package stream

import (
	"encoding/binary"
	"sync"
	"sync/atomic"
	"time"

	"git.sharkk.net/EQ2/Protocol/crypto"
	"git.sharkk.net/EQ2/Protocol/opcodes"
	"git.sharkk.net/EQ2/Protocol/packets"
	"github.com/panjf2000/gnet/v2"
)

// Stream implements EQ2's reliable UDP protocol
type Stream struct {
	conn gnet.Conn
	mu   sync.RWMutex

	// Connection state
	state     atomic.Value // StreamState
	sessionID uint32
	crcKey    uint32
	maxLen    uint16
	encodeKey int
	decodeKey int

	// Sequence management
	seqOut     uint16
	seqIn      uint16
	seqLastAck uint16

	// Acknowledgment tracking
	pendingAcks  map[uint16]*pendingPacket
	ackTimer     *time.Timer
	lastAckSent  time.Time
	ackThreshold time.Duration

	// Fragment assembly
	fragments  map[uint16]*fragmentBuffer
	nextFragID uint16

	// Packet queues
	reliableQueue   []*packets.ProtoPacket
	unreliableQueue []*packets.ProtoPacket
	resendQueue     []*pendingPacket

	// Opcode management
	opcodeManager opcodes.Manager
	opcodeSize    uint8

	// Cipher for encryption
	cipher *crypto.Ciphers

	// Timers
	keepAliveTimer *time.Timer
	timeoutTimer   *time.Timer

	// Stats
	packetsOut uint64
	packetsIn  uint64
	bytesOut   uint64
	bytesIn    uint64

	// Callbacks
	onPacket     func(*packets.AppPacket)
	onDisconnect func()
}

type pendingPacket struct {
	packet    *packets.ProtoPacket
	seq       uint16
	sentTime  time.Time
	attempts  int
	nextRetry time.Time
}

type fragmentBuffer struct {
	totalSize uint32
	chunks    map[uint16][]byte
	received  uint32
	startTime time.Time
}

type StreamState int

const (
	StateDisconnected StreamState = iota
	StateConnecting
	StateEstablished
	StateClosing
	StateClosed
)

// Config holds stream configuration
type Config struct {
	SessionID       uint32
	CRCKey          uint32
	MaxPacketSize   uint16
	EncodeKey       int
	DecodeKey       int
	OpcodeManager   opcodes.Manager
	OpcodeSize      uint8
	AckThreshold    time.Duration
	KeepaliveTime   time.Duration
	TimeoutDuration time.Duration
}

// NewStream creates a new EQStream instance
func NewStream(conn gnet.Conn, cfg *Config) *Stream {
	s := &Stream{
		conn:          conn,
		sessionID:     cfg.SessionID,
		crcKey:        cfg.CRCKey,
		maxLen:        cfg.MaxPacketSize,
		encodeKey:     cfg.EncodeKey,
		decodeKey:     cfg.DecodeKey,
		opcodeManager: cfg.OpcodeManager,
		opcodeSize:    cfg.OpcodeSize,
		ackThreshold:  cfg.AckThreshold,
		pendingAcks:   make(map[uint16]*pendingPacket),
		fragments:     make(map[uint16]*fragmentBuffer),
		seqOut:        0,
		seqIn:         0,
	}

	if s.maxLen == 0 {
		s.maxLen = packets.DefaultMTU
	}
	if s.ackThreshold == 0 {
		s.ackThreshold = 200 * time.Millisecond
	}

	s.state.Store(StateDisconnected)

	// Initialize cipher if keys provided
	if cfg.EncodeKey != 0 || cfg.DecodeKey != 0 {
		cipher, _ := crypto.NewCiphers(int64(cfg.EncodeKey))
		s.cipher = cipher
	}

	// Start keepalive timer
	if cfg.KeepaliveTime > 0 {
		s.keepAliveTimer = time.AfterFunc(cfg.KeepaliveTime, s.sendKeepalive)
	}

	return s
}

// Process handles incoming data from gnet
func (s *Stream) Process(data []byte) error {
	// Validate CRC
	if len(data) < 2 {
		return nil
	}

	// Check for CRC (last 2 bytes)
	if len(data) > 2 {
		providedCRC := binary.BigEndian.Uint16(data[len(data)-2:])
		calculatedCRC := crypto.CalculateCRC(data[:len(data)-2], s.crcKey)
		if providedCRC != calculatedCRC {
			return nil // Drop packet with bad CRC
		}
		data = data[:len(data)-2] // Strip CRC
	}

