SyncFlow/app/src/main/kotlin/com/syncflow/worker/FileWatchService.kt

package com.syncflow.worker

import android.app.*
import android.content.Context
import android.content.Intent
import android.database.ContentObserver
import android.net.Uri
import android.os.Build
import android.os.FileObserver
import android.os.Handler
import android.os.IBinder
import android.os.Looper
import android.provider.DocumentsContract
import androidx.core.app.NotificationCompat
import androidx.work.ExistingWorkPolicy
import androidx.work.WorkInfo
import androidx.work.WorkManager
import kotlinx.coroutines.flow.first
import com.syncflow.MainActivity
import com.syncflow.R
import com.syncflow.data.db.SyncFileStateDao
import com.syncflow.data.db.SyncPairDao
import com.syncflow.domain.model.ScheduleType
import dagger.hilt.android.AndroidEntryPoint
import kotlinx.coroutines.*
import kotlinx.coroutines.sync.Mutex
import kotlinx.coroutines.sync.withLock
import timber.log.Timber
import java.io.File
import javax.inject.Inject

@AndroidEntryPoint
class FileWatchService : Service() {

    @Inject lateinit var syncPairDao: SyncPairDao
    @Inject lateinit var fileStateDao: SyncFileStateDao

    private val scope = CoroutineScope(Dispatchers.IO + SupervisorJob())
    private val mainHandler = Handler(Looper.getMainLooper())
    // Prevents concurrent refresh() calls from doubling watchers + catchup scans
    private val refreshMutex = Mutex()

    // Multiple FileObserver instances per pair: one per directory (recursive)
    private val fileObservers = mutableMapOf<Long, MutableList<FileObserver>>()
    private val contentObservers = mutableMapOf<Long, ContentObserver>()
    private val debounceJobs = mutableMapOf<Long, Job>()
    // After a watcher-triggered sync completes, suppress FileObserver events for this long
    // to stop the feedback loop: sync writes files → FileObserver fires → another sync → repeat.
    private val syncCooldownUntil = mutableMapOf<Long, Long>()

    companion object {
        const val CHANNEL_WATCH = "sync_watching"
        private const val NOTIFICATION_ID = 1002

        fun start(context: Context) {
            val intent = Intent(context, FileWatchService::class.java)
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                context.startForegroundService(intent)
            } else {
                context.startService(intent)
            }
        }

        fun stop(context: Context) {
            context.stopService(Intent(context, FileWatchService::class.java))
        }
    }

    override fun onCreate() {
        super.onCreate()
        ensureChannel()
        startForeground(NOTIFICATION_ID, buildNotification(0))
    }

    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
        scope.launch { refresh() }
        return START_STICKY
    }

    override fun onDestroy() {
        clearWatchers()
        scope.cancel()
        super.onDestroy()
    }

    override fun onBind(intent: Intent?): IBinder? = null

    private suspend fun refresh() = refreshMutex.withLock {
        clearWatchers()
        val pairs = syncPairDao.getEnabled().filter { it.scheduleType == ScheduleType.ON_CHANGE }

        pairs.forEach { pair ->
            val pairId = pair.id
            val localPath = pair.localPath

            if (localPath.startsWith("content://")) {
                // Try to resolve the SAF tree URI to a real filesystem path so we can use
                // FileObserver. ContentObserver on a DocumentsProvider tree URI only fires
                // when changes come through the SAF API, not for raw filesystem writes.
                val realPath = safTreeUriToRealPath(localPath)
                if (realPath != null) {
                    watchPath(realPath, pairId, pair.wifiOnly, pair.chargingOnly)
                } else {
                    // Fallback: register a ContentObserver for SAF paths that can't be resolved
                    val treeUri = Uri.parse(localPath)
                    val observer = object : ContentObserver(mainHandler) {
                        override fun onChange(selfChange: Boolean) = onChangeDetected(pairId, pair.wifiOnly, pair.chargingOnly)
                        override fun onChange(selfChange: Boolean, uri: Uri?) = onChangeDetected(pairId, pair.wifiOnly, pair.chargingOnly)
                    }
                    contentResolver.registerContentObserver(treeUri, true, observer)
                    contentObservers[pairId] = observer
                    Timber.d("FileWatchService: watching SAF URI (ContentObserver fallback) for pair $pairId")
                }
            } else {
                watchPath(localPath, pairId, pair.wifiOnly, pair.chargingOnly)
            }
        }

        val count = fileObservers.keys.size + contentObservers.size
        updateNotification(count)

        if (count == 0) {
            Timber.d("FileWatchService: no ON_CHANGE pairs, stopping")
            stopSelf()
        }
    }

