import path from 'path';
import fs from 'fs/promises';
import fssync from 'fs';
import multer from 'multer';
import crypto from 'crypto';
import { isS3Enabled, deleteFromS3 } from './s3';

// ── File upload security configuration ────────────────────────────────────────

// Uploads directory for local disk mode
export const uploadsDir = path.resolve(process.cwd(), 'uploads');
if (!fssync.existsSync(uploadsDir)) {
  fssync.mkdirSync(uploadsDir, { recursive: true });
}
// Temp directory for S3 mode — files deleted after successful S3 upload
export const tmpUploadDir = path.resolve(process.cwd(), 'uploads/tmp');
if (!fssync.existsSync(tmpUploadDir)) {
  fssync.mkdirSync(tmpUploadDir, { recursive: true });
}

// ── Extension-based file classification (trusted source of truth) ─────────────
// All policy decisions (magic bytes, size limits, MIME consistency) use the
// file EXTENSION, not file.mimetype, because MIME is client-controlled.

// Extension → acceptable MIME types (browser may send any of these for that ext)
// application/octet-stream is always accepted as a fallback from some browsers/OSes
export const EXT_TO_MIME: Record<string, readonly string[]> = {
  jpg:  ['image/jpeg'],
  jpeg: ['image/jpeg'],
  png:  ['image/png'],
  gif:  ['image/gif'],
  webp: ['image/webp'],
  svg:  ['image/svg+xml'],
  pdf:  ['application/pdf'],
  doc:  ['application/msword'],
  docx: ['application/vnd.openxmlformats-officedocument.wordprocessingml.document'],
  xls:  ['application/vnd.ms-excel'],
  xlsx: ['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'],
  ppt:  ['application/vnd.ms-powerpoint'],
  pptx: ['application/vnd.openxmlformats-officedocument.presentationml.presentation'],
  txt:  ['text/plain'],
  csv:  ['text/csv', 'text/plain', 'application/csv'],
  zip:  ['application/zip', 'application/x-zip-compressed', 'application/x-zip'],
  rar:  ['application/x-rar-compressed', 'application/vnd.rar', 'application/x-rar'],
};

// Magic byte signatures keyed by EXTENSION (not MIME)
// A file renamed from .exe → .jpg will fail this check
export const EXT_MAGIC: Record<string, Buffer> = {
  jpg:  Buffer.from([0xFF, 0xD8, 0xFF]),
  jpeg: Buffer.from([0xFF, 0xD8, 0xFF]),
  png:  Buffer.from([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]),
  pdf:  Buffer.from([0x25, 0x50, 0x44, 0x46]), // %PDF
};

// Image extensions → лимит изображений; all others → документный лимит
// Лимиты настраиваются через env (в МБ), дефолты: 25 МБ изображения, 100 МБ документы
export const IMAGE_EXTENSIONS = new Set(['jpg', 'jpeg', 'png', 'gif', 'webp', 'svg']);
export const IMAGE_MAX_SIZE = Number(process.env.UPLOAD_IMAGE_MAX_MB || 25) * 1024 * 1024;
export const DOC_MAX_SIZE   = Number(process.env.UPLOAD_DOC_MAX_MB || 100) * 1024 * 1024;
// Жёсткий потолок multer (fileSize) — отдельный env, дефолт 100 МБ
export const UPLOAD_MAX_SIZE = Number(process.env.UPLOAD_MAX_MB || 100) * 1024 * 1024;

// Derives the lowercase extension from the original filename (trusted)
export function getFileExt(originalname: string): string {
  return path.extname(path.basename(originalname)).slice(1).toLowerCase();
}

