package namespace

import (
	"fmt"
	"os"
	"path/filepath"
	"strconv"
	"syscall"
)

var runtimeBaseDir = func() string {
	uid := os.Getuid()
	base := fmt.Sprintf("/run/user/%d/wg-wrap", uid)
	if envBase := os.Getenv("WG_WRAP_RUNTIME_DIR"); envBase != "" {
		return envBase
	}
	return base
}()

// SetRuntimeBaseDir allows tests to override the base directory for namespace pins and PID tracking.
func SetRuntimeBaseDir(path string) {
	runtimeBaseDir = path
}

// GetProfileNamespacePath returns the path to the pinned namespace file for a profile.
func GetProfileNamespacePath(profile string) string {
	return filepath.Join(runtimeBaseDir, "profiles", profile)
}

// GetPidsDirPath returns the path to the directory where process PIDs are tracked for a profile.
func GetPidsDirPath(profile string) string {
	return filepath.Join(GetProfileNamespacePath(profile), "pids")
}

// RegisterProcess marks the current process as using the specified profile.
func RegisterProcess(profile string) error {
	pidsDir := GetPidsDirPath(profile)
	if err := os.MkdirAll(pidsDir, 0755); err != nil {
		return fmt.Errorf("failed to create pids directory: %v", err)
	}

	pid := os.Getpid()
	pidFile := filepath.Join(pidsDir, strconv.Itoa(pid))
	if err := os.WriteFile(pidFile, []byte(""), 0644); err != nil {
		return fmt.Errorf("failed to register process pid %d: %v", pid, err)
	}
	return nil
}

// UnregisterProcess removes the current process from the profile's tracking.
func UnregisterProcess(profile string) error {
	pid := os.Getpid()
	pidFile := filepath.Join(GetPidsDirPath(profile), strconv.Itoa(pid))
	if err := os.Remove(pidFile); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("failed to unregister process pid %d: %v", pid, err)
	}
	return nil
}

// PruneStalePids removes PID files that no longer correspond to active processes.
func PruneStalePids(profile string) error {
	pidsDir := GetPidsDirPath(profile)
	files, err := os.ReadDir(pidsDir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("failed to read pids directory: %v", err)
	}

	for _, file := range files {
		pid, err := strconv.Atoi(file.Name())
		if err != nil {
			continue // Ignore non-numeric files
		}

		// Sending signal 0 checks if the process exists without actually killing it.
		process, err := os.FindProcess(pid)
		if err != nil {
			os.Remove(filepath.Join(pidsDir, file.Name()))
			continue
		}

		// On Unix, FindProcess always succeeds. We need to actually check if it's alive.
		err = process.Signal(syscall.Signal(0))
		if err != nil {
			// Process is gone
			os.Remove(filepath.Join(pidsDir, file.Name()))
		}
	}
	return nil
}

// IsLastProcess checks if the current process is the only active user of the profile.
func IsLastProcess(profile string) (bool, error) {
	pidsDir := GetPidsDirPath(profile)
	files, err := os.ReadDir(pidsDir)
	if err != nil {
		if os.IsNotExist(err) {
			return true, nil
		}
		return false, fmt.Errorf("failed to read pids directory: %w", err)
	}

	// We count how many PIDs are active, including ourselves.
	activeCount := 0
	for _, file := range files {
		pid, err := strconv.Atoi(file.Name())
		if err != nil {
			continue
		}
		process, err := os.FindProcess(pid)
		if err != nil {
			continue
		}
		if process.Signal(syscall.Signal(0)) == nil {
			activeCount++
		}
	}

	return activeCount <= 1, nil
}