import 'dart:io';

import 'package:path/path.dart' as p;
import 'package:path_provider/path_provider.dart';

import 'cloud/cloud_storage_provider.dart';
import 'database_service.dart';
import 'db_schema.dart';
import 'lock_coordinator.dart' as lock;

class SyncResult {
  final bool ranSync;
  final Object? error;

  SyncResult.skipped()
      : ranSync = false,
        error = null;

  SyncResult.success()
      : ranSync = true,
        error = null;

  SyncResult.failure(this.error) : ranSync = false;
}

/// Orchestrates one round of sync against the shared cloud folder — same
/// behavior no matter which [CloudStorageProvider] it's wired to: acquires
/// the cross-device lock, pulls + merges the remote database if it
/// changed, uploads any pending receipt photos, pushes the local database
/// back up, then releases the lock.
///
/// The merge itself runs as SQL directly against the local database with
/// the downloaded remote copy `ATTACH`ed, rather than decoding records into
/// Dart objects: for each table, `INSERT OR REPLACE` any remote row that's
/// new to us or has a newer `updated_at` than our copy. Rows we haven't
/// touched (including our own not-yet-pushed edits) are left alone by that
/// statement, so no separate "keep local" step is needed — see the README
/// for the full reasoning.
class CloudSyncService {
  final CloudStorageProvider provider;
  final DatabaseService databaseService;

  String? _appFolderId;
  String? _receiptsFolderId;
  final Map<String, String> _vinFolderIds = {};
  final Map<String, String> _monthFolderIds = {};
  String? _dataFileId;
  String? _lastKnownRemoteVersionTag;

  CloudSyncService({required this.provider, required this.databaseService});

  bool get isConfigured => _appFolderId != null;

  /// Call once a cloud app folder has been chosen (or restored at launch).
  void configure(String appFolderId) {
    _appFolderId = appFolderId;
    _receiptsFolderId = null;
    _vinFolderIds.clear();
    _monthFolderIds.clear();
    _dataFileId = null;
    _lastKnownRemoteVersionTag = null;
  }

  void clearConfiguration() {
    _appFolderId = null;
    _receiptsFolderId = null;
    _vinFolderIds.clear();
    _monthFolderIds.clear();
    _dataFileId = null;
    _lastKnownRemoteVersionTag = null;
  }

  /// Points this service at the `Show Me The Fuel Refund` folder under
  /// [parentId] (a folder the user picked in the folder browser, or —
  /// see [AppState.connectProvider] — the assumed root location a fresh
  /// connection defaults to) and configures this service to use it.
  /// Returns the resulting folder ID.
  ///
  /// If the user picked a folder that's *already* named
  /// `Show Me The Fuel Refund` — [currentFolderName] carries that name up
  /// from the browser — [parentId] is used directly instead of nesting
  /// another same-named folder inside it. Otherwise a folder picked at
  /// "My Files" root would end up as `/Show Me The Fuel Refund` on first
  /// setup, but re-picking that same folder later (e.g. after reinstalling)
  /// would double it up as `/Show Me The Fuel Refund/Show Me The Fuel
  /// Refund`.
  ///
  /// Otherwise, three cases:
  ///  - A same-named folder already exists directly under [parentId] (e.g.
  ///    one someone else already set up there to share) — adopt it as-is,
  ///    the same convergence behavior as before, so two people pointed at
  ///    the same shared parent end up sharing one app folder either way.
  ///  - This service already has an app folder configured somewhere else
  ///    (from a previous [selectAppFolder] call, or the root default a
  ///    fresh connection starts with) and [parentId] has no folder of its
  ///    own yet — *move* the existing one there via
  ///    [CloudStorageSession.moveFolder], preserving its contents, rather
  ///    than creating a fresh empty folder and abandoning the old one with
  ///    all its synced data still in it.
  ///  - Neither of the above (nothing configured yet, nothing at the
  ///    destination) — create a fresh one, same as always.
  Future<String> selectAppFolder(String parentId, {String? currentFolderName}) async {
    final session = provider.beginSession();
    try {
      if (currentFolderName == appFolderName) {
        configure(parentId);
        return parentId;
      }

      CloudFolder? existingAtDestination;
      for (final folder in await session.listFolders(parentId: parentId)) {
        if (folder.name == appFolderName) {
          existingAtDestination = folder;
          break;
        }
      }

      final String folderId;
      if (existingAtDestination != null) {
        folderId = existingAtDestination.id;
      } else if (_appFolderId != null) {
        folderId = await session.moveFolder(folderId: _appFolderId!, newParentId: parentId);
      } else {
        folderId = await session.findOrCreateFolder(parentId: parentId, name: appFolderName);
      }
      configure(folderId);
      return folderId;
    } finally {
      session.close();
    }
  }

