package eu.brassepc.fitnessdroid.data

import android.Manifest
import android.app.Notification
import android.app.NotificationChannel
import android.app.NotificationManager
import android.app.PendingIntent
import android.app.Service
import android.content.Context
import android.content.Intent
import android.content.pm.PackageManager
import android.content.pm.ServiceInfo
import android.location.Location
import android.location.LocationListener
import android.location.LocationManager
import android.os.Looper
import android.os.SystemClock
import androidx.core.app.NotificationCompat
import androidx.core.content.ContextCompat
import eu.brassepc.fitnessdroid.MainActivity
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.cancel
import kotlinx.coroutines.delay
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.StateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.launch

/** Spårningens fas: söker GPS-fix innan klockan startar, sen aktiv. */
enum class TrackingPhase { IDLE, SEARCHING_GPS, ACTIVE }

/** Läget för en pågående (eller nyss avslutad) aktivitetsspårning. */
data class TrackingState(
    val isActive: Boolean = false,
    val phase: TrackingPhase = TrackingPhase.IDLE,
    /** Aktivitetstypen som spåras */
    val typeId: Int = 0,
    val typeKey: String = "",
    val typeName: String = "",
    val category: String = "OTHER",
    val met: Double = 4.0,
    val isDistanceBased: Boolean = false,
    val startedAtEpochMs: Long = 0,
    val elapsedSeconds: Int = 0,
    val distanceMeters: Double = 0.0,
    val elevationGainMeters: Double = 0.0,
    /** Senaste GPS-position (lat, lon) + hela spåret */
    val points: List<Pair<Double, Double>> = emptyList(),
    val currentSpeedKmh: Double? = null,
    val kcal: Double? = null,
    val gpsFix: Boolean = false,
)

/**
 * Foreground-service som spårar en aktivitet: GPS-rutt, distans, höjdmeter,
 * tid och live-kcal. För icke-distansaktiviteter (fäktning m.m.) körs bara
 * timern — ingen GPS. UI:t läser [state]; servicen äger sanningen så
 * spårningen överlever att appen swipas bort från recents.
 */
class TrackingService : Service(), LocationListener {

    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)
    private var locationManager: LocationManager? = null

    private var weightKg: Double? = null
    private var activeSinceElapsed = 0L
    private var lastLocation: Location? = null
    // Glidande medel av höjd för att filtrera GPS-brus innan höjdmeter summeras
    private val altitudeWindow = ArrayDeque<Double>()
    private var smoothedAltitude: Double? = null

    override fun onCreate() {
        super.onCreate()
        createChannel()
    }

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        when (intent?.action) {
            ACTION_STOP -> {
                stopTracking()
                return START_NOT_STICKY
            }
            ACTION_START_NOW -> {
                activate("starta ändå")
                return START_STICKY
            }
            else -> {
                if (intent == null) return START_NOT_STICKY
                startTracking(intent)
            }
        }
        return START_STICKY
    }

    private fun startTracking(intent: Intent) {
        val distanceBased = intent.getBooleanExtra(EXTRA_DISTANCE_BASED, false)
        weightKg = intent.getDoubleExtra(EXTRA_WEIGHT_KG, -1.0).takeIf { it > 0 }

        _state.value = TrackingState(
            isActive = true,
            phase = if (distanceBased) TrackingPhase.SEARCHING_GPS else TrackingPhase.ACTIVE,
            typeId = intent.getIntExtra(EXTRA_TYPE_ID, 0),
            typeKey = intent.getStringExtra(EXTRA_TYPE_KEY) ?: "",
            typeName = intent.getStringExtra(EXTRA_TYPE_NAME) ?: "Aktivitet",
            category = intent.getStringExtra(EXTRA_CATEGORY) ?: "OTHER",
            met = intent.getDoubleExtra(EXTRA_MET, 4.0),
            isDistanceBased = distanceBased,
            startedAtEpochMs = System.currentTimeMillis(),
        )
        TrackLog.clear()
        TrackLog.log(
            "start: ${_state.value.typeName} (distans=$distanceBased, vikt=${weightKg ?: "?"} kg)" +
                if (distanceBased) " — väntar på GPS-fix" else ""
        )

        val type = if (distanceBased) {
            ServiceInfo.FOREGROUND_SERVICE_TYPE_LOCATION
        } else {
            // Timer-läge behöver ingen plats, men servicetypen är deklarerad som location
            ServiceInfo.FOREGROUND_SERVICE_TYPE_LOCATION
        }
        startForeground(NOTIFICATION_ID, buildNotification(), type)

        if (distanceBased) startGps()

