/**
 * run command — full backup run.
 */
import { mkdir, writeFile } from 'fs/promises';
import { join } from 'path';
import { run as spawn, capture } from '../spawn.js';
import { parseItemize } from '../itemize.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: dry } = config;
  const backend = getBackend(backendName);

  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 recover from partially-committed previous run

  // ── Phase 1: Ensure PEND exists ─────────────────────────────
  await setPhase(deltas, state, PHASES.CLEARING_PEND, dry);
  if (!dry) {
    await mkdir(pend, { recursive: true });
  } else {
    console.log(`[dry-run] mkdir -p ${pend}`);
  }

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

  // ── Phase 3: rsync SOURCE → PEND, capture change list ───────
  await setPhase(deltas, state, PHASES.RSYNC_REMOTE, dry);
  console.log('\n── rsync SOURCE → PEND ──');

  let changes = [];
  if (!dry) {
    const rsyncArgs = [
      '-aP',
      '--itemize-changes',
      '--delete',
      trailingSlash(source),
      trailingSlash(pend),
    ];
    const output = await capture('rsync', rsyncArgs);
    changes = parseItemize(output);
    console.log(`  ${changes.length} file(s) changed`);
    for (const c of changes) console.log(`  [${c.status}] ${c.path}`);
  } else {
    console.log(`$ rsync -aP --itemize-changes --delete ${trailingSlash(source)} ${trailingSlash(pend)}`);
    console.log('[dry-run] (change list will be determined at runtime)');
  }

  // ── Phase 4: Generate per-file deltas into DELTAS/tmp/N/ ────
  await setPhase(deltas, state, PHASES.GENERATING, dry);
  console.log('\n── Generate delta ──');

  const tmpDir  = join(deltas, 'tmp', String(seq));
  const filesDir = join(tmpDir, 'files');

  if (!dry) {
    await mkdir(filesDir, { recursive: true });
  } else {
    console.log(`[dry-run] mkdir -p ${filesDir}`);
  }

  const manifestChanges = [];

  for (const change of changes) {
    const deltaFilename = change.path.replaceAll('/', '__') + backend.ext;
    const outFile = join(filesDir, deltaFilename);

    if (change.status === 'deleted') {
      manifestChanges.push({ path: change.path, status: 'deleted' });
      continue;
    }

    const prevFile = join(prev, change.path);
    const newFile  = join(pend, change.path);

    console.log(`  [${change.status}] ${change.path}`);

    if (!dry) {
      await backend.createDelta(
        change.status === 'modified' ? prevFile : null,
        newFile,
        outFile,
      );
    } else {
      console.log(`[dry-run] ${change.status === 'modified'
        ? `zstd --patch-from ${prevFile} ${newFile} -o ${outFile}`
        : `zstd ${newFile} -o ${outFile}`}`);
    }

    manifestChanges.push({
      path: change.path,
      status: change.status,
      delta: join('files', deltaFilename),
    });
  }

  // ── Phase 5: Write manifest + atomic commit ──────────────────
  await setPhase(deltas, state, PHASES.COMMITTING, dry);
  console.log('\n── Commit delta ──');

  const manifest = {
    seq,
    timestamp: new Date().toISOString(),
    prev_seq: state.last_complete,
    backend: backendName,
    changes: manifestChanges,
  };

  const seqDir = join(deltas, String(seq));

  if (!dry) {
    await writeFile(join(tmpDir, 'manifest.json'), JSON.stringify(manifest, null, 2) + '\n');
    // Atomic rename: tmp/N → N
    await rename(tmpDir, seqDir);
    console.log(`  Committed to ${seqDir}`);
  } else {
    console.log(`[dry-run] write manifest to ${tmpDir}/manifest.json`);
    console.log(`[dry-run] rename ${tmpDir} → ${seqDir}`);
  }

  // ── Phase 6: Promote PEND → PREV ────────────────────────────
  await setPhase(deltas, state, PHASES.PROMOTING, dry);
  console.log('\n── Promote PEND → PREV ──');
  await spawn('rsync', ['-aP', '--delete', trailingSlash(pend), trailingSlash(prev)], { dryRun: dry });

  // ── 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. ${manifestChanges.length} file(s) in delta.`);
}

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

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