import 'dart:async';
import 'dart:convert';
import 'dart:io';

import '../../pb_auth.dart';
import 'waypoint_mission.dart';

/// One route as the API Server reports it: a [spec], or a tombstone (null
/// [spec]) left by a delete on some device. [updatedAt] is the
/// last-writer-wins clock either way.
class RemoteRoute {
  const RemoteRoute(this.id, this.updatedAt, this.spec);

  final String id;
  final DateTime updatedAt;
  final WaypointMissionSpec? spec;

  bool get deleted => spec == null;

  /// Reads one entry of the server's `/api/routes` view. Null when unusable.
  static RemoteRoute? fromView(Map<String, dynamic> v) {
    final String id = v['id'] as String? ?? '';
    final DateTime? at = DateTime.tryParse(v['updatedAt'] as String? ?? '');
    if (id.isEmpty || at == null) return null;
    if (v['deleted'] == true) return RemoteRoute(id, at, null);
    final Object? spec = v['spec'];
    if (spec is! Map) return null;
    try {
      final WaypointMissionSpec m = WaypointMissionSpec.fromJson(Map<String, dynamic>.from(spec));
      return RemoteRoute(id, at, m.copyWith(id: id, updatedAt: m.updatedAt ?? at));
    } catch (_) {
      return null;
    }
  }
}

/// The server half of the mission library. [ApiMissionRemote] is the real one.
abstract class MissionRemote {
  /// Who the routes belong to; empty while signed out (nothing syncs).
  String get account;

  /// Every route the account owns, tombstones included.
  Future<List<RemoteRoute>> pull();

  /// Stores [m]. Returns the server's copy when it holds a newer one (the
  /// write was refused), else null.
  Future<RemoteRoute?> push(WaypointMissionSpec m);

  /// Tombstones route [id] as deleted at [at]. Returns the server's copy when
  /// the route was changed after [at] (the delete was refused), else null.
  Future<RemoteRoute?> pushDelete(String id, DateTime at);
}

/// What [mergeMissions] decided.
class MissionMerge {
  const MissionMerge({required this.missions, required this.tombstones, required this.toPush, required this.toDelete});

  /// The library after the merge, newest first.
  final List<WaypointMissionSpec> missions;

  /// Local deletes the server has not heard of yet.
  final Map<String, DateTime> tombstones;

  /// Local routes newer than the server's copy (or unknown to it).
  final List<WaypointMissionSpec> toPush;

  /// Local deletes newer than the server's live copy.
  final Map<String, DateTime> toDelete;
}

final DateTime _epoch = DateTime.fromMillisecondsSinceEpoch(0, isUtc: true);

/// Last-writer-wins merge of the device's library with the server's, per
/// route id, by `updatedAt`. A delete counts as a write at the time it was
/// made, on either side. On a tie the server wins.
///
/// A route saved before it had an `updatedAt` is treated as the oldest
/// possible write (and stamped so it can be pushed).
MissionMerge mergeMissions({
  required List<WaypointMissionSpec> local,
  required Map<String, DateTime> tombstones,
  required List<RemoteRoute> remote,
}) {
  final Map<String, WaypointMissionSpec> mine = <String, WaypointMissionSpec>{
    for (final WaypointMissionSpec m in local) m.id: m.updatedAt == null ? m.copyWith(updatedAt: _epoch) : m,
  };
  final Map<String, RemoteRoute> theirs = <String, RemoteRoute>{for (final RemoteRoute r in remote) r.id: r};

  final Map<String, WaypointMissionSpec> out = <String, WaypointMissionSpec>{};
  final Map<String, DateTime> keepTombstones = <String, DateTime>{};
  final List<WaypointMissionSpec> toPush = <WaypointMissionSpec>[];
  final Map<String, DateTime> toDelete = <String, DateTime>{};

  final Set<String> ids = <String>{...mine.keys, ...tombstones.keys, ...theirs.keys};
  for (final String id in ids) {
    final WaypointMissionSpec? l = mine[id];
    final DateTime? t = tombstones[id];
    final RemoteRoute? r = theirs[id];

