// Copyright 2009 The Go Authors. All rights reserved.
// Copyright 2012-2013 The Gorilla Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package json

import (
	"encoding/json"
	"fmt"
	"io"
	"math/rand"
)

// ----------------------------------------------------------------------------
// Request and Response
// ----------------------------------------------------------------------------

// clientRequest represents a JSON-RPC request sent by a client.
type clientRequest struct {
	// A String containing the name of the method to be invoked.
	Method string `json:"method"`
	// Object to pass as request parameter to the method.
	Params [1]interface{} `json:"params"`
	// The request id. This can be of any type. It is used to match the
	// response with the request that it is replying to.
	Id uint64 `json:"id"`
}

// clientResponse represents a JSON-RPC response returned to a client.
type clientResponse struct {
	Result *json.RawMessage `json:"result"`
	Error  interface{}      `json:"error"`
	Id     uint64           `json:"id"`
}

// EncodeClientRequest encodes parameters for a JSON-RPC client request.
func EncodeClientRequest(method string, args interface{}) ([]byte, error) {
	c := &clientRequest{
		Method: method,
		Params: [1]interface{}{args},
		Id:     uint64(rand.Int63()),
	}
	return json.Marshal(c)
}

// DecodeClientResponse decodes the response body of a client request into
// the interface reply.
func DecodeClientResponse(r io.Reader, reply interface{}) error {
	var c clientResponse
	if err := json.NewDecoder(r).Decode(&c); err != nil {
		return err
	}
	if c.Error != nil {
		return &Error{Data: c.Error}
	}
	if c.Result == nil {
		return fmt.Errorf("Unexpected null result")
	}
	return json.Unmarshal(*c.Result, reply)
}