#!/usr/bin/env node
/**
 * normalize-commit-msg.js
 *
 * Git commit-msg hook: reads the commit message file, applies normalization
 * rules to the subject line, rewrites the file in place.
 *
 * Rules:
 *   1. Trim leading/trailing whitespace from the subject line
 *   2. Capitalize the first letter of the subject
 *   3. Strip a trailing period from the subject
 *   4. Warn (but do not block) if the subject exceeds 72 characters
 */

'use strict';

const fs = require('fs');

const MAX_SUBJECT_LEN = 72;

/**
 * Normalize the subject line of a commit message.
 * Returns { subject, warned } where warned is true if a length warning was emitted.
 *
 * @param {string} subject
 * @returns {{ subject: string, warned: boolean }}
 */
function normalizeSubject(subject) {
  let s = subject.trimEnd();

  // Trim leading whitespace
  s = s.trimStart();

  // Capitalize first letter
  if (s.length > 0) {
    s = s[0].toUpperCase() + s.slice(1);
  }

  // Strip trailing period
  if (s.endsWith('.')) {
    s = s.slice(0, -1);
  }

  const warned = s.length > MAX_SUBJECT_LEN;

  return { subject: s, warned };
}

/**
 * Normalize a full commit message string.
 * Only the subject line (first non-empty, non-comment line) is modified.
 *
 * @param {string} message
 * @returns {{ message: string, warned: boolean }}
 */
function normalizeMessage(message) {
  const lines = message.split('\n');
  let warned = false;

  // Find the subject line (first non-comment line)
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (!line.startsWith('#')) {
      const result = normalizeSubject(line);
      lines[i] = result.subject;
      warned = result.warned;
      break;
    }
  }

  return { message: lines.join('\n'), warned };
}

// Only run as a hook when invoked directly (not when required in tests)
if (require.main === module) {
  const msgFile = process.argv[2];
  if (!msgFile) {
    process.stderr.write('commit-msg hook: no message file argument\n');
    process.exit(1);
  }

  const original = fs.readFileSync(msgFile, 'utf8');
  const { message, warned } = normalizeMessage(original);

  if (warned) {
    process.stderr.write(
      `commit-msg warning: subject line exceeds ${MAX_SUBJECT_LEN} characters — consider shortening it.\n`
    );
  }

  fs.writeFileSync(msgFile, message, 'utf8');
  process.exit(0);
}

module.exports = { normalizeSubject, normalizeMessage };