges, ShowGaugeDigital, ShowTrendChart               bool
		}{
			Title:                    c.UI.Title,
			Subtitle:                 c.UI.Subtitle,
			LeftLabel:                c.UI.LeftLabel,
			RightLabel:               c.UI.RightLabel,
			UnitForce:                c.UI.UnitForce,
			UnitPct:                  c.UI.UnitPct,
			WarningPercent:           c.Thresholds.WarningPercent,
			CriticalPercent:          c.Thresholds.CriticalPercent,
			GaugeMaxPercent:          c.Thresholds.GaugeMaxPercent,
			ImbalanceWarningPercent:  c.Thresholds.ImbalanceWarningPercent,
			ImbalanceCriticalPercent: c.Thresholds.ImbalanceCriticalPercent,
			MaxTonnage:               c.Press.MaxTonnage,
			PollMs:                   c.PLC.PollMs,
			DefaultWindow:            fmt.Sprintf("%dm", c.Trend.Minutes),
			DefaultTrendWindow:       fmt.Sprintf("%dm", c.Trend.Minutes),
			UIRevision:               atomic.LoadUint64(&uiRevision),
			ShowHeaderControls:       boolValue(c.Modules.ShowHeaderControls, true),
			ShowVerdict:              boolValue(c.Modules.ShowVerdict, true),
			ShowSummaryBar:           boolValue(c.Modules.ShowSummaryBar, true),
			ShowOverview:             boolValue(c.Modules.ShowOverview, true),
			ShowIntelligence:         boolValue(c.Modules.ShowIntelligence, true),
			ShowAlarmTimeline:        boolValue(c.Modules.ShowAlarmTimeline, true),
			ShowGauges:               boolValue(c.Modules.ShowGauges, true),
			ShowGaugeDigital:         boolValue(c.Modules.ShowGaugeDigital, false),
			ShowTrendChart:           boolValue(c.Modules.ShowTrendChart, true),
		}

		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		if err := tmpl.Execute(w, data); err != nil {
			log.Printf("template execute error: %v", err)
		}
		return
	}
	http.NotFound(w, r)
}

// ---------------------------------------------------------------------------
// HTTP handlers — MQTT REST API
// ---------------------------------------------------------------------------

func apiMQTTStatus(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if mqttMgr == nil {
		writeJSON(w, http.StatusOK, MQTTStatusResponse{
			Enabled:    false,
			Connected:  false,
			Broker:     "",
			Subscribed: []string{},
		})
		return
	}
	writeJSON(w, http.StatusOK, mqttMgr.status())
}

func apiMQTTPublish(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodPost) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	if mqttMgr == nil {
		http.Error(w, `{"error":"MQTT not enabled"}`, http.StatusServiceUnavailable)
		return
	}

	var req MQTTPublishRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, `{"error":"invalid JSON body"}`, http.StatusBadRequest)
		return
	}
	if strings.TrimSpace(req.Topic) == "" {
		http.Error(w, `{"error":"topic required"}`, http.StatusBadRequest)
		return
	}
	if req.QoS < 0 || req.QoS > 2 {
		http.Error(w, `{"error":"qos must be 0, 1, or 2"}`, http.StatusBadRequest)
		return
	}

	if err := mqttMgr.publish(req.Topic, req.Payload, byte(req.QoS), req.Retain); err != nil {
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": err.Error()})
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "published", "topic": req.Topic})
}

func apiMQTTMessages(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	if mqttMgr == nil {
		writeJSON(w, http.StatusOK, map[string]any{"messages": []MQTTReceivedMsg{}, "enabled": false})
		return
	}
	limit := 50
	if raw := strings.TrimSpace(r.URL.Query().Get("limit")); raw != "" {
		if n, err := strconv.Atoi(raw); err == nil && n > 0 {
			limit = n
		}
	}
	msgs := mqttMgr.getMessages(limit)
	writeJSON(w, http.StatusOK, map[string]any{"messages": msgs, "count": len(msgs)})
}

func apiMQTTSubscribe(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodPost) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	if mqttMgr == nil {
		http.Error(w, `{"error":"MQTT not enabled"}`, http.StatusServiceUnavailable)
		return
	}

	var req MQTTSubscribeRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, `{"error":"invalid JSON body"}`, http.StatusBadRequest)
		return
	}
	if strings.TrimSpace(req.Topic) == "" {
		http.Error(w, `{"error":"topic required"}`, http.StatusBadRequest)
		return
	}
	if req.QoS < 0 || req.QoS > 2 {
		http.Error(w, `{"error":"qos must be 0, 1, or 2"}`, http.StatusBadRequest)
		return
	}

	if err := mqttMgr.subscribe(req.Topic, byte(req.QoS)); err != nil {
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": err.Error()})
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "subscribed", "topic": req.Topic})
}

