/**
 * zstd delta backend.
 *
 * Modified files: zstd --patch-from=prev new -o out.zst
 * New files:      zstd new -o out.zst  (no base, just compress)
 * Deleted files:  no delta file, manifest entry only
 */
import { run } from '../spawn.js';

export const name = 'zstd';
export const ext = '.zst';

/**
 * Create a delta from prevFile to newFile, output to outFile.
 * If prevFile is null, newFile is new — compress without a base.
 */
export async function createDelta(prevFile, newFile, outFile, { dryRun } = {}) {
  if (prevFile) {
    await run('zstd', ['--patch-from', prevFile, newFile, '-o', outFile, '-f'], { dryRun });
  } else {
    await run('zstd', [newFile, '-o', outFile, '-f'], { dryRun });
  }
}

/**
 * Apply a delta on top of prevFile to produce outFile.
 * If prevFile is null, the delta is a plain compressed file.
 */
export async function applyDelta(prevFile, deltaFile, outFile, { dryRun } = {}) {
  if (prevFile) {
    await run('zstd', ['-d', '--patch-from', prevFile, deltaFile, '-o', outFile, '-f'], { dryRun });
  } else {
    await run('zstd', ['-d', deltaFile, '-o', outFile, '-f'], { dryRun });
  }
}