        // Tick: tid + kcal + notis. Klockan räknar från att fasen blev ACTIVE.
        scope.launch {
            while (_state.value.isActive) {
                val s = _state.value
                if (s.phase != TrackingPhase.ACTIVE) {
                    delay(500)
                    continue
                }
                if (activeSinceElapsed == 0L) activeSinceElapsed = SystemClock.elapsedRealtime()
                val elapsed = ((SystemClock.elapsedRealtime() - activeSinceElapsed) / 1000).toInt()
                _state.value = s.copy(
                    elapsedSeconds = elapsed,
                    kcal = ActivityKcal.estimate(
                        met = s.met,
                        category = s.category,
                        isDistanceBased = s.isDistanceBased,
                        weightKg = weightKg,
                        durationSeconds = elapsed,
                        distanceMeters = s.distanceMeters.takeIf { it > 0 },
                        elevationGainMeters = s.elevationGainMeters.takeIf { it > 0 },
                        rpe = null,
                    ),
                )
                if (elapsed % 10 == 0) {
                    getSystemService(NotificationManager::class.java)
                        .notify(NOTIFICATION_ID, buildNotification())
                }
                delay(1000)
            }
        }
    }

    private fun startGps() {
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION)
            != PackageManager.PERMISSION_GRANTED
        ) {
            TrackLog.log("FEL: platsbehörighet saknas — ingen GPS-lyssning")
            return
        }
        locationManager = getSystemService(Context.LOCATION_SERVICE) as LocationManager
        TrackLog.log("GPS-lyssning begärd (GPS_PROVIDER, 2 s / 3 m)")
        runCatching {
            locationManager?.requestLocationUpdates(
                LocationManager.GPS_PROVIDER,
                2000L, // ms
                3f,    // meter
                this,
                Looper.getMainLooper(),
            )
        }
    }

    /** Gå från GPS-sökning till aktiv (klockan börjar ticka). */
    private fun activate(reason: String) {
        val s = _state.value
        if (!s.isActive || s.phase == TrackingPhase.ACTIVE) return
        TrackLog.log("aktiverad ($reason)")
        _state.value = s.copy(
            phase = TrackingPhase.ACTIVE,
            startedAtEpochMs = System.currentTimeMillis(),
        )
    }

    override fun onLocationChanged(location: Location) {
        val s = _state.value
        if (!s.isActive || !s.isDistanceBased) return
        val acc = if (location.hasAccuracy()) location.accuracy else -1f
        // Släng riktigt dåliga fixar
        if (location.hasAccuracy() && location.accuracy > 30f) {
            TrackLog.log("fix förkastad: noggrannhet ${"%.0f".format(acc)} m (>30)")
            return
        }
        TrackLog.log(
            "fix: acc=${"%.0f".format(acc)} m alt=${if (location.hasAltitude()) "%.0f".format(location.altitude) else "?"}" +
                " fart=${if (location.hasSpeed()) "%.1f".format(location.speed * 3.6) else "?"} km/h"
        )
        if (s.phase == TrackingPhase.SEARCHING_GPS) activate("GPS-fix")

        var distance = s.distanceMeters
        var elevGain = s.elevationGainMeters

        lastLocation?.let { prev ->
            val d = prev.distanceTo(location).toDouble()
            // Ignorera mikrobrus när man står stilla
            if (d >= 2.0) distance += d
        }

        if (location.hasAltitude()) {
            altitudeWindow.addLast(location.altitude)
            if (altitudeWindow.size > 5) altitudeWindow.removeFirst()
            val avg = altitudeWindow.average()
            smoothedAltitude?.let { prevAlt ->
                val delta = avg - prevAlt
                // Bara tydliga stigningar räknas som höjdmeter
                if (delta > 1.0) elevGain += delta
            }
            smoothedAltitude = avg
        }

        lastLocation = location
        _state.value = s.copy(
            distanceMeters = distance,
            elevationGainMeters = elevGain,
            points = s.points + (location.latitude to location.longitude),
            currentSpeedKmh = if (location.hasSpeed()) location.speed * 3.6 else null,
            gpsFix = true,
        )
    }

