/*
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"
	"sync"

	"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"
)

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)
}

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

type MsgPackHandler struct {
	logger          *logrus.Logger
	healthHandler   *health.Handler
	fetchCRLHandler *revoking.FetchCRLHandler
	currentCommand  *Command
	currentResponse *Response
	lock            sync.Mutex
}

func (m *MsgPackHandler) HandleCommandAnnounce(frame []byte) error {
	m.lock.Lock()
	defer m.lock.Unlock()

	var ann messages.CommandAnnounce

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

	m.logger.WithField("announcement", &ann).Info("received command announcement")

	m.currentCommand = &Command{Announce: &ann}

	return nil
}

func (m *MsgPackHandler) HandleCommand(frame []byte) error {
	m.lock.Lock()
	defer m.lock.Unlock()

	var clientError error

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

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

			break
		}

		m.currentResponse = response
	case messages.CmdFetchCRL:
		var command messages.FetchCRLCommand

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

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

			break
		}

		m.currentCommand.Command = command

		response, err := m.handleCommand()
		if err != nil {
			m.logger.WithError(err).Error("fetch CRL handling failed")

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

			break
		}

		m.currentResponse = response
	}

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

	m.logger.WithField(
		"command",
		m.currentCommand,
	).WithField(
		"response",
		m.currentResponse,
	).Info("handled command")

	m.currentCommand = nil

	return nil
}

func (m *MsgPackHandler) ResponseAnnounce() ([]byte, error) {
	m.lock.Lock()
	defer m.lock.Unlock()

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

	m.logger.WithField("announcement", &m.currentResponse.Announce).Info("write response announcement")

	return announceData, nil
}

func (m *MsgPackHandler) ResponseData() ([]byte, error) {
	m.lock.Lock()
	defer m.lock.Unlock()

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

	m.logger.WithField("response", &m.currentResponse.Response).Info("write response")

	return responseData, nil
}

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

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

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

		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 := m.currentCommand.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 {
			return nil, err
		}

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

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

	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
	}
}