import {
  Body,
  Controller,
  Delete,
  Get,
  Headers,
  NotFoundException,
  Param,
  Patch,
  Post,
  Query,
} from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { DataSource, Repository } from 'typeorm';
import { CreateMessageDto } from './dto.create-message.dto';
import { Channel } from '../entities/channel.entity';
import { Message } from '../entities/message.entity';
import { IdempotencyRecord } from '../entities/idempotency-record.entity';
import { EventsService } from '../events/events.service';
import { clampLimit, computeNextExpectedSeq } from './pagination.util';
import { RealtimeGateway } from '../realtime/realtime.gateway';

const EDIT_WINDOW_MS = 15 * 60 * 1000;
const DEFAULT_PAGE_LIMIT = 50;
const MAX_PAGE_LIMIT = 200;

@Controller('channels/:id/messages')
export class MessagingController {
  constructor(
    private readonly dataSource: DataSource,
    @InjectRepository(Channel)
    private readonly channelRepo: Repository<Channel>,
    @InjectRepository(Message)
    private readonly messageRepo: Repository<Message>,
    @InjectRepository(IdempotencyRecord)
    private readonly idemRepo: Repository<IdempotencyRecord>,
    private readonly events: EventsService,
    private readonly realtime: RealtimeGateway,
  ) {}

  private async getIdempotentResponse(
    scope: string,
    idempotencyKey?: string,
  ): Promise<Record<string, unknown> | null> {
    if (!idempotencyKey) return null;
    const row = await this.idemRepo.findOne({ where: { scope, idempotencyKey } });
    return row?.responseBody ?? null;
  }

  private async saveIdempotentResponse(
    scope: string,
    idempotencyKey: string | undefined,
    responseBody: Record<string, unknown>,
  ): Promise<void> {
    if (!idempotencyKey) return;
    const row = this.idemRepo.create({
      scope,
      idempotencyKey,
      responseBody,
    });
    await this.idemRepo.save(row);
  }

  private toView(m: Message) {
    return {
      messageId: m.messageId,
      seq: m.seq,
      content: m.content,
      authorUserId: m.authorUserId,
      replyToMessageId: m.replyToMessageId,
      mentions: m.mentions ?? [],
      attachments: m.attachments ?? [],
      createdAt: m.createdAt.toISOString(),
      editedAt: m.editedAt ? m.editedAt.toISOString() : null,
      deletedAt: m.deletedAt ? m.deletedAt.toISOString() : null,
      isDeleted: m.isDeleted,
    };
  }

  @Post()
  async create(
    @Param('id') channelId: string,
    @Body() body: CreateMessageDto,
    @Headers('idempotency-key') idempotencyKey?: string,
  ) {
    const scope = `POST:/channels/${channelId}/messages`;
    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
    if (existed) return existed;

    const message = await this.dataSource.transaction(async (manager) => {
      const channel = await manager.findOne(Channel, {
        where: { id: channelId },
        lock: { mode: 'pessimistic_write' },
      });
      if (!channel) {
        throw new NotFoundException('channel not found');
      }

      const nextSeq = channel.lastSeq + 1;
      channel.lastSeq = nextSeq;
      await manager.save(Channel, channel);

      const messageId = body.clientMessageId ?? `m-${channelId}-${nextSeq}`;
      const row = manager.create(Message, {
        messageId,
        channelId,
        conversationId: null,
        authorUserId: body.authorUserId ?? 'anonymous',
        seq: nextSeq,
        content: body.content,
        replyToMessageId: body.replyToMessageId ?? null,
        mentions: body.mentions ?? [],
        attachments: body.attachments ?? [],
        editedAt: null,
        deletedAt: null,
        isDeleted: false,
      });
      return manager.save(Message, row);
    });

    const responseBody = this.toView(message) as Record<string, unknown>;
    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);

    await this.events.emit({
      eventType: 'message.created',
      channelId,
      actorId: body.authorUserId ?? 'anonymous',
      data: responseBody,
    });
    this.realtime.emitChannelEvent(channelId, 'message.created', responseBody);

