package rpc

import (
	
	
	
	

	
	

	
	
)

// Engine handles RPC requests.
type Engine struct {
	send Send
	drop DropHandler

	mux sync.Mutex
	rpc map[int64]func(*bin.Buffer, error) error
	ack map[int64]chan struct{}

	clock         clock.Clock
	log           *zap.Logger
	retryInterval time.Duration
	maxRetries    int

	// Canceling pending requests in ForceClose.
	reqCtx    context.Context
	reqCancel context.CancelFunc

	wg     sync.WaitGroup
	closed uint32
}

// New creates new rpc Engine.
func ( Send,  Options) *Engine {
	.setDefaults()

	.Logger.Info("Initialized",
		zap.Duration("retry_interval", .RetryInterval),
		zap.Int("max_retries", .MaxRetries),
	)

	,  := context.WithCancel(context.Background())
	return &Engine{
		rpc: map[int64]func(*bin.Buffer, error) error{},
		ack: map[int64]chan struct{}{},

		send: ,
		drop: .DropHandler,

		log:           .Logger,
		maxRetries:    .MaxRetries,
		retryInterval: .RetryInterval,
		clock:         .Clock,

		reqCtx:    ,
		reqCancel: ,
	}
}

// Request represents client RPC request.
type Request struct {
	MsgID  int64
	SeqNo  int32
	Input  bin.Encoder
	Output bin.Decoder
}

// Do sends request to server and blocks until response is received, performing
// multiple retries if needed.
func ( *Engine) ( context.Context,  Request) error {
	if .isClosed() {
		return ErrEngineClosed
	}

	.wg.Add(1)
	defer .wg.Done()

	,  := context.WithCancel()
	defer ()

	 := .log.With(zap.Int64("msg_id", .MsgID))
	.Debug("Do called")

	 := make(chan struct{})

	var (
		// Handler result.
		 error
		// Needed to prevent multiple handler calls.
		 uint32
	)

	 := func( *bin.Buffer,  error) error {
		.Debug("Handler called")

		if  := atomic.CompareAndSwapUint32(&, 0, 1); ! {
			.Warn("Handler already called")

			return errors.New("handler already called")
		}

		defer ()
		defer close()

		if  != nil {
			 = 
			return nil
		}

		 = .Output.Decode()
		return 
	}

	// Setting callback that will be called if message is received.
	.mux.Lock()
	.rpc[.MsgID] = 
	.mux.Unlock()

	defer func() {
		// Ensuring that callback can't be called after function return.
		.mux.Lock()
		delete(.rpc, .MsgID)
		.mux.Unlock()
	}()

	// Start retrying.
	,  := .retryUntilAck(, )
	if  != nil && !errors.Is(, .Err()) {
		// If the retryCtx was canceled, then one of two things happened:
		//   1. User canceled the parent context.
		//   2. The RPC result came and callback canceled retryCtx.
		//
		// If this is not a Context’s error, most likely we did not receive ack
		// and exceeded the limit of attempts to send a request,
		// or could not write data to the connection, so we return an error.
		return errors.Wrap(, "retryUntilAck")
	}

	select {
	case <-.Done():
		if ! {
			return .Err()
		}

		// Set nop callback because server will respond with 'RpcDropAnswer' instead of expected result.
		//
		// NOTE(ccln): We can decode 'RpcDropAnswer' here but I see no reason to do this
		// because it will also come as a response to 'RPCDropAnswerRequest'.
		//
		// https://core.telegram.org/mtproto/service_messages#cancellation-of-an-rpc-query
		.mux.Lock()
		.rpc[.MsgID] = func( *bin.Buffer,  error) error { return nil }
		.mux.Unlock()

		if  := .drop();  != nil {
			.Info("Failed to drop request", zap.Error())
			return .Err()
		}

		.Debug("Request dropped")
		return .Err()
	case <-.reqCtx.Done():
		return errors.Wrap(.reqCtx.Err(), "engine forcibly closed")
	case <-:
		return 
	}
}

// retryUntilAck resends the request to the server until request is
// acknowledged.
//
// Returns nil if acknowledge was received or error otherwise.
func ( *Engine) ( context.Context,  Request) ( bool,  error) {
	,  := context.WithCancel()
	defer ()

	var (
		 = .waitAck(.MsgID)
		 = 0
		     = .log.Named("retry").With(zap.Int64("msg_id", .MsgID))
	)

	defer .removeAck(.MsgID)

	// Encoding request.
	if  := .send(, .MsgID, .SeqNo, .Input);  != nil {
		return false, errors.Wrap(, "send")
	}

	 := func() error {
		 := .clock.Timer(.retryInterval)
		defer clock.StopTimer()

		for {
			select {
			case <-.Done():
				return .Err()
			case <-.reqCtx.Done():
				return errors.Wrap(.reqCtx.Err(), "engine forcibly closed")
			case <-:
				.Debug("Acknowledged")
				return nil
			case <-.C():
				.Reset(.retryInterval)

				.Debug("Acknowledge timed out, performing retry")
				if  := .send(, .MsgID, .SeqNo, .Input);  != nil {
					if errors.Is(, context.Canceled) {
						return nil
					}

					.Error("Retry failed", zap.Error())
					return 
				}

				++
				if  >= .maxRetries {
					.Error("Retry limit reached", zap.Int64("msg_id", .MsgID))
					return &RetryLimitReachedErr{
						Retries: ,
					}
				}
			}
		}
	}

	return true, ()
}

// NotifyResult notifies engine about received RPC response.
func ( *Engine) ( int64,  *bin.Buffer) error {
	.mux.Lock()
	,  := .rpc[]
	.mux.Unlock()
	if ! {
		.log.Warn("rpc callback not set", zap.Int64("msg_id", ))
		return nil
	}

	return (, nil)
}

// NotifyError notifies engine about received RPC error.
func ( *Engine) ( int64,  error) {
	.mux.Lock()
	,  := .rpc[]
	.mux.Unlock()
	if ! {
		.log.Warn("rpc callback not set", zap.Int64("msg_id", ))
		return
	}

	// Callback with rpcError always return nil.
	_ = (nil, )
}

func ( *Engine) () bool {
	return atomic.LoadUint32(&.closed) == 1
}

// Close gracefully closes the engine.
// All pending requests will be awaited.
// All Do method calls of closed engine will return ErrEngineClosed error.
func ( *Engine) () {
	atomic.StoreUint32(&.closed, 1)
	.log.Info("Close called")
	.wg.Wait()
}

// ForceClose forcibly closes the engine.
// All pending requests will be canceled.
// All Do method calls of closed engine will return ErrEngineClosed error.
func ( *Engine) () {
	.reqCancel()
	.Close()
}