/*
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.
*/

// client simulator

package main

import (
	"context"
	"fmt"
	"log"
	"os"
	"sync"
	"time"

	"git.cacert.org/cacert-gosigner/pkg/messages"
	"github.com/justincpresley/go-cobs"
	"github.com/shamaton/msgpackgen/msgpack"
)

const cobsDelimiter = 0x00

var cobsConfig = cobs.Config{SpecialByte: cobsDelimiter, Delimiter: true, EndingSave: true}

func main() {
	errorLog := log.New(os.Stderr, "", log.LstdFlags)

	sim := &clientSimulator{
		errorLog: errorLog,
	}

	err := sim.Run()
	if err != nil {
		errorLog.Printf("simulator returned an error: %v", err)
	}
}

type clientSimulator struct {
	errorLog  *log.Logger
	commands  chan messages.Command
	responses chan []byte
}

func (c *clientSimulator) writeTestCommands(ctx context.Context) error {
	messages.RegisterGeneratedResolver()

	const healthInterval = 10 * time.Second

	timer := time.NewTimer(healthInterval)

	for {
		select {
		case <-ctx.Done():
			_ = timer.Stop()

			return nil
		case <-timer.C:
			c.commands <- messages.Command{
				Code:      messages.CmdHealth,
				TimeStamp: time.Now().UTC(),
			}

			timer.Reset(healthInterval)
		}
	}
}

func (c *clientSimulator) handleInput(ctx context.Context) error {
	const (
		bufferSize   = 1024 * 1024
		readInterval = 50 * time.Millisecond
	)

	buf := make([]byte, bufferSize)

	for {
		select {
		case <-ctx.Done():
			return nil
		default:
			count, err := os.Stdin.Read(buf)
			if err != nil {
				return err
			}

			if count == 0 {
				time.Sleep(readInterval)

				continue
			}

			data := buf[:count]

			err = cobs.Verify(data, cobsConfig)
			if err != nil {
				return err
			}

			c.responses <- cobs.Decode(data, cobsConfig)
		}
	}
}

func (c *clientSimulator) handleCommands(ctx context.Context) error {
	for {
		select {
		case command := <-c.commands:
			commandBytes, err := msgpack.Marshal(command)
			if err != nil {
				return fmt.Errorf("could not marshal command bytes: %w", err)
			}

			_, err = os.Stdout.Write(cobs.Encode(commandBytes, cobsConfig))
			if err != nil {
				return fmt.Errorf("write failed: %w", err)
			}

			responseBytes := <-c.responses

			var response messages.Response

			err = msgpack.Unmarshal(responseBytes, &response)
			if err != nil {
				return fmt.Errorf("could not unmarshal msgpack data: %w", err)
			}

			c.errorLog.Printf("received response: %+v", response)
		case <-ctx.Done():
			return nil
		}
	}
}

func (c *clientSimulator) Run() error {
	ctx, cancel := context.WithCancel(context.Background())

	c.commands = make(chan messages.Command)
	c.responses = make(chan []byte)

	wg := sync.WaitGroup{}
	wg.Add(2)

	var inputError, commandError error

	go func(inputErr error) {
		inputError = c.handleInput(ctx)

		cancel()

		wg.Done()
	}(inputError)

	go func(commandErr error) {
		commandErr = c.handleCommands(ctx)

		cancel()

		wg.Done()
	}(commandError)

	var result error

	if err := c.writeTestCommands(ctx); err != nil {
		c.errorLog.Printf("test commands failed: %v", err)
	}

	cancel()
	wg.Wait()

	if inputError != nil {
		c.errorLog.Printf("reading input failed: %v", inputError)
	}

	if commandError != nil {
		c.errorLog.Printf("sending commands failed: %v", commandError)
	}

	return result
}