package toki_socket

import (
	"errors"
	"fmt"
	"reflect"
	"sync"
	"sync/atomic"
	"time"

	"google.golang.org/protobuf/proto"

	"toki-labs.com/toki_socket/go/packets"
)

var ErrNotConnected = errors.New("not connected")

type ParserMap map[string]func([]byte) (proto.Message, error)

type Transport interface {
	WritePacket(base *packets.PacketBase) error
	Close() error
}

type pendingRequest struct {
	expectedTypeName string
	ch               chan proto.Message
	errCh            chan error
}

type queuedPacket struct {
	base *packets.PacketBase
	done chan error
}

type Communicator struct {
	mu              sync.RWMutex
	nonce           atomic.Int32
	isAlive         atomic.Bool
	parserMap       ParserMap
	handlers        map[string][]func(proto.Message)
	reqHandlers     map[string]func(proto.Message, int32)
	pendingRequests map[int32]*pendingRequest
	writeQueue      chan queuedPacket
	closed          chan struct{}
	closeOnce       sync.Once
	transport       Transport
	writeErrHandler func(error)
}

func TypeNameOf(m proto.Message) string {
	return string(proto.MessageName(m))
}

func NewCommunicator(transport Transport, parserMap ParserMap) *Communicator {
	c := &Communicator{}
	c.Initialize(transport, parserMap)
	return c
}

func (c *Communicator) Initialize(transport Transport, parserMap ParserMap) {
	c.transport = transport
	c.parserMap = make(ParserMap, len(parserMap)+1)
	for k, v := range parserMap {
		c.parserMap[k] = v
	}
	c.parserMap[TypeNameOf(&packets.HeartBeat{})] = func(b []byte) (proto.Message, error) {
		m := &packets.HeartBeat{}
		return m, proto.Unmarshal(b, m)
	}
	c.handlers = make(map[string][]func(proto.Message))
	c.reqHandlers = make(map[string]func(proto.Message, int32))
	c.pendingRequests = make(map[int32]*pendingRequest)
	c.writeQueue = make(chan queuedPacket, 64)
	c.closed = make(chan struct{})
	c.isAlive.Store(true)
	go c.writeLoop()
}

func (c *Communicator) IsAlive() bool {
	return c.isAlive.Load()
}

func (c *Communicator) SetWriteErrorHandler(fn func(error)) {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.writeErrHandler = fn
}

func (c *Communicator) nextNonce() int32 {
	return c.nonce.Add(1)
}

func (c *Communicator) shutdown() {
	c.isAlive.Store(false)
	c.closeOnce.Do(func() {
		close(c.closed)
	})
}

func (c *Communicator) writeLoop() {
	for {
		select {
		case item := <-c.writeQueue:
			err := c.transport.WritePacket(item.base)
			item.done <- err
			if err != nil {
				c.mu.RLock()
				handler := c.writeErrHandler
				c.mu.RUnlock()
				if handler != nil {
					handler(err)
				}
			}
		case <-c.closed:
			return
		}
	}
}

func (c *Communicator) QueuePacket(base *packets.PacketBase) error {
	if !c.IsAlive() {
		return ErrNotConnected
	}
	done := make(chan error, 1)
	select {
	case c.writeQueue <- queuedPacket{base: base, done: done}:
	case <-c.closed:
		return ErrNotConnected
	}
	select {
	case err := <-done:
		return err
	case <-c.closed:
		return ErrNotConnected
	}
}

func (c *Communicator) Send(m proto.Message) error {
	if !c.IsAlive() {
		return ErrNotConnected
	}
	data, err := proto.Marshal(m)
	if err != nil {
		return err
	}
	return c.QueuePacket(&packets.PacketBase{
		TypeName: TypeNameOf(m),
		Nonce:    c.nextNonce(),
		Data:     data,
	})
}

func (c *Communicator) SendRequest(req proto.Message, resType proto.Message, timeout time.Duration) (proto.Message, error) {
	if !c.IsAlive() {
		return nil, ErrNotConnected
	}
	if timeout <= 0 {
		timeout = 30 * time.Second
	}

	requestNonce := c.nextNonce()
	pending := &pendingRequest{
		expectedTypeName: TypeNameOf(resType),
		ch:               make(chan proto.Message, 1),
		errCh:            make(chan error, 1),
	}

	c.mu.Lock()
	c.pendingRequests[requestNonce] = pending
	c.mu.Unlock()

	data, err := proto.Marshal(req)
	if err != nil {
		c.removePending(requestNonce)
		return nil, err
	}
	err = c.QueuePacket(&packets.PacketBase{
		TypeName: TypeNameOf(req),
		Nonce:    requestNonce,
		Data:     data,
	})
	if err != nil {
		c.removePending(requestNonce)
		return nil, err
	}

	timer := time.NewTimer(timeout)
	defer timer.Stop()