// Validates original filename:
//   - extension must be in EXT_TO_MIME (whitelist)
//   - name part blocks path traversal, shell metacharacters and control characters
//   - Unicode letters (including Cyrillic), digits, spaces, dots, underscores and hyphens are allowed
export function validateFilename(originalname: string): { valid: boolean; reason?: string } {
  const basename = path.basename(originalname);
  const ext = path.extname(basename).slice(1).toLowerCase();
  if (!EXT_TO_MIME[ext]) {
    return { valid: false, reason: `Недопустимое расширение файла: .${ext}` };
  }
  const namePart = path.basename(basename, path.extname(basename));
  if (!namePart) {
    return { valid: false, reason: 'Пустое имя файла' };
  }
  // Block path traversal, shell metacharacters, and control characters
  // Allow Unicode letters (including Cyrillic), digits, spaces, dots, underscores, hyphens
  if (/[\/\\&|;$()<>\`\"'\x00-\x1f]/.test(namePart) || namePart.includes('..')) {
    return { valid: false, reason: 'Имя файла содержит недопустимые символы' };
  }
  return { valid: true };
}

// Checks declared MIME against the expected list for the given extension.
// Returns false if MIME is clearly wrong for the extension (e.g. .jpg + application/msword).
// application/octet-stream is always accepted as a browser fallback.
export function isMimeConsistentWithExt(ext: string, mime: string): boolean {
  if (mime === 'application/octet-stream') return true; // browser fallback — always ok
  const allowed = EXT_TO_MIME[ext];
  if (!allowed) return false;
  return allowed.includes(mime);
}

// Reads magic bytes from file on disk and compares against known signature for the extension.
// Returns true if no signature is defined for this extension (no check needed).
export async function checkMagicBytes(filePath: string, ext: string): Promise<boolean> {
  const signature = EXT_MAGIC[ext];
  if (!signature) return true;
  const fd = await fs.open(filePath, 'r');
  try {
    const buf = Buffer.alloc(signature.length);
    await fd.read(buf, 0, signature.length, 0);
    return buf.equals(signature);
  } finally {
    await fd.close();
  }
}

// Returns the size limit in bytes based on extension (trusted), not MIME (client-controlled)
export function getSizeLimit(ext: string): number {
  return IMAGE_EXTENSIONS.has(ext) ? IMAGE_MAX_SIZE : DOC_MAX_SIZE;
}

// Always use disk storage (tmpUploadDir for S3 mode so we can stream to S3, then delete)
const multerStorage = multer.diskStorage({
  destination: (_req, _file, cb) => cb(null, isS3Enabled ? tmpUploadDir : uploadsDir),
  filename: (_req, file, cb) => {
    const ext = getFileExt(file.originalname);
    const uniqueName = `${Date.now()}-${crypto.randomBytes(6).toString('hex')}.${ext}`;
    cb(null, uniqueName);
  },
});

export const upload = multer({
  storage: multerStorage,
  limits: { fileSize: UPLOAD_MAX_SIZE }, // жёсткий потолок (UPLOAD_MAX_MB); раздельная проверка по типам — в хендлере
  fileFilter: (_req, file, cb) => {
    // 1. Validate filename: strict regex + extension whitelist (extension is trusted)
    const { valid, reason } = validateFilename(file.originalname);
    if (!valid) {
      return cb(new Error(reason || 'Недопустимое имя файла'));
    }
    // 2. Reject if declared MIME is clearly incompatible with the extension
    //    (e.g. .jpg uploaded with Content-Type: application/msword is suspicious)
    const ext = getFileExt(file.originalname);
    if (!isMimeConsistentWithExt(ext, file.mimetype)) {
      return cb(new Error(`Тип файла (${file.mimetype}) не соответствует расширению .${ext}`));
    }
    cb(null, true);
  },
});
// ──────────────────────────────────────────────────────────────────────────────

// Удаляет физический файл из uploads/ по сохранённому значению поля (объект или JSON-строка)
// Извлекает все URL из значения файлового поля (одиночный объект, массив или JSON-строка)
export function extractFileUrls(fileValue: unknown): string[] {
  if (!fileValue) return [];
  // Массив объектов [{url, name, size}]
  if (Array.isArray(fileValue)) {
    return fileValue
      .filter((f): f is Record<string, unknown> => f && typeof f === 'object')
      .map(f => (typeof f.url === 'string' ? f.url : null))
      .filter((u): u is string => !!u);
  }
  // Одиночный объект {url, name, size}
  if (typeof fileValue === 'object') {
    const obj = fileValue as Record<string, unknown>;
    return typeof obj.url === 'string' ? [obj.url] : [];
  }
  // JSON-строка
  if (typeof fileValue === 'string' && fileValue) {
    try {
      return extractFileUrls(JSON.parse(fileValue));
    } catch {
      return fileValue ? [fileValue] : [];
    }
  }
  return [];
}

