'use strict'

var protocol = require('./constants')
var Buffer = require('safe-buffer').Buffer
var empty = Buffer.allocUnsafe(0)
var zeroBuf = Buffer.from([0])
var numbers = require('./numbers')
var nextTick = require('process-nextick-args').nextTick

var numCache = numbers.cache
var generateNumber = numbers.generateNumber
var generateCache = numbers.generateCache
var writeNumber = writeNumberCached
var toGenerate = true

function generate (packet, stream) {
  if (stream.cork) {
    stream.cork()
    nextTick(uncork, stream)
  }

  if (toGenerate) {
    toGenerate = false
    generateCache()
  }

  switch (packet.cmd) {
    case 'connect':
      return connect(packet, stream)
    case 'connack':
      return connack(packet, stream)
    case 'publish':
      return publish(packet, stream)
    case 'puback':
    case 'pubrec':
    case 'pubrel':
    case 'pubcomp':
    case 'unsuback':
      return confirmation(packet, stream)
    case 'subscribe':
      return subscribe(packet, stream)
    case 'suback':
      return suback(packet, stream)
    case 'unsubscribe':
      return unsubscribe(packet, stream)
    case 'pingreq':
    case 'pingresp':
    case 'disconnect':
      return emptyPacket(packet, stream)
    default:
      stream.emit('error', new Error('Unknown command'))
      return false
  }
}
/**
 * Controls numbers cache.
 * Set to "false" to allocate buffers on-the-flight instead of pre-generated cache
 */
Object.defineProperty(generate, 'cacheNumbers', {
  get: function () {
    return writeNumber === writeNumberCached
  },
  set: function (value) {
    if (value) {
      if (!numCache || Object.keys(numCache).length === 0) toGenerate = true
      writeNumber = writeNumberCached
    } else {
      toGenerate = false
      writeNumber = writeNumberGenerated
    }
  }
})

function uncork (stream) {
  stream.uncork()
}

function connect (opts, stream) {
  var settings = opts || {}
  var protocolId = settings.protocolId || 'MQTT'
  var protocolVersion = settings.protocolVersion || 4
  var will = settings.will
  var clean = settings.clean
  var keepalive = settings.keepalive || 0
  var clientId = settings.clientId || ''
  var username = settings.username
  var password = settings.password

  if (clean === undefined) clean = true

  var length = 0

  // Must be a string and non-falsy
  if (!protocolId ||
     (typeof protocolId !== 'string' && !Buffer.isBuffer(protocolId))) {
    stream.emit('error', new Error('Invalid protocolId'))
    return false
  } else length += protocolId.length + 2

  // Must be 3 or 4
  if (protocolVersion !== 3 && protocolVersion !== 4) {
    stream.emit('error', new Error('Invalid protocol version'))
    return false
  } else length += 1

  // ClientId might be omitted in 3.1.1, but only if cleanSession is set to 1
  if ((typeof clientId === 'string' || Buffer.isBuffer(clientId)) &&
     (clientId || protocolVersion === 4) && (clientId || clean)) {
    length += clientId.length + 2
  } else {
    if (protocolVersion < 4) {
      stream.emit('error', new Error('clientId must be supplied before 3.1.1'))
      return false
    }
    if ((clean * 1) === 0) {
      stream.emit('error', new Error('clientId must be given if cleanSession set to 0'))
      return false
    }
  }

  // Must be a two byte number
  if (typeof keepalive !== 'number' ||
      keepalive < 0 ||
      keepalive > 65535 ||
      keepalive % 1 !== 0) {
    stream.emit('error', new Error('Invalid keepalive'))
    return false
  } else length += 2

  // Connect flags
  length += 1

  // If will exists...
  if (will) {
    // It must be an object
    if (typeof will !== 'object') {
      stream.emit('error', new Error('Invalid will'))
      return false
    }
    // It must have topic typeof string
    if (!will.topic || typeof will.topic !== 'string') {
      stream.emit('error', new Error('Invalid will topic'))
      return false
    } else {
      length += Buffer.byteLength(will.topic) + 2
    }

