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/**
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 * Author/committer signature extracted from a Git commit object.
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 *
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 * Format reference
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 * - `Name <email> <unix-seconds> <tz>`
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 *   Example: `John Doe <john@example.com> 1694025600 +0000`
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 */
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export interface Signature {
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  name: string;
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  email: string;
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  when: number;
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  tz: string;
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}
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export interface CommitParsed {
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  tree: string;
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  parents: string[];
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  author?: Signature;
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  committer?: Signature;
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  message: string;
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}
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/**
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 * Parse a Git signature line (author or committer).
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 *
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 * @param sig - A single line like `Name <email> 1694025600 +0000`
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 * @returns A normalized `Signature` or `undefined` if the format does not match
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 */
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export function parseSignature(sig: string): Signature | undefined {
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  // Format: Name <email> 1694025600 +0000
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  const m = sig.match(/^(.*) <([^>]+)>\s+(\d+)\s+([+-]\d{4})$/);
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  if (!m) return undefined;
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  const name = m[1];
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  const email = m[2];
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  const when = parseInt(m[3], 10);
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  const tz = m[4];
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  return { name, email, when, tz };
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}
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/**
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 * Parse a commit payload string (without the Git object header).
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 *
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 * Expected input
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 * - The raw text after inflating a `commit` Git object and removing the
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 *   `<type> <len>\0` header. Contains RFC-2822-ish lines and a blank line before
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 *   the message body.
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 *
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 * Extracted fields
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 * - `tree`: the root tree OID the commit points to
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 * - `parents`: zero or more parent OIDs (first entry is the first-parent)
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 * - `author`, `committer`: parsed signatures if present
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 * - `message`: text after the first blank line (may be empty)
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 */
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export function parseCommitText(text: string): CommitParsed {
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  const mTree = text.match(/^tree ([0-9a-f]{40})/m);
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  const tree = mTree ? mTree[1] : "";
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  const parents = [...text.matchAll(/^parent ([0-9a-f]{40})/gm)].map((x) => x[1]);
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  const authorLine = (text.match(/^author (.+)$/m) || [])[1];
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  const committerLine = (text.match(/^committer (.+)$/m) || [])[1];
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  const author = authorLine ? parseSignature(authorLine) : undefined;
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  const committer = committerLine ? parseSignature(committerLine) : undefined;
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  const msgIdx = text.indexOf("\n\n");
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  const message = msgIdx >= 0 ? text.slice(msgIdx + 2) : "";
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  return { tree, parents, author, committer, message };
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}