module.exports = exports = Storage

var BitField = require('bitfield')
var BlockStream = require('block-stream2')
var debug = require('debug')('webtorrent:storage')
var dezalgo = require('dezalgo')
var eos = require('end-of-stream')
var EventEmitter = require('events').EventEmitter
var FileStream = require('./file-stream')
var inherits = require('inherits')
var mime = require('./mime.json')
var MultiStream = require('multistream')
var once = require('once')
var path = require('path')
var sha1 = require('simple-sha1')

var BLOCK_LENGTH = 16 * 1024

var BLOCK_BLANK = exports.BLOCK_BLANK = 0
var BLOCK_RESERVED = exports.BLOCK_RESERVED = 1
var BLOCK_WRITTEN = exports.BLOCK_WRITTEN = 2

function noop () {}

inherits(Piece, EventEmitter)

/**
 * A torrent piece
 *
 * @param {number} index  piece index
 * @param {string} hash   sha1 hash (hex) for this piece
 * @param {Buffer|number} buffer backing buffer, or piece length if backing buffer is lazy
 * @param {boolean=} noVerify skip piece verification (used when seeding a new file)
 */
function Piece (index, hash, buffer, noVerify) {
  var self = this
  EventEmitter.call(self)
  if (!debug.enabled) self.setMaxListeners(0)

  self.index = index
  self.hash = hash
  self.noVerify = !!noVerify

  if (typeof buffer === 'number') {
    // alloc buffer lazily
    self.buffer = null
    self.length = buffer
  } else {
    // use buffer provided
    self.buffer = buffer
    self.length = buffer.length
  }

  self._reset()
}

Piece.prototype.readBlock = function (offset, length, cb) {
  var self = this
  cb = dezalgo(cb)
  if (!self.buffer || !self._verifyOffset(offset)) {
    return cb(new Error('invalid block offset ' + offset))
  }
  cb(null, self.buffer.slice(offset, offset + length))
}

Piece.prototype.writeBlock = function (offset, buffer, cb) {
  var self = this
  cb = dezalgo(cb)
  if (!self._verifyOffset(offset) || !self._verifyBlock(offset, buffer)) {
    return cb(new Error('invalid block ' + offset + ':' + buffer.length))
  }
  self._lazyAllocBuffer()

  var i = offset / BLOCK_LENGTH
  if (self.blocks[i] === BLOCK_WRITTEN) {
    return cb(null)
  }

  buffer.copy(self.buffer, offset)
  self.blocks[i] = BLOCK_WRITTEN
  self.blocksWritten += 1

  if (self.blocksWritten === self.blocks.length) {
    self.verify()
  }

  cb(null)
}

Piece.prototype.reserveBlock = function (endGame) {
  var self = this
  var len = self.blocks.length
  for (var i = 0; i < len; i++) {
    if ((self.blocks[i] && !endGame) || self.blocks[i] === BLOCK_WRITTEN) {
      continue
    }
    self.blocks[i] = BLOCK_RESERVED
    return {
      offset: i * BLOCK_LENGTH,
      length: (i === len - 1)
        ? self.length - (i * BLOCK_LENGTH)
        : BLOCK_LENGTH
    }
  }
  return null
}

Piece.prototype.cancelBlock = function (offset) {
  var self = this
  if (!self._verifyOffset(offset)) {
    return false
  }

  var i = offset / BLOCK_LENGTH
  if (self.blocks[i] === BLOCK_RESERVED) {
    self.blocks[i] = BLOCK_BLANK
  }

  return true
}

Piece.prototype._reset = function () {
  var self = this
  self.verified = false
  self.blocks = new Buffer(Math.ceil(self.length / BLOCK_LENGTH))
  self.blocks.fill(0)
  self.blocksWritten = 0
}

Piece.prototype.verify = function (buffer) {
  var self = this
  buffer = buffer || self.buffer
  if (self.verified || !buffer) {
    return
  }

  if (self.noVerify) {
    self.verified = true
    onResult()
    return
  }

  sha1(buffer, function (expectedHash) {
    self.verified = (expectedHash === self.hash)
    onResult()
  })

  function onResult () {
    if (self.verified) {
      self.emit('done')
    } else {
      self.emit('warning', new Error('piece ' + self.index + ' failed verification'))
      self._reset()
    }
  }
}

