// Package eq2net implements the EverQuest 2 network protocol
package eq2net

import (
	"encoding/binary"
	"fmt"
	"net"
	"time"
)

// Protocol opcodes for low-level packet control
const (
	OPSessionRequest      = 0x0001
	OPSessionResponse     = 0x0002
	OPCombined           = 0x0003
	OPSessionDisconnect  = 0x0005
	OPKeepAlive          = 0x0006
	OPSessionStatRequest = 0x0007
	OPSessionStatResponse = 0x0008
	OPPacket             = 0x0009
	OPFragment           = 0x000D
	OPOutOfOrderAck      = 0x0011
	OPAck                = 0x0015
	OPAppCombined        = 0x0019
	OPOutOfSession       = 0x001D
)

// EQPacket is the base packet type for all EverQuest packets
type EQPacket struct {
	// Core packet data
	Buffer []byte
	Size   uint32
	Opcode uint16

	// Network information
	SrcIP   net.IP
	DstIP   net.IP
	SrcPort uint16
	DstPort uint16

	// Metadata
	Priority  uint32
	Timestamp time.Time
	Version   int16
}

// NewEQPacket creates a new packet with the specified opcode and data
func NewEQPacket(opcode uint16, data []byte) *EQPacket {
	p := &EQPacket{
		Opcode:    opcode,
		Timestamp: time.Now(),
	}
	
	if len(data) > 0 {
		p.Buffer = make([]byte, len(data))
		copy(p.Buffer, data)
		p.Size = uint32(len(data))
	}
	
	return p
}

// TotalSize returns the total packet size including opcode
func (p *EQPacket) TotalSize() uint32 {
	return p.Size + 2 // +2 for opcode
}

// SetNetworkInfo sets the source and destination network information
func (p *EQPacket) SetNetworkInfo(srcIP net.IP, srcPort uint16, dstIP net.IP, dstPort uint16) {
	p.SrcIP = srcIP
	p.SrcPort = srcPort
	p.DstIP = dstIP
	p.DstPort = dstPort
}

// CopyInfo copies network and timing information from another packet
func (p *EQPacket) CopyInfo(other *EQPacket) {
	p.SrcIP = other.SrcIP
	p.SrcPort = other.SrcPort
	p.DstIP = other.DstIP
	p.DstPort = other.DstPort
	p.Timestamp = other.Timestamp
	p.Version = other.Version
}

// EQProtocolPacket handles low-level protocol operations
type EQProtocolPacket struct {
	*EQPacket

	// Protocol state flags
	Compressed bool
	Prepared   bool
	Encrypted  bool
	Acked      bool

	// Reliability tracking
	SentTime     time.Time
	AttemptCount uint8
	Sequence     uint32
}

// NewEQProtocolPacket creates a new protocol packet
func NewEQProtocolPacket(opcode uint16, data []byte) *EQProtocolPacket {
	return &EQProtocolPacket{
		EQPacket: NewEQPacket(opcode, data),
	}
}

// NewEQProtocolPacketFromBuffer creates a protocol packet from raw buffer
func NewEQProtocolPacketFromBuffer(buffer []byte, opcodeOverride int) (*EQProtocolPacket, error) {
	if len(buffer) < 2 {
		return nil, fmt.Errorf("buffer too small for opcode")
	}

	var opcode uint16
	var dataOffset int

	if opcodeOverride >= 0 {
		opcode = uint16(opcodeOverride)
		dataOffset = 0
	} else {
		opcode = binary.BigEndian.Uint16(buffer[:2])
		dataOffset = 2
	}

	var data []byte
	if len(buffer) > dataOffset {
		data = buffer[dataOffset:]
	}

	return NewEQProtocolPacket(opcode, data), nil
}

// Serialize writes the protocol packet to a byte buffer
func (p *EQProtocolPacket) Serialize(offset int) []byte {
	// Allocate buffer for opcode + data
	result := make([]byte, 2+len(p.Buffer)-offset)
	
	// Write opcode (big-endian)
	if p.Opcode > 0xFF {
		binary.BigEndian.PutUint16(result[0:2], p.Opcode)
	} else {
		result[0] = 0
		result[1] = byte(p.Opcode)
	}
	