func apiMQTTUnsubscribe(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodDelete) {
		return
	}
	if !requireActiveLicense(w, r) {
		return
	}
	if mqttMgr == nil {
		http.Error(w, `{"error":"MQTT not enabled"}`, http.StatusServiceUnavailable)
		return
	}

	var req MQTTSubscribeRequest
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		http.Error(w, `{"error":"invalid JSON body"}`, http.StatusBadRequest)
		return
	}
	if strings.TrimSpace(req.Topic) == "" {
		http.Error(w, `{"error":"topic required"}`, http.StatusBadRequest)
		return
	}

	if err := mqttMgr.unsubscribe(req.Topic); err != nil {
		writeJSON(w, http.StatusBadGateway, map[string]string{"error": err.Error()})
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "unsubscribed", "topic": req.Topic})
}

// ---------------------------------------------------------------------------
// HTTP handlers — License API
// ---------------------------------------------------------------------------

type activateRequestBody struct {
	LicenseText string `json:"license_text"`
}

func apiLicenseStatus(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if licenseMgr == nil {
		writeJSON(w, http.StatusOK, LicenseStatus{
			Enabled: false,
			Mode:    "disabled",
			Message: "licensing disabled",
		})
		return
	}
	writeJSON(w, http.StatusOK, licenseMgr.Status())
}

func apiLicenseRequest(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodGet) {
		return
	}
	if licenseMgr == nil {
		writeJSON(w, http.StatusOK, map[string]any{"enabled": false})
		return
	}
	req := licenseMgr.BuildActivationRequest()
	writeJSON(w, http.StatusOK, req)
}

func apiLicenseActivate(w http.ResponseWriter, r *http.Request) {
	if !allowMethod(w, r, http.MethodPost) {
		return
	}
	if licenseMgr == nil {
		http.Error(w, `{"error":"licensing disabled"}`, http.StatusServiceUnavailable)
		return
	}

	raw, err := ioReadAllLimit(r.Body, 1<<20)
	if err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": err.Error()})
		return
	}
	payload := strings.TrimSpace(string(raw))
	if payload == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "request body is empty"})
		return
	}

	licenseText := payload
	var wrapped activateRequestBody
	if err := json.Unmarshal(raw, &wrapped); err == nil && strings.TrimSpace(wrapped.LicenseText) != "" {
		licenseText = wrapped.LicenseText
	}

	if err := licenseMgr.ActivateFromText(licenseText); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]any{
			"error":   err.Error(),
			"license": licenseMgr.Status(),
		})
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"status":  "activated",
		"license": licenseMgr.Status(),
	})
}

// ---------------------------------------------------------------------------
// Misc helpers
// ---------------------------------------------------------------------------

func ioReadAllLimit(r io.Reader, max int64) ([]byte, error) {
	lr := &io.LimitedReader{R: r, N: max + 1}
	data, err := io.ReadAll(lr)
	if err != nil {
		return nil, err
	}
	if int64(len(data)) > max {
		return nil, fmt.Errorf("payload too large")
	}
	return data, nil
}

func startLicenseHeartbeat(ctx context.Context) {
	if licenseMgr == nil {
		return
	}
	_ = licenseMgr.Touch()
	ticker := time.NewTicker(15 * time.Minute)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if err := licenseMgr.Touch(); err != nil {
				log.Printf("license heartbeat failed: %v", err)
			}
		}
	}
}

// ---------------------------------------------------------------------------
// main
// ---------------------------------------------------------------------------

func main() {
	wd, err := os.Getwd()
	if err != nil {
		log.Fatalf("failed to get working directory: %v", err)
	}

	configPath := filepath.Join(wd, "config.yaml")
	cfg, err = loadOrCreateConfig(configPath)
	if err != nil {
		log.Fatalf("failed to load config: %v", err)
	}
	if err := validateConfig(cfg); err != nil {
		log.Fatalf("invalid config: %v", err)
	}

	dbPath := cfg.DB.Path
	if !filepath.IsAbs(dbPath) {
		dbPath = filepath.Join(wd, dbPath)
	}

	db, err = initDatabase(dbPath, cfg.DB)
	if err != nil {
		log.Fatalf("failed to init database: %v", err)
	}
	defer db.Close()

	licenseDataDir := cfg.License.DataDir
	if !filepath.IsAbs(licenseDataDir) {
		licenseDataDir = filepath.Join(wd, licenseDataDir)
	}
	licenseMgr, err = NewLicenseManager(cfg.License, licenseDataDir)
	if err != nil {
		log.Fatalf("failed to initialize license manager: %v", err)
	}

	sampleCh = make(chan Sample, cfg.DB.WriterQueueSize)
	alarmCh = make(chan AlarmEvent, cfg.DB.AlarmQueueSize)

