import { BadRequestException, ForbiddenException, Injectable, NotFoundException } from '@nestjs/common';
import { ChatChannelType, Role, SyncOperation } from '@prisma/client';
import { PrismaClient } from '../prisma/prisma.module';
import { AuthenticatedUser } from '../auth/authenticated-request';
import { GuestJwtPayload } from '../auth/guest-auth.service';
import { SyncService } from '../sync/sync.service';
import { PushService } from '../push/push.service';

export type ChatCaller =
  | { kind: 'user'; user: AuthenticatedUser }
  | { kind: 'guest'; guest: GuestJwtPayload };

const CHANNEL_TITLES: Record<ChatChannelType, string> = {
  [ChatChannelType.GEMEINDE_GRUPPE]: 'Gemeinde-Gruppe',
  [ChatChannelType.DIREKT]: 'Direktnachricht',
  [ChatChannelType.LT_UEBERGREIFEND]: 'Leitungsteam',
  [ChatChannelType.BROADCAST]: 'Ankündigung',
  [ChatChannelType.GRUPPE]: 'Gruppenchat',
};

export interface CreateGruppeParticipants {
  userIds?: string[];
  guestIds?: string[];
}

@Injectable()
export class ChatService {
  constructor(
    private readonly prisma: PrismaClient,
    private readonly sync: SyncService,
    private readonly push: PushService,
  ) {}

  async createChannel(kcId: string, type: ChatChannelType, gemeindeId?: string) {
    const channel = await this.prisma.chatChannel.create({ data: { kcId, type, gemeindeId } });
    await this.sync.capture('ChatChannel', SyncOperation.CREATE, channel.id, channel);
    return channel;
  }

  /// Free-form group chat: created by a Leitungsteam member (any KC) or a
  /// Gemeinde Verantwortliche/r (their own KC — enforced by the RolesGuard's
  /// kcId scoping at the controller level). Konfis (guests) may be included
  /// directly, unlike DIREKT/GEMEINDE_GRUPPE channels which are team-only.
  async createGruppe(
    kcId: string,
    name: string | undefined,
    createdByUserId: string,
    participants: CreateGruppeParticipants,
  ) {
    const userIds = [...new Set(participants.userIds ?? [])];
    const guestIds = [...new Set(participants.guestIds ?? [])];

    if (userIds.length) {
      // A user may show up under more than one Gemeinde membership; just
      // make sure every requested id resolves to at least one row for this KC.
      const distinctUsers = await this.prisma.membership.findMany({
        where: { kcId, userId: { in: userIds } },
        select: { userId: true },
        distinct: ['userId'],
      });
      if (distinctUsers.length !== userIds.length) {
        throw new BadRequestException('One or more users are not part of this KC');
      }
    }
    if (guestIds.length) {
      const guestCount = await this.prisma.guestAccount.count({
        where: { id: { in: guestIds }, kcId },
      });
      if (guestCount !== guestIds.length) {
        throw new BadRequestException('One or more guests are not part of this KC');
      }
    }

    const channel = await this.prisma.chatChannel.create({
      data: {
        kcId,
        type: ChatChannelType.GRUPPE,
        name,
        createdByUserId,
        participants: {
          create: [
            ...(userIds.includes(createdByUserId) ? [] : [{ userId: createdByUserId }]),
            ...userIds.map((userId) => ({ userId })),
            ...guestIds.map((guestAccountId) => ({ guestAccountId })),
          ],
        },
      },
      include: { participants: true },
    });
    await this.sync.capture('ChatChannel', SyncOperation.CREATE, channel.id, channel);
    return channel;
  }

  /// Candidates a caller may add to a GRUPPE channel in this KC: every team
  /// member (any Gemeinde) plus every Konfi/guest, so a Verantwortliche/r can
  /// pick across Gemeinde boundaries as intended. Same authorization as
  /// creating a Gruppenchat (LT or Verantwortliche/r of this KC).
  async listPossibleParticipants(kcId: string, caller: AuthenticatedUser) {
    const isLt = caller.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
    const isVerantwortlicherHere = caller.memberships.some(
      (m) => m.kcId === kcId && m.role === Role.GEMEINDE_VERANTWORTLICHER,
    );
    if (!isLt && !isVerantwortlicherHere) {
      throw new ForbiddenException('Not allowed to list participants for this KC');
    }

    const [memberships, guests] = await Promise.all([
      this.prisma.membership.findMany({
        where: { kcId, status: 'ACTIVE' },
        include: { user: { select: { id: true, firstName: true, lastName: true, email: true } } },
        orderBy: { user: { lastName: 'asc' } },
      }),
      this.prisma.guestAccount.findMany({
        where: { kcId },
        select: { id: true, firstName: true, lastName: true, gemeindeId: true },
        orderBy: { lastName: 'asc' },
      }),
    ]);

    const seenUsers = new Set<string>();
    const users = [];
    for (const m of memberships) {
      if (seenUsers.has(m.userId)) continue;
      seenUsers.add(m.userId);
      users.push({
        userId: m.user.id,
        firstName: m.user.firstName,
        lastName: m.user.lastName,
        email: m.user.email,
        role: m.role,
        gemeindeId: m.gemeindeId,
      });
    }

    return {
      users,
      guests: guests.map((g) => ({
        guestId: g.id,
        firstName: g.firstName,
        lastName: g.lastName,
        gemeindeId: g.gemeindeId,
      })),
    };
  }

