/**
 * Checking uploaded images and serving uploaded files back.
 *
 * @module
 */

import type { Context } from "@oak/oak";
import { APIErrorCode } from "../../shared/api.ts";
import { APIException } from "./api-exception.ts";
import { serveFile } from "./serve-file.ts";
import {
  ALLOWED_IMAGE_MIMES,
  ATTACHMENTS_DIR,
  AVATARS_DIR,
  DUMPS_DIR,
  MAX_IMAGE_SIZE_BYTES,
  PLAYLIST_IMAGES_DIR,
  UPLOADS_DIR,
} from "../config.ts";

export {
  ALLOWED_IMAGE_MIMES,
  ATTACHMENTS_DIR,
  AVATARS_DIR,
  DUMPS_DIR,
  PLAYLIST_IMAGES_DIR,
  UPLOADS_DIR,
};

/**
 * Returns the MIME type of a JPEG, PNG, GIF or WebP image from its magic
 * bytes, ignoring the type the browser declared; null for anything else.
 */
export function detectImageMime(data: Uint8Array): string | null {
  if (data[0] === 0xFF && data[1] === 0xD8 && data[2] === 0xFF) {
    return "image/jpeg";
  }
  if (
    data[0] === 0x89 && data[1] === 0x50 && data[2] === 0x4E && data[3] === 0x47
  ) return "image/png";
  if (
    data[0] === 0x47 && data[1] === 0x49 && data[2] === 0x46 && data[3] === 0x38
  ) return "image/gif";
  // RIFF....WEBP
  if (
    data[0] === 0x52 && data[1] === 0x49 && data[2] === 0x46 &&
    data[3] === 0x46 &&
    data[8] === 0x57 && data[9] === 0x45 && data[10] === 0x42 &&
    data[11] === 0x50
  ) return "image/webp";
  return null;
}

/**
 * Checks an uploaded image's size and content, and returns its MIME type.
 *
 * @throws {APIException} 400 when it exceeds {@link MAX_IMAGE_SIZE_BYTES} or
 * isn't a JPEG, PNG, GIF or WebP image.
 */
export function validateImageUpload(data: Uint8Array): string {
  if (data.length > MAX_IMAGE_SIZE_BYTES) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      "File too large (max 5 MB)",
    );
  }
  const mime = detectImageMime(data);
  if (!mime) {
    throw new APIException(
      APIErrorCode.BAD_REQUEST,
      400,
      "File content is not a recognised image (JPEG, PNG, GIF, WebP)",
    );
  }
  return mime;
}

/**
 * Serves an uploaded file inline as `mime`, cached for `cacheMaxAge` seconds
 * (privately when `isPrivate`). Answers 404 and resolves false when the file
 * is missing.
 */
export async function serveUploadedFile(
  ctx: Context,
  filePath: string,
  mime: string,
  cacheMaxAge = 3600,
  isPrivate = false,
): Promise<boolean> {
  ctx.response.headers.set("Content-Disposition", "inline");
  ctx.response.headers.set("X-Content-Type-Options", "nosniff");
  ctx.response.headers.set("Cross-Origin-Resource-Policy", "cross-origin");
  const served = await serveFile(ctx, filePath, {
    mime,
    cacheControl: `${isPrivate ? "private" : "public"}, max-age=${cacheMaxAge}`,
  });
  if (!served) ctx.response.status = 404;
  return served;
}