  /// [keepLocalReceiptCopies] mirrors the Settings toggle: when true, a
  /// receipt photo's local copy is left in place after it's uploaded
  /// (useful for offline viewing / an on-device backup); when false
  /// (default), it's deleted once the cloud has it, matching the original
  /// "local is just a staging area" design.
  ///
  /// [staleLockAge] mirrors the Settings "Advanced" stale-lock timeout:
  /// how old another device's lock file has to be before this device
  /// treats it as abandoned (e.g. that device crashed or went offline
  /// mid-sync) and deletes it rather than waiting forever. Defaults to 10
  /// minutes, matching [defaultStaleLockMinutes] in app_state.dart.
  ///
  /// [beforeUpload], if given, is awaited once — after any pull/merge of
  /// remote changes has finished, but before anything local gets uploaded
  /// (pending receipt photos or the database snapshot itself). This is the
  /// one hook [AppState] uses to show the app's single ad placement, since
  /// it's meant to run before *pushing* local data up, not before *pulling*
  /// remote data down.
  Future<SyncResult> syncNow({
    bool keepLocalReceiptCopies = false,
    Duration staleLockAge = const Duration(minutes: 10),
    Future<void> Function()? beforeUpload,
  }) async {
    final appFolderId = _appFolderId;
    if (!provider.isSignedIn || appFolderId == null) {
      return SyncResult.skipped();
    }

    CloudStorageSession? session;
    String? lockFileId;

    try {
      session = provider.beginSession();

      lockFileId = await _acquireLock(
        session,
        appFolderId: appFolderId,
        username: provider.accountLabel!,
        staleAge: staleLockAge,
      );

      _receiptsFolderId ??=
          await session.findOrCreateFolder(parentId: appFolderId, name: receiptsFolderName);

      final remoteInfo = await session.findFile(folderId: appFolderId, name: dataFileName);
      _dataFileId = remoteInfo?.id;
      if (remoteInfo != null && remoteInfo.versionTag != _lastKnownRemoteVersionTag) {
        await _pullAndMerge(session, remoteInfo.id);
      }

      if (beforeUpload != null) {
        await beforeUpload();
      }

      final allReceiptsUploaded =
          await _uploadPendingReceipts(session, keepLocalCopies: keepLocalReceiptCopies);

      // Only push if every pending receipt made it up — otherwise we'd
      // either upload a row with a local-only file path (meaningless on
      // another device) or prematurely mark it clean.
      if (allReceiptsUploaded) {
        final pushedInfo = await _pushSnapshot(session, appFolderId);
        _lastKnownRemoteVersionTag = pushedInfo.versionTag;
      }

      return SyncResult.success();
    } catch (e) {
      return SyncResult.failure(e);
    } finally {
      if (lockFileId != null && session != null) {
        try {
          await session.deleteFile(lockFileId);
        } catch (_) {
          // Best-effort: if this fails, the staleness reap on other
          // devices' next sync attempt will clean it up.
        }
      }
      session?.close();
    }
  }

  Future<void> _pullAndMerge(CloudStorageSession session, String remoteFileId) async {
    final bytes = await session.downloadFileBytes(remoteFileId);
    final tempDir = await getTemporaryDirectory();
    final tempPath =
        p.join(tempDir.path, 'cloud_pull_${DateTime.now().microsecondsSinceEpoch}.db');
    final tempFile = File(tempPath);
    await tempFile.writeAsBytes(bytes, flush: true);

    try {
      final db = databaseService.rawDb;
      await db.execute("ATTACH DATABASE '${_escapeSqlLiteral(tempPath)}' AS remote_db");
      try {
        await db.execute(mergeVehiclesSql);
        await db.execute(mergeFuelEntriesSql);

        // ad_free_entitlement is a newer table than vehicles/fuel_entries —
        // unlike those two (present since the very first schema version, so
        // any remote snapshot ever pushed already has them), a remote
        // snapshot pushed before this table existed genuinely won't have
        // it. Merging against it unconditionally would throw ("no such
        // table") on exactly that snapshot; skipping when absent just means
        // "that older snapshot has no entitlement info to contribute",
        // which is correct — local's own value (if any) is left as-is.
        final remoteHasEntitlementTable = (await db.rawQuery(
          "SELECT 1 FROM remote_db.sqlite_master WHERE type = 'table' AND name = 'ad_free_entitlement'",
        )).isNotEmpty;
        if (remoteHasEntitlementTable) {
          await db.execute(mergeAdFreeEntitlementSql);
        }
      } finally {
        try {
          await db.execute('DETACH DATABASE remote_db');
        } catch (_) {
          // Don't let a detach failure mask a real merge error above.
        }
      }
    } finally {
      if (await tempFile.exists()) {
        await tempFile.delete();
      }
    }
  }