    private fun safTreeUriToRealPath(uriString: String): String? {
        return try {
            val treeUri = Uri.parse(uriString)
            val docId = DocumentsContract.getTreeDocumentId(treeUri)
            // docId format is "primary:RelativePath" for primary internal storage
            if (docId.startsWith("primary:")) {
                val relative = docId.removePrefix("primary:")
                "/storage/emulated/0/$relative"
            } else {
                null
            }
        } catch (e: Exception) {
            Timber.w("FileWatchService: could not resolve SAF URI to real path: $e")
            null
        }
    }

    private fun watchPath(path: String, pairId: Long, wifiOnly: Boolean, chargingOnly: Boolean) {
        val dir = File(path)
        if (!dir.exists()) {
            Timber.w("FileWatchService: path does not exist for pair $pairId: $path")
            return
        }
        fileObservers[pairId] = mutableListOf()
        // Set startup cooldown BEFORE registering watchers so inotify events that fire
        // immediately on registration don't trigger the debounce before catchupScan runs.
        syncCooldownUntil[pairId] = System.currentTimeMillis() + 15_000
        watchDirRecursive(dir, pairId, wifiOnly, chargingOnly)
        Timber.d("FileWatchService: watching pair $pairId at $path (${fileObservers[pairId]?.size} dirs)")
        scope.launch { catchupScan(pairId, dir, wifiOnly, chargingOnly) }
    }

    private fun watchDirRecursive(dir: File, pairId: Long, wifiOnly: Boolean, chargingOnly: Boolean) {
        if (!dir.isDirectory) return
        val mask = FileObserver.CREATE or FileObserver.DELETE or FileObserver.MODIFY or
                   FileObserver.MOVED_FROM or FileObserver.MOVED_TO
        val observer = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            object : FileObserver(dir, mask) {
                override fun onEvent(event: Int, path: String?) {
                    if (event and FileObserver.CREATE != 0 && path != null) {
                        val created = File(dir, path)
                        if (created.isDirectory) watchDirRecursive(created, pairId, wifiOnly, chargingOnly)
                    }
                    onChangeDetected(pairId, wifiOnly, chargingOnly)
                }
            }
        } else {
            @Suppress("DEPRECATION")
            object : FileObserver(dir.absolutePath, mask) {
                override fun onEvent(event: Int, path: String?) {
                    if (event and FileObserver.CREATE != 0 && path != null) {
                        val created = File(dir, path)
                        if (created.isDirectory) watchDirRecursive(created, pairId, wifiOnly, chargingOnly)
                    }
                    onChangeDetected(pairId, wifiOnly, chargingOnly)
                }
            }
        }
        observer.startWatching()
        fileObservers.getOrPut(pairId) { mutableListOf() }.add(observer)
        // Recursively watch existing subdirectories
        dir.listFiles()?.filter { it.isDirectory }?.forEach { sub ->
            watchDirRecursive(sub, pairId, wifiOnly, chargingOnly)
        }
    }

    private suspend fun catchupScan(pairId: Long, dir: File, wifiOnly: Boolean, chargingOnly: Boolean) {
        val known = fileStateDao.getForPair(pairId).associateBy { it.relativePath }
        if (known.isEmpty()) return // Never synced — first sync will be triggered manually

        val current = mutableMapOf<String, Long>()
        dir.walk().filter { it.isFile }.forEach { f ->
            current[f.relativeTo(dir).path.replace('\\', '/')] = f.lastModified()
        }

        val hasNew      = current.any { (rel, _) -> rel !in known }
        val hasModified = current.any { (rel, mtime) ->
            val s = known[rel]; s != null && s.localModifiedAt != null &&
            s.localModifiedAt.toEpochMilli() != mtime
        }
        val hasDeleted  = known.keys.any { rel -> rel !in current }

        if (hasNew || hasModified || hasDeleted) {
            Timber.d("FileWatchService: catchup detected changes for pair $pairId, scheduling sync")
            val pair = syncPairDao.getById(pairId) ?: return
            // Cancel any debounce that started before our startup cooldown was set
            debounceJobs[pairId]?.cancel()
            debounceJobs.remove(pairId)
            // Hold cooldown for duration of sync + 60s settle
            syncCooldownUntil[pairId] = System.currentTimeMillis() + 120_000
            val req = SyncWorker.buildOneTimeRequest(pairId, wifiOnly, chargingOnly)
            WorkManager.getInstance(applicationContext)
                .enqueueUniqueWork("catchup_$pairId", ExistingWorkPolicy.KEEP, req)
            scope.launch {
                try {
                    WorkManager.getInstance(applicationContext)
                        .getWorkInfoByIdFlow(req.id)
                        .first { it?.state?.isFinished == true }
                    syncCooldownUntil[pairId] = System.currentTimeMillis() + 60_000
                } catch (e: CancellationException) {
                    throw e
                } catch (_: Exception) {
                    syncCooldownUntil[pairId] = System.currentTimeMillis() + 60_000
                }
            }
        }
    }