    return responseBody;
  }

  @Patch(':messageId')
  async edit(
    @Param('id') channelId: string,
    @Param('messageId') messageId: string,
    @Body() body: { content?: string },
    @Headers('idempotency-key') idempotencyKey?: string,
  ) {
    const scope = `PATCH:/channels/${channelId}/messages/${messageId}`;
    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
    if (existed) return existed;

    const item = await this.messageRepo.findOne({ where: { channelId, messageId } });
    if (!item) return { status: 'not_found' };

    const now = Date.now();
    const createdAt = new Date(item.createdAt).getTime();
    if (now - createdAt > EDIT_WINDOW_MS) {
      return { status: 'edit_window_expired', messageId };
    }

    item.content = body.content ?? item.content;
    item.editedAt = new Date();
    const saved = await this.messageRepo.save(item);
    const responseBody = this.toView(saved) as Record<string, unknown>;
    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);

    await this.events.emit({
      eventType: 'message.updated',
      channelId,
      actorId: saved.authorUserId,
      data: responseBody,
    });
    this.realtime.emitChannelEvent(channelId, 'message.updated', responseBody);

    return responseBody;
  }

  @Delete(':messageId')
  async remove(
    @Param('id') channelId: string,
    @Param('messageId') messageId: string,
    @Headers('idempotency-key') idempotencyKey?: string,
  ) {
    const scope = `DELETE:/channels/${channelId}/messages/${messageId}`;
    const existed = await this.getIdempotentResponse(scope, idempotencyKey);
    if (existed) return existed;

    const item = await this.messageRepo.findOne({ where: { channelId, messageId } });
    if (!item) return { status: 'not_found' };

    item.isDeleted = true;
    item.deletedAt = new Date();
    item.content = '[deleted]';
    item.mentions = [];
    item.attachments = [];
    await this.messageRepo.save(item);

    const responseBody = {
      status: 'deleted',
      mode: 'soft',
      messageId,
    } as Record<string, unknown>;
    await this.saveIdempotentResponse(scope, idempotencyKey, responseBody);

    await this.events.emit({
      eventType: 'message.deleted',
      channelId,
      actorId: item.authorUserId,
      data: {
        messageId,
        seq: item.seq,
        deletedAt: item.deletedAt?.toISOString() ?? null,
      },
    });
    this.realtime.emitChannelEvent(channelId, 'message.deleted', {
      messageId,
      seq: item.seq,
      deletedAt: item.deletedAt?.toISOString() ?? null,
    });

    return responseBody;
  }

  @Get()
  async listBySeq(
    @Param('id') channelId: string,
    @Query('seq_from') seqFrom?: string,
    @Query('seq_to') seqTo?: string,
    @Query('limit') limit?: string,
  ) {
    const from = seqFrom ? Number(seqFrom) : 1;
    const to = seqTo ? Number(seqTo) : Number.MAX_SAFE_INTEGER;
    const safeLimit = clampLimit(limit, DEFAULT_PAGE_LIMIT, MAX_PAGE_LIMIT);

    if (from > to) {
      return {
        items: [],
        page: {
          seqFrom: from,
          seqTo: to,
          limit: safeLimit,
          returned: 0,
          hasMore: false,
          nextExpectedSeq: from,
          highestCommittedSeq: 0,
        },
      };
    }

    const channel = await this.channelRepo.findOne({ where: { id: channelId } });
    if (!channel) {
      throw new NotFoundException('channel not found');
    }

    const qb = this.messageRepo
      .createQueryBuilder('m')
      .where('m.channelId = :channelId', { channelId })
      .andWhere('m.seq >= :from', { from })
      .andWhere('m.seq <= :to', { to })
      .orderBy('m.seq', 'ASC');

    const total = await qb.getCount();
    const rows = await qb.limit(safeLimit).getMany();
    const items = rows.map((m) => this.toView(m));

    const nextExpectedSeq = computeNextExpectedSeq(
      from,
      rows.map((row) => row.seq),
    );

    return {
      items,
      page: {
        seqFrom: from,
        seqTo: to,
        limit: safeLimit,
        returned: items.length,
        hasMore: total > items.length,
        nextExpectedSeq,
        highestCommittedSeq: channel.lastSeq,
      },
    };
  }
}