package websocket

import (
	"encoding/binary"
	"fmt"
	"io"
	"unicode/utf8"
)

var ErrUnmaskedFrame = fmt.Errorf("Received unmasked frame")
var ErrTooLongControlFrame = fmt.Errorf("Received a control frame that is fragmented or too long")
var ErrInvalidFragment = fmt.Errorf("Received invalid fragmentation")
var ErrUnexpectedContinuation = fmt.Errorf("Received unexpected continuation frame")
var ErrInvalidSize = fmt.Errorf("Received invalid payload size")
var ErrInvalidPayload = fmt.Errorf("Received invalid utf8 payload")
var ErrInvalidCloseStatus = fmt.Errorf("Received invalid close status")
var ErrInvalidOpCode = fmt.Errorf("Received invalid OpCode")
var ErrReservedBits = fmt.Errorf("Received reserved bits")
var CloseFrame = fmt.Errorf("Received close Frame")

// Maximum Header Size  = Final/OpCode + isMask/Length + Length + Mask
const maximumHeaderSize = 1 + 1 + 8 + 4
const maxWriteChunk = 0x7fff

// Lists websocket close status
type MessageError uint16

const (
	NONE                MessageError = 0
	NORMAL              MessageError = 1000
	GOING_AWAY          MessageError = 1001
	PROTOCOL_ERR        MessageError = 1002
	UNACCEPTABLE_OPCODE MessageError = 1003
	INVALID_PAYLOAD     MessageError = 1007 // utf8
	MESSAGE_TOO_LARGE   MessageError = 1009
)

// Lists websocket message types
type MessageType byte

const (
	CONTINUATION MessageType = 0x00
	TEXT         MessageType = 0x01
	BINARY       MessageType = 0x02
	CLOSE        MessageType = 0x08
	PING         MessageType = 0x09
	PONG         MessageType = 0x0a
)

// Represents a websocket message
type Message struct {
	Final bool
	Type  MessageType
	Size  uint
	Data  []byte
}

// receive reads a message form reader
func readMessage(reader io.Reader) (*Message, error) {

	var err error
	var tmpBuf []byte
	var mask []byte
	var cursor int

	m := new(Message)

	/* (2) Byte 1: FIN and OpCode */
	tmpBuf = make([]byte, 1)
	err = readBytes(reader, tmpBuf)
	if err != nil {
		return m, err
	}

	// check reserved bits
	if tmpBuf[0]&0x70 != 0 {
		return m, ErrReservedBits
	}

	m.Final = bool(tmpBuf[0]&0x80 == 0x80)
	m.Type = MessageType(tmpBuf[0] & 0x0f)

	/* (3) Byte 2: Mask and Length[0] */
	tmpBuf = make([]byte, 1)
	err = readBytes(reader, tmpBuf)
	if err != nil {
		return m, err
	}

	// if mask, byte array not nil
	if tmpBuf[0]&0x80 == 0x80 {
		mask = make([]byte, 0)
	}

	// payload length
	m.Size = uint(tmpBuf[0] & 0x7f)

	/* (4) Extended payload */
	if m.Size == 127 {

		tmpBuf = make([]byte, 8)
		err := readBytes(reader, tmpBuf)
		if err != nil {
			return m, err
		}

		m.Size = uint(binary.BigEndian.Uint64(tmpBuf))

	} else if m.Size == 126 {

		tmpBuf = make([]byte, 2)
		err := readBytes(reader, tmpBuf)
		if err != nil {
			return m, err
		}

		m.Size = uint(binary.BigEndian.Uint16(tmpBuf))

	}

	/* (5) Masking key */
	if mask != nil {

		tmpBuf = make([]byte, 4)
		err := readBytes(reader, tmpBuf)
		if err != nil {
			return m, err
		}

		mask = make([]byte, 4)
		copy(mask, tmpBuf)

	}

	/* (6) Read payload by chunks */
	m.Data = make([]byte, int(m.Size))

	cursor = 0

	// {1} While we have data to read //
	for uint(cursor) < m.Size {

		// {2} Try to read (at least 1 byte) //
		nbread, err := io.ReadAtLeast(reader, m.Data[cursor:m.Size], 1)
		if err != nil {
			return m, err
		}

		// {3} Unmask data //
		if mask != nil {
			for i, l := cursor, cursor+nbread; i < l; i++ {

				mi := i % 4 // mask index
				m.Data[i] = m.Data[i] ^ mask[mi]

