/*
 * app-log.js — the persistent log this app never had.
 *
 * Every child (voice process, congregation server, translation model) writes
 * to stdout, and main.js forwards that to ITS stdout — which, for an app
 * launched from the Finder, is nowhere. So the morning a service went wrong
 * there was a caption transcript and not one line saying what the voice
 * process had decided to do. This module tees everything to
 * <dataDir>/logs/app.log, rotated so it can never fill a disk.
 *
 * Deliberately boring: synchronous appends (a crash must not lose the line
 * that explains it), a size cap, three generations, and every failure
 * swallowed — logging must never be the thing that takes the service down.
 */
'use strict';
const fs = require('fs');
const path = require('path');

const MAX_BYTES = 2 * 1024 * 1024;   // rotate past 2 MB
const KEEP = 3;                      // app.log, app.log.1, app.log.2

function createAppLog(dir, name) {
  name = name || 'app.log';
  const file = path.join(dir, name);
  let size = 0;
  try { fs.mkdirSync(dir, { recursive: true }); } catch (_) {}
  try { size = fs.statSync(file).size; } catch (_) { size = 0; }

  function rotate() {
    try {
      for (let i = KEEP - 1; i >= 1; i--) {
        const from = file + (i === 1 ? '' : '.' + (i - 1));
        const to = file + '.' + i;
        try { fs.renameSync(from, to); } catch (_) {}
      }
    } catch (_) {}
    size = 0;
  }

  function stamp() {
    const d = new Date();
    const p = (n, w) => String(n).padStart(w || 2, '0');
    return d.getFullYear() + '-' + p(d.getMonth() + 1) + '-' + p(d.getDate()) + ' ' +
           p(d.getHours()) + ':' + p(d.getMinutes()) + ':' + p(d.getSeconds()) + '.' + p(d.getMilliseconds(), 3);
  }

  /* Write one or more lines under a source tag. Multi-line chunks from a
     child's stdout are split so every line carries its own stamp and tag. */
  function write(tag, chunk) {
    try {
      const text = String(chunk == null ? '' : chunk);
      if (!text.trim()) return;
      const lines = text.replace(/\r/g, '').split('\n').filter((l) => l.length);
      const out = lines.map((l) => stamp() + ' [' + tag + '] ' + l).join('\n') + '\n';
      /* Bytes, not characters: accented Spanish and CJK log lines are 2-3
         bytes a character, and a character count let a generation reach 6 MB. */
      const bytes = Buffer.byteLength(out, 'utf8');
      if (size + bytes > MAX_BYTES) rotate();
      fs.appendFileSync(file, out);
      size += bytes;
    } catch (_) { /* never let logging take anything down */ }
  }

  /* Attach to a child process: tee stdout/stderr to the file. Returns the
     child for chaining. The caller may still forward to its own stdout. */
  function tee(child, tag) {
    if (child && child.stdout) child.stdout.on('data', (d) => write(tag, d));
    if (child && child.stderr) child.stderr.on('data', (d) => write(tag + ':err', d));
    return child;
  }

  return { write, tee, file, rotate };
}

module.exports = { createAppLog, MAX_BYTES, KEEP };