export const MAX_FORM_ANSWER_IMAGE_BYTES = 50 * 1024 * 1024;

const ALLOWED_IMAGE_MIME_TYPES = new Set([
  "image/png",
  "image/jpeg",
  "image/webp",
  "image/gif",
]);

const ALLOWED_IMAGE_EXTENSIONS = new Set(["png", "jpg", "jpeg", "webp", "gif"]);

export function validateImageUploadFile(
  file: Pick<File, "name" | "type" | "size">,
  bytes?: Uint8Array
) {
  if (!ALLOWED_IMAGE_MIME_TYPES.has(file.type)) {
    throw new Error("Only PNG, JPG, WebP, and GIF images are allowed");
  }

  if (file.size > MAX_FORM_ANSWER_IMAGE_BYTES) {
    throw new Error("Image must be 50MB or smaller");
  }

  if (file.size === 0) {
    throw new Error("Image cannot be empty");
  }

  const extension = (file.name.split(".").pop() || "").toLowerCase();
  if (!ALLOWED_IMAGE_EXTENSIONS.has(extension)) {
    throw new Error("Invalid image extension");
  }

  if (bytes && !hasMatchingImageSignature(file.type, bytes)) {
    throw new Error("Image contents do not match the declared image type");
  }
}

function hasMatchingImageSignature(type: string, bytes: Uint8Array) {
  if (type === "image/png") {
    return bytes.length >= 8 &&
      bytes.slice(0, 8).every((value, index) => value === [137, 80, 78, 71, 13, 10, 26, 10][index]);
  }

  if (type === "image/jpeg") {
    return bytes.length >= 3 && bytes[0] === 0xff && bytes[1] === 0xd8 && bytes[2] === 0xff;
  }

  if (type === "image/gif") {
    return bytes.length >= 6 &&
      (String.fromCharCode(...bytes.slice(0, 6)) === "GIF87a" ||
        String.fromCharCode(...bytes.slice(0, 6)) === "GIF89a");
  }

  if (type === "image/webp") {
    return bytes.length >= 12 &&
      String.fromCharCode(...bytes.slice(0, 4)) === "RIFF" &&
      String.fromCharCode(...bytes.slice(8, 12)) === "WEBP";
  }

  return false;
}

export function cdnUrl(id: string | null | undefined) {
  return id ? `/cdn/${id}` : "";
}

export type CdnResponseRecord = {
  data: Buffer;
  type: string;
  size: number;
};

export function cdnImageResponse(record: CdnResponseRecord) {
  return new Response(new Uint8Array(record.data), {
    headers: {
      "Content-Type": record.type,
      "Content-Length": String(record.size),
      "Cache-Control": "public, max-age=31536000, immutable",
      "X-Content-Type-Options": "nosniff",
    },
  });
}