	select {
	case res := <-pending.ch:
		return res, nil
	case err := <-pending.errCh:
		return nil, err
	case <-timer.C:
		c.removePending(requestNonce)
		return nil, fmt.Errorf("request timeout for nonce %d", requestNonce)
	case <-c.closed:
		c.removePending(requestNonce)
		return nil, ErrNotConnected
	}
}

func (c *Communicator) AddListener(typeName string, fn func(proto.Message)) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if _, ok := c.reqHandlers[typeName]; ok {
		panic(fmt.Sprintf("type %s is already registered with AddRequestListener", typeName))
	}
	c.handlers[typeName] = append(c.handlers[typeName], fn)
}

func (c *Communicator) RemoveListeners(typeName string) {
	c.mu.Lock()
	defer c.mu.Unlock()
	delete(c.handlers, typeName)
}

func (c *Communicator) AddRequestListener(typeName string, fn func(proto.Message, int32)) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if len(c.handlers[typeName]) > 0 {
		panic(fmt.Sprintf("type %s is already registered with AddListener", typeName))
	}
	if _, ok := c.reqHandlers[typeName]; ok {
		panic(fmt.Sprintf("type %s is already registered with AddRequestListener", typeName))
	}
	c.reqHandlers[typeName] = fn
}

func (c *Communicator) OnReceivedData(typeName string, data []byte, incomingNonce, responseNonce int32) {
	if responseNonce > 0 {
		c.handleResponse(typeName, data, responseNonce)
		return
	}

	c.mu.RLock()
	reqHandler := c.reqHandlers[typeName]
	listeners := append([]func(proto.Message){}, c.handlers[typeName]...)
	c.mu.RUnlock()

	if reqHandler != nil {
		msg, err := c.parse(typeName, data)
		if err != nil {
			return
		}
		go reqHandler(msg, incomingNonce)
		return
	}

	if len(listeners) == 0 {
		return
	}
	msg, err := c.parse(typeName, data)
	if err != nil {
		return
	}
	for _, listener := range listeners {
		listener(msg)
	}
}

func (c *Communicator) handleResponse(typeName string, data []byte, responseNonce int32) {
	pending := c.removePending(responseNonce)
	if pending == nil {
		return
	}
	if typeName != pending.expectedTypeName {
		pending.errCh <- fmt.Errorf("response type mismatch for nonce %d: expected %s, got %s", responseNonce, pending.expectedTypeName, typeName)
		return
	}
	msg, err := c.parse(typeName, data)
	if err != nil {
		pending.errCh <- err
		return
	}
	pending.ch <- msg
}

func (c *Communicator) parse(typeName string, data []byte) (proto.Message, error) {
	c.mu.RLock()
	parser := c.parserMap[typeName]
	c.mu.RUnlock()
	if parser == nil {
		return nil, fmt.Errorf("protobuf parser is not registered for type %s", typeName)
	}
	return parser(data)
}

func (c *Communicator) removePending(nonce int32) *pendingRequest {
	c.mu.Lock()
	defer c.mu.Unlock()
	pending := c.pendingRequests[nonce]
	delete(c.pendingRequests, nonce)
	return pending
}

func AddListenerTyped[T proto.Message](c *Communicator, fn func(T)) {
	typeName := TypeNameOf(newMessageOf[T]())
	c.AddListener(typeName, func(m proto.Message) {
		typed, ok := m.(T)
		if !ok {
			panic(fmt.Sprintf("received %T for listener %s", m, typeName))
		}
		fn(typed)
	})
}

func AddRequestListenerTyped[Req proto.Message, Res proto.Message](c *Communicator, fn func(Req) (Res, error)) {
	reqTypeName := TypeNameOf(newMessageOf[Req]())
	c.AddRequestListener(reqTypeName, func(m proto.Message, requestNonce int32) {
		req, ok := m.(Req)
		if !ok {
			return
		}
		res, err := fn(req)
		if err != nil || !c.IsAlive() {
			return
		}
		data, err := proto.Marshal(res)
		if err != nil {
			return
		}
		_ = c.QueuePacket(&packets.PacketBase{
			TypeName:      TypeNameOf(res),
			Nonce:         c.nextNonce(),
			ResponseNonce: requestNonce,
			Data:          data,
		})
	})
}

func SendRequestTyped[Req proto.Message, Res proto.Message](c *Communicator, req Req, timeout time.Duration) (Res, error) {
	resType := newMessageOf[Res]()
	msg, err := c.SendRequest(req, resType, timeout)
	if err != nil {
		var zero Res
		return zero, err
	}
	res, ok := msg.(Res)
	if !ok {
		var zero Res
		return zero, fmt.Errorf("received %T, expected %T", msg, resType)
	}
	return res, nil
}

func newMessageOf[T proto.Message]() T {
	var zero T
	t := reflect.TypeOf(zero)
	if t == nil || t.Kind() != reflect.Ptr {
		panic("protobuf type parameter must be a pointer message type")
	}
	return reflect.New(t.Elem()).Interface().(T)
}