  /// Adds a team user or a guest/Konfi to an existing GRUPPE channel. Only
  /// the channel's creator or a Leitungsteam member may manage participants.
  async addParticipant(
    channelId: string,
    caller: ChatCaller,
    target: { userId?: string; guestId?: string },
  ) {
    const channel = await this.getGruppeForManagementOrThrow(channelId, caller);

    if (!target.userId && !target.guestId) {
      throw new BadRequestException('userId or guestId is required');
    }
    if (target.userId && target.guestId) {
      throw new BadRequestException('Provide either userId or guestId, not both');
    }

    if (target.userId) {
      const isMember = await this.prisma.membership.findFirst({
        where: { kcId: channel.kcId, userId: target.userId },
      });
      if (!isMember) {
        throw new BadRequestException('User is not part of this KC');
      }
      const participant = await this.prisma.chatParticipant.upsert({
        where: { channelId_userId: { channelId, userId: target.userId } },
        create: { channelId, userId: target.userId },
        update: {},
      });
      await this.sync.capture('ChatParticipant', SyncOperation.CREATE, participant.id, participant);
      return participant;
    }

    const guest = await this.prisma.guestAccount.findFirst({
      where: { id: target.guestId, kcId: channel.kcId },
    });
    if (!guest) {
      throw new BadRequestException('Guest is not part of this KC');
    }
    const participant = await this.prisma.chatParticipant.upsert({
      where: { channelId_guestAccountId: { channelId, guestAccountId: target.guestId! } },
      create: { channelId, guestAccountId: target.guestId },
      update: {},
    });
    await this.sync.capture('ChatParticipant', SyncOperation.CREATE, participant.id, participant);
    return participant;
  }

  /// Removes a team user or a guest/Konfi from a GRUPPE channel. Same
  /// authorization as addParticipant.
  async removeParticipant(
    channelId: string,
    caller: ChatCaller,
    target: { userId?: string; guestId?: string },
  ) {
    await this.getGruppeForManagementOrThrow(channelId, caller);

    if (!target.userId && !target.guestId) {
      throw new BadRequestException('userId or guestId is required');
    }

    const existing = await this.prisma.chatParticipant.findFirst({
      where: {
        channelId,
        userId: target.userId ?? undefined,
        guestAccountId: target.guestId ?? undefined,
      },
    });
    if (!existing) return { ok: true };

    await this.prisma.chatParticipant.delete({ where: { id: existing.id } });
    await this.sync.capture('ChatParticipant', SyncOperation.DELETE, existing.id, { id: existing.id });
    return { ok: true };
  }

  private async getGruppeForManagementOrThrow(channelId: string, caller: ChatCaller) {
    if (caller.kind !== 'user') {
      throw new ForbiddenException('Guests may not manage channel participants');
    }
    const channel = await this.prisma.chatChannel.findUnique({ where: { id: channelId } });
    if (!channel || channel.type !== ChatChannelType.GRUPPE) {
      throw new NotFoundException('Gruppenchat not found');
    }
    const { user } = caller;
    const isLt = user.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
    const isCreator = channel.createdByUserId === user.userId;
    const isVerantwortlicherHere = user.memberships.some(
      (m) => m.kcId === channel.kcId && m.role === Role.GEMEINDE_VERANTWORTLICHER,
    );
    if (!isLt && !isCreator && !isVerantwortlicherHere) {
      throw new ForbiddenException('Not allowed to manage this Gruppenchat');
    }
    return channel;
  }

  async getOrCreateDirectChannel(kcId: string, userAId: string, userBId: string) {
    const existing = await this.prisma.chatChannel.findFirst({
      where: {
        kcId,
        type: ChatChannelType.DIREKT,
        AND: [
          { participants: { some: { userId: userAId } } },
          { participants: { some: { userId: userBId } } },
        ],
      },
    });
    if (existing) return existing;
    const channel = await this.prisma.chatChannel.create({
      data: {
        kcId,
        type: ChatChannelType.DIREKT,
        participants: { create: [{ userId: userAId }, { userId: userBId }] },
      },
    });
    await this.sync.capture('ChatChannel', SyncOperation.CREATE, channel.id, channel);
    return channel;
  }

