import { execa } from "execa";

/**
 * Parse `git status --porcelain` (v1) output into repo-relative paths.
 *
 * Each line is `XY <path>`, where `XY` is the two-character status code. For
 * rename/copy entries (`R`/`C`) the path is `old -> new`; we return the new
 * path. Pure so it can be unit-tested without a real repository.
 */
export function parsePorcelain(output: string): string[] {
  return output
    .split("\n")
    .map((line) => line.replace(/\r$/, ""))
    .filter((line) => line.length > 0)
    .map((line) => {
      // Strip the "XY " status prefix (status chars + a single space).
      const path = line.slice(3);
      const arrow = path.indexOf(" -> ");
      return arrow === -1 ? path : path.slice(arrow + 4);
    });
}

/** Repo-relative paths that differ from HEAD (modified, staged, or untracked). */
export async function listDirtyPaths(repoRoot: string): Promise<string[]> {
  const { stdout } = await execa("git", ["status", "--porcelain"], {
    cwd: repoRoot,
  });
  return parsePorcelain(stdout);
}

/**
 * Create a path-limited commit of a single file. Committing the path directly
 * (`git commit -- <path>`) records only that file's working-tree changes,
 * regardless of what else is staged.
 */
export async function commitPath(
  repoRoot: string,
  relPath: string,
  message: string,
): Promise<{ ok: true } | { ok: false; error: string }> {
  const result = await execa(
    "git",
    ["commit", "-m", message, "--", relPath],
    { cwd: repoRoot, reject: false },
  );
  if (result.exitCode === 0) return { ok: true };
  const error =
    (result.stderr || result.stdout || "").trim() ||
    `git commit exited with code ${result.exitCode}`;
  return { ok: false, error };
}

/** The full sha HEAD points at, or null when it cannot be read. */
export async function headSha(repoRoot: string): Promise<string | null> {
  const result = await execa("git", ["rev-parse", "HEAD"], {
    cwd: repoRoot,
    reject: false,
  });
  const sha = result.exitCode === 0 ? String(result.stdout).trim() : "";
  return /^[0-9a-f]{40,64}$/.test(sha) ? sha : null;
}