Piece.prototype._verifyOffset = function (offset) {
  var self = this
  if (offset % BLOCK_LENGTH === 0) {
    return true
  } else {
    self.emit(
      'warning',
      new Error('invalid block offset ' + offset + ', not multiple of ' + BLOCK_LENGTH)
    )
    return false
  }
}

Piece.prototype._verifyBlock = function (offset, buffer) {
  var self = this
  if (buffer.length === BLOCK_LENGTH) {
    // normal block length
    return true
  } else if (buffer.length === self.length - offset &&
    self.length - offset < BLOCK_LENGTH) {
    // last block in piece is allowed to be less than block length
    return true
  } else {
    self.emit('warning', new Error('invalid block size ' + buffer.length))
    return false
  }
}

Piece.prototype._lazyAllocBuffer = function () {
  var self = this
  if (!self.buffer) {
    self.buffer = new Buffer(self.length)
  }
}

inherits(File, EventEmitter)

/**
 * A torrent file
 *
 * @param {Storage} storage       Storage container object
 * @param {Object}  file          the file object from the parsed torrent
 * @param {Array.<Piece>} pieces  backing pieces for this file
 * @param {number}  pieceLength   the length in bytes of a non-terminal piece
 */
function File (storage, file, pieces, pieceLength) {
  var self = this
  EventEmitter.call(self)
  if (!debug.enabled) self.setMaxListeners(0)

  self.storage = storage
  self.name = file.name
  self.path = file.path
  self.length = file.length
  self.offset = file.offset
  self.pieces = pieces
  self.pieceLength = pieceLength

  self.done = false

  self.pieces.forEach(function (piece) {
    piece.on('done', function () {
      self._checkDone()
    })
  })

  // if the file is zero-length, it will be done upon initialization
  self._checkDone()
}

/**
 * Selects the file to be downloaded, but at a lower priority than files with streams.
 * Useful if you know you need the file at a later stage.
 */
File.prototype.select = function () {
  var self = this
  if (self.pieces.length > 0) {
    var start = self.pieces[0].index
    var end = self.pieces[self.pieces.length - 1].index
    self.storage.emit('select', start, end, false)
  }
}

/**
 * Deselects the file, which means it won't be downloaded unless someone creates a stream
 * for it.
 */
File.prototype.deselect = function () {
  var self = this
  if (self.pieces.length > 0) {
    var start = self.pieces[0].index
    var end = self.pieces[self.pieces.length - 1].index
    self.storage.emit('deselect', start, end, false)
  }
}

/**
 * Create a readable stream to the file. Pieces needed by the stream will be prioritized
 * highly and fetched from the swarm first.
 *
 * @param {Object} opts
 * @param {number} opts.start stream slice of file, starting from this byte (inclusive)
 * @param {number} opts.end   stream slice of file, ending with this byte (inclusive)
 * @return {stream.Readable}
 */
File.prototype.createReadStream = function (opts) {
  var self = this
  if (!opts) opts = {}
  if (opts.pieceLength == null) opts.pieceLength = self.pieceLength
  var stream = new FileStream(self, opts)
  self.storage.emit('select', stream.startPiece, stream.endPiece, true, stream.notify.bind(stream))
  eos(stream, function () {
    self.storage.emit('deselect', stream.startPiece, stream.endPiece, true)
  })

  return stream
}

/**
 * Note: This function is async to support different types of (async) storage backends in
 * the future.
 * @param {function} cb
 */
File.prototype.getBlobURL = function (cb) {
  var self = this
  if (typeof window === 'undefined') throw new Error('browser-only method')

  self.getBuffer(function (err, buffer) {
    if (err) return cb(err)
    var type = mime[path.extname(self.name).toLowerCase()]
    var blob = type
      ? new window.Blob([ buffer ], { type: type })
      : new window.Blob([ buffer ])
    var url = window.URL.createObjectURL(blob)
    cb(null, url)
  })
}

/**
 * @param {function} cb
 */
File.prototype.getBuffer = function (cb) {
  var self = this
  cb = dezalgo(once(cb))

  var buffer
  if (self.storage.buffer) {
    // Use the in-memory buffer (when possible) for better memory utilization
    var onDone = function () {
      buffer = self.storage.buffer.slice(self.offset, self.offset + self.length)
      cb(null, buffer)
    }
    if (self.done) onDone()
    else self.once('done', onDone)
  } else {
    buffer = new Buffer(self.length)
    var start = 0
    self.createReadStream()
      .on('data', function (chunk) {
        chunk.copy(buffer, start)
        start += chunk.length
      })
      .on('end', function () {
        cb(null, buffer)
      })
      .on('error', cb)
  }
}

