import {
  BadRequestException,
  Injectable,
  NotFoundException,
} from '@nestjs/common';
import { InjectRepository } from '@nestjs/typeorm';
import { createReadStream } from 'node:fs';
import { mkdir, readFile, unlink, writeFile } from 'node:fs/promises';
import { basename, isAbsolute, join, relative, resolve } from 'node:path';
import { randomUUID } from 'node:crypto';
import { PDFParse } from 'pdf-parse';
import { In, Repository } from 'typeorm';
import { AiExcelReaderService } from './ai-excel-reader.service';
import { AiAttachment } from './entities';

const MAX_FILE_BYTES = 10 * 1024 * 1024;
const MAX_MODEL_IMAGE_BYTES = 20 * 1024 * 1024;
const ACCEPTED_MIME_TYPES = new Set([
  'image/jpeg',
  'image/png',
  'image/webp',
  'application/pdf',
  'text/csv',
  'application/csv',
  'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
  'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
  'application/vnd.openxmlformats-officedocument.presentationml.presentation',
]);

export interface AiAttachmentModelPart {
  attachment: AiAttachment;
  text?: string;
  imageDataUrl?: string;
}

@Injectable()
export class AiAttachmentService {
  private readonly storageRoot =
    resolve(process.env.AI_ATTACHMENT_DIR || join(process.cwd(), 'data', 'ai-attachments'));

  constructor(
    @InjectRepository(AiAttachment)
    private readonly attachments: Repository<AiAttachment>,
    private readonly excelReader: AiExcelReaderService,
  ) {}

  async upload(userId: number, file: Express.Multer.File): Promise<AiAttachment> {
    if (!file?.buffer?.length) throw new BadRequestException('请选择附件');
    if (file.size > MAX_FILE_BYTES) throw new BadRequestException('单个附件不能超过 10MB');

    const mimeType = this.detectMimeType(file.buffer, file.mimetype);
    if (!ACCEPTED_MIME_TYPES.has(mimeType)) {
      throw new BadRequestException('仅支持图片、PDF、Word 和 Excel 文件');
    }
    this.assertDeclaredType(file.mimetype, mimeType);
    this.assertFileExtension(file.originalname, mimeType);

    await mkdir(this.storageRoot, { recursive: true });
    const extension = this.extensionForMime(mimeType);
    const storageKey = `${userId}/${randomUUID()}.${extension}`;
    const absolutePath = this.resolveStoragePath(storageKey);
    await mkdir(join(this.storageRoot, String(userId)), { recursive: true });
    await writeFile(absolutePath, file.buffer, { flag: 'wx' });

    let entity: AiAttachment;
    try {
      entity = await this.attachments.save(
        this.attachments.create({
          userId,
          originalName: this.decodeFilename(basename(file.originalname)).slice(0, 255),
          mimeType,
          size: file.size,
          storageKey,
          processingStatus: 'processing',
          extractedText: null,
          processingError: null,
          imageWidth: null,
          imageHeight: null,
        }),
      );
    } catch (error) {
      await unlink(absolutePath).catch(() => undefined);
      throw error;
    }

    try {
      entity.extractedText = await this.extractText(file.buffer, mimeType);
      entity.processingStatus = 'ready';
    } catch {
      entity.processingStatus = 'failed';
      entity.processingError = '文件内容解析失败';
    }
    entity = await this.attachments.save(entity);
    return entity;
  }

  async removeUnbound(userId: number, id: number): Promise<void> {
    const attachment = await this.requireOwned(userId, id, true);
    if (attachment.messages?.length) throw new BadRequestException('已发送的附件不能单独删除');
    await this.attachments.remove(attachment);
    await unlink(this.resolveStoragePath(attachment.storageKey)).catch(() => undefined);
  }

  async removeOrphans(userId: number, ids: number[]): Promise<void> {
    const uniqueIds = [...new Set(ids)].filter((id) => Number.isInteger(id) && id > 0);
    if (!uniqueIds.length) return;
    const attachments = await this.attachments.find({
      where: { id: In(uniqueIds), userId },
      relations: { messages: true },
    });
    for (const attachment of attachments) {
      if (attachment.messages?.length) continue;
      await this.attachments.remove(attachment);
      await unlink(this.resolveStoragePath(attachment.storageKey)).catch(() => undefined);
    }
  }

