/*
 * Copyright 2015, The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package rpc

import (
	"bufio"
	"io"

	"android.googlesource.com/platform/tools/gpu/binary"
	"android.googlesource.com/platform/tools/gpu/log"
	"android.googlesource.com/platform/tools/gpu/multiplexer"
)

// Handler is the signature for a function that handles incoming rpc calls.
type Handler func(interface{}) binary.Encodable

// Server implements the receiving side of a client server rpc pair.
// It listens on the reader for calls, and dispatches them to the supplied handler.
// Any result returned from the handler is then sent back down the writer.
func Serve(logger log.Logger, r io.Reader, w io.Writer, mtu int, handler Handler) {
	multiplexer.New(r, w, mtu, func(channel io.ReadWriteCloser) {
		// If Close fails, multiplexer already knows, so we ignore the error
		defer channel.Close()

		w := bufio.NewWriterSize(channel, mtu)
		// Flush only fails if channel fails, multiplexer already knows, so we ignore the error
		defer w.Flush()

		d := binary.NewDecoder(channel)
		e := binary.NewEncoder(w)

		// Check the RPC header
		if val, err := d.Uint32(); val != header || err != nil {
			logger.Error("%v", ErrInvalidHeader)
			e.Object(ErrInvalidHeader)
			return
		}

		// Decode the call
		val, err := d.Object()
		if err != nil {
			logger.Error("Error decoding call: %v", err)
			e.Object(NewError("Failed to decode call. Reason: %v", err))
			return
		}

		// Invoke the call
		res := handler(val)

		// Encode the call result
		if err := e.Object(res); err != nil {
			logger.Error("Error encoding result for %T: %v", val, err)
			e.Object(NewError("Failed to encode call result. Reason: %v", err))
			return
		}
	})
}