    // The device's own latest word on this route: a save, or a delete.
    final bool localDeleted = t != null && (l == null || !t.isBefore(l.updatedAt!));
    final DateTime? localAt = localDeleted ? t : l?.updatedAt;

    if (r == null) {
      // The server never had it: push a save; a delete has nothing to undo.
      if (!localDeleted && l != null) {
        out[id] = l;
        toPush.add(l);
      }
      continue;
    }
    if (localAt == null || !localAt.isAfter(r.updatedAt)) {
      // The server's copy (or its delete) is the newest word.
      if (!r.deleted) out[id] = r.spec!;
      continue;
    }
    if (localDeleted) {
      if (!r.deleted) {
        keepTombstones[id] = t;
        toDelete[id] = t;
      }
    } else {
      out[id] = l!;
      toPush.add(l);
    }
  }

  final List<WaypointMissionSpec> missions = out.values.toList()
    ..sort((WaypointMissionSpec a, WaypointMissionSpec b) => b.updatedAt!.compareTo(a.updatedAt!));
  return MissionMerge(missions: missions, tombstones: keepTombstones, toPush: toPush, toDelete: toDelete);
}

/// [MissionRemote] over the API Server's `/api/routes`, as the signed-in
/// pilot ([auth]).
class ApiMissionRemote implements MissionRemote {
  ApiMissionRemote({PbAuth? auth}) : _auth = auth;

  final PbAuth? _auth;
  PbAuth get _a => _auth ?? auth;

  static const Duration _timeout = Duration(seconds: 10);

  @override
  String get account => _a.isAuthed ? (_a.userEmail.isEmpty ? '_' : _a.userEmail) : '';

  @override
  Future<List<RemoteRoute>> pull() async {
    final (int status, Map<String, dynamic> body) = await _send('GET', '/api/routes?mine=1&includeDeleted=1');
    if (status != 200) throw MissionSyncException(status, body);
    return <RemoteRoute>[
      for (final Object? v in (body['routes'] as List<Object?>? ?? const <Object?>[]))
        if (v is Map)
          if (RemoteRoute.fromView(Map<String, dynamic>.from(v)) case final RemoteRoute r) r,
    ];
  }

  @override
  Future<RemoteRoute?> push(WaypointMissionSpec m) async {
    final (int status, Map<String, dynamic> body) =
        await _send('PUT', '/api/routes/${Uri.encodeComponent(m.id)}', body: m.toJson());
    if (status == 200 || status == 201) return null;
    return _conflict(status, body);
  }

  @override
  Future<RemoteRoute?> pushDelete(String id, DateTime at) async {
    final String when = Uri.encodeQueryComponent(at.toUtc().toIso8601String());
    final (int status, Map<String, dynamic> body) = await _send('DELETE', '/api/routes/${Uri.encodeComponent(id)}?at=$when');
    // 404: the server never had it, which is as deleted as it gets.
    if (status == 200 || status == 404) return null;
    return _conflict(status, body);
  }

  RemoteRoute _conflict(int status, Map<String, dynamic> body) {
    final Object? route = body['route'];
    final RemoteRoute? r = status == 409 && route is Map ? RemoteRoute.fromView(Map<String, dynamic>.from(route)) : null;
    if (r == null) throw MissionSyncException(status, body);
    return r;
  }

  Future<(int, Map<String, dynamic>)> _send(String method, String path, {Object? body}) async {
    final HttpClient http = HttpClient()..connectionTimeout = _timeout;
    try {
      final HttpClientRequest req = await http.openUrl(method, Uri.parse('${_a.serverUrl}$path'));
      req.headers.set(HttpHeaders.authorizationHeader, _a.token);
      if (body != null) {
        req.headers.contentType = ContentType.json;
        req.add(utf8.encode(jsonEncode(body)));
      }
      final HttpClientResponse resp = await req.close().timeout(_timeout);
      final String text = await resp.transform(utf8.decoder).join().timeout(_timeout);
      Map<String, dynamic> json = <String, dynamic>{};
      try {
        final Object? decoded = text.isEmpty ? null : jsonDecode(text);
        if (decoded is Map) json = Map<String, dynamic>.from(decoded);
      } catch (_) {}
      return (resp.statusCode, json);
    } finally {
      http.close(force: true);
    }
  }
}

class MissionSyncException implements Exception {
  const MissionSyncException(this.status, this.body);
  final int status;
  final Map<String, dynamic> body;

  @override
  String toString() => (body['error'] ?? 'Route sync failed ($status)').toString();
}