/**
 * Local filesystem backend. Stores files at `${root}/<key>` on disk and serves
 * downloads via a CRM-internal proxy route (`/api/storage/[token]`) that
 * verifies an HMAC token before streaming the bytes. Used for single-VPS
 * deployments where running MinIO is overkill.
 *
 * §14.9a critical mitigations:
 *
 * - Storage keys are validated against `^[a-zA-Z0-9/_.-]+$`. Anything containing
 *   `..` or that resolves to an absolute path is rejected.
 * - The resolved path is checked with `path.resolve` against the resolved
 *   storage root (realpath form) — symlink escapes are blocked.
 * - The storage root is created with mode `0o700` (owner only).
 * - Refuses to start when `MULTI_NODE_DEPLOYMENT === 'true'` — multi-node
 *   deployments must use an S3-compatible store.
 * - Proxy download URLs carry an HMAC-signed payload (key + expiry); the
 *   route refuses to stream a key whose token doesn't verify.
 */

import { createHash, createHmac, randomUUID, timingSafeEqual } from 'node:crypto';
import { createReadStream } from 'node:fs';
import * as fs from 'node:fs/promises';
import * as path from 'node:path';
import { Readable } from 'node:stream';

import { env } from '@/lib/env';
import { NotFoundError, ValidationError } from '@/lib/errors';
import { logger } from '@/lib/logger';
import { decrypt } from '@/lib/utils/encryption';

import type { PresignOpts, PutOpts, StorageBackend } from './index';

// ─── key validation ─────────────────────────────────────────────────────────

const VALID_KEY_RE = /^[a-zA-Z0-9/_.-]+$/;

/**
 * Validate a storage key. Rejects:
 * - empty / whitespace
 * - characters outside `[a-zA-Z0-9/_.-]`
 * - traversal segments (`..`, `/..`, `../`)
 * - absolute paths (leading `/`)
 * - segments starting with `.` (hidden files / dotfiles other than the
 *   intentional dot-extension at the end)
 *
 * Use this both at write time AND at read time — a key fed back from the DB
 * could in theory have been tampered with at rest.
 */
export function validateStorageKey(key: string): void {
  if (typeof key !== 'string' || key.length === 0) {
    throw new ValidationError('Storage key must be a non-empty string');
  }
  if (key.length > 1024) {
    throw new ValidationError('Storage key exceeds 1024 chars');
  }
  if (key.startsWith('/') || key.startsWith('\\')) {
    throw new ValidationError('Storage key must not be absolute');
  }
  if (!VALID_KEY_RE.test(key)) {
    throw new ValidationError('Storage key contains forbidden characters');
  }
  // Reject any traversal segment in any normalized form.
  const segments = key.split('/');
  for (const seg of segments) {
    if (seg === '..' || seg === '.' || seg === '') {
      throw new ValidationError('Storage key has empty or traversal segment');
    }
  }
}

// ─── HMAC token helpers ─────────────────────────────────────────────────────

interface ProxyTokenPayload {
  /** Storage key (validated). */
  k: string;
  /** Expiry epoch seconds. */
  e: number;
  /** Random nonce so two URLs for the same (key, expiry) differ. */
  n: string;
  /** Optional download filename. */
  f?: string;
  /** Optional content-type override. */
  c?: string;
}

function b64urlEncode(buf: Buffer): string {
  return buf.toString('base64').replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}

function b64urlDecode(s: string): Buffer {
  const pad = s.length % 4 === 0 ? '' : '='.repeat(4 - (s.length % 4));
  return Buffer.from(s.replace(/-/g, '+').replace(/_/g, '/') + pad, 'base64');
}

export function signProxyToken(payload: ProxyTokenPayload, secret: string): string {
  const json = JSON.stringify(payload);
  const body = b64urlEncode(Buffer.from(json, 'utf8'));
  const sig = createHmac('sha256', secret).update(body).digest();
  return `${body}.${b64urlEncode(sig)}`;
}

export function verifyProxyToken(
  token: string,
  secret: string,
): { ok: true; payload: ProxyTokenPayload } | { ok: false; reason: string } {
  if (typeof token !== 'string' || !token.includes('.')) {
    return { ok: false, reason: 'malformed' };
  }
  const [body, sigB64] = token.split('.', 2);
  if (!body || !sigB64) return { ok: false, reason: 'malformed' };