			}
		}

		// {4} Update cursor //
		cursor += nbread

	}

	// return error if unmasked frame
	// we have to fully read it for read buffer to be clean
	err = nil
	if mask == nil {
		err = ErrUnmaskedFrame
	}

	return m, err

}

// Send sends a frame over a socket
func (m Message) Send(writer io.Writer) error {

	header := make([]byte, 0, maximumHeaderSize)

	// fix size
	if uint(len(m.Data)) <= m.Size {
		m.Size = uint(len(m.Data))
	}

	/* (1) Byte 0 : FIN + opcode */
	var final byte = 0x80
	if !m.Final {
		final = 0
	}
	header = append(header, final|byte(m.Type))

	/* (2) Get payload length */
	if m.Size < 126 { // simple

		header = append(header, byte(m.Size))

	} else if m.Size <= 0xffff { // extended: 16 bits

		header = append(header, 126)

		buf := make([]byte, 2)
		binary.BigEndian.PutUint16(buf, uint16(m.Size))
		header = append(header, buf...)

	} else if m.Size <= 0xffffffffffffffff { // extended: 64 bits

		header = append(header, 127)

		buf := make([]byte, 8)
		binary.BigEndian.PutUint64(buf, uint64(m.Size))
		header = append(header, buf...)

	}

	/* (3) Build write buffer */
	writeBuf := make([]byte, 0, len(header)+int(m.Size))
	writeBuf = append(writeBuf, header...)
	writeBuf = append(writeBuf, m.Data[0:m.Size]...)

	/* (4) Send over socket by chunks */
	toWrite := len(header) + int(m.Size)
	cursor := 0
	for cursor < toWrite {

		maxBoundary := cursor + maxWriteChunk
		if maxBoundary > toWrite {
			maxBoundary = toWrite
		}

		// Try to wrote (at max 1024 bytes) //
		nbwritten, err := writer.Write(writeBuf[cursor:maxBoundary])
		if err != nil {
			return err
		}

		// Update cursor //
		cursor += nbwritten

	}

	return nil
}

// Check for message errors with:
// (m) the current message
// (fragment) whether there is a fragment in construction
// returns the message error
func (m *Message) check(fragment bool) error {

	/* (1) Invalid first fragment (not TEXT nor BINARY) */
	if !m.Final && !fragment && m.Type != TEXT && m.Type != BINARY {
		return ErrInvalidFragment
	}

	/* (2) Waiting fragment but received standalone frame */
	if fragment && m.Type != CONTINUATION && m.Type != CLOSE && m.Type != PING && m.Type != PONG {
		return ErrInvalidFragment
	}

	/* (3) Control frame too long */
	if (m.Type == CLOSE || m.Type == PING || m.Type == PONG) && (m.Size > 125 || !m.Final) {
		return ErrTooLongControlFrame
	}

	switch m.Type {
	case CONTINUATION:
		// unexpected continuation
		if !fragment {
			return ErrUnexpectedContinuation
		}
		return nil

	case TEXT:
		if m.Final && !utf8.Valid(m.Data) {
			return ErrInvalidPayload
		}
		return nil

	case BINARY:
		return nil

	case CLOSE:
		// incomplete code
		if m.Size == 1 {
			return ErrInvalidCloseStatus
		}

		// invalid utf-8 reason
		if m.Size > 2 && !utf8.Valid(m.Data[2:]) {
			return ErrInvalidPayload
		}

		// invalid code
		if m.Size >= 2 {
			c := binary.BigEndian.Uint16(m.Data[0:2])

			if c < 1000 || c >= 1004 && c <= 1006 || c >= 1012 && c <= 1016 || c == 1100 || c == 2000 || c == 2999 {
				return ErrInvalidCloseStatus
			}
		}
		return CloseFrame

	case PING:
		return nil

	case PONG:
		return nil

	default:
		return ErrInvalidOpCode

	}

	return nil
}

// readBytes reads from a reader into a byte array
// until the byte length is fully filled with data
// loops while there is no error
//
// It manages connections which chunks data
func readBytes(reader io.Reader, buffer []byte) error {

	var cur, len int = 0, len(buffer)

	// try to read until the full size is read
	for cur < len {

		nbread, err := reader.Read(buffer[cur:])
		if err != nil {
			return err
		}

		cur += nbread
	}

	return nil

}