package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/url"
	"os"
	"path/filepath"
)

const configFileName = "config.json"

type Config struct {
	APIURL            string `json:"api_url"`
	AutoChangeEnabled bool   `json:"auto_change_enabled"`
	IntervalMinutes   int    `json:"interval_minutes"`
	MaxCacheCount     int    `json:"max_cache_count"`
	WallpaperStyle    string `json:"wallpaper_style"`
	StartWithWindows  bool   `json:"start_with_windows"`
}

func defaultConfig() Config {
	return Config{
		IntervalMinutes: 30,
		MaxCacheCount:   10,
		WallpaperStyle:  "keep",
	}
}

func loadOrCreateConfig(path string) (Config, bool, error) {
	data, err := os.ReadFile(path)
	if errors.Is(err, os.ErrNotExist) {
		cfg := defaultConfig()
		if err := saveConfig(path, cfg); err != nil {
			return Config{}, false, err
		}
		return cfg, true, nil
	}
	if err != nil {
		return Config{}, false, fmt.Errorf("读取配置文件: %w", err)
	}

	var cfg Config
	if err := json.Unmarshal(data, &cfg); err != nil {
		return Config{}, false, fmt.Errorf("解析配置文件: %w", err)
	}
	if err := cfg.validate(false); err != nil {
		return Config{}, false, fmt.Errorf("配置文件无效: %w", err)
	}
	return cfg, false, nil
}

func saveConfig(path string, cfg Config) error {
	if err := cfg.validate(false); err != nil {
		return err
	}
	data, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return fmt.Errorf("编码配置文件: %w", err)
	}
	data = append(data, '\n')
	if err := atomicWriteFile(path, data, 0o644); err != nil {
		return fmt.Errorf("保存配置文件: %w", err)
	}
	return nil
}

func (c Config) validate(requireURL bool) error {
	if c.IntervalMinutes <= 0 {
		return errors.New("自动切换间隔必须大于 0 分钟")
	}
	if c.MaxCacheCount <= 0 {
		return errors.New("缓存数量必须大于 0")
	}
	if requireURL && c.APIURL == "" {
		return errors.New("请先设置随机图片 API 地址")
	}
	if c.APIURL != "" {
		u, err := url.ParseRequestURI(c.APIURL)
		if err != nil || u.Host == "" || (u.Scheme != "http" && u.Scheme != "https") {
			return errors.New("API 地址必须是有效的 HTTP 或 HTTPS 地址")
		}
	}
	if !validWallpaperStyle(c.WallpaperStyle) {
		return errors.New("不支持的壁纸显示方式")
	}
	return nil
}

func atomicWriteFile(path string, data []byte, perm os.FileMode) error {
	dir := filepath.Dir(path)
	tmp, err := os.CreateTemp(dir, ".gowallpaper-*")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)

	if err := tmp.Chmod(perm); err != nil {
		tmp.Close()
		return err
	}
	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Sync(); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
		return err
	}
	return os.Rename(tmpName, path)
}