library angel_framework.core.hooked_service;

import 'dart:async';

import '../util.dart';
import 'metadata.dart';
import 'request_context.dart';
import 'response_context.dart';
import 'routable.dart';
import 'server.dart';
import 'service.dart';

/// Wraps another service in a service that broadcasts events on actions.
class HookedService<Id, Data, T extends Service<Id, Data>>
    extends Service<Id, Data> {
  final List<StreamController<HookedServiceEvent>> _ctrl = [];

  /// Tbe service that is proxied by this hooked one.
  final T inner;

  final HookedServiceEventDispatcher<Id, Data, T> beforeIndexed =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> beforeRead =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> beforeCreated =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> beforeModified =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> beforeUpdated =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> beforeRemoved =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterIndexed =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterRead =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterCreated =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterModified =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterUpdated =
      new HookedServiceEventDispatcher<Id, Data, T>();
  final HookedServiceEventDispatcher<Id, Data, T> afterRemoved =
      new HookedServiceEventDispatcher<Id, Data, T>();

  HookedService(this.inner) {
    // Clone app instance
    if (inner.app != null) this.app = inner.app;
  }

  RequestContext _getRequest(Map params) {
    if (params == null) return null;
    return params['__requestctx'] as RequestContext;
  }

  ResponseContext _getResponse(Map params) {
    if (params == null) return null;
    return params['__responsectx'] as ResponseContext;
  }

  Map<String, dynamic> _stripReq(Map<String, dynamic> params) {
    if (params == null)
      return params;
    else
      return params.keys
          .where((key) => key != '__requestctx' && key != '__responsectx')
          .fold<Map<String, dynamic>>(
              {}, (map, key) => map..[key] = params[key]);
  }

  /// Closes any open [StreamController]s on this instance. **Internal use only**.
  @override
  Future close() {
    _ctrl.forEach((c) => c.close());
    beforeIndexed._close();
    beforeRead._close();
    beforeCreated._close();
    beforeModified._close();
    beforeUpdated._close();
    beforeRemoved._close();
    afterIndexed._close();
    afterRead._close();
    afterCreated._close();
    afterModified._close();
    afterUpdated._close();
    afterRemoved._close();
    inner.close();
    return new Future.value();
  }

  /// Adds hooks to this instance.
  void addHooks(Angel app) {
    Hooks hooks = getAnnotation(inner, Hooks, app.container.reflector);
    List<HookedServiceEventListener<Id, Data, T>> before = [], after = [];

    if (hooks != null) {
      before.addAll(hooks.before);
      after.addAll(hooks.after);
    }

    void applyListeners(
        Function fn, HookedServiceEventDispatcher<Id, Data, T> dispatcher,
        [bool isAfter]) {
      Hooks hooks = getAnnotation(fn, Hooks, app.container.reflector);
      final listeners = <HookedServiceEventListener<Id, Data, T>>[]
        ..addAll(isAfter == true ? after : before);

      if (hooks != null)
        listeners.addAll(isAfter == true ? hooks.after : hooks.before);

      listeners.forEach(dispatcher.listen);
    }

    applyListeners(inner.index, beforeIndexed);
    applyListeners(inner.read, beforeRead);
    applyListeners(inner.create, beforeCreated);
    applyListeners(inner.modify, beforeModified);
    applyListeners(inner.update, beforeUpdated);
    applyListeners(inner.remove, beforeRemoved);
    applyListeners(inner.index, afterIndexed, true);
    applyListeners(inner.read, afterRead, true);
    applyListeners(inner.create, afterCreated, true);
    applyListeners(inner.modify, afterModified, true);
    applyListeners(inner.update, afterUpdated, true);
    applyListeners(inner.remove, afterRemoved, true);
  }

