import type { AttachmentMimeType } from '@dorfteich/shared';

/**
 * Magic-byte signatures for the raster-image allowlist (ADR 0011). The
 * client-declared MIME type and filename extension are never trusted —
 * only the actual bytes decide, which is what catches a renamed
 * `.html`-as-`.png` upload.
 */
const SIGNATURES: ReadonlyArray<{
  mimeType: AttachmentMimeType;
  matches: (buf: Buffer) => boolean;
}> = [
  {
    mimeType: 'image/png',
    matches: (buf) =>
      buf.length >= 8 &&
      buf.subarray(0, 8).equals(Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])),
  },
  {
    mimeType: 'image/jpeg',
    matches: (buf) => buf.length >= 3 && buf[0] === 0xff && buf[1] === 0xd8 && buf[2] === 0xff,
  },
  {
    mimeType: 'image/gif',
    matches: (buf) =>
      buf.length >= 6 &&
      (buf.toString('ascii', 0, 6) === 'GIF87a' || buf.toString('ascii', 0, 6) === 'GIF89a'),
  },
  {
    mimeType: 'image/webp',
    matches: (buf) =>
      buf.length >= 12 &&
      buf.toString('ascii', 0, 4) === 'RIFF' &&
      buf.toString('ascii', 8, 12) === 'WEBP',
  },
];

/** Returns the sniffed raster-image MIME type, or null when the bytes match none of the allowed signatures. */
export function sniffImageMimeType(buffer: Buffer): AttachmentMimeType | null {
  return SIGNATURES.find((signature) => signature.matches(buffer))?.mimeType ?? null;
}

/**
 * Heuristic SVG detection: an XML document whose leading bytes contain an
 * `<svg` tag. SVG has no binary magic number (it is XML), so we scan the
 * head, tolerating a BOM, an XML prolog, and a leading DOCTYPE/comment. This
 * only gates *candidacy*; the bytes are still sanitized or rejected per the
 * SVG policy before storage, so a false positive is harmless.
 */
export function looksLikeSvg(buffer: Buffer): boolean {
  return buffer.subarray(0, 1024).toString('utf8').toLowerCase().includes('<svg');
}