import { createHash } from "node:crypto";
import { DAEMON_RELEASE_POLICY } from "./daemon-policy.mjs";

const CHECKSUMS_FILE = "checksums.txt";
const API_MAX_BYTES = 2 * 1024 * 1024;
const CHECKSUMS_MAX_BYTES = 64 * 1024;
const ASSET_MAX_BYTES = 128 * 1024 * 1024;

export class ReleaseVerificationError extends Error {
  constructor(code, message) {
    super(message);
    this.name = "ReleaseVerificationError";
    this.code = code;
  }
}

function fail(code, message) {
  throw new ReleaseVerificationError(code, message);
}

function versionTuple(value) {
  const match = /^(\d+)\.(\d+)\.(\d+)$/.exec(value);
  if (!match) return null;
  const parts = match.slice(1).map(Number);
  return parts.every(Number.isSafeInteger) ? parts : null;
}

function compareVersions(left, right) {
  for (let index = 0; index < 3; index += 1) {
    if (left[index] !== right[index]) return left[index] - right[index];
  }
  return 0;
}

export function parseReleaseTag(rawTag) {
  const tag = String(rawTag ?? "").trim();
  const match = /^v(\d+\.\d+\.\d+)$/.exec(tag);
  if (!match) fail("invalid_release_tag", "tag 必须是稳定版本 vX.Y.Z");
  const version = match[1];
  const current = versionTuple(version);
  const minimum = versionTuple(DAEMON_RELEASE_POLICY.minimumVersion);
  if (!current || !minimum || compareVersions(current, minimum) < 0) {
    fail(
      "incompatible_release_version",
      `Cloud daemon 版本不得低于 v${DAEMON_RELEASE_POLICY.minimumVersion}`,
    );
  }
  return { tag, version };
}

function sha256(bytes) {
  return createHash("sha256").update(bytes).digest("hex");
}

function githubHeaders(token, accept = "application/vnd.github+json") {
  return {
    accept,
    "user-agent": "nekonest-cloud-release-verifier",
    "x-github-api-version": "2022-11-28",
    ...(token ? { authorization: `Bearer ${token}` } : {}),
  };
}

async function fetchBytes(fetchImpl, url, options) {
  let response;
  try {
    response = await fetchImpl(url, {
      headers: githubHeaders(options.authenticated ? options.token : undefined, options.accept),
      redirect: "follow",
      signal: AbortSignal.timeout(30_000),
    });
  } catch {
    fail("release_fetch_failed", `${options.label} 请求失败`);
  }
  if (!response?.ok) {
    fail("release_fetch_rejected", `${options.label} 返回 HTTP ${response?.status ?? "unknown"}`);
  }
  const declared = response.headers.get("content-length");
  if (declared && (!/^\d+$/.test(declared) || Number(declared) > options.maxBytes)) {
    fail("release_response_too_large", `${options.label} 超过大小上限`);
  }
  let bytes;
  try {
    bytes = new Uint8Array(await response.arrayBuffer());
  } catch {
    fail("release_response_read_failed", `${options.label} 响应读取失败`);
  }
  if (bytes.byteLength > options.maxBytes) {
    fail("release_response_too_large", `${options.label} 超过大小上限`);
  }
  return bytes;
}

function exactDownloadUrl(tag, filename) {
  return `https://github.com/${DAEMON_RELEASE_POLICY.repository}/releases/download/${tag}/${filename}`;
}

function validateAsset(record, tag, filename) {
  if (!record || typeof record !== "object") fail("release_asset_missing", `缺少 ${filename}`);
  if (record.name !== filename || record.browser_download_url !== exactDownloadUrl(tag, filename)) {
    fail("release_asset_url_mismatch", `${filename} 不是精确 tag 的官方资产`);
  }
  if (
    record.state !== "uploaded" ||
    !Number.isSafeInteger(record.size) ||
    record.size < 1 ||
    record.size > ASSET_MAX_BYTES
  ) {
    fail("release_asset_size_invalid", `${filename} 的资产大小无效`);
  }
  const digest = String(record.digest ?? "").toLowerCase();
  if (!/^sha256:[0-9a-f]{64}$/.test(digest)) {
    fail("release_asset_digest_missing", `${filename} 缺少 GitHub SHA-256 digest`);
  }
  return { ...record, digest: digest.slice("sha256:".length) };
}

function indexRequiredAssets(release, tag) {
  if (!Array.isArray(release.assets)) fail("release_assets_invalid", "Release assets 不是数组");
  const requiredNames = [
    ...DAEMON_RELEASE_POLICY.assets.map((asset) => asset.filename),
    CHECKSUMS_FILE,
  ];
  const indexed = new Map();
  for (const name of requiredNames) {
    const matches = release.assets.filter((asset) => asset?.name === name);
    if (matches.length !== 1) {
      fail(
        matches.length === 0 ? "release_asset_missing" : "release_asset_duplicate",
        `${name} 必须恰好出现一次`,
      );
    }
    indexed.set(name, validateAsset(matches[0], tag, name));
  }
  return indexed;
}