  List<RequestHandler> get bootstrappers =>
      new List<RequestHandler>.from(super.bootstrappers)
        ..add((RequestContext req, ResponseContext res) {
          req.serviceParams
            ..['__requestctx'] = req
            ..['__responsectx'] = res;
          return true;
        });

  void addRoutes([Service s]) {
    super.addRoutes(s ?? inner);
  }

  /// Runs the [listener] before every service method specified.
  void before(Iterable<String> eventNames,
      HookedServiceEventListener<Id, Data, T> listener) {
    eventNames.map((name) {
      switch (name) {
        case HookedServiceEvent.indexed:
          return beforeIndexed;
        case HookedServiceEvent.read:
          return beforeRead;
        case HookedServiceEvent.created:
          return beforeCreated;
        case HookedServiceEvent.modified:
          return beforeModified;
        case HookedServiceEvent.updated:
          return beforeUpdated;
        case HookedServiceEvent.removed:
          return beforeRemoved;
        default:
          throw new ArgumentError('Invalid service method: ${name}');
      }
    }).forEach((HookedServiceEventDispatcher<Id, Data, T> dispatcher) =>
        dispatcher.listen(listener));
  }

  /// Runs the [listener] after every service method specified.
  void after(Iterable<String> eventNames,
      HookedServiceEventListener<Id, Data, T> listener) {
    eventNames.map((name) {
      switch (name) {
        case HookedServiceEvent.indexed:
          return afterIndexed;
        case HookedServiceEvent.read:
          return afterRead;
        case HookedServiceEvent.created:
          return afterCreated;
        case HookedServiceEvent.modified:
          return afterModified;
        case HookedServiceEvent.updated:
          return afterUpdated;
        case HookedServiceEvent.removed:
          return afterRemoved;
        default:
          throw new ArgumentError('Invalid service method: ${name}');
      }
    }).forEach((HookedServiceEventDispatcher<Id, Data, T> dispatcher) =>
        dispatcher.listen(listener));
  }

  /// Runs the [listener] before every service method.
  void beforeAll(HookedServiceEventListener<Id, Data, T> listener) {
    beforeIndexed.listen(listener);
    beforeRead.listen(listener);
    beforeCreated.listen(listener);
    beforeModified.listen(listener);
    beforeUpdated.listen(listener);
    beforeRemoved.listen(listener);
  }

  /// Runs the [listener] after every service method.
  void afterAll(HookedServiceEventListener<Id, Data, T> listener) {
    afterIndexed.listen(listener);
    afterRead.listen(listener);
    afterCreated.listen(listener);
    afterModified.listen(listener);
    afterUpdated.listen(listener);
    afterRemoved.listen(listener);
  }

  /// Returns a [Stream] of all events fired before every service method.
  ///
  /// *NOTE*: Only use this if you do not plan to modify events. There is no guarantee
  /// that events coming out of this [Stream] will see changes you make within the [Stream]
  /// callback.
  Stream<HookedServiceEvent<Id, Data, T>> beforeAllStream() {
    var ctrl = new StreamController<HookedServiceEvent<Id, Data, T>>();
    _ctrl.add(ctrl);
    before(HookedServiceEvent.all, ctrl.add);
    return ctrl.stream;
  }

  /// Returns a [Stream] of all events fired after every service method.
  ///
  /// *NOTE*: Only use this if you do not plan to modify events. There is no guarantee
  /// that events coming out of this [Stream] will see changes you make within the [Stream]
  /// callback.
  Stream<HookedServiceEvent<Id, Data, T>> afterAllStream() {
    var ctrl = new StreamController<HookedServiceEvent<Id, Data, T>>();
    _ctrl.add(ctrl);
    before(HookedServiceEvent.all, ctrl.add);
    return ctrl.stream;
  }

  /// Returns a [Stream] of all events fired before every service method specified.
  ///
  /// *NOTE*: Only use this if you do not plan to modify events. There is no guarantee
  /// that events coming out of this [Stream] will see changes you make within the [Stream]
  /// callback.
  Stream<HookedServiceEvent<Id, Data, T>> beforeStream(
      Iterable<String> eventNames) {
    var ctrl = new StreamController<HookedServiceEvent<Id, Data, T>>();
    _ctrl.add(ctrl);
    before(eventNames, ctrl.add);
    return ctrl.stream;
  }

