import { createHash } from 'crypto';
import { readFile } from 'fs-promise';

/**
 * Computes hashes for the contents of each file given.
 *
 * @param {Array} of {String} full paths
 * @return {Map}
 */

export default async function hashes (files) {
  const map = new Map();
  await Promise.all(files.map(async (name) => {
    const data = await readFile(name);
    const h = hash(data);
    const entry = map.get(h);
    if (entry) {
      entry.names.push(name);
    } else {
      map.set(hash(data), { names: [name], data });
    }
  }));
  return map;
}

/**
 * Computes a hash for the given buf.
 *
 * @param {Buffer} file data
 * @return {String} hex digest
 */

function hash (buf) {
  return createHash('sha1')
    .update(buf)
    .digest('hex');
}