File.prototype._checkDone = function () {
  var self = this
  self.done = self.pieces.every(function (piece) {
    return piece.verified
  })

  if (self.done) {
    process.nextTick(function () {
      self.emit('done')
    })
  }
}

inherits(Storage, EventEmitter)

/**
 * Storage for a torrent download. Handles the complexities of reading and writing
 * to pieces and files.
 *
 * @param {Object} parsedTorrent
 * @param {Object} opts
 */
function Storage (parsedTorrent, opts) {
  var self = this
  EventEmitter.call(self)
  if (!debug.enabled) self.setMaxListeners(0)
  if (!opts) opts = {}

  self.bitfield = new BitField(parsedTorrent.pieces.length)

  self.done = false
  self.closed = false
  self.readonly = true

  if (!opts.nobuffer) {
    self.buffer = new Buffer(parsedTorrent.length)
  }

  var pieceLength = self.pieceLength = parsedTorrent.pieceLength
  var lastPieceLength = parsedTorrent.lastPieceLength
  var numPieces = parsedTorrent.pieces.length

  self.pieces = parsedTorrent.pieces.map(function (hash, index) {
    var start = index * pieceLength
    var end = start + (index === numPieces - 1 ? lastPieceLength : pieceLength)

    // if we're backed by a buffer, the piece's buffer will reference the same memory.
    // otherwise, the piece's buffer will be lazily created on demand
    var buffer = (self.buffer ? self.buffer.slice(start, end) : end - start)

    var piece = new Piece(index, hash, buffer, !!opts.noVerify)
    piece.on('done', self._onPieceDone.bind(self, piece))
    return piece
  })

  self.files = parsedTorrent.files.map(function (fileObj) {
    var start = fileObj.offset
    var end = start + fileObj.length - 1

    var startPiece = start / pieceLength | 0
    var endPiece = end / pieceLength | 0
    var pieces = self.pieces.slice(startPiece, endPiece + 1)

    var file = new File(self, fileObj, pieces, pieceLength)
    file.on('done', self._onFileDone.bind(self, file))
    return file
  })
}

Storage.BLOCK_LENGTH = BLOCK_LENGTH

Storage.prototype.load = function (streams, cb) {
  var self = this
  if (!Array.isArray(streams)) streams = [ streams ]
  cb = once(cb || function () {})

  var pieceIndex = 0
  var multistream = new MultiStream(streams)
  var blockstream = new BlockStream(self.pieceLength, { zeroPadding: false })

  multistream.on('error', onError)

  self.once('done', onDone)

  multistream
    .pipe(blockstream)
    .on('data', onData)
    .on('error', onError)

  function onData (piece) {
    var index = pieceIndex
    pieceIndex += 1

    var blockIndex = 0
    var s = new BlockStream(BLOCK_LENGTH, { zeroPadding: false })

    s.on('data', onBlockData)
    s.on('end', onBlockEnd)

    function onBlockData (block) {
      var offset = blockIndex * BLOCK_LENGTH
      blockIndex += 1
      self.writeBlock(index, offset, block)
    }

    function onBlockEnd () {
      blockCleanup()
    }

    function blockCleanup () {
      s.removeListener('data', onBlockData)
      s.removeListener('end', onBlockEnd)
    }

    s.end(piece)
  }

  function onError (err) {
    cleanup()
    cb(err)
  }

  function onDone () {
    cleanup()
    cb(null)
  }

  function cleanup () {
    multistream.removeListener('error', onError)
    blockstream.removeListener('data', onData)
    blockstream.removeListener('error', onError)
    self.removeListener('done', onDone)
  }
}

Object.defineProperty(Storage.prototype, 'downloaded', {
  get: function () {
    var self = this
    return self.pieces.reduce(function (total, piece) {
      return total + (piece.verified ? piece.length : piece.blocksWritten * BLOCK_LENGTH)
    }, 0)
  }
})

/**
 * The number of missing pieces. Used to implement 'end game' mode.
 */
Object.defineProperty(Storage.prototype, 'numMissing', {
  get: function () {
    var self = this
    var numMissing = self.pieces.length
    for (var index = 0, len = self.pieces.length; index < len; index++) {
      numMissing -= self.bitfield.get(index)
    }
    return numMissing
  }
})

