// lib/stats/event-emit.mjs
// Atomic JSONL append for autonomy-lifecycle events (plan-v2 Step 6).
//
// Writes one line per event to <data dir>/trekexecute-stats.jsonl, where the data
// dir is resolved by stats-append.mjs's resolveStatsDir: CLAUDE_PLUGIN_DATA when
// the harness provides it, else the plugin's directory under ~/.claude/plugins/data/,
// the one scripts/yardstick.mjs reads (one resolver, no second copy here). The Bash tool env carries no
// CLAUDE_PLUGIN_DATA, so the old "unset -> silent skip" dropped every event the
// command prose emitted. A failed write is REPORTED ({written:false, reason}),
// never thrown: stats still never block the 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, main-merge-approved,
// main-merge-declined, gates_mode_flag_override, 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 '{...}'
//   node lib/stats/event-emit.mjs --event main-merge-gate --payload - <<'JSON'   (payload on stdin)
//   → prints {"written":true,"path":...} exit 0 | {"written":false,"reason":...} exit 1
//     (usage error, payload-not-json and a failed write alike). The command prose
//     prints the reason and continues.
//
// Import direction: event-emit imports stats-append; stats-append must never
// import event-emit (that would be a cycle).

import { appendFileSync, existsSync, mkdirSync, readFileSync, realpathSync } from 'node:fs';
import { dirname, join } from 'node:path';
import { fileURLToPath } from 'node:url';
import { resolveStatsDir } from './stats-append.mjs';

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

const STATS_FILENAME = 'trekexecute-stats.jsonl';

/**
 * Resolve the stats file path: CLAUDE_PLUGIN_DATA when set, else the directory
 * stats-append.mjs and scripts/yardstick.mjs use. Never null.
 */
export function resolveStatsPath(env = process.env) {
  return join(resolveStatsDir(env), 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 — a failed write is returned as {written:false,
 * reason} 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);
  try {
    const dir = dirname(path);
    if (!existsSync(dir)) {
      // A dir that cannot be created is reported, never thrown.
      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;
}

// Run as a CLI? Compared as real paths: `file://${argv[1]}` misses a path with a
// space (URL-encoded) and a symlink (import.meta.url is the realpath).
function isMain() {
  try {
    return realpathSync(process.argv[1]) === realpathSync(fileURLToPath(import.meta.url));
  } catch {
    return false;
  }
}

if (isMain()) {
  const args = parseArgs(process.argv.slice(2));
  let result;
  if (!args.event) {
    result = { written: false, path: null, reason: 'usage: --event NAME [--payload JSON]' };
  } else {
    let payload = {};
    let bad = false;
    if (args.payload) {
      // `-` = read it from stdin: a quoted heredoc passes it with nothing expanded.
      try { payload = JSON.parse(args.payload === '-' ? readFileSync(0, 'utf8') : args.payload); } catch { bad = true; }
    }
    result = bad ? { written: false, path: null, reason: 'payload-not-json' } : emit(args.event, payload);
  }
  process.stdout.write(JSON.stringify(result) + '\n');
  process.exit(result.written ? 0 : 1);
}