  async open(userId: number, id: number): Promise<{
    attachment: AiAttachment;
    stream: ReturnType<typeof createReadStream>;
  }> {
    const attachment = await this.requireOwned(userId, id);
    return {
      attachment,
      stream: createReadStream(this.resolveStoragePath(attachment.storageKey)),
    };
  }

  async requireReadyOwned(userId: number, ids: number[]): Promise<AiAttachment[]> {
    const uniqueIds = [...new Set(ids)];
    if (uniqueIds.length > 5) throw new BadRequestException('每条消息最多添加 5 个附件');
    if (!uniqueIds.length) return [];
    const attachments = await this.attachments.findByIds(uniqueIds);
    if (attachments.length !== uniqueIds.length || attachments.some((item) => item.userId !== userId)) {
      throw new BadRequestException('附件不存在或无权访问');
    }
    if (attachments.some((item) => item.processingStatus !== 'ready')) {
      throw new BadRequestException('附件仍在处理或处理失败');
    }
    return uniqueIds.map((id) => attachments.find((item) => item.id === id)!);
  }

  async toModelParts(
    attachments: AiAttachment[],
    supportsVision: boolean,
  ): Promise<AiAttachmentModelPart[]> {
    const imageAttachments = attachments.filter((attachment) => attachment.mimeType.startsWith('image/'));
    if (imageAttachments.length && !supportsVision) {
      throw new BadRequestException('当前模型未启用图片理解能力');
    }
    const imageBytes = imageAttachments.reduce((total, attachment) => total + attachment.size, 0);
    if (imageBytes > MAX_MODEL_IMAGE_BYTES) {
      throw new BadRequestException('单次消息图片总大小不能超过 20MB');
    }
    const parts: AiAttachmentModelPart[] = [];
    for (const attachment of attachments) {
      if (attachment.mimeType.startsWith('image/')) {
        const buffer = await readFile(this.resolveStoragePath(attachment.storageKey));
        parts.push({
          attachment,
          imageDataUrl: `data:${attachment.mimeType};base64,${buffer.toString('base64')}`,
        });
      } else {
        parts.push({
          attachment,
          text: attachment.extractedText || '',
        });
      }
    }
    return parts;
  }

  serialize(attachment: AiAttachment): Record<string, unknown> {
    return {
      id: attachment.id,
      name: attachment.originalName,
      mimeType: attachment.mimeType,
      size: attachment.size,
      status: attachment.processingStatus,
      error: attachment.processingError,
      url: `/api/ai/chat/attachments/${attachment.id}`,
      createdAt: attachment.createdAt,
    };
  }

  private async requireOwned(
    userId: number,
    id: number,
    includeMessages = false,
  ): Promise<AiAttachment> {
    const attachment = await this.attachments.findOne({
      where: { id, userId },
      ...(includeMessages ? { relations: { messages: true } } : {}),
    });
    if (!attachment) throw new NotFoundException('附件不存在');
    return attachment;
  }

  private async extractText(buffer: Buffer, mimeType: string): Promise<string | null> {
    if (mimeType.startsWith('image/')) return null;
    if (mimeType === 'application/pdf') {
      const parser = new PDFParse({ data: buffer });
      try {
        const result = await parser.getText();
        return this.normalizeExtractedText(result.text);
      } finally {
        await parser.destroy();
      }
    }
    if (mimeType.includes('wordprocessingml')) {
      const mammoth = await import('mammoth');
      const result = await mammoth.extractRawText({ buffer });
      return this.normalizeExtractedText(result.value);
    }
    if (mimeType.includes('csv')) {
      return this.normalizeExtractedText(buffer.toString('utf8').replace(/^\uFEFF/, ''));
    }
    if (mimeType.includes('spreadsheetml')) {
      return this.normalizeExtractedText(await this.excelReader.extractText(buffer));
    }
    return null;
  }

  /**
   * Read the stored file content of an already-owned attachment so the AI
   * chat agent can page through large workbooks on demand.
   */
  async readStoredBuffer(attachment: AiAttachment): Promise<Buffer> {
    return readFile(this.resolveStoragePath(attachment.storageKey));
  }

