const os = require('os');
const path = require('path');
const fs = require('fs').promises;
const core = require('@actions/core');
const tc = require('@actions/tool-cache');
const cache = require('@actions/cache');
const common = require('./common');
const minisign = require('./minisign');

// Upstream's minisign key, from https://ziglang.org/download
const MINISIGN_KEY = 'RWSGOq2NVecA2UPNdBUZykf1CCb147pkmdtYxgb3Ti+JO/wCYvhbAb/U';

// The base URL of the official builds of Zig. This is only used as a fallback, if all mirrors fail.
const CANONICAL = 'https://ziglang.org/builds';

// The list of mirrors we attempt to fetch from. These need not be trusted, as
// we always verify the minisign signature.
const MIRRORS = [
  // TODO: are there any more mirrors around?
  'https://pkg.machengine.org/zig',
];

async function downloadFromMirror(mirror, tarball_name, tarball_ext) {
  const tarball_path = await tc.downloadTool(`${mirror}/${tarball_name}${tarball_ext}`);

  const signature_response = await fetch(`${mirror}/${tarball_name}${tarball_ext}.minisig`);
  const signature_data = Buffer.from(await signature_response.arrayBuffer());

  const tarball_data = await fs.readFile(tarball_path);

  const key = minisign.parseKey(MINISIGN_KEY);
  const signature = minisign.parseSignature(signature_data);
  if (!minisign.verifySignature(key, signature, tarball_data)) {
    throw new Error(`signature verification failed for '${mirror}/${tarball_name}${tarball_ext}'`);
  }

  return tarball_path;
}

async function downloadTarball(tarball_name, tarball_ext) {
  // We will attempt all mirrors before making a last-ditch attempt to the official download.
  // To avoid hammering a single mirror, we first randomize the array.
  const shuffled_mirrors = MIRRORS.map((m) => [m, Math.random()]).sort((a, b) => a[1] - b[1]).map((a) => a[0]);
  for (const mirror of shuffled_mirrors) {
    core.info(`Attempting mirror: ${mirror}`);
    try {
      return await downloadFromMirror(mirror, tarball_name, tarball_ext);
    } catch (e) {
      core.info(`Mirror failed with error: ${e}`);
      // continue loop to next mirror
    }
  }
  core.info(`Attempting official: ${CANONICAL}`);
  return await downloadFromMirror(CANONICAL, tarball_name, tarball_ext);
}

async function retrieveTarball(tarball_name, tarball_ext) {
  const cache_key = `setup-zig-tarball-${tarball_name}`;
  const tarball_cache_path = await common.getTarballCachePath();

  if (await cache.restoreCache([tarball_cache_path], cache_key)) {
    return tarball_cache_path;
  }

  core.info(`Cache miss. Fetching Zig ${await common.getVersion()}`);
  const downloaded_path = await downloadTarball(tarball_name, tarball_ext);
  await fs.copyFile(downloaded_path, tarball_cache_path)
  await cache.saveCache([tarball_cache_path], cache_key);
  return tarball_cache_path;
}

async function main() {
  try {
    // We will check whether Zig is stored in the cache. We use two separate caches.
    // * 'tool-cache' caches the final extracted directory if the same Zig build is used multiple
    //   times by one job. We have this dependency anyway for archive extraction.
    // * 'cache' only caches the unextracted archive, but it does so across runs. It's a little
    //   less efficient, but still much preferable to fetching Zig from a mirror. We have this
    //   dependency anyway for caching the global Zig cache.

    let zig_dir = tc.find('zig', await common.getVersion());
    if (!zig_dir) {
      const tarball_name = await common.getTarballName();
      const tarball_ext = await common.getTarballExt();

      const tarball_path = await retrieveTarball(tarball_name, tarball_ext);

      core.info(`Extracting tarball ${tarball_name}${tarball_ext}`);

      const zig_parent_dir = tarball_ext === 'zip' ?
        await tc.extractZip(tarball_path) :
        await tc.extractTar(tarball_path, null, 'xJ'); // J for xz

      const zig_inner_dir = path.join(zig_parent_dir, tarball_name);
      zig_dir = await tc.cacheDir(zig_inner_dir, 'zig', await common.getVersion());
    }

    core.addPath(zig_dir);
    await cache.restoreCache([await common.getZigCachePath()], await common.getCachePrefix());
    // Direct Zig to use the global cache as every local cache, so that we get maximum benefit from the caching above.
    core.exportVariable('ZIG_LOCAL_CACHE_DIR', await common.getZigCachePath());
  } catch (err) {
    core.setFailed(err.message);
  }
}

main();