    private fun onChangeDetected(pairId: Long, wifiOnly: Boolean, chargingOnly: Boolean) {
        // Ignore events fired by our own sync writing files — prevents the feedback loop
        // where downloaded/uploaded files trigger another sync indefinitely.
        if (System.currentTimeMillis() < (syncCooldownUntil[pairId] ?: 0L)) {
            Timber.d("FileWatchService: suppressing change event for pair $pairId (sync cooldown)")
            return
        }

        debounceJobs[pairId]?.cancel()
        debounceJobs[pairId] = scope.launch {
            delay(5_000)
            // Re-check: catchupScan or another path may have already set a cooldown
            // and handled this sync while we were waiting.
            if (System.currentTimeMillis() < (syncCooldownUntil[pairId] ?: 0L)) {
                Timber.d("FileWatchService: debounce fired but cooldown active for pair $pairId, skipping")
                return@launch
            }
            val pair = syncPairDao.getById(pairId)
            if (pair == null || !pair.isEnabled) return@launch
            Timber.d("FileWatchService: triggering sync for pair $pairId after debounce")

            // Block new triggers from this point until 60s after sync completes
            syncCooldownUntil[pairId] = System.currentTimeMillis() + 120_000

            val req = SyncWorker.buildOneTimeRequest(pairId, wifiOnly, chargingOnly, silent = true)
            WorkManager.getInstance(applicationContext)
                .enqueueUniqueWork("onchange_$pairId", ExistingWorkPolicy.KEEP, req)

            updateNotificationDynamic("Syncing: ${pair.name}…")

            scope.launch {
                try {
                    val info = WorkManager.getInstance(applicationContext)
                        .getWorkInfoByIdFlow(req.id)
                        .first { it?.state?.isFinished == true }
                    // Extend cooldown: 60s after sync finishes to let filesystem settle
                    syncCooldownUntil[pairId] = System.currentTimeMillis() + 60_000
                    val summary = info?.outputData?.getString(SyncWorker.KEY_RESULT_SUMMARY)
                    val watchCount = fileObservers.keys.size + contentObservers.size
                    val watching = "Watching $watchCount folder${if (watchCount != 1) "s" else ""}"
                    if (info?.state == WorkInfo.State.SUCCEEDED && summary != null) {
                        updateNotificationDynamic("${pair.name}: $summary — $watching")
                    } else {
                        updateNotificationDynamic("$watching")
                    }
                    delay(12_000)
                    updateNotificationDynamic(null)
                } catch (e: CancellationException) {
                    throw e
                } catch (_: Exception) {
                    syncCooldownUntil[pairId] = System.currentTimeMillis() + 60_000
                    updateNotificationDynamic(null)
                }
            }
        }
    }

    private fun clearWatchers() {
        fileObservers.values.flatten().forEach { it.stopWatching() }
        fileObservers.clear()
        contentObservers.values.forEach { contentResolver.unregisterContentObserver(it) }
        contentObservers.clear()
        debounceJobs.values.forEach { it.cancel() }
        debounceJobs.clear()
        syncCooldownUntil.clear()
    }

    private fun ensureChannel() {
        val nm = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        if (nm.getNotificationChannel(CHANNEL_WATCH) == null) {
            nm.createNotificationChannel(
                NotificationChannel(CHANNEL_WATCH, "File watching", NotificationManager.IMPORTANCE_LOW).apply {
                    description = "Background service watching folders for changes"
                    setShowBadge(false)
                }
            )
        }
    }

    private fun buildNotification(count: Int, overrideText: String? = null): Notification {
        val tapIntent = PendingIntent.getActivity(
            this, 0,
            Intent(this, MainActivity::class.java).apply { flags = Intent.FLAG_ACTIVITY_SINGLE_TOP },
            PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE,
        )
        return NotificationCompat.Builder(this, CHANNEL_WATCH)
            .setContentTitle("SyncFlow")
            .setContentText(
                overrideText ?: if (count > 0) "Watching $count folder${if (count != 1) "s" else ""} for changes"
                else "Starting file watcher…"
            )
            .setSmallIcon(R.drawable.ic_sync)
            .setContentIntent(tapIntent)
            .setOngoing(true)
            .setPriority(NotificationCompat.PRIORITY_MIN)
            .build()
    }

    private fun updateNotification(count: Int) {
        val nm = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        nm.notify(NOTIFICATION_ID, buildNotification(count))
    }

    private fun updateNotificationDynamic(overrideText: String?) {
        val count = fileObservers.keys.size + contentObservers.size
        val nm = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
        nm.notify(NOTIFICATION_ID, buildNotification(count, overrideText))
    }
}