    // Payload
    if (will.payload && will.payload) {
      if (will.payload.length >= 0) {
        if (typeof will.payload === 'string') {
          length += Buffer.byteLength(will.payload) + 2
        } else {
          length += will.payload.length + 2
        }
      } else {
        stream.emit('error', new Error('Invalid will payload'))
        return false
      }
    } else {
      length += 2
    }
  }

  // Username
  var providedUsername = false
  if (username != null) {
    if (isStringOrBuffer(username)) {
      providedUsername = true
      length += Buffer.byteLength(username) + 2
    } else {
      stream.emit('error', new Error('Invalid username'))
      return false
    }
  }

  // Password
  if (password != null) {
    if (!providedUsername) {
      stream.emit('error', new Error('Username is required to use password'))
      return false
    }

    if (isStringOrBuffer(password)) {
      length += byteLength(password) + 2
    } else {
      stream.emit('error', new Error('Invalid password'))
      return false
    }
  }

  // Generate header
  stream.write(protocol.CONNECT_HEADER)

  // Generate length
  writeLength(stream, length)

  // Generate protocol ID
  writeStringOrBuffer(stream, protocolId)
  stream.write(
    protocolVersion === 4 ? protocol.VERSION4 : protocol.VERSION3
  )

  // Connect flags
  var flags = 0
  flags |= (username != null) ? protocol.USERNAME_MASK : 0
  flags |= (password != null) ? protocol.PASSWORD_MASK : 0
  flags |= (will && will.retain) ? protocol.WILL_RETAIN_MASK : 0
  flags |= (will && will.qos) ? will.qos << protocol.WILL_QOS_SHIFT : 0
  flags |= will ? protocol.WILL_FLAG_MASK : 0
  flags |= clean ? protocol.CLEAN_SESSION_MASK : 0

  stream.write(Buffer.from([flags]))

  // Keepalive
  writeNumber(stream, keepalive)

  // Client ID
  writeStringOrBuffer(stream, clientId)

  // Will
  if (will) {
    writeString(stream, will.topic)
    writeStringOrBuffer(stream, will.payload)
  }

  // Username and password
  if (username != null) {
    writeStringOrBuffer(stream, username)
  }
  if (password != null) {
    writeStringOrBuffer(stream, password)
  }
  // This is a small packet that happens only once on a stream
  // We assume the stream is always free to receive more data after this
  return true
}

function connack (opts, stream) {
  var settings = opts || {}
  var rc = settings.returnCode

  // Check return code
  if (typeof rc !== 'number') {
    stream.emit('error', new Error('Invalid return code'))
    return false
  }

  stream.write(protocol.CONNACK_HEADER)
  writeLength(stream, 2)
  stream.write(opts.sessionPresent ? protocol.SESSIONPRESENT_HEADER : zeroBuf)

  return stream.write(Buffer.from([rc]))
}

function publish (opts, stream) {
  var settings = opts || {}
  var qos = settings.qos || 0
  var retain = settings.retain ? protocol.RETAIN_MASK : 0
  var topic = settings.topic
  var payload = settings.payload || empty
  var id = settings.messageId

  var length = 0

  // Topic must be a non-empty string or Buffer
  if (typeof topic === 'string') length += Buffer.byteLength(topic) + 2
  else if (Buffer.isBuffer(topic)) length += topic.length + 2
  else {
    stream.emit('error', new Error('Invalid topic'))
    return false
  }

  // Get the payload length
  if (!Buffer.isBuffer(payload)) length += Buffer.byteLength(payload)
  else length += payload.length

  // Message ID must a number if qos > 0
  if (qos && typeof id !== 'number') {
    stream.emit('error', new Error('Invalid messageId'))
    return false
  } else if (qos) length += 2

