const { Readable } = require("node:stream");
const { pipeline } = require("node:stream/promises");
const { AssetError } = require("./errors");

function readableBody(body) {
  if (body && typeof body.pipe === "function") return body;
  if (Buffer.isBuffer(body) || body instanceof Uint8Array) {
    return Readable.from([body]);
  }
  if (body && typeof body.getReader === "function") {
    return Readable.fromWeb(body);
  }
  throw new AssetError(
    "STORAGE_INCONSISTENCY",
    "Stored asset bytes could not be streamed",
    { statusCode: 503 },
  );
}

function validateDescriptor(descriptor) {
  if (
    typeof descriptor.contentType !== "string" ||
    !Number.isSafeInteger(descriptor.contentLength) ||
    descriptor.contentLength < 0
  ) {
    throw new AssetError(
      "STORAGE_INCONSISTENCY",
      "Stored asset metadata is incomplete",
      { statusCode: 503 },
    );
  }
}

function setCommonHeaders(response, descriptor) {
  response.set("Content-Type", descriptor.contentType);
  response.set("Content-Length", String(descriptor.contentLength));
  response.set("X-Content-Type-Options", "nosniff");
}

async function storedBody(assetService, descriptor) {
  const stored = await assetService.readStoredObject(descriptor);
  return readableBody(stored.body);
}

async function sendImmutableMedia(assetService, response, descriptor) {
  validateDescriptor(descriptor);
  const body = await storedBody(assetService, descriptor);
  setCommonHeaders(response, descriptor);
  response.set("Cache-Control", "public, max-age=31536000, immutable");
  response.set("ETag", `"${descriptor.hash}"`);
  await pipeline(body, response);
}

async function sendOriginal(assetService, response, descriptor) {
  validateDescriptor(descriptor);
  const body = await storedBody(assetService, descriptor);
  response.attachment(descriptor.asset.original_filename);
  setCommonHeaders(response, descriptor);
  response.set("Cache-Control", "private, no-store");
  await pipeline(body, response);
}

module.exports = {
  sendImmutableMedia,
  sendOriginal,
};