package eq2net

import (
	"bytes"
	"compress/zlib"
	"encoding/binary"
	"fmt"
	"net"
	"time"
	"unsafe"
)

// Packet represents a base packet structure
type Packet struct {
	Buffer    []byte
	Size      uint32
	SrcIP     net.IP
	SrcPort   uint16
	DstIP     net.IP
	DstPort   uint16
	Priority  uint32
	Timestamp time.Time
	Version   int16
	Opcode    uint16
}

// NewPacket creates a new packet
func NewPacket(op uint16, buf []byte) *Packet {
	p := &Packet{
		Opcode:    op,
		Size:      uint32(len(buf)),
		Timestamp: time.Now(),
	}
	if buf != nil {
		p.Buffer = make([]byte, len(buf))
		copy(p.Buffer, buf)
	}
	return p
}

// SetSrcInfo sets source IP and port
func (p *Packet) SetSrcInfo(ip net.IP, port uint16) {
	p.SrcIP = ip
	p.SrcPort = port
}

// SetDstInfo sets destination IP and port
func (p *Packet) SetDstInfo(ip net.IP, port uint16) {
	p.DstIP = ip
	p.DstPort = port
}

// GetRawOpcode returns the raw opcode
func (p *Packet) GetRawOpcode() uint16 {
	return p.Opcode
}

// ProtocolPacket represents a protocol-level packet
type ProtocolPacket struct {
	*Packet
	EQ2Compressed    bool
	PacketPrepared   bool
	PacketEncrypted  bool
	Acked            bool
	SentTime         int32
	AttemptCount     int8
	Sequence         uint16
}

// NewProtocolPacket creates a new protocol packet from raw data
func NewProtocolPacket(buf []byte, opcode int) *ProtocolPacket {
	if len(buf) < 2 {
		return nil
	}

	var op uint16
	if opcode >= 0 {
		op = uint16(opcode)
	} else {
		op = binary.BigEndian.Uint16(buf[:2])
		buf = buf[2:]
	}

	pp := &ProtocolPacket{
		Packet: NewPacket(op, buf),
	}
	return pp
}

// NewProtocolPacketWithOp creates a new protocol packet with specific opcode
func NewProtocolPacketWithOp(op uint16, buf []byte) *ProtocolPacket {
	return &ProtocolPacket{
		Packet: NewPacket(op, buf),
	}
}

// ValidateCRC validates the CRC of a packet
func ValidateCRC(buffer []byte, length int, key uint32) bool {
	// SessionRequest, SessionResponse, OutOfSession are not CRC'd
	if len(buffer) >= 2 && buffer[0] == 0x00 && 
		(buffer[1] == OPSessionRequest || buffer[1] == OPSessionResponse || buffer[1] == OPOutOfSession) {
		return true
	}
	
	// Check for special case
	if len(buffer) >= 4 && buffer[2] == 0x00 && buffer[3] == 0x19 {
		return true
	}

	// Calculate and compare CRC
	if length < 2 {
		return false
	}
	
	compCRC := CalculateCRC16(buffer[:length-2], key)
	packetCRC := binary.BigEndian.Uint16(buffer[length-2:])
	
	return packetCRC == 0 || compCRC == packetCRC
}

// Serialize serializes the protocol packet
func (p *ProtocolPacket) Serialize(offset int8) []byte {
	// Calculate size including opcode
	totalSize := len(p.Buffer) + 2
	if offset != 0 {
		totalSize += int(offset)
	}

	result := make([]byte, totalSize)
	pos := 0

	// Add offset if needed
	if offset != 0 {
		pos = int(offset)
	}

	// Write opcode
	binary.BigEndian.PutUint16(result[pos:], p.Opcode)
	pos += 2

	// Copy buffer
	if p.Buffer != nil {
		copy(result[pos:], p.Buffer)
	}

	return result
}

// Copy creates a copy of the protocol packet
func (p *ProtocolPacket) Copy() *ProtocolPacket {
	newPacket := &ProtocolPacket{
		Packet:          NewPacket(p.Opcode, p.Buffer),
		EQ2Compressed:   p.EQ2Compressed,
		PacketPrepared:  p.PacketPrepared,
		PacketEncrypted: p.PacketEncrypted,
		Acked:           p.Acked,
		SentTime:        p.SentTime,
		AttemptCount:    p.AttemptCount,
		Sequence:        p.Sequence,
	}
	newPacket.Version = p.Version
	newPacket.Priority = p.Priority
	return newPacket
}

// Combine combines two protocol packets
func (p *ProtocolPacket) Combine(rhs *ProtocolPacket) bool {
	if rhs.Opcode != p.Opcode {
		return false
	}

