// lib/stats/event-emit.mjs
// Atomic JSONL append for autonomy-lifecycle events (plan-v2 Step 6).
//
// Writes one line per event to ${CLAUDE_PLUGIN_DATA}/ultraexecute-stats.jsonl
// (or override via CLAUDE_PLUGIN_DATA env var; falls back to silent skip if
// the directory doesn't exist — stats failures must NEVER block workflow).
//
// Every emission carries:
//   - ts          : ISO-8601 timestamp (REQUIRED per SC4 contract)
//   - event       : the requested event name
//   - known_event : true for recognized events, false otherwise
//   - payload     : caller-supplied object (may be {})
//
// Recognized events: brief-approved, main-merge-gate, user_input.
// Unknown event names are still emitted (with known_event: false) so that
// the audit trail is complete; downstream consumers filter as needed.
//
// CLI shim:
//   node lib/stats/event-emit.mjs --event brief-approved --payload '{...}'
//   → exit 0 (always); silent on stat dir absence.

import { appendFileSync, existsSync, mkdirSync } from 'node:fs';
import { dirname, join } from 'node:path';

export const KNOWN_EVENTS = Object.freeze(new Set([
  'brief-approved',
  'main-merge-gate',
  'user_input',
]));

const STATS_FILENAME = 'ultraexecute-stats.jsonl';

/**
 * Resolve the stats file path. Honors CLAUDE_PLUGIN_DATA env var.
 * Returns null if no plugin-data dir is configured (silent-skip mode).
 */
export function resolveStatsPath(env = process.env) {
  const dir = env.CLAUDE_PLUGIN_DATA;
  if (!dir || typeof dir !== 'string' || dir.length === 0) return null;
  return join(dir, STATS_FILENAME);
}

/**
 * Build the JSON record. Pure — no I/O.
 */
export function buildRecord(event, payload = {}, now = new Date()) {
  if (typeof event !== 'string' || event.length === 0) {
    throw new TypeError('event must be a non-empty string');
  }
  return {
    ts: now.toISOString(),
    event,
    known_event: KNOWN_EVENTS.has(event),
    payload: (payload && typeof payload === 'object') ? payload : {},
  };
}

/**
 * Emit an event. Never throws — stat failures are swallowed silently
 * because lifecycle telemetry must not block the user's workflow.
 *
 * @returns {{ written: boolean, path: string | null, reason?: string }}
 */
export function emit(event, payload = {}, opts = {}) {
  const env = opts.env || process.env;
  const now = opts.now || new Date();
  let record;
  try {
    record = buildRecord(event, payload, now);
  } catch (e) {
    return { written: false, path: null, reason: `record-build: ${e.message}` };
  }
  const path = opts.path || resolveStatsPath(env);
  if (!path) return { written: false, path: null, reason: 'CLAUDE_PLUGIN_DATA unset' };
  try {
    const dir = dirname(path);
    if (!existsSync(dir)) {
      // Best-effort dir creation; if it fails, swallow and skip.
      try { mkdirSync(dir, { recursive: true }); } catch { return { written: false, path, reason: 'dir-mkdir-failed' }; }
    }
    appendFileSync(path, JSON.stringify(record) + '\n');
    return { written: true, path };
  } catch (e) {
    return { written: false, path, reason: `append-failed: ${e.message}` };
  }
}

// ---- CLI shim ----------------------------------------------------------------

function parseArgs(argv) {
  const out = {};
  for (let i = 0; i < argv.length; i++) {
    const a = argv[i];
    if (a === '--event') out.event = argv[++i];
    else if (a === '--payload') out.payload = argv[++i];
  }
  return out;
}

if (import.meta.url === `file://${process.argv[1]}`) {
  const args = parseArgs(process.argv.slice(2));
  if (!args.event) {
    process.stdout.write(JSON.stringify({ written: false, reason: 'usage: --event NAME [--payload JSON]' }) + '\n');
    process.exit(0); // never block: usage error still exits clean
  }
  let payload = {};
  if (args.payload) {
    try { payload = JSON.parse(args.payload); }
    catch {
      process.stdout.write(JSON.stringify({ written: false, reason: 'payload-not-json' }) + '\n');
      process.exit(0);
    }
  }
  const result = emit(args.event, payload);
  process.stdout.write(JSON.stringify(result) + '\n');
  process.exit(0);
}