package vsockping

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"log/slog"
	"net"
	"strings"
	"time"

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

const (
	Port             uint32 = 42070
	RequestLine             = "PING\n"
	ResponseLine            = "PONG\n"
	GuestBinaryName         = "banger-vsock-pingd"
	GuestInstallPath        = "/usr/local/bin/" + GuestBinaryName
	ServiceName             = "banger-vsock-pingd.service"
	serviceUnit             = `[Unit]
Description=Banger vsock ping responder
After=network.target

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

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

func Ping(ctx context.Context, logger *slog.Logger, socketPath string) error {
	conn, err := sdkvsock.DialContext(
		ctx,
		socketPath,
		Port,
		sdkvsock.WithRetryTimeout(3*time.Second),
		sdkvsock.WithRetryInterval(100*time.Millisecond),
	)
	if err != nil {
		return err
	}
	defer conn.Close()

	if deadline, ok := ctx.Deadline(); ok {
		_ = conn.SetDeadline(deadline)
	} else {
		_ = conn.SetDeadline(time.Now().Add(3 * time.Second))
	}

	if _, err := io.WriteString(conn, RequestLine); err != nil {
		return err
	}
	line, err := bufio.NewReader(conn).ReadString('\n')
	if err != nil {
		return err
	}
	if strings.TrimSpace(line) != strings.TrimSpace(ResponseLine) {
		return fmt.Errorf("unexpected vsock ping response %q", strings.TrimSpace(line))
	}
	if logger != nil {
		logger.Debug("vsock ping 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 ServeConn(conn net.Conn) error {
	defer conn.Close()
	_ = conn.SetDeadline(time.Now().Add(5 * time.Second))
	line, err := bufio.NewReader(conn).ReadString('\n')
	if err != nil {
		return err
	}
	if strings.TrimSpace(line) != strings.TrimSpace(RequestLine) {
		return fmt.Errorf("unexpected request %q", strings.TrimSpace(line))
	}
	_, err = io.WriteString(conn, ResponseLine)
	return err
}