//go:build darwin

package service

import (
	"fmt"
	"os"
	"os/exec"
	"os/signal"
	"strings"
	"syscall"
	"time"
)

// dnsManager manages macOS DNS settings via networksetup(8). Direct port of
// MacOSDNSManager in macos_service_wrapper.py.
type dnsManager struct{}

func (dnsManager) getNetworkServices() []string {
	out, err := exec.Command("networksetup", "-listallnetworkservices").CombinedOutput()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to list network services: %v\n", err)
		return nil
	}
	lines := strings.Split(string(out), "\n")
	var services []string
	for _, line := range lines[1:] { // skip header
		line = strings.TrimSpace(line)
		if line != "" && !strings.HasPrefix(line, "*") {
			services = append(services, line)
		}
	}
	return services
}

func (dnsManager) getCurrentDNS(service string) []string {
	out, err := exec.Command("networksetup", "-getdnsservers", service).CombinedOutput()
	if err != nil {
		return []string{"Empty"}
	}
	var servers []string
	for _, line := range strings.Split(string(out), "\n") {
		line = strings.TrimSpace(line)
		if line != "" && !strings.Contains(line, " ") {
			servers = append(servers, line)
		}
	}
	return servers
}

func (dnsManager) setDNS(service string, servers []string) bool {
	var err error
	if len(servers) == 0 {
		_, err = exec.Command("networksetup", "-setdnsservers", service, "empty").CombinedOutput()
	} else {
		args := append([]string{"-setdnsservers", service}, servers...)
		_, err = exec.Command("networksetup", args...).CombinedOutput()
	}
	if err != nil {
		fmt.Fprintf(os.Stderr, "Failed to set DNS for %s: %v\n", service, err)
		return false
	}
	return true
}

// mihomoWrapper wraps the mihomo process on macOS, managing DNS settings
// around its lifecycle. Direct port of MihomoServiceWrapper in
// macos_service_wrapper.py.
type mihomoWrapper struct {
	executable   string
	args         []string
	configDir    string
	process      *exec.Cmd
	dns          dnsManager
	originalDNS  map[string][]string
	shuttingDown bool
}

func (w *mihomoWrapper) start() bool {
	cmd := exec.Command(w.executable, w.args...)
	cmd.Dir = w.configDir
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	if err := cmd.Start(); err != nil {
		fmt.Fprintf(os.Stderr, "Failed to start service: %v\n", err)
		return false
	}
	w.process = cmd
	fmt.Fprintf(os.Stderr, "Started mihomo service (PID: %d)\n", cmd.Process.Pid)

	w.originalDNS = make(map[string][]string)
	dnsServer := "223.6.6.6"
	for _, svc := range w.dns.getNetworkServices() {
		original := w.dns.getCurrentDNS(svc)
		w.originalDNS[svc] = original

		if w.dns.setDNS(svc, []string{dnsServer}) {
			fmt.Fprintf(os.Stderr, "Set DNS for %s: %s\n", svc, dnsServer)
		} else {
			fmt.Fprintf(os.Stderr, "Warning: Failed to set DNS for %s\n", svc)
		}
	}

	return true
}

func (w *mihomoWrapper) stop() bool {
	for svc, servers := range w.originalDNS {
		if w.dns.setDNS(svc, servers) {
			if len(servers) > 0 && servers[0] != "Empty" {
				fmt.Fprintf(os.Stderr, "Restored DNS for %s: %s\n", svc, strings.Join(servers, ", "))
			} else {
				fmt.Fprintf(os.Stderr, "Reset DNS for %s to automatic\n", svc)
			}
		} else {
			fmt.Fprintf(os.Stderr, "Warning: Failed to restore DNS for %s\n", svc)
		}
	}

	if w.process != nil && w.process.Process != nil {
		w.process.Process.Signal(syscall.SIGTERM)
		done := make(chan error, 1)
		go func() { done <- w.process.Wait() }()
		select {
		case <-done:
		case <-time.After(5 * time.Second):
			w.process.Process.Kill()
			<-done
		}
		fmt.Fprintf(os.Stderr, "Stopped mihomo service (PID: %d)\n", w.process.Process.Pid)
	}

	return true
}

func (w *mihomoWrapper) run() {
	w.shuttingDown = false

	sigCh := make(chan os.Signal, 1)
	signal.Notify(sigCh, syscall.SIGTERM, syscall.SIGINT)

	if !w.start() {
		os.Exit(1)
	}

	fmt.Fprintln(os.Stderr, "Service started, press Ctrl+C to stop")

	waitCh := make(chan error, 1)
	go func() { waitCh <- w.process.Wait() }()

	select {
	case <-waitCh:
		fmt.Fprintf(os.Stderr, "Process exited with code: %d\n", w.process.ProcessState.ExitCode())
		w.stop()
	case sig := <-sigCh:
		fmt.Fprintf(os.Stderr, "Received signal %v, shutting down...\n", sig)
		w.shuttingDown = true
		w.stop()
		os.Exit(0)
	}
}

// RunMacOSWrapper runs the mihomo process with DNS management, blocking
// until it exits or a termination signal is received. Invoked by the
// hidden `ssm service run-macos <executable> <configDir> [args...]` command
// that the generated launchd plist points at (see service_darwin.go),
// replacing the standalone macos_service_wrapper.py script.
func RunMacOSWrapper(executable, configDir string, args []string) error {
	if _, err := os.Stat(executable); err != nil {
		return fmt.Errorf("executable not found: %s", executable)
	}
	if _, err := os.Stat(configDir); err != nil {
		return fmt.Errorf("config directory not found: %s", configDir)
	}

	w := &mihomoWrapper{
		executable: executable,
		args:       args,
		configDir:  configDir,
	}
	w.run()
	return nil
}