package main

import (
	"bytes"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"
)

func lockFilePath() string {
	return filepath.Join(appDir(), ".hpltoolbox.lock")
}

// focusExistingInstance returns true if another instance was found and
// successfully asked to focus its window. In that case the caller should exit.
// Returns false if no live instance exists (and clears any stale lock).
func focusExistingInstance() bool {
	data, err := os.ReadFile(lockFilePath())
	if err != nil {
		return false
	}
	parts := strings.Split(strings.TrimSpace(string(data)), "\n")
	if len(parts) != 2 {
		_ = os.Remove(lockFilePath())
		return false
	}
	pid, errPid := strconv.Atoi(strings.TrimSpace(parts[0]))
	port, errPort := strconv.Atoi(strings.TrimSpace(parts[1]))
	if errPid != nil || errPort != nil {
		_ = os.Remove(lockFilePath())
		return false
	}

	// Quick liveness check: PID must exist.
	if proc, err := os.FindProcess(pid); err != nil || proc == nil {
		_ = os.Remove(lockFilePath())
		return false
	}

	// Ask the running instance to focus its window.
	client := &http.Client{Timeout: 1500 * time.Millisecond}
	url := fmt.Sprintf("http://127.0.0.1:%d/api/focus", port)
	resp, err := client.Post(url, "application/json", bytes.NewReader(nil))
	if err != nil {
		// Lock file is stale (process died but didn't clean up).
		_ = os.Remove(lockFilePath())
		return false
	}
	_ = resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		_ = os.Remove(lockFilePath())
		return false
	}
	return true
}

func writeLockFile(port int) error {
	content := fmt.Sprintf("%d\n%d\n", os.Getpid(), port)
	return os.WriteFile(lockFilePath(), []byte(content), 0644)
}

func removeLockFile() {
	_ = os.Remove(lockFilePath())
}