	// Decrypt if needed
	if s.cipher != nil {
		s.cipher.Decrypt(data)
	}

	// Parse protocol opcode
	if len(data) < 2 {
		return nil
	}
	opcode := binary.BigEndian.Uint16(data[:2])

	switch opcode {
	case opcodes.OP_SessionRequest:
		return s.handleSessionRequest(data[2:])
	case opcodes.OP_SessionResponse:
		return s.handleSessionResponse(data[2:])
	case opcodes.OP_Packet:
		return s.handlePacket(data[2:])
	case opcodes.OP_Fragment:
		return s.handleFragment(data[2:])
	case opcodes.OP_Ack:
		return s.handleAck(data[2:])
	case opcodes.OP_Combined:
		return s.handleCombined(data[2:])
	case opcodes.OP_AppCombined:
		return s.handleAppCombined(data[2:])
	case opcodes.OP_KeepAlive:
		s.resetTimeout()
		return nil
	case opcodes.OP_SessionDisconnect:
		return s.handleDisconnect()
	}

	atomic.AddUint64(&s.packetsIn, 1)
	atomic.AddUint64(&s.bytesIn, uint64(len(data)))

	return nil
}

// handlePacket processes reliable packets
func (s *Stream) handlePacket(data []byte) error {
	if len(data) < 2 {
		return nil
	}

	seq := binary.BigEndian.Uint16(data[:2])
	data = data[2:]

	s.mu.Lock()
	defer s.mu.Unlock()

	// Check sequence
	if seq != s.seqIn {
		// Out of order - send immediate ACK
		s.sendAckImmediate(seq)
		return nil
	}

	// Update sequence
	s.seqIn++

	// Schedule ACK
	s.scheduleAck(seq)

	// Process packet data
	return s.processPacketData(data)
}

// handleFragment assembles fragmented packets
func (s *Stream) handleFragment(data []byte) error {
	if len(data) < 8 {
		return nil
	}

	seq := binary.BigEndian.Uint16(data[:2])
	fragSeq := binary.BigEndian.Uint16(data[2:4])
	fragTotal := binary.BigEndian.Uint16(data[4:6])
	fragCur := binary.BigEndian.Uint16(data[6:8])
	data = data[8:]

	s.mu.Lock()
	defer s.mu.Unlock()

	// Get or create fragment buffer
	frag, exists := s.fragments[fragSeq]
	if !exists {
		frag = &fragmentBuffer{
			totalSize: uint32(fragTotal),
			chunks:    make(map[uint16][]byte),
			startTime: time.Now(),
		}
		s.fragments[fragSeq] = frag
	}

	// Store chunk
	frag.chunks[fragCur] = append([]byte(nil), data...)
	frag.received++

	// Check if complete
	if frag.received == uint32(fragTotal) {
		// Reassemble
		complete := make([]byte, 0)
		for i := uint16(0); i < fragTotal; i++ {
			if chunk, ok := frag.chunks[i]; ok {
				complete = append(complete, chunk...)
			}
		}
		delete(s.fragments, fragSeq)

		// Process reassembled packet
		return s.processPacketData(complete)
	}

	// Schedule ACK for fragment
	s.scheduleAck(seq)

	return nil
}

// handleAck processes acknowledgments
func (s *Stream) handleAck(data []byte) error {
	if len(data) < 2 {
		return nil
	}

	ackSeq := binary.BigEndian.Uint16(data[:2])

	s.mu.Lock()
	defer s.mu.Unlock()

	// Remove from pending
	if pending, exists := s.pendingAcks[ackSeq]; exists {
		delete(s.pendingAcks, ackSeq)
		// Update RTT stats here if needed
		_ = pending
	}

	// Update last ACK seen
	if ackSeq > s.seqLastAck {
		s.seqLastAck = ackSeq
	}

	return nil
}

// SendPacket sends an application packet
func (s *Stream) SendPacket(app *packets.AppPacket) error {
	// Convert to protocol packet
	proto := s.appToProto(app)

	// Check if needs fragmentation
	if proto.Size() > uint32(s.maxLen) {
		return s.sendFragmented(proto)
	}

	// Add to appropriate queue
	if app.Priority > packets.PriorityNormal {
		s.mu.Lock()
		s.reliableQueue = append(s.reliableQueue, proto)
		s.mu.Unlock()
	} else {
		s.mu.Lock()
		s.unreliableQueue = append(s.unreliableQueue, proto)
		s.mu.Unlock()
	}

	// Process queues
	return s.processQueues()
}

// sendReliable sends a reliable packet with sequence number
func (s *Stream) sendReliable(proto *packets.ProtoPacket) error {
	s.mu.Lock()
	seq := s.seqOut
	s.seqOut++
	s.mu.Unlock()

	// Build packet with sequence
	data := make([]byte, proto.Size()+2)
	binary.BigEndian.PutUint16(data[:2], seq)
	proto.Serialize(data[2:], 0)

