package json

import (
	"encoding/json"
	"io"
	"sync"

	"git.loafle.net/commons_go/rpc/codec"
	"git.loafle.net/commons_go/rpc/protocol"
)

// ----------------------------------------------------------------------------
// Request
// ----------------------------------------------------------------------------

// serverRequest represents a JSON-RPC request received by the server.
type serverRequest struct {
	// JSON-RPC protocol.
	Version string `json:"jsonrpc"`

	// A String containing the name of the method to be invoked.
	Method string `json:"method"`

	// A Structured value to pass as arguments to the method.
	Params *json.RawMessage `json:"params,omitempty"`

	// The request id. MUST be a string, number or null.
	// Our implementation will not do type checking for id.
	// It will be copied as it is.
	ID *json.RawMessage `json:"id,omitempty"`
}

// ----------------------------------------------------------------------------
// ServerRequestCodec
// ----------------------------------------------------------------------------

// newRequestCodec returns a new ServerRequestCodec.
func newServerRequestCodec(r io.Reader, codec codec.Codec) (protocol.ServerRequestCodec, error) {
	// Decode the request body and check if RPC method is valid.
	req := retainServerRequest()
	err := json.NewDecoder(r).Decode(req)
	if err == io.ErrUnexpectedEOF || err == io.EOF {
		return nil, err
	}
	if err != nil {
		err = &Error{
			Code:    E_PARSE,
			Message: err.Error(),
			Data:    req,
		}
	}
	if req.Version != Version {
		err = &Error{
			Code:    E_INVALID_REQ,
			Message: "jsonrpc must be " + Version,
			Data:    req,
		}
	}

	return retainServerRequestCodec(req, err, codec), nil
}

// ServerRequestCodec decodes and encodes a single request.
type ServerRequestCodec struct {
	req   *serverRequest
	err   error
	codec codec.Codec
}

// Close is callback function that end of request.
func (src *ServerRequestCodec) Close() {
	if nil != src.req {
		releaseServerRequest(src.req)
	}
	releaseServerRequestCodec(src)
}

// Method returns the RPC method for the current request.
//
// The method uses a dotted notation as in "Service.Method".
func (src *ServerRequestCodec) Method() string {
	return src.req.Method
}

// ReadRequest fills the request object for the RPC method.
//
// ReadRequest parses request parameters in two supported forms in
// accordance with http://www.jsonrpc.org/specification#parameter_structures
//
// by-position: params MUST be an Array, containing the
// values in the Server expected order.
//
// by-name: params MUST be an Object, with member names
// that match the Server expected parameter names. The
// absence of expected names MAY result in an error being
// generated. The names MUST match exactly, including
// case, to the method's expected parameters.
func (src *ServerRequestCodec) ReadParams(args []interface{}) error {
	if src.err == nil && src.req.Params != nil {
		// Note: if src.req.Params is nil it's not an error, it's an optional member.
		// JSON params structured object. Unmarshal to the args object.

		// if err := json.Unmarshal(*src.req.Params, &args); err != nil {
		// 	// Clearly JSON params is not a structured object,
		// 	// fallback and attempt an unmarshal with JSON params as
		// 	// array value and RPC params is struct. Unmarshal into
		// 	// array containing the request struct.
		// 	src.err = &Error{
		// 		Code:    E_INVALID_REQ,
		// 		Message: err.Error(),
		// 		Data:    src.req.Params,
		// 	}
		// }
		raws := make([]json.RawMessage, len(args))
		if err := json.Unmarshal(*src.req.Params, &raws); err != nil {
			src.err = &Error{
				Code:    E_INVALID_REQ,
				Message: err.Error(),
				Data:    src.req.Params,
			}
			return src.err
		}

		for indexI := 0; indexI < len(args); indexI++ {
			raw := raws[indexI]
			arg := args[indexI]
			if err := json.Unmarshal(raw, &arg); err != nil {
				src.err = &Error{
					Code:    E_INVALID_REQ,
					Message: err.Error(),
					Data:    src.req.Params,
				}
				return src.err
			}
		}
	}
	return src.err
}

func (src *ServerRequestCodec) Params() ([]string, error) {
	if src.err == nil && src.req.Params != nil {
		var results []string

		if err := json.Unmarshal(*src.req.Params, &results); err != nil {
			src.err = &Error{
				Code:    E_INVALID_REQ,
				Message: err.Error(),
				Data:    src.req.Params,
			}
			return nil, src.err
		}

		return results, nil
	}
	return nil, src.err
}

// WriteResponse encodes the response and writes it to the ResponseWriter.
func (src *ServerRequestCodec) WriteResponse(w io.Writer, reply interface{}) error {
	res := retainServerResponse(reply, nil, src.req.ID)
	return src.writeServerResponse(w, res)
}

// WriteError encodes the response and writes it to the ResponseWriter.
func (src *ServerRequestCodec) WriteError(w io.Writer, status int, err error) error {
	jsonErr, ok := err.(*Error)
	if !ok {
		jsonErr = &Error{
			Code:    E_SERVER,
			Message: err.Error(),
		}
	}
	res := retainServerResponse(nil, jsonErr, src.req.ID)
	return src.writeServerResponse(w, res)
}

func (src *ServerRequestCodec) writeServerResponse(w io.Writer, res *serverResponse) error {
	defer func() {
		releaseServerResponse(res)
	}()
	// ID is null for notifications and they don't have a response.
	if src.req.ID != nil {
		msg := retainServerMessage(protocol.MessageTypeResponse, res)
		defer func() {
			releaseServerMessage(msg)
		}()
		encoder := json.NewEncoder(src.codec.Encode(w))
		// Not sure in which case will this happen. But seems harmless.
		if err := encoder.Encode(msg); nil != err {
			return err
		}
	}
	return nil
}

var serverRequestCodecPool sync.Pool

func retainServerRequestCodec(req *serverRequest, err error, codec codec.Codec) *ServerRequestCodec {
	var src *ServerRequestCodec
	v := serverRequestCodecPool.Get()
	if v == nil {
		src = &ServerRequestCodec{}
	} else {
		src = v.(*ServerRequestCodec)
	}

	src.req = req
	src.err = err
	src.codec = codec

	return src
}

func releaseServerRequestCodec(src *ServerRequestCodec) {
	src.req = nil
	src.err = nil
	src.codec = nil

	serverRequestCodecPool.Put(src)
}

var serverRequestPool sync.Pool

func retainServerRequest() *serverRequest {
	v := serverRequestPool.Get()
	if v == nil {
		return &serverRequest{}
	}
	return v.(*serverRequest)
}

func releaseServerRequest(sr *serverRequest) {
	sr.Method = ""
	sr.Params = nil
	sr.ID = nil

	serverRequestPool.Put(sr)
}