function parseChecksums(bytes) {
  const text = new TextDecoder("utf-8", { fatal: true }).decode(bytes);
  const checksums = new Map();
  for (const rawLine of text.split(/\r?\n/)) {
    const line = rawLine.trim();
    if (!line) continue;
    const match = /^([0-9a-fA-F]{64})\s+\*?([^\s]+)$/.exec(line);
    if (!match) fail("checksums_format_invalid", "checksums.txt 包含无效行");
    const filename = match[2];
    if (checksums.has(filename)) fail("checksums_duplicate", `${filename} 摘要重复`);
    checksums.set(filename, match[1].toLowerCase());
  }
  return checksums;
}

export async function verifyDaemonRelease(input) {
  const { tag, version } = parseReleaseTag(input.tag);
  const fetchImpl = input.fetchImpl ?? globalThis.fetch;
  if (typeof fetchImpl !== "function") fail("fetch_unavailable", "当前 Node 不支持 fetch");
  const apiUrl = `https://api.github.com/repos/${DAEMON_RELEASE_POLICY.repository}/releases/tags/${tag}`;
  const apiBytes = await fetchBytes(fetchImpl, apiUrl, {
    token: input.token,
    authenticated: true,
    label: "GitHub Release API",
    maxBytes: API_MAX_BYTES,
  });
  let release;
  try {
    release = JSON.parse(new TextDecoder().decode(apiBytes));
  } catch {
    fail("release_json_invalid", "GitHub Release API 返回了无效 JSON");
  }
  const publishedAt = new Date(release?.published_at ?? "");
  if (
    release?.tag_name !== tag ||
    release?.draft !== false ||
    release?.prerelease !== false ||
    release?.html_url !== `https://github.com/${DAEMON_RELEASE_POLICY.repository}/releases/tag/${tag}` ||
    !Number.isFinite(publishedAt.getTime())
  ) {
    fail("release_identity_invalid", "Release 必须是精确 tag 的公开稳定版本");
  }

  const assetsByName = indexRequiredAssets(release, tag);
  const checksumAsset = assetsByName.get(CHECKSUMS_FILE);
  const checksumsBytes = await fetchBytes(fetchImpl, checksumAsset.browser_download_url, {
    token: input.token,
    label: CHECKSUMS_FILE,
    accept: "application/octet-stream",
    maxBytes: CHECKSUMS_MAX_BYTES,
  });
  if (checksumsBytes.byteLength !== checksumAsset.size || sha256(checksumsBytes) !== checksumAsset.digest) {
    fail("checksums_asset_mismatch", "checksums.txt 大小或 GitHub digest 不匹配");
  }
  const checksums = parseChecksums(checksumsBytes);

  const verifiedAssets = [];
  for (const policyAsset of DAEMON_RELEASE_POLICY.assets) {
    const releaseAsset = assetsByName.get(policyAsset.filename);
    const expected = checksums.get(policyAsset.filename);
    if (!expected) fail("checksums_entry_missing", `${policyAsset.filename} 没有摘要`);
    if (releaseAsset.digest !== expected) {
      fail("release_digest_mismatch", `${policyAsset.filename} 的 API digest 与清单不一致`);
    }
    const bytes = await fetchBytes(fetchImpl, releaseAsset.browser_download_url, {
      token: input.token,
      label: policyAsset.filename,
      accept: "application/octet-stream",
      maxBytes: ASSET_MAX_BYTES,
    });
    if (bytes.byteLength !== releaseAsset.size) {
      fail("release_asset_size_mismatch", `${policyAsset.filename} 实际大小不匹配`);
    }
    if (sha256(bytes) !== expected) {
      fail("release_asset_hash_mismatch", `${policyAsset.filename} 实际 SHA-256 不匹配`);
    }
    verifiedAssets.push({
      ...policyAsset,
      sha256: expected,
      size: bytes.byteLength,
      downloadUrl: releaseAsset.browser_download_url,
    });
  }

  return {
    repository: DAEMON_RELEASE_POLICY.repository,
    tag,
    version,
    releasePageUrl: release.html_url,
    releaseBaseUrl: `https://github.com/${DAEMON_RELEASE_POLICY.repository}/releases/download/${tag}`,
    checksumsUrl: checksumAsset.browser_download_url,
    checksumsSha256: checksumAsset.digest,
    publishedAt: publishedAt.toISOString(),
    assets: verifiedAssets,
  };
}

export function formatCloudReleaseEnvironment(verified) {
  const lines = [
    `NEKONEST_CLOUD_DAEMON_RELEASE_VERSION=${verified.version}`,
    `NEKONEST_CLOUD_DAEMON_RELEASE_BASE_URL=${verified.releaseBaseUrl}`,
  ];
  for (const asset of verified.assets) lines.push(`${asset.checksumEnv}=${asset.sha256}`);
  return lines.join("\n");
}