package vsockagent

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net"
	"net/http"
	"time"

	sdkvsock "github.com/firecracker-microvm/firecracker-go-sdk/vsock"
	"github.com/sirupsen/logrus"
)

const (
	Port             uint32 = 42070
	HealthPath              = "/healthz"
	HealthyStatus           = "ok"
	GuestBinaryName         = "banger-vsock-agent"
	GuestInstallPath        = "/usr/local/bin/" + GuestBinaryName
	ServiceName             = "banger-vsock-agent.service"
	serviceUnit             = `[Unit]
Description=Banger vsock agent
After=network.target

[Service]
Type=simple
ExecStart=/usr/local/bin/banger-vsock-agent
Restart=on-failure
RestartSec=1

[Install]
WantedBy=multi-user.target
`
	modulesLoadConfig = "vsock\nvmw_vsock_virtio_transport\n"
)

type HealthResponse struct {
	Status string `json:"status"`
}

func NewHandler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc(HealthPath, func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet {
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		_ = json.NewEncoder(w).Encode(HealthResponse{Status: HealthyStatus})
	})
	return mux
}

func Health(ctx context.Context, logger *slog.Logger, socketPath string) error {
	transport := &http.Transport{
		DisableKeepAlives: true,
		DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
			return sdkvsock.DialContext(
				ctx,
				socketPath,
				Port,
				sdkvsock.WithRetryTimeout(3*time.Second),
				sdkvsock.WithRetryInterval(100*time.Millisecond),
				sdkvsock.WithLogger(newLogger(logger)),
			)
		},
	}
	defer transport.CloseIdleConnections()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "http://vsock"+HealthPath, nil)
	if err != nil {
		return err
	}
	resp, err := (&http.Client{Transport: transport}).Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
		return fmt.Errorf("unexpected health status %d: %s", resp.StatusCode, string(body))
	}
	var payload HealthResponse
	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
		return err
	}
	if payload.Status != HealthyStatus {
		return fmt.Errorf("unexpected health response status %q", payload.Status)
	}
	if logger != nil {
		logger.Debug("vsock health ok", "vsock_path", socketPath, "vsock_port", Port)
	}
	return nil
}

func ServiceUnit() string {
	return serviceUnit
}

func ModulesLoadConfig() string {
	return modulesLoadConfig
}

func ReminderMessage(name string) string {
	return fmt.Sprintf("session ended; %s is still running (stop it with 'banger vm stop %s')", name, name)
}

func WarningMessage(name string, err error) string {
	if err == nil {
		return ""
	}
	return fmt.Sprintf("warning: failed to check whether %s is still running: %v", name, err)
}

func newLogger(base *slog.Logger) *logrus.Entry {
	logger := logrus.New()
	logger.SetOutput(io.Discard)
	logger.SetLevel(logrus.DebugLevel)
	logger.AddHook(slogHook{logger: base})
	return logrus.NewEntry(logger)
}

type slogHook struct {
	logger *slog.Logger
}

func (h slogHook) Levels() []logrus.Level {
	return logrus.AllLevels
}

func (h slogHook) Fire(entry *logrus.Entry) error {
	if h.logger == nil {
		return nil
	}
	level := slog.LevelDebug
	switch entry.Level {
	case logrus.ErrorLevel, logrus.FatalLevel, logrus.PanicLevel:
		level = slog.LevelError
	case logrus.WarnLevel:
		level = slog.LevelWarn
	case logrus.InfoLevel:
		level = slog.LevelInfo
	}
	attrs := make([]any, 0, len(entry.Data)*2)
	for key, value := range entry.Data {
		attrs = append(attrs, key, value)
	}
	h.logger.Log(context.Background(), level, entry.Message, attrs...)
	return nil
}

func IsServerClosed(err error) bool {
	return errors.Is(err, http.ErrServerClosed)
}