const reverse = require('buffer-reverse')
const CryptoJS = require('crypto-js')
const treeify = require('treeify')

/**
 * Class reprensenting a Merkle Tree
 * @namespace MerkleTree
 */
class MerkleTree {
  /**
   * @desc Constructs a Merkle Tree.
   * All nodes and leaves are stored as Buffers.
   * Lonely leaf nodes are promoted to the next level up without being hashed again.
   * @param {Buffer[]} leaves - Array of hashed leaves. Each leaf must be a Buffer.
   * @param {Function} hashAlgorithm - Algorithm used for hashing leaves and nodes
   * @param {Object} options - Additional options
   * @param {Boolean} options.isBitcoinTree - If set to `true`, constructs the Merkle
   * Tree using the [Bitcoin Merkle Tree implementation](http://www.righto.com/2014/02/bitcoin-mining-hard-way-algorithms.html). Enable it when you need
   * to replicate Bitcoin constructed Merkle Trees. In Bitcoin Merkle Trees, single nodes are combined with themselves, and each output hash is hashed again.
   * @example
   * const MerkleTree = require('merkletreejs')
   * const crypto = require('crypto')
   *
   * function sha256(data) {
   *   // returns Buffer
   *   return crypto.createHash('sha256').update(data).digest()
   * }
   *
   * const leaves = ['a', 'b', 'c'].map(x => sha3(x))
   *
   * const tree = new MerkleTree(leaves, sha256)
   */
  constructor(leaves, hashAlgorithm, options={}) {
    this.hashAlgo = bufferifyFn(hashAlgorithm)
    this.leaves = leaves.map(bufferify)
    this.layers = [this.leaves]
    this.isBitcoinTree = !!options.isBitcoinTree

    this.createHashes(this.leaves)
  }

  // TODO: documentation
  createHashes(nodes) {
    while (nodes.length > 1) {

      const layerIndex = this.layers.length

      this.layers.push([])

      for (let i = 0; i < nodes.length - 1; i += 2) {
        const left = nodes[i]
        const right = nodes[i+1]
        let data = null

        if (this.isBitcoinTree) {
          data = Buffer.concat([reverse(left), reverse(right)])
        } else {
          data = Buffer.concat([left, right])
        }

        let hash = this.hashAlgo(data)

        // double hash if bitcoin tree
        if (this.isBitcoinTree) {
          hash = reverse(this.hashAlgo(hash))
        }

        this.layers[layerIndex].push(hash)
      }

      // is odd number of nodes
      if (nodes.length % 2 === 1) {
        let data = nodes[nodes.length-1]
        let hash = data

        // is bitcoin tree
        if (this.isBitcoinTree) {
          // Bitcoin method of duplicating the odd ending nodes
          data = Buffer.concat([reverse(data), reverse(data)])
          hash = this.hashAlgo(data)
          hash = reverse(this.hashAlgo(hash))
        }

        this.layers[layerIndex].push(hash)
      }

      nodes = this.layers[layerIndex]
    }

  }

  /**
   * getLeaves
   * @desc Returns array of leaves of Merkle Tree.
   * @return {Buffer[]}
   * @example
   * const leaves = tree.getLeaves()
   */
  getLeaves() {
    return this.leaves
  }

  /**
   * getLayers
   * @desc Returns array of all layers of Merkle Tree, including leaves and root.
   * @return {Buffer[]}
   * @example
   * const layers = tree.getLayers()
   */
  getLayers() {
    return this.layers
  }

  /**
   * getRoot
   * @desc Returns the Merkle root hash as a Buffer.
   * @return {Buffer}
   * @example
   * const root = tree.getRoot()
   */
  getRoot() {
    return this.layers[this.layers.length-1][0] || Buffer.from([])
  }

  /**
   * getProof
   * @desc Returns the proof for a target leaf.
   * @param {Buffer} leaf - Target leaf
   * @param {Number} [index] - Target leaf index in leaves array.
   * Use if there are leaves containing duplicate data in order to distinguish it.
   * @return {Object[]} - Array of objects containing a position property of type string
   * with values of 'left' or 'right' and a data property of type Buffer.
   * @example
   * const proof = tree.getProof(leaves[2])
   *
   * @example
   * const leaves = ['a', 'b', 'a'].map(x => sha3(x))
   * const tree = new MerkleTree(leaves, sha3)
   * const proof = tree.getProof(leaves[2], 2)
   */
  getProof(leaf, index) {
    leaf = bufferify(leaf)
    const proof = []

    if (typeof index !== 'number') {
      index = -1

      for (let i = 0; i < this.leaves.length; i++) {
        if (Buffer.compare(leaf, this.leaves[i]) === 0) {
          index = i
        }
      }
    }

    if (index <= -1) {
      return []
    }

    if (this.isBitcoinTree && index === (this.leaves.length - 1)) {

      // Proof Generation for Bitcoin Trees

      for (let i = 0; i < this.layers.length - 1; i++) {
        const layer = this.layers[i]
        const isRightNode = index % 2
        const pairIndex = (isRightNode ? index - 1: index)

        if (pairIndex < layer.length) {
          proof.push({
            position: isRightNode ? 'left': 'right',
            data: layer[pairIndex]
          })
        }