/**
 * Reads a block from a piece.
 *
 * @param {number}    index    piece index
 * @param {number}    offset   byte offset within piece
 * @param {number}    length   length in bytes to read from piece
 * @param {function}  cb
 */
Storage.prototype.readBlock = function (index, offset, length, cb) {
  var self = this
  cb = dezalgo(cb)
  var piece = self.pieces[index]
  if (!piece) return cb(new Error('invalid piece index ' + index))
  piece.readBlock(offset, length, cb)
}

/**
 * Writes a block to a piece.
 *
 * @param {number}  index    piece index
 * @param {number}  offset   byte offset within piece
 * @param {Buffer}  buffer   buffer to write
 * @param {function}  cb
 */
Storage.prototype.writeBlock = function (index, offset, buffer, cb) {
  var self = this
  if (!cb) cb = noop
  cb = dezalgo(cb)

  if (self.readonly) return cb(new Error('cannot write to readonly storage'))
  var piece = self.pieces[index]
  if (!piece) return cb(new Error('invalid piece index ' + index))
  piece.writeBlock(offset, buffer, cb)
}

/**
 * Reads a piece or a range of a piece.
 *
 * @param {number}   index         piece index
 * @param {Object=}  range         optional range within piece
 * @param {number}   range.offset  byte offset within piece
 * @param {number}   range.length  length in bytes to read from piece
 * @param {function} cb
 * @param {boolean}  force         optionally overrides default check preventing reading
 *                                 from unverified piece
 */
Storage.prototype.read = function (index, range, cb, force) {
  var self = this

  if (typeof range === 'function') {
    force = cb
    cb = range
    range = null
  }
  cb = dezalgo(cb)

  var piece = self.pieces[index]
  if (!piece) {
    return cb(new Error('invalid piece index ' + index))
  }

  if (!piece.verified && !force) {
    return cb(new Error('Storage.read called on incomplete piece ' + index))
  }

  var offset = 0
  var length = piece.length

  if (range) {
    offset = range.offset || 0
    length = range.length || length
  }

  if (piece.buffer) {
    // shortcut for piece with static backing buffer
    return cb(null, piece.buffer.slice(offset, offset + length))
  }

  var blocks = []
  function readNextBlock () {
    if (length <= 0) return cb(null, Buffer.concat(blocks))

    var blockOffset = offset
    var blockLength = Math.min(BLOCK_LENGTH, length)

    offset += blockLength
    length -= blockLength

    self.readBlock(index, blockOffset, blockLength, function (err, block) {
      if (err) return cb(err)

      blocks.push(block)
      readNextBlock()
    })
  }

  readNextBlock()
}

/**
 * Reserves a block from the given piece.
 *
 * @param {number}  index    piece index
 * @param {Boolean} endGame  whether or not end game mode is enabled
 *
 * @returns {Object|null} reservation with offset and length or null if failed.
 */
Storage.prototype.reserveBlock = function (index, endGame) {
  var self = this
  var piece = self.pieces[index]
  if (!piece) return null

  return piece.reserveBlock(endGame)
}

/**
 * Cancels a previous block reservation from the given piece.
 *
 * @param {number}  index   piece index
 * @param {number}  offset  byte offset of block in piece
 *
 * @returns {Boolean}
 */
Storage.prototype.cancelBlock = function (index, offset) {
  var self = this
  var piece = self.pieces[index]
  if (!piece) return false

  return piece.cancelBlock(offset)
}

/**
 * Removes and cleans up any backing store for this storage.
 * @param {function=} cb
 */
Storage.prototype.remove = function (cb) {
  if (cb) dezalgo(cb)(null)
}

/**
 * Closes the backing store for this storage.
 * @param {function=} cb
 */
Storage.prototype.close = function (cb) {
  var self = this
  self.closed = true
  if (cb) dezalgo(cb)(null)
}

//
// HELPER METHODS
//

Storage.prototype._onPieceDone = function (piece) {
  var self = this
  self.bitfield.set(piece.index)
  debug('piece done ' + piece.index + ' (' + self.numMissing + ' still missing)')
  self.emit('piece', piece)
}

Storage.prototype._onFileDone = function (file) {
  var self = this
  debug('file done ' + file.name)
  self.emit('file', file)

  self._checkDone()
}

Storage.prototype._checkDone = function () {
  var self = this

  if (!self.done && self.files.every(function (file) { return file.done })) {
    self.done = true
    self.emit('done')
  }
}