import { Store } from '@ngrx/store';
import { firstValueFrom } from 'rxjs';
import type { Room, User } from '../../shared-kernel';
import {
  type RoomSignalSource,
  type ServerSourceSelector,
  type ServerDirectoryFacade,
  areRoomSignalSourcesEqual,
  CLIENT_UPDATE_REQUIRED_MESSAGE
} from '../../domains/server-directory';
import { RealtimeSessionFacade } from '../../core/realtime';
import { RoomsActions } from './rooms.actions';
import { resolveUserDisplayName, extractRoomIdFromUrl } from './rooms.helpers';

export interface RoomSignalConnectionPlan {
  fallbackSources: RoomSignalSource[];
  primarySource: RoomSignalSource | null;
  room: Room;
}

/**
 * Encapsulates signaling-server connection, fallback cascade, and
 * navigation versioning logic that was previously inlined in
 * {@link RoomsEffects}.
 *
 * Instantiated by `RoomsEffects` (not an Angular service) - it receives
 * the required dependencies through its constructor.
 */
export class RoomSignalingConnection {
  latestNavigatedRoomId: string | null = null;
  private readonly roomSignalFallbackSources = new Map<string, RoomSignalSource>();
  private roomNavigationRequestVersion = 0;

  constructor(
    private readonly webrtc: RealtimeSessionFacade,
    private readonly serverDirectory: ServerDirectoryFacade,
    private readonly store: Store
  ) {}

  // ── Navigation versioning ──────────────────────────────────────

  beginRoomNavigation(roomId: string): number {
    this.roomNavigationRequestVersion += 1;
    this.latestNavigatedRoomId = roomId;

    return this.roomNavigationRequestVersion;
  }

  isCurrentRoomNavigation(roomId: string, navigationRequestVersion?: number): boolean {
    if (typeof navigationRequestVersion !== 'number') {
      return true;
    }

    return navigationRequestVersion === this.roomNavigationRequestVersion
      && roomId === this.latestNavigatedRoomId;
  }

  deleteRoomFallbackSource(roomId: string): void {
    this.roomSignalFallbackSources.delete(roomId);
  }

  // ── Primary connection entry points ────────────────────────────

  async connectToRoomSignaling(
    room: Room,
    user: User | null,
    resolvedOderId?: string,
    savedRooms: Room[] = [],
    options: { showCompatibilityError?: boolean; navigationRequestVersion?: number } = {}
  ): Promise<void> {
    const shouldShowCompatibilityError = options.showCompatibilityError ?? false;
    const navigationRequestVersion = options.navigationRequestVersion;
    const isViewedRoom = () => room.id === this.latestNavigatedRoomId;

    await this.serverDirectory.awaitInitialServerHealthCheck();

    if (!this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
      return;
    }

    const connectionPlan = await this.resolveRoomSignalConnectionPlan(room);

    if (!this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
      return;
    }

    const sessionFallbackSource = this.roomSignalFallbackSources.get(room.id);
    const connectionCandidates: {
      isExistingFallback?: boolean;
      isFallback?: boolean;
      isPrimary?: boolean;
      source: RoomSignalSource;
    }[] = [];
    const pushConnectionCandidate = (
      source: RoomSignalSource | null | undefined,
      flags: { isExistingFallback?: boolean; isFallback?: boolean; isPrimary?: boolean } = {}
    ) => {
      if (!source || !this.resolveRoomSignalSelector(source, room.name)) {
        return;
      }

      if (connectionCandidates.some((candidate) => areRoomSignalSourcesEqual(candidate.source, source))) {
        return;
      }

      connectionCandidates.push({
        ...flags,
        source
      });
    };

    if (sessionFallbackSource && this.webrtc.hasJoinedServer(room.id)) {
      pushConnectionCandidate(sessionFallbackSource, { isExistingFallback: true, isFallback: true });
    }

    pushConnectionCandidate(connectionPlan.primarySource, { isPrimary: true });

    for (const fallbackSource of connectionPlan.fallbackSources) {
      pushConnectionCandidate(fallbackSource, { isFallback: true });
    }

    let attemptedFallback = false;

    for (const candidate of connectionCandidates) {
      const selector = this.resolveRoomSignalSelector(candidate.source, connectionPlan.room.name);

      if (!selector) {
        continue;
      }

      const isCompatible = await this.serverDirectory.ensureEndpointVersionCompatibility(selector);

      if (!this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
        return;
      }

      if (!isCompatible) {
        // Warning: offline/unreachable endpoints also fail this check. Only
        // version-incompatible primary endpoints should stop fallback; transient
        // 521/522/network failures must continue to the next active endpoint.
        const endpoint = this.serverDirectory.resolveRoomEndpoint(candidate.source);
        const isEndpointIncompatible = endpoint?.status === 'incompatible';

        if (candidate.isPrimary && isEndpointIncompatible) {
          if (shouldShowCompatibilityError) {
            this.store.dispatch(
              RoomsActions.setSignalServerCompatibilityError({ message: CLIENT_UPDATE_REQUIRED_MESSAGE })
            );
          }