        // set index to parent index
        index = (index / 2)|0

        }

        return proof

      } else {

        // Proof Generation for Non-Bitcoin Trees

        for (let i = 0; i < this.layers.length; i++) {
          const layer = this.layers[i]
          const isRightNode = index % 2
          const pairIndex = (isRightNode ? index - 1 : index + 1)

          if (pairIndex < layer.length) {
            proof.push({
              position: isRightNode ? 'left': 'right',
              data: layer[pairIndex]
            })
          }

          // set index to parent index
          index = (index / 2)|0

          }

          return proof

        }
      }

  /**
   * verify
   * @desc Returns true if the proof path (array of hashes) can connect the target node
   * to the Merkle root.
   * @param {Object[]} proof - Array of proof objects that should connect
   * target node to Merkle root.
   * @param {Buffer} targetNode - Target node Buffer
   * @param {Buffer} root - Merkle root Buffer
   * @return {Boolean}
   * @example
   * const root = tree.getRoot()
   * const proof = tree.getProof(leaves[2])
   * const verified = tree.verify(proof, leaves[2], root)
   *
   */
  verify(proof, targetNode, root) {
    let hash = bufferify(targetNode)
    root = bufferify(root)

    if (!Array.isArray(proof) ||
        !proof.length ||
        !targetNode ||
        !root) {
      return false
    }

    for (let i = 0; i < proof.length; i++) {
      const node = proof[i]
      const isLeftNode = (node.position === 'left')
      const buffers = []

      if (this.isBitcoinTree) {
        buffers.push(reverse(hash))

        buffers[isLeftNode ? 'unshift' : 'push'](reverse(node.data))

        hash = this.hashAlgo(Buffer.concat(buffers))
        hash = reverse(this.hashAlgo(hash))

      } else {
        buffers.push(hash)

        buffers[isLeftNode ? 'unshift' : 'push'](node.data)

        hash = this.hashAlgo(Buffer.concat(buffers))
      }
    }

    return Buffer.compare(hash, root) === 0
  }

  // TODO: documentation
  getLayersAsObject() {
    const layers = this.getLayers().map(x => x.map(x => x.toString('hex')))
    const objs = []
    for (let i = 0; i < layers.length; i++) {
      const arr = []
      for (let j = 0; j < layers[i].length; j++) {
        const obj = { [layers[i][j]]: null }
        if (objs.length) {
          obj[layers[i][j]] = {}
          const a = objs.shift()
          const akey = Object.keys(a)[0]
          obj[layers[i][j]][akey] = a[akey]
          if (objs.length) {
            const b = objs.shift()
            const bkey = Object.keys(b)[0]
            obj[layers[i][j]][bkey] = b[bkey]
          }
        }

        arr.push(obj)
      }

      objs.push(...arr)
    }

    return objs[0]
  }

  // TODO: documentation
  print() {
    MerkleTree.print(this)
  }

  // TODO: documentation
  toTreeString() {
    const obj = this.getLayersAsObject()
    return treeify.asTree(obj, true)
  }

  // TODO: documentation
  toString() {
    return this.toTreeString()
  }

  // TODO: documentation
  static bufferify(x) {
    return bufferify(x)
  }

  // TODO: documentation
  static print(tree) {
    console.log(tree.toString())
  }
}

function bufferify(x) {
  if (!Buffer.isBuffer(x)) {
    // crypto-js support
    if (typeof x === 'object' && x.words) {
      return Buffer.from(x.toString(CryptoJS.enc.Hex), 'hex')
    } else if (isHexStr(x)) {
      return Buffer.from(x, 'hex')
    } else if (typeof x === 'string') {
      return Buffer.from(x)
    }
  }

  return x
}

function bufferifyFn (f) {
  return function (x) {
    const v = f(x)
    if (Buffer.isBuffer(v)) {
      return v
    }

    // crypto-js support
    return Buffer.from(f(CryptoJS.enc.Hex.parse(x.toString('hex'))).toString(CryptoJS.enc.Hex), 'hex')
  }
}

function isHexStr(v) {
  return (typeof v === 'string' && /^(0x)?[0-9A-Fa-f]*$/.test(v))
}

module.exports = MerkleTree