// ethash.js
// Tim Hughes <tim@twistedfury.com>
// Revision 19

/*jslint node: true, shadow:true */
"use strict";

var Keccak = require('./keccak');
var util = require('./util');
var ethUtil = require('ethereumjs-util');

// 32-bit unsigned modulo
function mod32(x, n) {
  return (x >>> 0) % (n >>> 0);
}

function fnv(x, y) {
  // js integer multiply by 0x01000193 will lose precision
  return ((x * 0x01000000 | 0) + (x * 0x193 | 0)) ^ y;
}

function computeCache(params, seedWords) {
  var cache = new Uint32Array(params.cacheSize >> 2);
  var cacheNodeCount = params.cacheSize >> 6;

  // Initialize cache
  var keccak = new Keccak();
  keccak.digestWords(cache, 0, 16, seedWords, 0, seedWords.length);
  for (var n = 1; n < cacheNodeCount; ++n) {
    keccak.digestWords(cache, n << 4, 16, cache, (n - 1) << 4, 16);
  }

  var tmp = new Uint32Array(16);

  // Do randmemohash passes
  for (var r = 0; r < params.cacheRounds; ++r) {
    for (var n = 0; n < cacheNodeCount; ++n) {
      var p0 = mod32(n + cacheNodeCount - 1, cacheNodeCount) << 4;
      var p1 = mod32(cache[n << 4 | 0], cacheNodeCount) << 4;

      for (var w = 0; w < 16; w = (w + 1) | 0) {
        tmp[w] = cache[p0 | w] ^ cache[p1 | w];
      }

      keccak.digestWords(cache, n << 4, 16, tmp, 0, tmp.length);
    }
  }
  return cache;
}

function computeDagNode(o_node, params, cache, keccak, nodeIndex) {
  var cacheNodeCount = params.cacheSize >> 6;
  var dagParents = params.dagParents;

  var c = (nodeIndex % cacheNodeCount) << 4;
  var mix = o_node;
  for (var w = 0; w < 16; ++w) {
    mix[w] = cache[c | w];
  }
  mix[0] ^= nodeIndex;
  keccak.digestWords(mix, 0, 16, mix, 0, 16);

  for (var p = 0; p < dagParents; ++p) {
    // compute cache node (word) index
    c = mod32(fnv(nodeIndex ^ p, mix[p & 15]), cacheNodeCount) << 4;

    for (var w = 0; w < 16; ++w) {
      mix[w] = fnv(mix[w], cache[c | w]);
    }
  }

  keccak.digestWords(mix, 0, 16, mix, 0, 16);
}

function computeHashInner(mix, params, cache, keccak, tempNode) {
  var mixParents = params.mixParents | 0;
  var mixWordCount = params.mixSize >> 2;
  var mixNodeCount = mixWordCount >> 4;
  var dagPageCount = (params.dagSize / params.mixSize) >> 0;

  // grab initial first word
  var s0 = mix[0];

  // initialise mix from initial 64 bytes
  for (var w = 16; w < mixWordCount; ++w) {
    mix[w] = mix[w & 15];
  }

  for (var a = 0; a < mixParents; ++a) {
    var p = mod32(fnv(s0 ^ a, mix[a & (mixWordCount - 1)]), dagPageCount);
    var d = (p * mixNodeCount) | 0;

    for (var n = 0, w = 0; n < mixNodeCount; ++n, w += 16) {
      computeDagNode(tempNode, params, cache, keccak, (d + n) | 0);

      for (var v = 0; v < 16; ++v) {
        mix[w | v] = fnv(mix[w | v], tempNode[v]);
      }
    }
  }
}

function convertSeed(seed) {
  // todo, reconcile with spec, byte ordering?
  // todo, big-endian conversion
  var newSeed = util.toWords(seed);
  if (newSeed === null)
    throw Error("Invalid seed '" + seed + "'");
  return newSeed;
}

var params = exports.params = {
  REVISION: 23,
  DATASET_BYTES_INIT: 1073741824,
  DATASET_BYTES_GROWTH: 8388608,
  CACHE_BYTES_INIT: 1073741824,
  CACHE_BYTES_GROWTH: 131072,
  EPOCH_LENGTH: 30000,
  MIX_BYTES: 128,
  HASH_BYTES: 64,
  DATASET_PARENTS: 256,
  CACHE_ROUNDS: 3,
  ACCESSES: 64
};

var cache_sizes = require('./cache_sizes');
var dag_sizes = require('./dag_sizes');

exports.calcSeed = function(blockNum) {
  var epoch;

  var seed = new Uint8Array(32);

  if (blockNum > cache_sizes.length * params.EPOCH_LENGTH) {
    return new Error('Time to upgrade to POS!!!');
  } else {
    epoch = Math.floor(blockNum / params.EPOCH_LENGTH);

    for (var i = 0; i < epoch; i++) {
      seed = ethUtil.sha3(new Buffer(seed));
    }
    return seed;
  }
};

exports.defaultParams = function() {
  return {
    cacheSize: 1048384,
    cacheRounds: 3,
    dagSize: 1073739904,
    dagParents: 256,
    mixSize: 128,
    mixParents: 64
  };
};

exports.Ethash = function(params, seed) {
  // precompute cache and related values
  // seed = convertSeed(seed);
  var cache = computeCache(params, seed);

  // preallocate buffers/etc
  var initBuf = new ArrayBuffer(96);
  var initBytes = new Uint8Array(initBuf);
  var initWords = new Uint32Array(initBuf);
  var mixWords = new Uint32Array(params.mixSize / 4);
  var tempNode = new Uint32Array(16);
  var keccak = new Keccak();

  var retWords = new Uint32Array(8);
  var retBytes = new Uint8Array(retWords.buffer); // supposedly read-only

  this.hash = function(header, nonce) {
    // compute initial hash
    initBytes.set(header, 0);
    initBytes.set(nonce, 32);
    keccak.digestWords(initWords, 0, 16, initWords, 0, 8 + nonce.length / 4);

    // compute mix
    for (var i = 0; i !== 16; ++i) {
      mixWords[i] = initWords[i];
    }
    computeHashInner(mixWords, params, cache, keccak, tempNode);

    // compress mix and append to initWords
    for (var i = 0; i !== mixWords.length; i += 4) {
      initWords[16 + i / 4] = fnv(fnv(fnv(mixWords[i], mixWords[i + 1]), mixWords[i + 2]), mixWords[i + 3]);
    }

    // final Keccak hashes
    keccak.digestWords(retWords, 0, 8, initWords, 0, 24); // Keccak-256(s + cmix)
    return retBytes;
  };

  this.cacheDigest = function() {
    return keccak.digest(32, new Uint8Array(cache.buffer));
  };
};