package service

/*
Copyright 2025 Suyono <suyono3484@gmail.com>

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.
*/

import (
	"context"
	"fmt"
	"golang.org/x/sys/unix"
	"net"
	"os"
	"os/exec"
	"sync/atomic"
	"syscall"
	"time"

	pb "gitea.suyono.dev/suyono/go-agent/proto"
	"gitea.suyono.dev/suyono/go-agent/storage"
	"github.com/rs/zerolog"
	"github.com/rs/zerolog/diode"
	"github.com/rs/zerolog/log"
	"google.golang.org/grpc"
	"google.golang.org/protobuf/types/known/emptypb"
)

type Option interface {
	SocketPath() string
	StopGraceTime() time.Duration
	Background() bool
	ExecArgs() []string
	ExecEnv() []string
	ExecLogPath() string
	Umask() int
}

type Storage interface {
	Get(string) (string, error)
	Set(string, string) error
	Shutdown() error
}

type BgProcFlag int

const (
	child BgProcFlag = iota
	parent
)

const (
	goAgentDaemonEnvFlag = "GO_AGENT_DAEMON"
	goAgentDaemonLogPath = "GO_AGENT_DAEMON_LOG"
)

type server struct {
	pb.UnimplementedAgentServer
	stor Storage
}

func (s *server) Get(ctx context.Context, req *pb.CacheGetRequest) (*pb.CacheValue, error) {
	val, err := s.stor.Get(req.GetKey())
	if err != nil {
		return nil, err
	}

	result := &pb.CacheValue{
		Status: "OK",
		Value:  val,
	}
	return result, nil
}

func (s *server) Set(ctx context.Context, req *pb.CacheSetRequest) (*pb.SetStatus, error) {
	err := s.stor.Set(req.GetKey(), req.GetValue())
	if err != nil {
		log.Error().Err(err).Caller().Msg("failed to set cache")
		return nil, err
	}
	return &pb.SetStatus{
		Status: "OK",
	}, nil
}

func (s *server) Shutdown(context.Context, *emptypb.Empty) (*emptypb.Empty, error) {
	if err := s.stor.Shutdown(); err != nil {
		return nil, err
	}
	return &emptypb.Empty{}, nil
}

func ExecBackground(opt Option) (BgProcFlag, error) {
	var (
		cmd     *exec.Cmd
		envVal  string
		logPath string
		err     error
		f       *os.File
	)

	args := opt.ExecArgs()
	envVal = os.Getenv(goAgentDaemonEnvFlag)
	if !opt.Background() || len(args) == 0 || envVal == "1" {
		if envVal == "1" {
			logPath = os.Getenv(goAgentDaemonLogPath)
			if logPath == "" {
				panic(fmt.Errorf("cannot start background process without log path"))
			}

			if f, err = os.OpenFile(logPath, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0600); err != nil {
				panic(fmt.Errorf("opening log file: %w", err))
			}

			log.Logger = zerolog.New(diode.NewWriter(f, 1000, 10*time.Millisecond, func(missed int) {
				fmt.Printf("Logger Dropped %d messages", missed)
			}))
		}

		return child, nil
	}

	if opt.ExecLogPath() == "" {
		return parent, fmt.Errorf("cannot start background process without log path")
	}

	if len(args) > 1 {
		cmd = exec.Command(args[0], args[1:]...)
	} else {
		cmd = exec.Command(args[0])
	}
	cmd.Env = append(os.Environ(), opt.ExecEnv()...)
	cmd.Env = append(cmd.Env,
		fmt.Sprintf("%s=1", goAgentDaemonEnvFlag),
		fmt.Sprintf("%s=%s", goAgentDaemonLogPath, opt.ExecLogPath()))
	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
	cmd.Stdin, cmd.Stdout, cmd.Stderr = nil, nil, nil

	if err = cmd.Start(); err != nil {
		return parent, err
	}

	return parent, nil
}

func Serve(ctx context.Context, opt Option) error {
	var (
		l      net.Listener
		err    error
		errC   error
		ok     bool
		sw     *atomic.Bool
		cancel context.CancelFunc
		bgFlag BgProcFlag
	)

	if bgFlag, err = ExecBackground(opt); err != nil {
		return fmt.Errorf("could not start background process: %w", err)
	}
	if bgFlag == parent {
		return nil
	}

	_ = os.Remove(opt.SocketPath())

	oldUmask := unix.Umask(opt.Umask())
	if l, err = net.Listen("unix", opt.SocketPath()); err != nil {
		return fmt.Errorf("failed to listen on unix socket: %w", err)
	}
	unix.Umask(oldUmask)

	grpcServer := grpc.NewServer()
	ctx, cancel = context.WithCancel(ctx)
	pb.RegisterAgentServer(grpcServer, &server{
		stor: storage.NewInMap(cancel),
	})
	errChan := make(chan error, 1)
	sw = new(atomic.Bool)
	sw.Store(false)

	go func() {
		err := grpcServer.Serve(l)
		sw.Swap(true)
		if err != nil {
			errChan <- err
		}
		close(errChan)
		cancel()
	}()

	<-ctx.Done()
	if !sw.Load() {
		grpcServer.GracefulStop()
	}

	fst := time.NewTimer(opt.StopGraceTime())
	err = nil
fsl:
	for {
		select {
		case errC, ok = <-errChan:
			if !ok {
				break fsl
			}
			if errC != nil {
				err = errC
			}
		case <-fst.C:
			if !sw.Load() {
				grpcServer.Stop()
			}
			break fsl
		}
	}

	return err
}

func (s *server) Ping(ctx context.Context, req *emptypb.Empty) (*emptypb.Empty, error) {
	return &emptypb.Empty{}, nil
}