  /** Resolved absolute path of a stored attachment (for OfficeCli). */
  storagePathFor(attachment: AiAttachment): string {
    return this.resolveStoragePath(attachment.storageKey);
  }

  private normalizeExtractedText(value: string): string {
    return value.split('\u0000').join('').replace(/\r\n/g, '\n').trim();
  }

  private assertDeclaredType(declared: string, detected: string): void {
    if (!declared || declared === 'application/octet-stream') return;
    if (detected.includes('csv') || declared.includes('csv')) return;
    if (declared !== detected) throw new BadRequestException('附件类型与文件内容不一致');
  }

  private assertFileExtension(filename: string, mimeType: string): void {
    const extension = basename(filename).toLowerCase().split('.').pop();
    const expected: Record<string, string[]> = {
      'image/jpeg': ['jpg', 'jpeg'],
      'image/png': ['png'],
      'image/webp': ['webp'],
      'application/pdf': ['pdf'],
      'text/csv': ['csv'],
      'application/csv': ['csv'],
      'application/vnd.openxmlformats-officedocument.wordprocessingml.document': ['docx'],
      'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet': ['xlsx'],
      'application/vnd.openxmlformats-officedocument.presentationml.presentation': ['pptx'],
    };
    if (!extension || !expected[mimeType]?.includes(extension)) {
      throw new BadRequestException('附件扩展名与文件内容不一致');
    }
  }

  private detectMimeType(buffer: Buffer, declaredMimeType: string): string {
    if (buffer.subarray(0, 3).equals(Buffer.from([0xff, 0xd8, 0xff]))) return 'image/jpeg';
    if (buffer.subarray(0, 8).equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]))) {
      return 'image/png';
    }
    if (
      buffer.subarray(0, 4).toString('ascii') === 'RIFF' &&
      buffer.subarray(8, 12).toString('ascii') === 'WEBP'
    ) {
      return 'image/webp';
    }
    if (buffer.subarray(0, 5).toString('ascii') === '%PDF-') return 'application/pdf';
    const isZip =
      buffer.subarray(0, 4).equals(Buffer.from([0x50, 0x4b, 0x03, 0x04])) ||
      buffer.subarray(0, 4).equals(Buffer.from([0x50, 0x4b, 0x05, 0x06])) ||
      buffer.subarray(0, 4).equals(Buffer.from([0x50, 0x4b, 0x07, 0x08]));
    if (
      isZip &&
      (declaredMimeType.includes('wordprocessingml') ||
        declaredMimeType.includes('spreadsheetml') ||
        declaredMimeType.includes('presentationml'))
    ) {
      return declaredMimeType;
    }
    if (/csv/i.test(declaredMimeType)) return 'text/csv';
    return 'application/octet-stream';
  }

  /**
   * Browsers send UTF-8 filenames in the multipart header, which multer
   * decodes as Latin-1 — the stored name then looks like mojibake
   * (e.g. `26暑期...`). Re-decode when the bytes are valid UTF-8 and
   * contain CJK; otherwise keep the original name untouched.
   */
  private decodeFilename(name: string): string {
    if (!/[\u00c0-\u00ff]/.test(name)) return name;
    try {
      const decoded = Buffer.from(name, 'latin1').toString('utf8');
      if (decoded.includes('\uFFFD')) return name;
      if (!/[\u4e00-\u9fff]/.test(decoded)) return name;
      return decoded;
    } catch {
      return name;
    }
  }

  private extensionForMime(mimeType: string): string {
    const extensions: Record<string, string> = {
      'image/jpeg': 'jpg',
      'image/png': 'png',
      'image/webp': 'webp',
      'application/pdf': 'pdf',
      'text/csv': 'csv',
      'application/csv': 'csv',
      'application/vnd.openxmlformats-officedocument.wordprocessingml.document': 'docx',
      'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet': 'xlsx',
      'application/vnd.openxmlformats-officedocument.presentationml.presentation': 'pptx',
    };
    return extensions[mimeType] || 'bin';
  }

  private resolveStoragePath(storageKey: string): string {
    const safeKey = storageKey.replace(/[^a-zA-Z0-9/_.-]/g, '');
    if (safeKey !== storageKey) throw new BadRequestException('附件路径无效');
    const absolutePath = resolve(this.storageRoot, safeKey);
    const relativePath = relative(this.storageRoot, absolutePath);
    if (relativePath.startsWith('..') || isAbsolute(relativePath)) {
      throw new BadRequestException('附件路径无效');
    }
    return absolutePath;
  }
}