/**
 * State management — tracks sequence numbers and run phases in DELTAS/state.json.
 * The state file is a recoverable cache; source of truth is the DELTAS directory.
 */
import { readFile, writeFile } from 'fs/promises';
import { join } from 'path';

const STATE_FILE = 'state.json';

export async function readState(deltasDir) {
  const path = join(deltasDir, STATE_FILE);
  try {
    const raw = await readFile(path, 'utf8');
    return JSON.parse(raw);
  } catch {
    // Missing or unreadable — reconstruct from directory scan
    return reconstructState(deltasDir);
  }
}

export async function writeState(deltasDir, state) {
  const path = join(deltasDir, STATE_FILE);
  await writeFile(path, JSON.stringify(state, null, 2) + '\n', 'utf8');
}

async function reconstructState(deltasDir) {
  // TODO: scan DELTAS for highest committed sequence number
  // For now, start fresh
  return { next_seq: 1, last_complete: 0, phase: 'idle' };
}

export const PHASES = {
  IDLE:           'idle',
  CLEARING_PEND:  'clearing_pend',
  RSYNC_LOCAL:    'rsync_local',
  RSYNC_REMOTE:   'rsync_remote',
  GENERATING:     'generating_delta',
  COMMITTING:     'committing',
  PROMOTING:      'promoting_prev',
};