  /// Returns a [Stream] of all events fired AFTER every service method specified.
  ///
  /// *NOTE*: Only use this if you do not plan to modify events. There is no guarantee
  /// that events coming out of this [Stream] will see changes you make within the [Stream]
  /// callback.
  Stream<HookedServiceEvent<Id, Data, T>> afterStream(
      Iterable<String> eventNames) {
    var ctrl = new StreamController<HookedServiceEvent<Id, Data, T>>();
    _ctrl.add(ctrl);
    after(eventNames, ctrl.add);
    return ctrl.stream;
  }

  /// Runs the [listener] before [create], [modify] and [update].
  void beforeModify(HookedServiceEventListener<Id, Data, T> listener) {
    beforeCreated.listen(listener);
    beforeModified.listen(listener);
    beforeUpdated.listen(listener);
  }

  @override
  Future index([Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeIndexed
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.indexed,
            params: params))
        .then((before) {
      if (before._canceled) {
        return beforeIndexed
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.indexed,
                params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.index(params).then((result) {
        return afterIndexed
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.indexed,
                params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  @override
  Future read(Id id, [Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeRead
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.read,
            id: id, params: params))
        .then((before) {
      if (before._canceled) {
        return beforeRead
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.read,
                id: id, params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.read(id, params).then((result) {
        return afterRead
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.read,
                id: id, params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  @override
  Future create(Data data, [Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeCreated
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.created,
            data: data, params: params))
        .then((before) {
      if (before._canceled) {
        return beforeCreated
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.created,
                data: data, params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.create(data, params).then((result) {
        return afterCreated
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.created,
                data: data, params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  @override
  Future modify(Id id, Data data, [Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeModified
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.modified,
            id: id, data: data, params: params))
        .then((before) {
      if (before._canceled) {
        return beforeModified
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.modified,
                id: id, data: data, params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.modify(id, data, params).then((result) {
        return afterModified
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.created,
                id: id, data: data, params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  @override
  Future update(Id id, Data data, [Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeUpdated
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.updated,
            id: id, data: data, params: params))
        .then((before) {
      if (before._canceled) {
        return beforeUpdated
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.updated,
                id: id, data: data, params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.update(id, data, params).then((result) {
        return afterUpdated
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.updated,
                id: id, data: data, params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  @override
  Future remove(Id id, [Map<String, dynamic> _params]) {
    var params = _stripReq(_params);
    return beforeRemoved
        ._emit(new HookedServiceEvent(false, _getRequest(_params),
            _getResponse(_params), inner, HookedServiceEvent.removed,
            id: id, params: params))
        .then((before) {
      if (before._canceled) {
        return beforeRemoved
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.removed,
                id: id, params: params, result: before.result))
            .then((after) => after.result);
      }

      return inner.remove(id, params).then((result) {
        return afterRemoved
            ._emit(new HookedServiceEvent(true, _getRequest(_params),
                _getResponse(_params), inner, HookedServiceEvent.removed,
                id: id, params: params, result: result))
            .then((after) => after.result);
      });
    });
  }

  /// Fires an `after` event. This will not be propagated to clients,
  /// but will be broadcasted to WebSockets, etc.
  Future<HookedServiceEvent<Id, Data, T>> fire(String eventName, result,
      [HookedServiceEventListener<Id, Data, T> callback]) {
    HookedServiceEventDispatcher<Id, Data, T> dispatcher;

    switch (eventName) {
      case HookedServiceEvent.indexed:
        dispatcher = afterIndexed;
        break;
      case HookedServiceEvent.read:
        dispatcher = afterRead;
        break;
      case HookedServiceEvent.created:
        dispatcher = afterCreated;
        break;
      case HookedServiceEvent.modified:
        dispatcher = afterModified;
        break;
      case HookedServiceEvent.updated:
        dispatcher = afterUpdated;
        break;
      case HookedServiceEvent.removed:
        dispatcher = afterRemoved;
        break;
      default:
        throw new ArgumentError("Invalid service event name: '$eventName'");
    }

    var ev =
        new HookedServiceEvent<Id, Data, T>(true, null, null, inner, eventName);
    return fireEvent(dispatcher, ev, callback);
  }