	// Copy packet data
	if len(p.Buffer) > offset {
		copy(result[2:], p.Buffer[offset:])
	}
	
	return result
}

// IsProtocolPacket checks if the opcode is a valid protocol packet
func IsProtocolPacket(opcode uint16) bool {
	switch opcode {
	case OPSessionRequest, OPSessionDisconnect, OPKeepAlive,
		OPSessionStatResponse, OPPacket, OPCombined, OPFragment,
		OPAck, OPOutOfOrderAck, OPOutOfSession:
		return true
	default:
		return false
	}
}

// Copy creates a deep copy of the protocol packet
func (p *EQProtocolPacket) Copy() *EQProtocolPacket {
	newPacket := &EQProtocolPacket{
		EQPacket: NewEQPacket(p.Opcode, p.Buffer),
		Compressed: p.Compressed,
		Prepared:   p.Prepared,
		Encrypted:  p.Encrypted,
		Acked:      p.Acked,
		SentTime:   p.SentTime,
		AttemptCount: p.AttemptCount,
		Sequence:   p.Sequence,
	}
	newPacket.CopyInfo(p.EQPacket)
	return newPacket
}

// EQApplicationPacket represents high-level application packets
type EQApplicationPacket struct {
	*EQPacket
	
	// Cached emulator opcode
	EmuOpcode uint16
	
	// Opcode size (1 or 2 bytes)
	OpcodeSize uint8
}

// DefaultOpcodeSize is the default size for application opcodes
var DefaultOpcodeSize uint8 = 2

// NewEQApplicationPacket creates a new application packet
func NewEQApplicationPacket(opcode uint16, data []byte) *EQApplicationPacket {
	return &EQApplicationPacket{
		EQPacket:   NewEQPacket(opcode, data),
		EmuOpcode:  opcode,
		OpcodeSize: DefaultOpcodeSize,
	}
}

// Serialize writes the application packet to a byte buffer
func (p *EQApplicationPacket) Serialize() []byte {
	opcodeBytes := p.OpcodeSize
	
	// Special handling for opcodes with low byte = 0x00
	if p.OpcodeSize == 2 && (p.Opcode&0x00FF) == 0 {
		opcodeBytes = 3
	}
	
	result := make([]byte, uint32(opcodeBytes)+p.Size)
	
	if p.OpcodeSize == 1 {
		result[0] = byte(p.Opcode)
	} else {
		if (p.Opcode & 0x00FF) == 0 {
			result[0] = 0
			binary.BigEndian.PutUint16(result[1:3], p.Opcode)
		} else {
			binary.BigEndian.PutUint16(result[0:2], p.Opcode)
		}
	}
	
	// Copy data after opcode
	if p.Size > 0 {
		copy(result[opcodeBytes:], p.Buffer)
	}
	
	return result
}

// Copy creates a deep copy of the application packet
func (p *EQApplicationPacket) Copy() *EQApplicationPacket {
	newPacket := &EQApplicationPacket{
		EQPacket:   NewEQPacket(p.Opcode, p.Buffer),
		EmuOpcode:  p.EmuOpcode,
		OpcodeSize: p.OpcodeSize,
	}
	newPacket.CopyInfo(p.EQPacket)
	return newPacket
}

// PacketCombiner handles combining multiple packets for efficient transmission
type PacketCombiner struct {
	maxSize int
}

// NewPacketCombiner creates a new packet combiner with max size limit
func NewPacketCombiner(maxSize int) *PacketCombiner {
	return &PacketCombiner{maxSize: maxSize}
}

// CombineProtocolPackets combines multiple protocol packets into one
func (c *PacketCombiner) CombineProtocolPackets(packets []*EQProtocolPacket) *EQProtocolPacket {
	if len(packets) == 0 {
		return nil
	}
	
	if len(packets) == 1 {
		return packets[0]
	}
	
	// Calculate total size needed
	totalSize := 0
	for _, p := range packets {
		totalSize += 1 + int(p.TotalSize()) // 1 byte for size prefix
	}
	
	if totalSize > c.maxSize {
		return nil // Too large to combine
	}
	
	// Build combined packet buffer
	buffer := make([]byte, totalSize)
	offset := 0
	
	for _, p := range packets {
		// Write size prefix
		buffer[offset] = byte(p.TotalSize())
		offset++
		
		// Serialize packet
		serialized := p.Serialize(0)
		copy(buffer[offset:], serialized)
		offset += len(serialized)
	}
	
	// Create combined packet
	combined := NewEQProtocolPacket(OPCombined, buffer)
	if len(packets) > 0 {
		combined.CopyInfo(packets[0].EQPacket)
	}
	
	return combined
}