  // Header
  stream.write(protocol.PUBLISH_HEADER[qos][opts.dup ? 1 : 0][retain ? 1 : 0])

  // Remaining length
  writeLength(stream, length)

  // Topic
  writeNumber(stream, byteLength(topic))
  stream.write(topic)

  // Message ID
  if (qos > 0) writeNumber(stream, id)

  // Payload
  return stream.write(payload)
}

/* Puback, pubrec, pubrel and pubcomp */
function confirmation (opts, stream) {
  var settings = opts || {}
  var type = settings.cmd || 'puback'
  var id = settings.messageId
  var dup = (settings.dup && type === 'pubrel') ? protocol.DUP_MASK : 0
  var qos = 0

  if (type === 'pubrel') qos = 1

  // Check message ID
  if (typeof id !== 'number') {
    stream.emit('error', new Error('Invalid messageId'))
    return false
  }

  // Header
  stream.write(protocol.ACKS[type][qos][dup][0])

  // Length
  writeLength(stream, 2)

  // Message ID
  return writeNumber(stream, id)
}

function subscribe (opts, stream) {
  var settings = opts || {}
  var dup = settings.dup ? protocol.DUP_MASK : 0
  var id = settings.messageId
  var subs = settings.subscriptions

  var length = 0

  // Check message ID
  if (typeof id !== 'number') {
    stream.emit('error', new Error('Invalid messageId'))
    return false
  } else length += 2

  // Check subscriptions
  if (typeof subs === 'object' && subs.length) {
    for (var i = 0; i < subs.length; i += 1) {
      var itopic = subs[i].topic
      var iqos = subs[i].qos

      if (typeof itopic !== 'string') {
        stream.emit('error', new Error('Invalid subscriptions - invalid topic'))
        return false
      }
      if (typeof iqos !== 'number') {
        stream.emit('error', new Error('Invalid subscriptions - invalid qos'))
        return false
      }

      length += Buffer.byteLength(itopic) + 2 + 1
    }
  } else {
    stream.emit('error', new Error('Invalid subscriptions'))
    return false
  }

  // Generate header
  stream.write(protocol.SUBSCRIBE_HEADER[1][dup ? 1 : 0][0])

  // Generate length
  writeLength(stream, length)

  // Generate message ID
  writeNumber(stream, id)

  var result = true

  // Generate subs
  for (var j = 0; j < subs.length; j++) {
    var sub = subs[j]
    var jtopic = sub.topic
    var jqos = sub.qos

    // Write topic string
    writeString(stream, jtopic)

    // Write qos
    result = stream.write(protocol.QOS[jqos])
  }

  return result
}

function suback (opts, stream) {
  var settings = opts || {}
  var id = settings.messageId
  var granted = settings.granted

  var length = 0

  // Check message ID
  if (typeof id !== 'number') {
    stream.emit('error', new Error('Invalid messageId'))
    return false
  } else length += 2

  // Check granted qos vector
  if (typeof granted === 'object' && granted.length) {
    for (var i = 0; i < granted.length; i += 1) {
      if (typeof granted[i] !== 'number') {
        stream.emit('error', new Error('Invalid qos vector'))
        return false
      }
      length += 1
    }
  } else {
    stream.emit('error', new Error('Invalid qos vector'))
    return false
  }

  // header
  stream.write(protocol.SUBACK_HEADER)

  // Length
  writeLength(stream, length)