  /// Sends an arbitrary event down the hook chain.
  Future<HookedServiceEvent<Id, Data, T>> fireEvent(
      HookedServiceEventDispatcher<Id, Data, T> dispatcher,
      HookedServiceEvent<Id, Data, T> event,
      [HookedServiceEventListener<Id, Data, T> callback]) {
    Future f;
    if (callback != null && event?._canceled != true)
      f = new Future.sync(() => callback(event));
    f ??= new Future.value();
    return f.then((_) => dispatcher._emit(event));
  }
}

/// Fired when a hooked service is invoked.
class HookedServiceEvent<Id, Data, T extends Service<Id, Data>> {
  static const String indexed = 'indexed';
  static const String read = 'read';
  static const String created = 'created';
  static const String modified = 'modified';
  static const String updated = 'updated';
  static const String removed = 'removed';

  static const List<String> all = const [
    indexed,
    read,
    created,
    modified,
    updated,
    removed
  ];

  /// Use this to end processing of an event.
  void cancel([result]) {
    _canceled = true;
    this.result = result ?? this.result;
  }

  /// Resolves a service from the application.
  ///
  /// Shorthand for `e.service.app.service(...)`.
  Service getService(Pattern path) => service.app.findService(path);

  bool _canceled = false;
  String _eventName;
  Id _id;
  bool _isAfter;
  Data data;
  Map<String, dynamic> _params;
  RequestContext _request;
  ResponseContext _response;
  var result;

  String get eventName => _eventName;

  Id get id => _id;

  bool get isAfter => _isAfter == true;

  bool get isBefore => !isAfter;

  Map get params => _params;

  RequestContext get request => _request;

  ResponseContext get response => _response;

  /// The inner service whose method was hooked.
  T service;

  HookedServiceEvent(this._isAfter, this._request, this._response, this.service,
      String this._eventName,
      {Id id, this.data, Map<String, dynamic> params, this.result}) {
    _id = id;
    _params = params ?? {};
  }
}

/// Triggered on a hooked service event.
typedef FutureOr HookedServiceEventListener<Id, Data,
    T extends Service<Id, Data>>(HookedServiceEvent<Id, Data, T> event);

/// Can be listened to, but events may be canceled.
class HookedServiceEventDispatcher<Id, Data, T extends Service<Id, Data>> {
  final List<StreamController<HookedServiceEvent<Id, Data, T>>> _ctrl = [];
  final List<HookedServiceEventListener<Id, Data, T>> listeners = [];

  void _close() {
    _ctrl.forEach((c) => c.close());
    listeners.clear();
  }

  /// Fires an event, and returns it once it is either canceled, or all listeners have run.
  Future<HookedServiceEvent<Id, Data, T>> _emit(
      HookedServiceEvent<Id, Data, T> event) {
    if (event?._canceled == true || event == null || listeners.isEmpty)
      return new Future.value(event);

    var f = new Future<HookedServiceEvent<Id, Data, T>>.value(event);

    for (var listener in listeners) {
      f = f.then((event) {
        if (event._canceled) return event;
        return new Future.sync(() => listener(event)).then((_) => event);
      });
    }

    return f;
  }

  /// Returns a [Stream] containing all events fired by this dispatcher.
  ///
  /// *NOTE*: Callbacks on the returned [Stream] cannot be guaranteed to run before other [listeners].
  /// Use this only if you need a read-only stream of events.
  Stream<HookedServiceEvent<Id, Data, T>> asStream() {
    // TODO: Close StreamController
    var ctrl = new StreamController<HookedServiceEvent<Id, Data, T>>();
    _ctrl.add(ctrl);
    listen(ctrl.add);
    return ctrl.stream;
  }

  /// Registers the listener to be called whenever an event is triggered.
  void listen(HookedServiceEventListener<Id, Data, T> listener) {
    listeners.add(listener);
  }
}