  /// Uploads any receipt images still needing it (a local path but no
  /// cloud file ID yet — see [FuelEntry.needsReceiptUpload]). Returns true
  /// only if every pending image made it up — see [syncNow] for why a
  /// partial failure here blocks the push step entirely rather than
  /// pushing something with a leftover local-only path.
  ///
  /// Deliberately filters on `receipt_drive_file_id IS NULL` (see
  /// [pendingReceiptUploadWhereClause]), not just "has a local path": once
  /// [keepLocalCopies] is honored below, an already-uploaded row can still
  /// have a local path (kept on purpose), and re-matching it here would
  /// re-upload the same photo as a duplicate cloud file on every sync.
  Future<bool> _uploadPendingReceipts(
    CloudStorageSession session, {
    required bool keepLocalCopies,
  }) async {
    final db = databaseService.rawDb;
    final rows = await db.query('fuel_entries', where: pendingReceiptUploadWhereClause);
    if (rows.isEmpty) return true;

    final vehicleRows = await db.query('vehicles', columns: ['id', 'vin']);
    final vinByVehicleId = {for (final v in vehicleRows) v['id'] as String: v['vin'] as String};

    var allSucceeded = true;
    for (final row in rows) {
      final id = row['id'] as String;
      final localPath = row['receipt_image_path'] as String;
      final localFile = File(localPath);

      if (!await localFile.exists()) {
        // Nothing left to upload; clear the dangling reference.
        await db.update('fuel_entries', {'receipt_image_path': null},
            where: 'id = ?', whereArgs: [id]);
        continue;
      }

      final vin = vinByVehicleId[row['vehicle_id']];
      if (vin == null) {
        // Vehicle row is missing outright (shouldn't normally happen);
        // nothing sane to file this under.
        allSucceeded = false;
        continue;
      }
      final date = DateTime.fromMillisecondsSinceEpoch(row['date'] as int);

      try {
        final folderId = await _receiptFolderFor(session, vin, date);
        final uploaded = await session.uploadFile(
          folderId: folderId,
          name: '$id${p.extension(localPath)}',
          localFile: localFile,
          contentType: 'image/jpeg',
        );
        if (!keepLocalCopies) {
          await databaseService.deleteReceiptImageFile(localPath);
        }
        await db.update(
          'fuel_entries',
          {
            'receipt_drive_file_id': uploaded.id,
            'receipt_image_path': keepLocalCopies ? localPath : null,
          },
          where: 'id = ?',
          whereArgs: [id],
        );
      } catch (_) {
        allSucceeded = false;
      }
    }
    return allSucceeded;
  }

  /// Finds-or-creates the `Receipts/<vin>/<yyyy.mm>` subfolder for [vin] and
  /// [date] (the fuel entry's purchase date, not upload time), caching both
  /// levels for the rest of this [CloudSyncService]'s lifetime (cleared by
  /// [configure]/[clearConfiguration]) so repeated uploads for the same
  /// vehicle/month in one sync — or across syncs — don't re-issue the
  /// lookup.
  Future<String> _receiptFolderFor(CloudStorageSession session, String vin, DateTime date) async {
    final vinFolderId = _vinFolderIds[vin] ??
        await session.findOrCreateFolder(
          parentId: _receiptsFolderId!,
          name: sanitizedPathSegment(vin),
        );
    _vinFolderIds[vin] = vinFolderId;

    final month = monthFolderName(date);
    final monthCacheKey = '$vin/$month';
    final monthFolderId = _monthFolderIds[monthCacheKey] ??
        await session.findOrCreateFolder(parentId: vinFolderId, name: month);
    _monthFolderIds[monthCacheKey] = monthFolderId;

    return monthFolderId;
  }

  /// Uploads the current local database file as the new remote copy, then
  /// clears the dirty flag on every row now that local matches the cloud.
  ///
  /// Reads the live database file directly rather than a `VACUUM INTO`
  /// snapshot: sqflite uses SQLite's default rollback-journal mode (not
  /// WAL) unless explicitly configured otherwise, so the main file is a
  /// complete, valid database as soon as the last write's Future
  /// completes. `wal_checkpoint` is run first anyway as cheap insurance in
  /// case that ever changes. This also sidesteps `VACUUM INTO` needing
  /// SQLite 3.27+, which isn't guaranteed on very old Android versions.
  Future<CloudFileInfo> _pushSnapshot(CloudStorageSession session, String appFolderId) async {
    final db = databaseService.rawDb;
    await db.rawQuery('PRAGMA wal_checkpoint(TRUNCATE)');

    final info = await session.uploadFile(
      folderId: appFolderId,
      name: dataFileName,
      existingFileId: _dataFileId,
      localFile: File(databaseService.databasePath),
      contentType: 'application/x-sqlite3',
    );
    _dataFileId = info.id;

    await db.update('vehicles', {'dirty': 0});
    await db.update('fuel_entries', {'dirty': 0});

    return info;
  }

  String _escapeSqlLiteral(String value) => value.replaceAll("'", "''");

  Future<String> _acquireLock(
    CloudStorageSession session, {
    required String appFolderId,
    required String username,
    required Duration staleAge,
  }) {
    return lock.acquireLock(
      username: username,
      createLock: (name) => session.createLockFile(folderId: appFolderId, name: name),
      listLocks: () => session.listLockFiles(appFolderId),
      deleteLock: session.deleteFile,
      staleAge: staleAge,
    );
  }
}