// Package wine supervises the optional installed Wine Access accessibility
// helper. Native Wine objects stay in that process; Go receives D-Bus messages.
package wine

import (
	"context"
	"errors"
	"log/slog"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"syscall"
	"time"
)

const managedKey = "CTHULHU_WINE_ACCESS_MANAGED"

type prefix struct {
	path, loader string
	environment  map[string]string
}

type process struct {
	cmd      *exec.Cmd
	done     chan struct{}
	started  time.Time
	seen     time.Time
	failures int
	next     time.Time
}

type Manager struct {
	logger   *slog.Logger
	helper   string
	procRoot string
	cancel   context.CancelFunc
	done     chan struct{}
}

func New(logger *slog.Logger) *Manager {
	if logger == nil {
		logger = slog.New(slog.DiscardHandler)
	}
	return &Manager{logger: logger, helper: helperPath(), procRoot: "/proc"}
}

func helperPath() string {
	return findHelper([]string{
		filepath.Join(os.Getenv("HOME"), ".local", "libexec", "wine-access", "wine-access.exe"),
		filepath.Join(os.Getenv("HOME"), ".local", "libexec", "cthulhu", "wine", "cthulhu-wine-access.exe"),
		"/usr/local/libexec/wine-access/wine-access.exe",
		"/usr/libexec/wine-access/wine-access.exe",
		"/usr/libexec/cthulhu/wine/cthulhu-wine-access.exe",
	})
}

func findHelper(candidates []string) string {
	if path := os.Getenv("CTHULHU_WINE_ACCESS_HELPER"); executable(path) {
		return path
	}
	for _, path := range candidates {
		if executable(path) {
			return path
		}
	}
	for _, name := range []string{"wine-access.exe", "cthulhu-wine-access.exe"} {
		if path, err := exec.LookPath(name); err == nil {
			return path
		}
	}
	return ""
}

func executable(path string) bool {
	if path == "" {
		return false
	}
	info, err := os.Stat(path)
	return err == nil && info.Mode().IsRegular() && info.Mode().Perm()&0111 != 0
}

func (manager *Manager) Start(ctx context.Context) error {
	if manager.helper == "" {
		manager.logger.Info("Wine accessibility helper unavailable")
		return nil
	}
	if manager.cancel != nil {
		return errors.New("Wine accessibility manager already started")
	}
	workerCtx, cancel := context.WithCancel(ctx)
	manager.cancel = cancel
	manager.done = make(chan struct{})
	go manager.run(workerCtx)
	return nil
}

func (manager *Manager) Stop(ctx context.Context) error {
	if manager.cancel == nil {
		return nil
	}
	manager.cancel()
	select {
	case <-manager.done:
		return nil
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (manager *Manager) run(ctx context.Context) {
	defer close(manager.done)
	active := make(map[string]*process)
	ticker := time.NewTicker(2 * time.Second)
	defer ticker.Stop()
	manager.poll(active)
	for {
		select {
		case <-ctx.Done():
			for _, child := range active {
				stop(child)
			}
			return
		case <-ticker.C:
			manager.poll(active)
		}
	}
}

func (manager *Manager) poll(active map[string]*process) {
	now := time.Now()
	discovered := discover(manager.procRoot, uint32(os.Getuid()))
	for path, source := range discovered {
		child := active[path]
		if child == nil {
			child = &process{}
			active[path] = child
		}
		child.seen = now
		if child.cmd != nil {
			select {
			case <-child.done:
				if now.Sub(child.started) < 10*time.Second {
					child.failures++
				} else {
					child.failures = 0
				}
				child.next = now.Add(backoff(child.failures))
				child.cmd = nil
			default:
				continue
			}
		}
		if now.Before(child.next) {
			continue
		}
		if err := manager.launch(child, source, now); err != nil {
			child.failures++
			child.next = now.Add(backoff(child.failures))
			manager.logger.Warn("start Wine accessibility helper", "error", err)
		}
	}
	for path, child := range active {
		if _, found := discovered[path]; !found && now.Sub(child.seen) >= 10*time.Second {
			stop(child)
			delete(active, path)
		}
	}
}

func backoff(failures int) time.Duration {
	if failures > 6 {
		failures = 6
	}
	return time.Duration(1<<failures) * time.Second
}

