//go:build linux

package namespace

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

	"git.theodohertyfamily.com/tools/wg-wrap/internal/paths"
	"golang.org/x/sys/unix"
)

// PinNamespace binds the current network namespace to the profile's namespace path.
// This prevents the kernel from destroying the namespace when all processes exit.
func PinNamespace(pm *paths.PathManager, profile string) error {
	nsPath := GetProfileNamespacePath(pm, profile)
	profilesDir := filepath.Dir(nsPath)
	if err := os.MkdirAll(profilesDir, 0755); err != nil {
		return fmt.Errorf("failed to create profiles directory: %w", err)
	}

	// 1. Create an empty file to serve as the mount point
	if err := os.WriteFile(nsPath, []byte(""), 0644); err != nil {
		return fmt.Errorf("failed to create namespace pin file: %w", err)
	}

	// 2. Bind-mount the current network namespace to the file.
	// This increments the kernel's reference count for the namespace.
	if err := unix.Mount("/proc/self/ns/net", nsPath, "", unix.MS_BIND, ""); err != nil {
		return fmt.Errorf("failed to bind-mount network namespace: %w", err)
	}

	return nil
}

// UnpinNamespace unmounts and removes the pinned namespace file.
func UnpinNamespace(pm *paths.PathManager, profile string) error {
	nsPath := GetProfileNamespacePath(pm, profile)

	if _, err := os.Stat(nsPath); os.IsNotExist(err) {
		return nil
	}

	// 1. Unmount the namespace first.
	// If this is the last reference to the namespace, the kernel will destroy it.
	if err := unix.Unmount(nsPath, 0); err != nil {
		return fmt.Errorf("failed to unmount namespace %s: %w", nsPath, err)
	}

	// 2. Remove the mount point file.
	if err := os.Remove(nsPath); err != nil {
		return fmt.Errorf("failed to remove pin file %s: %w", nsPath, err)
	}

	pidsDir := GetPidsDirPath(pm, profile)

	// Try to remove pids directory and empty parent directories
	_ = os.Remove(pidsDir)
	_ = os.Remove(filepath.Dir(pidsDir))
	_ = os.Remove(filepath.Dir(filepath.Dir(pidsDir)))

	return nil
}

// FindActiveProfilePid looks for an active PID running under the specified profile.
// Returns 0 if no active process is found.
func FindActiveProfilePid(pm *paths.PathManager, profile string) (int, error) {
	if err := PruneStalePids(pm, profile); err != nil {
		return 0, fmt.Errorf("failed to prune stale pids: %w", err)
	}

	pidsDir := GetPidsDirPath(pm, profile)
	files, err := os.ReadDir(pidsDir)
	if err != nil {
		if os.IsNotExist(err) {
			return 0, nil
		}
		return 0, fmt.Errorf("failed to read pids dir: %w", err)
	}

	for _, file := range files {
		pid, err := strconv.Atoi(file.Name())
		if err != nil {
			continue
		}
		// Since we already pruned stale pids, the first file we find is an active pid!
		return pid, nil
	}

	return 0, nil
}