var Buffer = require('buffer').Buffer;
var intSize = 4;
var zeroBuffer = Buffer.alloc(intSize);
zeroBuffer.fill(0);
var chrsz = 8;

function toArray(buf, bigEndian) {
  if (buf.length % intSize !== 0) {
    var len = buf.length + (intSize - (buf.length % intSize));
    buf = Buffer.concat([buf, zeroBuffer], len);
  }

  var arr = [];
  var fn = bigEndian ? buf.readInt32BE : buf.readInt32LE;
  for (var i = 0; i < buf.length; i += intSize) {
    arr.push(fn.call(buf, i));
  }
  return arr;
}

function toBuffer(arr, size, bigEndian) {
  var buf = Buffer.alloc(size);
  var fn = bigEndian ? buf.writeInt32BE : buf.writeInt32LE;
  for (var i = 0; i < arr.length; i++) {
    fn.call(buf, arr[i], i * 4, true);
  }
  return buf;
}

function hash(buf, fn, hashSize, bigEndian) {
  if (!Buffer.isBuffer(buf)) buf = Buffer.from(buf);
  var arr = fn(toArray(buf, bigEndian), buf.length * chrsz);
  return toBuffer(arr, hashSize, bigEndian);
}

module.exports = { hash: hash };