	// Create new buffer with combined size
	newSize := len(p.Buffer) + len(rhs.Buffer)
	newBuffer := make([]byte, newSize)
	
	copy(newBuffer, p.Buffer)
	copy(newBuffer[len(p.Buffer):], rhs.Buffer)
	
	p.Buffer = newBuffer
	p.Size = uint32(newSize)
	
	return true
}

// IsProtocolPacket checks if a buffer contains a protocol packet
func IsProtocolPacket(inBuff []byte, length uint32, trimCRC bool) bool {
	if length < 2 {
		return false
	}

	opcode := binary.BigEndian.Uint16(inBuff)
	
	switch uint8(opcode & 0xFF) {
	case OPSessionRequest, OPSessionResponse, OPCombined, 
	     OPSessionDisconnect, OPKeepAlive, OPServerKeyRequest,
	     OPSessionStatResponse, OPPacket, OPFragment,
	     OPOutOfOrderAck, OPAck, OPAppCombined, OPOutOfSession:
		return true
	}
	
	return false
}

// Decompress decompresses a buffer
func Decompress(buffer []byte, length uint32, newbuf []byte, newbufsize uint32) (uint32, error) {
	reader := bytes.NewReader(buffer[:length])
	zlibReader, err := zlib.NewReader(reader)
	if err != nil {
		return 0, err
	}
	defer zlibReader.Close()

	buf := bytes.NewBuffer(newbuf[:0])
	n, err := buf.ReadFrom(zlibReader)
	if err != nil {
		return 0, err
	}

	if uint32(n) > newbufsize {
		return 0, fmt.Errorf("decompressed size exceeds buffer size")
	}

	return uint32(n), nil
}

// Compress compresses a buffer
func Compress(buffer []byte, length uint32, newbuf []byte, newbufsize uint32) (uint32, error) {
	var buf bytes.Buffer
	writer := zlib.NewWriter(&buf)
	
	_, err := writer.Write(buffer[:length])
	if err != nil {
		return 0, err
	}
	
	err = writer.Close()
	if err != nil {
		return 0, err
	}

	compressed := buf.Bytes()
	if uint32(len(compressed)) > newbufsize {
		return 0, fmt.Errorf("compressed size exceeds buffer size")
	}

	copy(newbuf, compressed)
	return uint32(len(compressed)), nil
}

// ChatDecode decodes chat data
func ChatDecode(buffer []byte, size int, decodeKey int) {
	for i := 0; i+4 <= size; i++ {
		c := buffer[i]
		buffer[i] = buffer[i+2]
		buffer[i+2] = c
		c = buffer[i+1]
		buffer[i+1] = buffer[i+3]
		buffer[i+3] = c
		
		key := uint32(decodeKey)
		p := (*uint32)(unsafe.Pointer(&buffer[i]))
		*p = (*p) ^ key
		i += 3
	}
}

// ChatEncode encodes chat data  
func ChatEncode(buffer []byte, size int, encodeKey int) {
	for i := 0; i+4 <= size; i++ {
		key := uint32(encodeKey)
		p := (*uint32)(unsafe.Pointer(&buffer[i]))
		*p = (*p) ^ key
		
		c := buffer[i]
		buffer[i] = buffer[i+2]
		buffer[i+2] = c
		c = buffer[i+1]
		buffer[i+1] = buffer[i+3]
		buffer[i+3] = c
		i += 3
	}
}

// ApplicationPacket represents an application-level packet
type ApplicationPacket struct {
	*Packet
	EmuOpcode      EmuOpcode
	AppOpcodeSize  uint8
}

// NewApplicationPacket creates a new application packet
func NewApplicationPacket(op EmuOpcode, buf []byte) *ApplicationPacket {
	ap := &ApplicationPacket{
		Packet:        NewPacket(0, buf),
		EmuOpcode:     op,
		AppOpcodeSize: 2, // Default for world/zone
	}
	return ap
}

// SetOpcode sets the opcode
func (p *ApplicationPacket) SetOpcode(op EmuOpcode) {
	p.EmuOpcode = op
	p.Opcode = uint16(op)
}

// GetOpcode returns the opcode
func (p *ApplicationPacket) GetOpcode() EmuOpcode {
	return p.EmuOpcode
}

// Copy creates a copy of the application packet
func (p *ApplicationPacket) Copy() *ApplicationPacket {
	newPacket := &ApplicationPacket{
		Packet:        NewPacket(p.Opcode, p.Buffer),
		EmuOpcode:     p.EmuOpcode,
		AppOpcodeSize: p.AppOpcodeSize,
	}
	newPacket.Version = p.Version
	return newPacket
}

// Serialize serializes the application packet
func (p *ApplicationPacket) Serialize() []byte {
	size := len(p.Buffer) + int(p.AppOpcodeSize)
	result := make([]byte, size)
	
	// Write opcode based on size
	if p.AppOpcodeSize == 1 {
		result[0] = uint8(p.Opcode)
		copy(result[1:], p.Buffer)
	} else {
		binary.LittleEndian.PutUint16(result, p.Opcode)
		copy(result[2:], p.Buffer)
	}
	
	return result
}

// Combine combines two application packets
func (p *ApplicationPacket) Combine(rhs *ApplicationPacket) bool {
	if rhs.EmuOpcode != p.EmuOpcode {
		return false
	}

	newSize := len(p.Buffer) + len(rhs.Buffer)
	newBuffer := make([]byte, newSize)
	
	copy(newBuffer, p.Buffer)
	copy(newBuffer[len(p.Buffer):], rhs.Buffer)
	
	p.Buffer = newBuffer
	p.Size = uint32(newSize)
	
	return true
}