/**
 * Author/committer signature extracted from a Git commit object.
 *
 * Format reference
 * - `Name <email> <unix-seconds> <tz>`
 *   Example: `John Doe <john@example.com> 1694025600 +0000`
 */
export interface Signature {
  name: string;
  email: string;
  when: number;
  tz: string;
}

export interface CommitParsed {
  tree: string;
  parents: string[];
  author?: Signature;
  committer?: Signature;
  message: string;
}

/**
 * Parse a Git signature line (author or committer).
 *
 * @param sig - A single line like `Name <email> 1694025600 +0000`
 * @returns A normalized `Signature` or `undefined` if the format does not match
 */
export function parseSignature(sig: string): Signature | undefined {
  // Format: Name <email> 1694025600 +0000
  const m = sig.match(/^(.*) <([^>]+)>\s+(\d+)\s+([+-]\d{4})$/);
  if (!m) return undefined;
  const name = m[1];
  const email = m[2];
  const when = parseInt(m[3], 10);
  const tz = m[4];
  return { name, email, when, tz };
}

/**
 * Parse a commit payload string (without the Git object header).
 *
 * Expected input
 * - The raw text after inflating a `commit` Git object and removing the
 *   `<type> <len>\0` header. Contains RFC-2822-ish lines and a blank line before
 *   the message body.
 *
 * Extracted fields
 * - `tree`: the root tree OID the commit points to
 * - `parents`: zero or more parent OIDs (first entry is the first-parent)
 * - `author`, `committer`: parsed signatures if present
 * - `message`: text after the first blank line (may be empty)
 */
export function parseCommitText(text: string): CommitParsed {
  const mTree = text.match(/^tree ([0-9a-f]{40})/m);
  const tree = mTree ? mTree[1] : "";
  const parents = [...text.matchAll(/^parent ([0-9a-f]{40})/gm)].map((x) => x[1]);
  const authorLine = (text.match(/^author (.+)$/m) || [])[1];
  const committerLine = (text.match(/^committer (.+)$/m) || [])[1];
  const author = authorLine ? parseSignature(authorLine) : undefined;
  const committer = committerLine ? parseSignature(committerLine) : undefined;
  const msgIdx = text.indexOf("\n\n");
  const message = msgIdx >= 0 ? text.slice(msgIdx + 2) : "";
  return { tree, parents, author, committer, message };
}