  async listChannelsForCaller(kcId: string, caller: ChatCaller) {
    if (caller.kind === 'guest') {
      return this.prisma.chatChannel.findMany({
        where: {
          kcId,
          OR: [
            { type: ChatChannelType.BROADCAST },
            { type: ChatChannelType.GRUPPE, participants: { some: { guestAccountId: caller.guest.guestId } } },
          ],
        },
      });
    }
    const { user } = caller;
    const isLt = user.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
    if (isLt) {
      return this.prisma.chatChannel.findMany({ where: { kcId } });
    }
    const gemeindeIds = user.memberships
      .filter((m) => m.kcId === kcId && m.gemeindeId)
      .map((m) => m.gemeindeId as string);
    return this.prisma.chatChannel.findMany({
      where: {
        kcId,
        OR: [
          { type: ChatChannelType.BROADCAST },
          { type: ChatChannelType.GEMEINDE_GRUPPE, gemeindeId: { in: gemeindeIds } },
          { type: ChatChannelType.DIREKT, participants: { some: { userId: user.userId } } },
          { type: ChatChannelType.GRUPPE, participants: { some: { userId: user.userId } } },
        ],
      },
    });
  }

  async assertCanRead(channelId: string, caller: ChatCaller) {
    return this.getChannelForCallerOrThrow(channelId, caller, 'read');
  }

  async assertCanWrite(channelId: string, caller: ChatCaller) {
    return this.getChannelForCallerOrThrow(channelId, caller, 'write');
  }

  private async getChannelForCallerOrThrow(
    channelId: string,
    caller: ChatCaller,
    mode: 'read' | 'write',
  ) {
    const channel = await this.prisma.chatChannel.findUnique({
      where: { id: channelId },
      include: { participants: true },
    });
    if (!channel) {
      throw new NotFoundException('Channel not found');
    }

    if (caller.kind === 'guest') {
      if (channel.type === ChatChannelType.BROADCAST && mode === 'read') {
        if (caller.guest.kcId !== channel.kcId) {
          throw new ForbiddenException('Guest does not belong to this KC');
        }
        return channel;
      }
      if (channel.type === ChatChannelType.GRUPPE) {
        const isParticipant = channel.participants.some(
          (p) => p.guestAccountId === caller.guest.guestId,
        );
        if (!isParticipant) {
          throw new ForbiddenException('Not a participant of this Gruppenchat');
        }
        return channel;
      }
      throw new ForbiddenException('Guests may only read broadcast channels or their Gruppenchats');
    }

    const { user } = caller;
    const isLt = user.memberships.some((m) => m.role === Role.LEITUNGSTEAM);
    if (isLt) {
      return channel;
    }
    if (channel.kcId && !user.memberships.some((m) => m.kcId === channel.kcId)) {
      throw new ForbiddenException('Not a member of this KC');
    }

    switch (channel.type) {
      case ChatChannelType.BROADCAST:
        if (mode === 'write') {
          throw new ForbiddenException('Only Leitungsteam may post broadcasts');
        }
        return channel;
      case ChatChannelType.LT_UEBERGREIFEND:
        throw new ForbiddenException('Leitungsteam-only channel');
      case ChatChannelType.GEMEINDE_GRUPPE: {
        const inGemeinde = user.memberships.some(
          (m) => m.kcId === channel.kcId && m.gemeindeId === channel.gemeindeId,
        );
        if (!inGemeinde) {
          throw new ForbiddenException('Not a member of this Gemeinde');
        }
        return channel;
      }
      case ChatChannelType.DIREKT: {
        const isParticipant = channel.participants.some((p) => p.userId === user.userId);
        if (!isParticipant) {
          throw new ForbiddenException('Not a participant of this conversation');
        }
        return channel;
      }
      case ChatChannelType.GRUPPE: {
        const isParticipant = channel.participants.some((p) => p.userId === user.userId);
        if (!isParticipant) {
          throw new ForbiddenException('Not a participant of this Gruppenchat');
        }
        return channel;
      }
      default:
        throw new ForbiddenException('Unknown channel type');
    }
  }

  async sendMessage(channelId: string, caller: ChatCaller, body: string) {
    const channel = await this.assertCanWrite(channelId, caller);
    const message = await this.prisma.chatMessage.create({
      data: {
        channelId,
        body,
        senderUserId: caller.kind === 'user' ? caller.user.userId : null,
        senderGuestId: caller.kind === 'guest' ? caller.guest.guestId : null,
      },
    });
    await this.sync.capture('ChatMessage', SyncOperation.CREATE, message.id, message);

    void this.push.notifyChannel(
      channelId,
      {
        title: CHANNEL_TITLES[channel?.type ?? ChatChannelType.GEMEINDE_GRUPPE],
        body: body.length > 140 ? `${body.slice(0, 137)}…` : body,
        data: { channelId },
      },
      {
        userId: caller.kind === 'user' ? caller.user.userId : null,
        guestId: caller.kind === 'guest' ? caller.guest.guestId : null,
      },
    );

    return message;
  }

  async listMessages(channelId: string, caller: ChatCaller) {
    await this.assertCanRead(channelId, caller);
    return this.prisma.chatMessage.findMany({
      where: { channelId },
      orderBy: { createdAt: 'asc' },
    });
  }
}