  const expected = createHmac('sha256', secret).update(body).digest();
  let provided: Buffer;
  try {
    provided = b64urlDecode(sigB64);
  } catch {
    return { ok: false, reason: 'malformed' };
  }
  if (provided.length !== expected.length) return { ok: false, reason: 'sig-mismatch' };
  if (!timingSafeEqual(provided, expected)) return { ok: false, reason: 'sig-mismatch' };

  let payload: ProxyTokenPayload;
  try {
    payload = JSON.parse(b64urlDecode(body).toString('utf8')) as ProxyTokenPayload;
  } catch {
    return { ok: false, reason: 'malformed-payload' };
  }

  if (typeof payload.e !== 'number' || payload.e * 1000 < Date.now()) {
    return { ok: false, reason: 'expired' };
  }
  try {
    validateStorageKey(payload.k);
  } catch {
    return { ok: false, reason: 'invalid-key' };
  }
  return { ok: true, payload };
}

// ─── backend ────────────────────────────────────────────────────────────────

interface FilesystemConfig {
  root: string;
  /** AES-GCM-encrypted HMAC secret. When absent, falls back to a derived secret. */
  proxyHmacSecretEncrypted: string | null;
}

export class FilesystemBackend implements StorageBackend {
  readonly name = 'filesystem' as const;

  private rootResolved: string;
  private hmacSecret: string;

  private constructor(rootResolved: string, hmacSecret: string) {
    this.rootResolved = rootResolved;
    this.hmacSecret = hmacSecret;
  }

  /** Throws if multi-node mode is set or the root isn't writable. */
  static async create(cfg: FilesystemConfig): Promise<FilesystemBackend> {
    if (process.env.MULTI_NODE_DEPLOYMENT === 'true') {
      throw new Error(
        'FilesystemBackend cannot start when MULTI_NODE_DEPLOYMENT=true. ' +
          'Use an S3-compatible backend for multi-node deployments.',
      );
    }
    const rootInput = cfg.root || './storage';
    const rootAbs = path.isAbsolute(rootInput) ? rootInput : path.resolve(process.cwd(), rootInput);
    await fs.mkdir(rootAbs, { recursive: true, mode: 0o700 });
    // Defensive: re-chmod even if it already existed.
    await fs.chmod(rootAbs, 0o700).catch(() => undefined);
    // Use realpath so symlinked roots are flattened to their actual location;
    // we then compare every per-key resolution against this exact prefix.
    const rootResolved = await fs.realpath(rootAbs);

    const hmacSecret = resolveHmacSecret(cfg.proxyHmacSecretEncrypted);
    logger.info({ root: rootResolved }, 'FilesystemBackend ready');
    return new FilesystemBackend(rootResolved, hmacSecret);
  }

  /**
   * Resolve a (validated) storage key to an absolute path under the root.
   * Throws if the resolved path escapes the storage root via symlink/.. tricks.
   */
  private resolveKey(key: string): string {
    validateStorageKey(key);
    const joined = path.join(this.rootResolved, key);
    const resolved = path.resolve(joined);
    if (resolved !== this.rootResolved && !resolved.startsWith(this.rootResolved + path.sep)) {
      throw new ValidationError('Storage key escapes storage root');
    }
    return resolved;
  }

  async put(
    key: string,
    body: Buffer | NodeJS.ReadableStream,
    opts: PutOpts,
  ): Promise<{ key: string; sizeBytes: number; sha256: string }> {
    const target = this.resolveKey(key);
    await fs.mkdir(path.dirname(target), { recursive: true, mode: 0o700 });

    const buffer = Buffer.isBuffer(body) ? body : await streamToBuffer(body);
    const sha256 = opts.sha256 ?? createHash('sha256').update(buffer).digest('hex');