  // Message ID
  writeNumber(stream, id)

  return stream.write(Buffer.from(granted))
}

function unsubscribe (opts, stream) {
  var settings = opts || {}
  var id = settings.messageId
  var dup = settings.dup ? protocol.DUP_MASK : 0
  var unsubs = settings.unsubscriptions

  var length = 0

  // Check message ID
  if (typeof id !== 'number') {
    stream.emit('error', new Error('Invalid messageId'))
    return false
  } else {
    length += 2
  }
  // Check unsubs
  if (typeof unsubs === 'object' && unsubs.length) {
    for (var i = 0; i < unsubs.length; i += 1) {
      if (typeof unsubs[i] !== 'string') {
        stream.emit('error', new Error('Invalid unsubscriptions'))
        return false
      }
      length += Buffer.byteLength(unsubs[i]) + 2
    }
  } else {
    stream.emit('error', new Error('Invalid unsubscriptions'))
    return false
  }

  // Header
  stream.write(protocol.UNSUBSCRIBE_HEADER[1][dup ? 1 : 0][0])

  // Length
  writeLength(stream, length)

  // Message ID
  writeNumber(stream, id)

  // Unsubs
  var result = true
  for (var j = 0; j < unsubs.length; j++) {
    result = writeString(stream, unsubs[j])
  }

  return result
}

function emptyPacket (opts, stream) {
  return stream.write(protocol.EMPTY[opts.cmd])
}

/**
 * calcLengthLength - calculate the length of the remaining
 * length field
 *
 * @api private
 */
function calcLengthLength (length) {
  if (length >= 0 && length < 128) return 1
  else if (length >= 128 && length < 16384) return 2
  else if (length >= 16384 && length < 2097152) return 3
  else if (length >= 2097152 && length < 268435456) return 4
  else return 0
}

function genBufLength (length) {
  var digit = 0
  var pos = 0
  var buffer = Buffer.allocUnsafe(calcLengthLength(length))

  do {
    digit = length % 128 | 0
    length = length / 128 | 0
    if (length > 0) digit = digit | 0x80

    buffer.writeUInt8(digit, pos++)
  } while (length > 0)

  return buffer
}

/**
 * writeLength - write an MQTT style length field to the buffer
 *
 * @param <Buffer> buffer - destination
 * @param <Number> pos - offset
 * @param <Number> length - length (>0)
 * @returns <Number> number of bytes written
 *
 * @api private
 */

var lengthCache = {}
function writeLength (stream, length) {
  var buffer = lengthCache[length]

  if (!buffer) {
    buffer = genBufLength(length)
    if (length < 16384) lengthCache[length] = buffer
  }

  stream.write(buffer)
}

/**
 * writeString - write a utf8 string to the buffer
 *
 * @param <Buffer> buffer - destination
 * @param <Number> pos - offset
 * @param <String> string - string to write
 * @return <Number> number of bytes written
 *
 * @api private
 */

function writeString (stream, string) {
  var strlen = Buffer.byteLength(string)
  writeNumber(stream, strlen)

  stream.write(string, 'utf8')
}

/**
 * writeNumber - write a two byte number to the buffer
 *
 * @param <Buffer> buffer - destination
 * @param <Number> pos - offset
 * @param <String> number - number to write
 * @return <Number> number of bytes written
 *
 * @api private
 */
function writeNumberCached (stream, number) {
  return stream.write(numCache[number])
}
function writeNumberGenerated (stream, number) {
  return stream.write(generateNumber(number))
}

/**
 * writeStringOrBuffer - write a String or Buffer with the its length prefix
 *
 * @param <Buffer> buffer - destination
 * @param <Number> pos - offset
 * @param <String> toWrite - String or Buffer
 * @return <Number> number of bytes written
 */
function writeStringOrBuffer (stream, toWrite) {
  if (typeof toWrite === 'string') {
    writeString(stream, toWrite)
  } else if (toWrite) {
    writeNumber(stream, toWrite.length)
    stream.write(toWrite)
  } else writeNumber(stream, 0)
}

function byteLength (bufOrString) {
  if (!bufOrString) return 0
  else if (bufOrString instanceof Buffer) return bufOrString.length
  else return Buffer.byteLength(bufOrString)
}

function isStringOrBuffer (field) {
  return typeof field === 'string' || field instanceof Buffer
}

module.exports = generate