package json

import (
	"encoding/json"
	"io"

	"git.loafle.net/commons_go/rpc/codec"
	"git.loafle.net/commons_go/rpc/protocol"
	crp "git.loafle.net/commons_go/rpc/protocol"
	cuej "git.loafle.net/commons_go/util/encoding/json"
)

// ----------------------------------------------------------------------------
// 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.
	decoder := json.NewDecoder(r)
	if nil == r {
		return nil, io.EOF
	}

	req := &serverRequest{}
	err := decoder.Decode(req)
	if err == io.ErrUnexpectedEOF || err == io.EOF {
		return nil, err
	}
	if err != nil {
		err = &Error{
			Code:    crp.E_PARSE,
			Message: err.Error(),
			Data:    req,
		}
	}
	if req.Version != Version {
		err = &Error{
			Code:    crp.E_INVALID_REQ,
			Message: "jsonrpc must be " + Version,
			Data:    req,
		}
	}

	return &ServerRequestCodec{req: req, err: err, codec: codec}, nil
}

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

// 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 scr.request.Params is nil it's not an error, it's an optional member.
		// JSON params structured object. Unmarshal to the args object.
		if err := cuej.SetValueWithJSONStringArray(*src.req.Params, args); nil != err {
			src.err = &Error{
				Code:    crp.E_INVALID_REQ,
				Message: err.Error(),
				Data:    src.req.Params,
			}
			return src.err
		}
		return nil
	}
	return src.err
}

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

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

		return values, 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 := &serverResponse{Version: Version, Result: reply, ID: 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:    crp.E_SERVER,
			Message: err.Error(),
		}
	}
	res := &serverResponse{Version: Version, Error: jsonErr, ID: src.req.ID}
	return src.writeServerResponse(w, res)
}

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