	log.Printf("S7-1200 Force Monitor v%s", version)
	log.Printf("Config:  %s", configPath)
	log.Printf("DB:      %s", dbPath)
	log.Printf("PLC:     ip=%s db=%d rack=%d slot=%d poll=%dms",
		cfg.PLC.IP, cfg.PLC.DBNum, cfg.PLC.Rack, cfg.PLC.Slot, cfg.PLC.PollMs)
	log.Printf("Press:   MAX_TONNAGE=%.2f %s", cfg.Press.MaxTonnage, cfg.UI.UnitForce)
	if licenseMgr != nil {
		ls := licenseMgr.Status()
		log.Printf("License: mode=%s locked=%v fingerprint=%s", ls.Mode, ls.Locked, ls.FingerprintShort)
	}

	if cfg.MQTT.Enabled {
		mqttMgr = newMQTTManager(cfg.MQTT)
		mqttAlarmCh = make(chan AlarmEvent, 256)
		go mqttAlarmWorker()
		if err := mqttMgr.connect(); err != nil {
			log.Printf("MQTT initial connect failed (will retry): %v", err)
		} else {
			log.Printf("MQTT: connected to %s (prefix=%s)", cfg.MQTT.Broker, cfg.MQTT.TopicPrefix)
		}
	} else {
		log.Printf("MQTT: disabled (set mqtt.enabled: true in config to enable)")
	}

	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	if err := startConfigWatcher(ctx, configPath); err != nil {
		log.Printf("config watch disabled: %v", err)
	} else {
		log.Printf("Config watcher enabled for %s", configPath)
	}

	dbCfg := cfg.DB

	var wg sync.WaitGroup
	wg.Add(4)
	go func() { defer wg.Done(); startDBWriter(ctx, db, dbCfg.BatchSize, dbCfg.FlushIntervalMs) }()
	go func() { defer wg.Done(); startAlarmWriter(ctx, db, dbCfg.BatchSize, dbCfg.FlushIntervalMs) }()
	go func() { defer wg.Done(); startDBCleanup(ctx, db, dbCfg.RetentionDays, dbCfg.CleanupIntervalHr) }()
	go func() { defer wg.Done(); startPLCPoller(ctx) }()

	if cfg.MQTT.Enabled {
		wg.Add(1)
		go func() { defer wg.Done(); startMQTTPublisher(ctx) }()
	}

	wg.Add(1)
	go func() { defer wg.Done(); startLicenseHeartbeat(ctx) }()

	mux := http.NewServeMux()

	staticDir := http.Dir("static")
	fileServer := http.FileServer(staticDir)
	mux.Handle("/static/", http.StripPrefix("/static/", fileServer))
	mux.HandleFunc("/", serveUI)

	mux.HandleFunc("/api/data", apiData)
	mux.HandleFunc("/api/ui-revision", apiUIRevision)
	mux.HandleFunc("/api/config/public", apiPublicConfig)
	mux.HandleFunc("/api/history", apiHistory)
	mux.HandleFunc("/api/trend", apiTrend)
	mux.HandleFunc("/api/alarms", apiAlarms)

	mux.HandleFunc("/api/mqtt/status", apiMQTTStatus)
	mux.HandleFunc("/api/mqtt/publish", apiMQTTPublish)
	mux.HandleFunc("/api/mqtt/messages", apiMQTTMessages)
	mux.HandleFunc("/api/mqtt/subscribe", apiMQTTSubscribe)
	mux.HandleFunc("/api/mqtt/unsubscribe", apiMQTTUnsubscribe)

	mux.HandleFunc("/api/license/status", apiLicenseStatus)
	mux.HandleFunc("/api/license/request", apiLicenseRequest)
	mux.HandleFunc("/api/license/activate", apiLicenseActivate)

	srv := &http.Server{
		Addr:         cfg.Server.ListenAddr,
		Handler:      mux,
		ReadTimeout:  15 * time.Second,
		WriteTimeout: 15 * time.Second,
		IdleTimeout:  60 * time.Second,
	}

	log.Printf("Listening on http://localhost%s", cfg.Server.ListenAddr)
	log.Printf("License API: GET /api/license/status | GET /api/license/request | POST /api/license/activate")

	go func() {
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			log.Fatalf("HTTP server error: %v", err)
		}
	}()

	<-ctx.Done()
	log.Println("Shutting down — flushing DB writers...")

	shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := srv.Shutdown(shutdownCtx); err != nil {
		log.Printf("HTTP server shutdown error: %v", err)
	}

	if mqttMgr != nil {
		mqttMgr.disconnect()
		log.Println("MQTT disconnected")
	}

	wg.Wait()
	log.Println("Shutdown complete")
}