          if (isViewedRoom()) {
            this.store.dispatch(RoomsActions.setSignalServerReconnecting({ isReconnecting: false }));
          }

          return;
        }

        continue;
      }

      if (candidate.isFallback && !candidate.isExistingFallback && !attemptedFallback) {
        attemptedFallback = true;

        if (isViewedRoom()) {
          this.store.dispatch(RoomsActions.setSignalServerReconnecting({ isReconnecting: true }));
        }
      }

      const connected = await this.connectRoomToSignalSource(
        connectionPlan.room,
        candidate.source,
        user,
        resolvedOderId,
        savedRooms,
        navigationRequestVersion
      );

      if (!this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
        return;
      }

      if (!connected) {
        continue;
      }

      if (candidate.isFallback) {
        this.roomSignalFallbackSources.set(room.id, candidate.source);
      } else {
        this.roomSignalFallbackSources.delete(room.id);
      }

      if (shouldShowCompatibilityError) {
        this.store.dispatch(RoomsActions.setSignalServerCompatibilityError({ message: null }));
      }

      if (isViewedRoom()) {
        this.store.dispatch(RoomsActions.setSignalServerReconnecting({ isReconnecting: false }));
      }

      return;
    }

    if (shouldShowCompatibilityError) {
      this.store.dispatch(RoomsActions.setSignalServerCompatibilityError({ message: null }));
    }

    if (isViewedRoom()) {
      this.store.dispatch(RoomsActions.setSignalServerReconnecting({ isReconnecting: true }));
    }
  }

  syncSavedRoomConnections(
    user: User | null,
    currentRoom: Room | null,
    savedRooms: Room[],
    currentUrl: string
  ): void {
    if (!user || savedRooms.length === 0) {
      return;
    }

    const watchedRoomId = extractRoomIdFromUrl(currentUrl);
    const roomsToSync = currentRoom ? this.includeRoom(savedRooms, currentRoom) : savedRooms;
    const roomsBySignalingUrl = new Map<string, Room[]>();

    for (const room of roomsToSync) {
      const wsUrl = this.resolveRoomSignalingUrl(room);

      if (!wsUrl) {
        continue;
      }

      const groupedRooms = roomsBySignalingUrl.get(wsUrl) ?? [];

      if (!groupedRooms.some((groupedRoom) => groupedRoom.id === room.id)) {
        groupedRooms.push(room);
      }

      roomsBySignalingUrl.set(wsUrl, groupedRooms);
    }

    for (const groupedRooms of roomsBySignalingUrl.values()) {
      const preferredRoom = groupedRooms.find((room) => room.id === watchedRoomId)
        ?? (currentRoom && groupedRooms.some((room) => room.id === currentRoom.id)
          ? currentRoom
          : null)
        ?? groupedRooms[0]
        ?? null;

      if (!preferredRoom) {
        continue;
      }

      const shouldShowCompatibilityError = preferredRoom.id === watchedRoomId
        || (!!currentRoom && preferredRoom.id === currentRoom.id);

      void this.connectToRoomSignaling(preferredRoom, user, user.oderId || this.webrtc.peerId(), roomsToSync, {
        showCompatibilityError: shouldShowCompatibilityError
      });
    }
  }

  resolveRoomSignalingUrl(room: Room): string {
    const selector = this.resolveRoomSignalSelector(this.getPreferredRoomSignalSource(room), room.name);

    return selector ? this.serverDirectory.getWebSocketUrl(selector) : '';
  }

  resolveRoomSignalSource(
    room: Pick<Room, 'name' | 'sourceId' | 'sourceName' | 'sourceUrl'>
  ): RoomSignalSource {
    return this.serverDirectory.normaliseRoomSignalSource({
      sourceId: room.sourceId,
      sourceName: room.sourceName,
      sourceUrl: room.sourceUrl,
      fallbackName: room.sourceName ?? room.name
    }, {
      ensureEndpoint: !!room.sourceUrl
    });
  }

  resolveRoomSignalSelector(
    source: RoomSignalSource | null | undefined,
    fallbackName: string
  ): ServerSourceSelector | undefined {
    if (!source) {
      return undefined;
    }

    return this.serverDirectory.buildRoomSignalSelector({
      ...source,
      fallbackName: source.sourceName ?? fallbackName
    }, {
      ensureEndpoint: !!source.sourceUrl
    });
  }

  // ── Internal helpers ───────────────────────────────────────────

  private async resolveRoomSignalConnectionPlan(room: Room): Promise<RoomSignalConnectionPlan> {
    let resolvedRoom = this.repairRoomSignalSource(room, this.resolveRoomSignalSource(room));
    let primarySource = this.resolveRoomSignalSource(resolvedRoom);

    if (!this.webrtc.hasJoinedServer(room.id)) {
      const selector = this.resolveRoomSignalSelector(primarySource, resolvedRoom.name);
      // Warning: getServer returns null for both SERVER_NOT_FOUND and transient
      // endpoint failures. Always search active endpoints before deciding the
      // saved room source is stale, otherwise a Cloudflare/origin outage pins
      // reconnects to the dead endpoint.
      const authoritativeServer = (
        selector
          ? await firstValueFrom(this.serverDirectory.getServer(room.id, selector))
          : null
      ) ?? await firstValueFrom(this.serverDirectory.findServerAcrossActiveEndpoints(room.id, primarySource));