    private fun stopTracking() {
        val s = _state.value
        TrackLog.log(
            "stopp: ${s.elapsedSeconds}s, ${"%.0f".format(s.distanceMeters)} m, " +
                "+${"%.0f".format(s.elevationGainMeters)} hm, ${s.points.size} punkter, kcal=${s.kcal?.toInt() ?: "?"}"
        )
        locationManager?.removeUpdates(this)
        _state.value = _state.value.copy(isActive = false)
        stopForeground(STOP_FOREGROUND_REMOVE)
        stopSelf()
    }

    override fun onDestroy() {
        locationManager?.removeUpdates(this)
        if (_state.value.isActive) _state.value = _state.value.copy(isActive = false)
        scope.cancel()
        super.onDestroy()
    }

    override fun onBind(intent: Intent?) = null

    private fun createChannel() {
        val channel = NotificationChannel(
            CHANNEL_ID, "Aktivitetsspårning", NotificationManager.IMPORTANCE_LOW,
        ).apply { description = "Pågående aktivitet (GPS/timer)" }
        getSystemService(NotificationManager::class.java).createNotificationChannel(channel)
    }

    private fun buildNotification(): Notification {
        val s = _state.value
        val open = PendingIntent.getActivity(
            this, 0,
            Intent(this, MainActivity::class.java),
            PendingIntent.FLAG_IMMUTABLE,
        )
        val text = buildString {
            append(formatElapsed(s.elapsedSeconds))
            if (s.isDistanceBased) append(" · ${"%.2f".format(s.distanceMeters / 1000)} km")
            s.kcal?.let { append(" · ${it.toInt()} kcal") }
        }
        return NotificationCompat.Builder(this, CHANNEL_ID)
            .setSmallIcon(android.R.drawable.ic_menu_mylocation)
            .setContentTitle(s.typeName)
            .setContentText(text)
            .setOngoing(true)
            .setOnlyAlertOnce(true)
            .setContentIntent(open)
            .build()
    }

    private fun formatElapsed(sec: Int): String {
        val h = sec / 3600
        val m = (sec % 3600) / 60
        val s = sec % 60
        return if (h > 0) "%d:%02d:%02d".format(h, m, s) else "%d:%02d".format(m, s)
    }

    companion object {
        private const val CHANNEL_ID = "activity_tracking"
        private const val NOTIFICATION_ID = 44

        const val ACTION_STOP = "eu.brassepc.fitnessdroid.TRACKING_STOP"
        const val ACTION_START_NOW = "eu.brassepc.fitnessdroid.TRACKING_START_NOW"
        const val EXTRA_TYPE_ID = "typeId"
        const val EXTRA_TYPE_KEY = "typeKey"
        const val EXTRA_TYPE_NAME = "typeName"
        const val EXTRA_CATEGORY = "category"
        const val EXTRA_MET = "met"
        const val EXTRA_DISTANCE_BASED = "distanceBased"
        const val EXTRA_WEIGHT_KG = "weightKg"

        private val _state = MutableStateFlow(TrackingState())
        /** Läses av UI:t — servicen äger sanningen. */
        val state: StateFlow<TrackingState> = _state.asStateFlow()

        fun start(context: Context, type: ActivityType, weightKg: Double?) {
            val intent = Intent(context, TrackingService::class.java).apply {
                putExtra(EXTRA_TYPE_ID, type.id)
                putExtra(EXTRA_TYPE_KEY, type.key)
                putExtra(EXTRA_TYPE_NAME, type.nameSv)
                putExtra(EXTRA_CATEGORY, type.category)
                putExtra(EXTRA_MET, type.met)
                putExtra(EXTRA_DISTANCE_BASED, type.isDistanceBased)
                weightKg?.let { putExtra(EXTRA_WEIGHT_KG, it) }
            }
            context.startForegroundService(intent)
        }

        fun stop(context: Context) {
            context.startService(
                Intent(context, TrackingService::class.java).apply { action = ACTION_STOP }
            )
        }

        /** "Starta ändå" — börja räkna tid utan att vänta på GPS-fixen. */
        fun startNow(context: Context) {
            context.startService(
                Intent(context, TrackingService::class.java).apply { action = ACTION_START_NOW }
            )
        }
    }
}