/*
Copyright 2022 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

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 protocol handles the protocol message marshaling and unmarshalling.
package protocol

import (
	"errors"
	"fmt"

	"github.com/shamaton/msgpackgen/msgpack"
	"github.com/sirupsen/logrus"

	"git.cacert.org/cacert-gosigner/pkg/x509/revoking"

	"git.cacert.org/cacert-gosigner/pkg/health"
	"git.cacert.org/cacert-gosigner/pkg/messages"
)

// Handler is responsible for parsing incoming frames and calling commands
type Handler interface {
	HandleCommandAnnounce([]byte) (*messages.CommandAnnounce, error)
	HandleCommand(*messages.CommandAnnounce, []byte) ([]byte, []byte, error)
}

type MsgPackHandler struct {
	logger          *logrus.Logger
	healthHandler   *health.Handler
	fetchCRLHandler *revoking.FetchCRLHandler
}

func (m *MsgPackHandler) HandleCommandAnnounce(frame []byte) (*messages.CommandAnnounce, error) {
	var ann messages.CommandAnnounce

	if err := msgpack.Unmarshal(frame, &ann); err != nil {
		return nil, fmt.Errorf("could not unmarshal command announcement: %w", err)
	}

	m.logger.Infof("received command announcement %+v", ann)

	return &ann, nil
}

func (m *MsgPackHandler) HandleCommand(announce *messages.CommandAnnounce, frame []byte) ([]byte, []byte, error) {
	var (
		response         *Response
		clientError, err error
	)

	switch announce.Code {
	case messages.CmdHealth:
		// health has no payload, ignore the frame
		response, err = m.handleCommand(&Command{Announce: announce, Command: nil})
		if err != nil {
			m.logger.WithError(err).Error("health handling failed")

			clientError = errors.New("could not handle request")
		}
	case messages.CmdFetchCRL:
		var command messages.FetchCRLCommand

		err = msgpack.Unmarshal(frame, &command)
		if err != nil {
			m.logger.WithError(err).Error("unmarshal failed")

			clientError = errors.New("could not unmarshal fetch crl command")

			break
		}

		response, err = m.handleCommand(&Command{Announce: announce, Command: command})
		if err != nil {
			m.logger.WithError(err).Error("fetch CRL handling failed")

			clientError = errors.New("could not handle request")
		}
	}

	if clientError != nil {
		response = buildErrorResponse(clientError.Error())
	}

	announceData, err := msgpack.Marshal(response.Announce)
	if err != nil {
		return nil, nil, fmt.Errorf("could not marshal response announcement: %w", err)
	}

	responseData, err := msgpack.Marshal(response.Response)
	if err != nil {
		return nil, nil, fmt.Errorf("could not marshal response: %w", err)
	}

	return announceData, responseData, nil
}

type Command struct {
	Announce *messages.CommandAnnounce
	Command  interface{}
}

type Response struct {
	Announce *messages.ResponseAnnounce
	Response interface{}
}

func (r *Response) String() string {
	return fmt.Sprintf("Response[Code=%s] created=%s data=%s", r.Announce.Code, r.Announce.Created, r.Response)
}

func (m *MsgPackHandler) handleCommand(command *Command) (*Response, error) {
	var (
		err          error
		responseData interface{}
		responseCode messages.ResponseCode
	)

	switch command.Announce.Code {
	case messages.CmdHealth:
		var res *health.Result

		res, err = m.healthHandler.CheckHealth()
		if err != nil {
			break
		}

		response := messages.HealthResponse{
			Version: res.Version,
			Healthy: res.Healthy,
		}

		for _, info := range res.Info {
			response.Info = append(response.Info, &messages.HealthInfo{
				Source:   info.Source,
				Healthy:  info.Healthy,
				MoreInfo: info.MoreInfo,
			})
		}

		responseCode, responseData = messages.RespHealth, response
	case messages.CmdFetchCRL:
		var res *revoking.Result

		fetchCRLPayload, ok := command.Command.(messages.FetchCRLCommand)
		if !ok {
			return nil, fmt.Errorf("could not use payload as FetchCRLPayload")
		}

		res, err = m.fetchCRLHandler.FetchCRL(fetchCRLPayload.IssuerID)
		if err != nil {
			break
		}

		response := messages.FetchCRLResponse{
			IsDelta: false,
			CRLData: res.Data,
		}

		responseCode, responseData = messages.RespFetchCRL, response
	default:
		return nil, fmt.Errorf("unhandled command %v", command)
	}

	if err != nil {
		return nil, fmt.Errorf("error from command handler: %w", err)
	}

	return &Response{
		Announce: messages.BuildResponseAnnounce(responseCode),
		Response: responseData,
	}, nil
}

func buildErrorResponse(errMsg string) *Response {
	return &Response{
		Announce: messages.BuildResponseAnnounce(messages.RespError),
		Response: messages.ErrorResponse{Message: errMsg},
	}
}

func New(logger *logrus.Logger, handlers ...RegisterHandler) (Handler, error) {
	messages.RegisterGeneratedResolver()

	h := &MsgPackHandler{
		logger: logger,
	}

	for _, reg := range handlers {
		reg(h)
	}

	return h, nil
}

type RegisterHandler func(handler *MsgPackHandler)

func RegisterHealthHandler(healthHandler *health.Handler) func(*MsgPackHandler) {
	return func(h *MsgPackHandler) {
		h.healthHandler = healthHandler
	}
}

func RegisterFetchCRLHandler(fetchCRLHandler *revoking.FetchCRLHandler) func(handler *MsgPackHandler) {
	return func(h *MsgPackHandler) {
		h.fetchCRLHandler = fetchCRLHandler
	}
}