    // Atomic write via temp + rename so partial writes don't leave half-files.
    const tmp = `${target}.${randomUUID()}.tmp`;
    await fs.writeFile(tmp, buffer, { mode: 0o600 });
    // realpath the temp to make sure the final-rename target resolves correctly
    // even if some segment of the path is a symlink we just created.
    await fs.rename(tmp, target);

    return { key, sizeBytes: buffer.length, sha256 };
  }

  async get(key: string): Promise<NodeJS.ReadableStream> {
    const target = this.resolveKey(key);
    try {
      const stat = await fs.stat(target);
      if (!stat.isFile()) throw new NotFoundError(`Storage object ${key}`);
    } catch (err) {
      const code = (err as NodeJS.ErrnoException).code;
      if (code === 'ENOENT') throw new NotFoundError(`Storage object ${key}`);
      throw err;
    }
    return createReadStream(target);
  }

  async head(key: string): Promise<{ sizeBytes: number; contentType: string } | null> {
    const target = this.resolveKey(key);
    try {
      const stat = await fs.stat(target);
      if (!stat.isFile()) return null;
      // Filesystem doesn't track content-type. Caller should consult the DB
      // (or sniff via ext) — we return application/octet-stream as a default.
      return { sizeBytes: stat.size, contentType: extToContentType(target) };
    } catch (err) {
      const code = (err as NodeJS.ErrnoException).code;
      if (code === 'ENOENT') return null;
      throw err;
    }
  }

  async delete(key: string): Promise<void> {
    const target = this.resolveKey(key);
    try {
      await fs.unlink(target);
    } catch (err) {
      const code = (err as NodeJS.ErrnoException).code;
      if (code === 'ENOENT') return;
      throw err;
    }
  }

  /**
   * Filesystem mode never exposes a direct upload URL. The CRM-internal proxy
   * accepts uploads via the regular API surface (multipart POST to /api/v1/...
   * or PUT to /api/storage/[token]). We return a placeholder PUT URL pointing
   * at the proxy so the contract stays uniform.
   */
  async presignUpload(
    key: string,
    opts: PresignOpts,
  ): Promise<{ url: string; method: 'PUT' | 'POST' }> {
    validateStorageKey(key);
    const expiresAt = Math.floor(Date.now() / 1000) + (opts.expirySeconds ?? 900);
    const token = signProxyToken(
      { k: key, e: expiresAt, n: randomUUID(), c: opts.contentType },
      this.hmacSecret,
    );
    return { url: `/api/storage/${token}`, method: 'PUT' };
  }

  async presignDownload(key: string, opts: PresignOpts): Promise<{ url: string; expiresAt: Date }> {
    validateStorageKey(key);
    const expirySec = opts.expirySeconds ?? 900;
    const expiresAtSec = Math.floor(Date.now() / 1000) + expirySec;
    const token = signProxyToken(
      { k: key, e: expiresAtSec, n: randomUUID(), f: opts.filename, c: opts.contentType },
      this.hmacSecret,
    );
    return {
      url: `/api/storage/${token}`,
      expiresAt: new Date(expiresAtSec * 1000),
    };
  }

  /** Used by the proxy route — returns the validated absolute path. */
  resolveKeyForProxy(key: string): string {
    return this.resolveKey(key);
  }

  /** Used by the proxy route — same HMAC secret as presignDownload. */
  getHmacSecret(): string {
    return this.hmacSecret;
  }
}

// ─── helpers ────────────────────────────────────────────────────────────────

function resolveHmacSecret(encryptedSecret: string | null): string {
  if (encryptedSecret) {
    try {
      return decrypt(encryptedSecret);
    } catch (err) {
      logger.error({ err }, 'Failed to decrypt storage_proxy_hmac_secret_encrypted');
    }
  }
  // Derive a stable per-process secret from BETTER_AUTH_SECRET so dev mode
  // works without explicit configuration. In production the admin UI writes
  // an encrypted random secret.
  const seed = process.env.BETTER_AUTH_SECRET ?? env.BETTER_AUTH_SECRET ?? 'storage-default';
  return createHash('sha256').update(`storage-proxy:${seed}`).digest('hex');
}

async function streamToBuffer(stream: NodeJS.ReadableStream): Promise<Buffer> {
  const chunks: Buffer[] = [];
  for await (const chunk of stream as Readable) {
    chunks.push(Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk as string));
  }
  return Buffer.concat(chunks);
}

function extToContentType(filename: string): string {
  const ext = path.extname(filename).toLowerCase();
  switch (ext) {
    case '.pdf':
      return 'application/pdf';
    case '.png':
      return 'image/png';
    case '.jpg':
    case '.jpeg':
      return 'image/jpeg';
    case '.json':
      return 'application/json';
    case '.txt':
      return 'text/plain';
    case '.csv':
      return 'text/csv';
    case '.zip':
      return 'application/zip';
    default:
      return 'application/octet-stream';
  }
}