func (manager *Manager) launch(child *process, source prefix, now time.Time) error {
	cmd := exec.Command(manager.helper)
	cmd.Stdin = nil
	cmd.Stdout = nil
	cmd.Stderr = nil
	cmd.SysProcAttr = &syscall.SysProcAttr{Setsid: true}
	environment := os.Environ()
	for _, key := range []string{"DISPLAY", "WAYLAND_DISPLAY", "XDG_RUNTIME_DIR", "DBUS_SESSION_BUS_ADDRESS"} {
		if value := source.environment[key]; value != "" {
			environment = append(environment, key+"="+value)
		}
	}
	environment = append(environment, "WINEPREFIX="+source.path, managedKey+"=1")
	if source.loader != "" {
		environment = append(environment, "WINELOADER="+source.loader)
	}
	cmd.Env = environment
	if err := cmd.Start(); err != nil {
		return err
	}
	child.cmd, child.done, child.started = cmd, make(chan struct{}), now
	go manager.wait(cmd, child)
	manager.logger.Info("Wine accessibility helper started")
	return nil
}

func (manager *Manager) wait(cmd *exec.Cmd, child *process) {
	err := cmd.Wait()
	if err != nil {
		manager.logger.Warn("Wine accessibility helper exited", "error", err)
	} else {
		manager.logger.Info("Wine accessibility helper exited")
	}
	close(child.done)
}

func stop(child *process) {
	if child.cmd == nil {
		return
	}
	select {
	case <-child.done:
		child.cmd = nil
		return
	default:
	}
	_ = child.cmd.Process.Signal(syscall.SIGTERM)
	select {
	case <-child.done:
	case <-time.After(2 * time.Second):
		_ = child.cmd.Process.Kill()
		<-child.done
	}
	child.cmd = nil
}

func discover(root string, uid uint32) map[string]prefix {
	result := make(map[string]prefix)
	entries, err := os.ReadDir(root)
	if err != nil {
		return result
	}
	for _, entry := range entries {
		if _, err := strconv.Atoi(entry.Name()); err != nil {
			continue
		}
		base := filepath.Join(root, entry.Name())
		info, err := os.Stat(base)
		if err != nil {
			continue
		}
		stat, ok := info.Sys().(*syscall.Stat_t)
		if !ok || stat.Uid != uid {
			continue
		}
		exe, err := os.Readlink(filepath.Join(base, "exe"))
		if err != nil {
			continue
		}
		name := strings.ToLower(filepath.Base(exe))
		if name != "wine" && name != "wine64" && name != "wine-preloader" && name != "wine64-preloader" {
			continue
		}
		commandLine, err := os.ReadFile(filepath.Join(base, "cmdline"))
		if err != nil || !applicationProcess(string(commandLine)) {
			continue
		}
		raw, err := os.ReadFile(filepath.Join(base, "environ"))
		if err != nil {
			continue
		}
		environment := make(map[string]string)
		for _, item := range strings.Split(string(raw), "\x00") {
			key, value, found := strings.Cut(item, "=")
			if found {
				environment[key] = value
			}
		}
		if environment[managedKey] == "1" {
			continue
		}
		path := environment["WINEPREFIX"]
		if path == "" && environment["STEAM_COMPAT_DATA_PATH"] != "" {
			path = filepath.Join(environment["STEAM_COMPAT_DATA_PATH"], "pfx")
		}
		// Wine defaults to .wine in the launching process's home directory.
		// Use that process's HOME, which may differ from the reader's HOME.
		if path == "" && filepath.IsAbs(environment["HOME"]) {
			path = filepath.Join(environment["HOME"], ".wine")
		}
		if path == "" {
			continue
		}
		path = filepath.Clean(path)
		if resolved, err := filepath.EvalSymlinks(path); err == nil {
			path = resolved
		}
		if !filepath.IsAbs(path) {
			continue
		}
		loader := environment["WINELOADER"]
		if !executable(loader) {
			loader = exe
			if strings.HasSuffix(name, "-preloader") {
				loader = strings.TrimSuffix(exe, "-preloader")
			}
			if !executable(loader) {
				loader = ""
			}
		}
		result[path] = prefix{path: path, loader: loader, environment: environment}
	}
	return result
}

// Wine services use the same Unix loader as applications and can outlive them.
// Counting them keeps the helper alive indefinitely and can open an otherwise
// unused virtual desktop when the reader starts.
func applicationProcess(commandLine string) bool {
	arguments := strings.Split(commandLine, "\x00")
	program := strings.ToLower(strings.TrimSpace(arguments[0]))
	if program == "" {
		return false
	}
	program = filepath.Base(strings.ReplaceAll(program, "\\", "/"))
	switch program {
	case "", "services.exe", "winedevice.exe", "svchost.exe", "plugplay.exe", "rpcss.exe", "lsass.exe", "wineboot.exe", "winemenubuilder.exe":
		return false
	case "explorer.exe":
		// Ordinary Explorer windows are applications; its desktop host is not.
		for _, argument := range arguments[1:] {
			argument = strings.ToLower(strings.TrimSpace(argument))
			if argument == "/desktop" || strings.HasPrefix(argument, "/desktop=") {
				return false
			}
		}
	}
	return true
}