      if (authoritativeServer) {
        const authoritativeSource = this.serverDirectory.normaliseRoomSignalSource({
          sourceId: authoritativeServer.sourceId ?? primarySource.sourceId,
          sourceName: authoritativeServer.sourceName ?? primarySource.sourceName,
          sourceUrl: authoritativeServer.sourceUrl ?? primarySource.sourceUrl,
          fallbackName: authoritativeServer.sourceName ?? primarySource.sourceName ?? resolvedRoom.name
        }, {
          ensureEndpoint: !!(authoritativeServer.sourceUrl ?? primarySource.sourceUrl)
        });

        resolvedRoom = this.repairRoomSignalSource(resolvedRoom, authoritativeSource);
        primarySource = authoritativeSource;
      }
    }

    const fallbackSources = this.serverDirectory.getFallbackRoomEndpoints(primarySource)
      .map((endpoint) => this.serverDirectory.normaliseRoomSignalSource({
        sourceId: endpoint.id,
        sourceName: endpoint.name,
        sourceUrl: endpoint.url,
        fallbackName: endpoint.name
      }))
      .filter((source, index, sources) =>
        sources.findIndex((candidate) => areRoomSignalSourcesEqual(candidate, source)) === index
      );

    return {
      fallbackSources,
      primarySource: this.resolveRoomSignalSelector(primarySource, resolvedRoom.name) ? primarySource : null,
      room: resolvedRoom
    };
  }

  private async connectRoomToSignalSource(
    room: Room,
    source: RoomSignalSource,
    user: User | null,
    resolvedOderId: string | undefined,
    savedRooms: Room[],
    navigationRequestVersion?: number
  ): Promise<boolean> {
    const selector = this.resolveRoomSignalSelector(source, room.name);

    if (!selector) {
      return false;
    }

    const wsUrl = this.serverDirectory.getWebSocketUrl(selector);
    const oderId = resolvedOderId || user?.oderId || this.webrtc.peerId();
    const displayName = resolveUserDisplayName(user);
    const description = user?.description;
    const profileUpdatedAt = user?.profileUpdatedAt;
    const sameSignalRooms = this.getRoomsForSignalingUrl(this.includeRoom(savedRooms, room), wsUrl);
    const backgroundRooms = sameSignalRooms.filter((candidate) => candidate.id !== room.id);
    const joinCurrentEndpointRooms = () => {
      if (!this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
        return;
      }

      this.webrtc.setCurrentServer(room.id);
      this.webrtc.identify(oderId, displayName, wsUrl, {
        description,
        profileUpdatedAt,
        homeSignalServerUrl: user?.homeSignalServerUrl
      });

      for (const backgroundRoom of backgroundRooms) {
        this.webrtc.joinRoom(backgroundRoom.id, oderId, wsUrl);
      }

      if (this.webrtc.hasJoinedServer(room.id)) {
        this.webrtc.switchServer(room.id, oderId, wsUrl);
      } else {
        this.webrtc.joinRoom(room.id, oderId, wsUrl);
      }
    };

    if (this.webrtc.isSignalingConnectedTo(wsUrl)) {
      joinCurrentEndpointRooms();
      return true;
    }

    try {
      const connected = await firstValueFrom(this.webrtc.connectToSignalingServer(wsUrl));

      if (!connected || !this.isCurrentRoomNavigation(room.id, navigationRequestVersion)) {
        return false;
      }

      joinCurrentEndpointRooms();
      return true;
    } catch {
      return false;
    }
  }

  private repairRoomSignalSource(room: Room, source: RoomSignalSource | null): Room {
    if (!source || areRoomSignalSourcesEqual(room, source)) {
      return room;
    }

    const changes: Partial<Room> = {
      sourceId: source.sourceId,
      sourceName: source.sourceName,
      sourceUrl: source.sourceUrl
    };

    this.store.dispatch(RoomsActions.updateRoom({
      roomId: room.id,
      changes
    }));

    return {
      ...room,
      ...changes
    };
  }

  private getPreferredRoomSignalSource(room: Room): RoomSignalSource {
    const fallbackSource = this.roomSignalFallbackSources.get(room.id);

    if (fallbackSource && this.webrtc.hasJoinedServer(room.id)) {
      return fallbackSource;
    }

    return this.resolveRoomSignalSource(room);
  }

  private includeRoom(rooms: Room[], room: Room): Room[] {
    return rooms.some((candidate) => candidate.id === room.id)
      ? rooms
      : [...rooms, room];
  }

  private getRoomsForSignalingUrl(rooms: Room[], wsUrl: string): Room[] {
    const seenRoomIds = new Set<string>();
    const matchingRooms: Room[] = [];

    for (const room of rooms) {
      if (seenRoomIds.has(room.id)) {
        continue;
      }

      if (this.resolveRoomSignalingUrl(room) !== wsUrl) {
        continue;
      }

      seenRoomIds.add(room.id);
      matchingRooms.push(room);
    }

    return matchingRooms;
  }
}