import { readFileSync } from "node:fs";
import { fileURLToPath } from "node:url";

type ReadTextFile = (path: string) => string;

const FULL_SHA_RE = /^[0-9a-f]{40}$/i;
const DEFAULT_BUILD_COMMIT_PATH = fileURLToPath(
  new URL("../../.paperclip-build-commit", import.meta.url),
);
const DEFAULT_BUILD_INFO_PATH = fileURLToPath(new URL("./build-info.json", import.meta.url));

export function parseBuildCommit(value: string | null | undefined): string | null {
  const commit = value?.trim() ?? "";
  return FULL_SHA_RE.test(commit) ? commit.toLowerCase() : null;
}

export function readBuildCommit(
  opts: {
    environmentCommit?: string | null;
    buildCommitPath?: string;
    buildInfoPath?: string;
    readTextFile?: ReadTextFile;
  } = {},
): string | null {
  const environmentCommit = parseBuildCommit(
    opts.environmentCommit === undefined
      ? process.env.PAPERCLIP_BUILD_COMMIT
      : opts.environmentCommit,
  );
  if (environmentCommit) return environmentCommit;

  const readTextFile = opts.readTextFile ?? ((path: string) => readFileSync(path, "utf8"));
  try {
    const markerCommit = parseBuildCommit(readTextFile(opts.buildCommitPath ?? DEFAULT_BUILD_COMMIT_PATH));
    if (markerCommit) return markerCommit;
  } catch { /* The deployment marker is absent in npm packages. */ }
  try {
    const stamp = JSON.parse(readTextFile(opts.buildInfoPath ?? DEFAULT_BUILD_INFO_PATH));
    return typeof stamp?.commit === "string" ? parseBuildCommit(stamp.commit) : null;
  } catch {
    return null;
  }
}