export async function deleteFileByUrl(url: string): Promise<void> {
  if (isS3Enabled) {
    // S3-режим: извлекаем ключ из URL вида /api/files/:key
    const key = url.startsWith('/api/files/') ? url.slice('/api/files/'.length) : path.basename(url);
    if (!key || key.includes('..') || key.includes('/')) return;
    await deleteFromS3(key);
  } else {
    // Локальный режим: удаляем с диска
    const filename = path.basename(url);
    if (!filename || filename.includes('..') || !filename.includes('-')) return;
    try {
      await fs.unlink(path.join(uploadsDir, filename));
    } catch (e: unknown) {
      if ((e as NodeJS.ErrnoException).code !== 'ENOENT') {
        console.error('Ошибка удаления файла с диска:', e);
      }
    }
  }
}

// Удаляет все файлы из значения поля (используется при полном удалении поля)
export async function deleteUploadedFile(fileValue: unknown): Promise<void> {
  const urls = extractFileUrls(fileValue);
  for (const url of urls) {
    await deleteFileByUrl(url);
  }
}

// Удаляет только файлы, которые были в oldValue но исчезли в newValue
export async function deleteRemovedFiles(oldValue: unknown, newValue: unknown): Promise<void> {
  const oldUrls = new Set(extractFileUrls(oldValue));
  const newUrls = new Set(extractFileUrls(newValue));
  for (const url of oldUrls) {
    if (!newUrls.has(url)) {
      await deleteFileByUrl(url);
    }
  }
}

// ── Pending-upload registry for new-task flows ────────────────────────────────
// Tracks uploads that have been accepted but not yet committed to a saved task.
// Key: `${userId}_${fieldId}`; entries expire after 60 minutes.
// This allows the server to enforce per-field limits without trusting the client.
export interface PendingUploadEntry {
  url: string;
  size: number;
  expiresAt: number;
}
export const pendingUploads = new Map<string, PendingUploadEntry[]>();
export const PENDING_UPLOAD_TTL_MS = 60 * 60 * 1000; // 1 hour

export function getPendingKey(userId: number, fieldId: number): string {
  return `${userId}_${fieldId}`;
}

export function getActivePendingUploads(key: string): PendingUploadEntry[] {
  const now = Date.now();
  const entries = pendingUploads.get(key) || [];
  const expired = entries.filter(e => e.expiresAt <= now);
  const active = entries.filter(e => e.expiresAt > now);
  if (active.length !== entries.length) {
    pendingUploads.set(key, active);
    // Удаляем осиротевшие файлы (disk или S3) асинхронно
    expired.forEach(e => deleteFileByUrl(e.url).catch(() => {/* ignore */}));
  }
  return active;
}

export function addPendingUpload(key: string, url: string, size: number): void {
  const active = getActivePendingUploads(key);
  active.push({ url, size, expiresAt: Date.now() + PENDING_UPLOAD_TTL_MS });
  pendingUploads.set(key, active);
}

export function commitPendingUploads(userId: number, fieldId: number, committedUrls: string[]): void {
  const key = getPendingKey(userId, fieldId);
  const active = getActivePendingUploads(key);
  const urlSet = new Set(committedUrls);
  pendingUploads.set(key, active.filter(e => !urlSet.has(e.url)));
}

export function sweepPendingUploads(): void {
  const now = Date.now();
  for (const [key, entries] of pendingUploads.entries()) {
    const expired = entries.filter(e => e.expiresAt <= now);
    const active = entries.filter(e => e.expiresAt > now);
    if (expired.length > 0) {
      if (active.length === 0) {
        pendingUploads.delete(key);
      } else {
        pendingUploads.set(key, active);
      }
      expired.forEach(e => deleteFileByUrl(e.url).catch(() => {/* ignore */}));
    }
  }
}
// Run orphan sweep every hour
setInterval(sweepPendingUploads, 60 * 60 * 1000);
// ──────────────────────────────────────────────────────────────────────────────