/**
 * run command — full backup run.
 */
import { rm, mkdir } from 'fs/promises';
import { join } from 'path';
import { run as spawn } from '../spawn.js';
import { getBackend } from '../backends/index.js';
import { readState, writeState, PHASES } from '../state.js';

export async function runCommand(config) {
  const { source, prev, pend, deltas, backend: backendName, dryRun } = config;
  const backend = getBackend(backendName);
  const dry = dryRun;

  if (dry) console.log('[dry-run] No changes will be made.\n');

  // ── Load state ──────────────────────────────────────────────
  const state = await readState(deltas);
  const seq = state.next_seq;

  console.log(`Starting run — seq ${seq} (last complete: ${state.last_complete})`);

  // TODO: detect and handle partially-committed previous run

  // ── Phase 1: Clear PEND ─────────────────────────────────────
  await setPhase(deltas, state, PHASES.CLEARING_PEND, dry);
  console.log('\n── Clear PEND ──');
  if (!dry) {
    await rm(pend, { recursive: true, force: true });
    await mkdir(pend, { recursive: true });
  } else {
    console.log(`[dry-run] rm -rf ${pend} && mkdir -p ${pend}`);
  }

  // ── Phase 2: rsync PREV → PEND (local seed) ─────────────────
  await setPhase(deltas, state, PHASES.RSYNC_LOCAL, dry);
  console.log('\n── rsync PREV → PEND (local seed) ──');
  await spawn('rsync', ['-aP', trailingSlash(prev), pend], { dryRun: dry });

  // ── Phase 3: rsync SOURCE → PEND (remote changes) ───────────
  await setPhase(deltas, state, PHASES.RSYNC_REMOTE, dry);
  console.log('\n── rsync SOURCE → PEND ──');
  await spawn('rsync', ['-aP', trailingSlash(source), pend], { dryRun: dry });

  // ── Phase 4: Generate delta ──────────────────────────────────
  await setPhase(deltas, state, PHASES.GENERATING, dry);
  console.log('\n── Generate delta ──');
  // TODO: walk PREV and PEND, diff per file, build manifest

  // ── Phase 5: Commit delta ────────────────────────────────────
  await setPhase(deltas, state, PHASES.COMMITTING, dry);
  console.log('\n── Commit delta ──');
  // TODO: atomic rename DELTAS/tmp/N → DELTAS/N

  // ── Phase 6: Promote PEND → PREV ────────────────────────────
  await setPhase(deltas, state, PHASES.PROMOTING, dry);
  console.log('\n── Promote PEND → PREV ──');
  // TODO: mv PEND PREV (swap)

  // ── Done ─────────────────────────────────────────────────────
  state.last_complete = seq;
  state.next_seq = seq + 1;
  state.phase = PHASES.IDLE;
  if (!dry) await writeState(deltas, state);

  console.log(`\nRun complete — seq ${seq} committed.`);
}

async function setPhase(deltas, state, phase, dry) {
  state.phase = phase;
  if (!dry) await writeState(deltas, state);
}

function trailingSlash(p) {
  return p.endsWith('/') ? p : p + '/';
}