	// Track for retransmission
	pending := &pendingPacket{
		packet:    proto,
		seq:       seq,
		sentTime:  time.Now(),
		attempts:  1,
		nextRetry: time.Now().Add(time.Second),
	}

	s.mu.Lock()
	s.pendingAcks[seq] = pending
	s.mu.Unlock()

	// Send with protocol header
	return s.sendRaw(opcodes.OP_Packet, data)
}

// sendRaw sends raw data with protocol opcode
func (s *Stream) sendRaw(opcode uint16, data []byte) error {
	// Build packet: opcode + data + CRC
	packet := make([]byte, 2+len(data)+2)
	binary.BigEndian.PutUint16(packet[:2], opcode)
	copy(packet[2:], data)

	// Add CRC
	crc := crypto.CalculateCRC(packet[:len(packet)-2], s.crcKey)
	binary.BigEndian.PutUint16(packet[len(packet)-2:], crc)

	// Encrypt if needed
	if s.cipher != nil {
		s.cipher.Encrypt(packet)
	}

	// Send via gnet
	atomic.AddUint64(&s.packetsOut, 1)
	atomic.AddUint64(&s.bytesOut, uint64(len(packet)))

	return s.conn.AsyncWrite(packet, nil)
}

// Helper methods

func (s *Stream) processPacketData(data []byte) error {
	// Create ProtoPacket from raw data
	proto := packets.NewProtoPacketFromRaw(data, -1, s.opcodeManager)

	// Decompress if needed
	proto.DecompressPacket()

	// Convert to AppPacket
	app := proto.MakeApplicationPacket(s.opcodeSize)

	// Deliver to callback
	if s.onPacket != nil {
		s.onPacket(app)
	}

	return nil
}

func (s *Stream) scheduleAck(seq uint16) {
	if s.ackTimer == nil {
		s.ackTimer = time.AfterFunc(s.ackThreshold, func() {
			s.sendAckImmediate(seq)
		})
	}
}

func (s *Stream) sendAckImmediate(seq uint16) error {
	data := make([]byte, 2)
	binary.BigEndian.PutUint16(data, seq)
	return s.sendRaw(opcodes.OP_Ack, data)
}

func (s *Stream) sendKeepalive() {
	s.sendRaw(opcodes.OP_KeepAlive, nil)
	// Reschedule
	if s.keepAliveTimer != nil {
		s.keepAliveTimer.Reset(10 * time.Second)
	}
}

func (s *Stream) resetTimeout() {
	if s.timeoutTimer != nil {
		s.timeoutTimer.Reset(30 * time.Second)
	}
}

func (s *Stream) appToProto(app *packets.AppPacket) *packets.ProtoPacket {
	proto := packets.NewProtoPacket(app.Opcode, app.Buffer, s.opcodeManager)
	proto.CopyInfo(app.Packet)
	return proto
}

func (s *Stream) processQueues() error {
	// Process reliable queue first
	s.mu.Lock()
	for len(s.reliableQueue) > 0 {
		proto := s.reliableQueue[0]
		s.reliableQueue = s.reliableQueue[1:]
		s.mu.Unlock()
		if err := s.sendReliable(proto); err != nil {
			return err
		}
		s.mu.Lock()
	}
	s.mu.Unlock()

	return nil
}

func (s *Stream) sendFragmented(proto *packets.ProtoPacket) error {
	// Fragment implementation
	return nil // TODO
}

func (s *Stream) handleSessionRequest(data []byte) error {
	// Session setup
	s.state.Store(StateConnecting)
	return nil
}

func (s *Stream) handleSessionResponse(data []byte) error {
	s.state.Store(StateEstablished)
	return nil
}

func (s *Stream) handleCombined(data []byte) error {
	// Process combined packets
	return nil
}

func (s *Stream) handleAppCombined(data []byte) error {
	// Process app-combined packets
	return nil
}

func (s *Stream) handleDisconnect() error {
	s.state.Store(StateClosed)
	if s.onDisconnect != nil {
		s.onDisconnect()
	}
	return nil
}

// SetPacketCallback sets the callback for received packets
func (s *Stream) SetPacketCallback(fn func(*packets.AppPacket)) {
	s.onPacket = fn
}

// Close closes the stream
func (s *Stream) Close() error {
	s.state.Store(StateClosed)
	// Send disconnect
	s.sendRaw(opcodes.OP_SessionDisconnect, nil)
	// Clean up timers
	if s.keepAliveTimer != nil {
		s.keepAliveTimer.Stop()
	}
	if s.ackTimer != nil {
		s.ackTimer.Stop()
	}
	return nil
}