// Package config 解析 client.yaml / server.yaml 配置（设计.md §14）。
package config

import (
	"fmt"
	"os"

	"gopkg.in/yaml.v3"
)

// ClientConfig 客户端配置（设计.md §14.2）。
type ClientConfig struct {
	Client struct {
		WindowWidth    int     `yaml:"window_width"`
		WindowHeight   int     `yaml:"window_height"`
		WindowTitle    string  `yaml:"window_title"`
		VSync          bool    `yaml:"vsync"`
		FOV            float64 `yaml:"fov"`
		RenderDistance int     `yaml:"render_distance"`
		Language       string  `yaml:"language"`
		Graphics       struct {
			SmoothLighting bool `yaml:"smooth_lighting"`
			Mipmap         bool `yaml:"mipmap"`
			Anisotropic    int  `yaml:"anisotropic"`
		} `yaml:"graphics"`
		Audio struct {
			Volume float64 `yaml:"volume"`
			Music  bool    `yaml:"music"`
		} `yaml:"audio"`
	} `yaml:"client"`
}

// DefaultClient 客户端默认配置。
func DefaultClient() *ClientConfig {
	c := &ClientConfig{}
	c.Client.WindowWidth = 1280
	c.Client.WindowHeight = 720
	c.Client.WindowTitle = "年糕历险记"
	c.Client.VSync = true
	c.Client.FOV = 70
	c.Client.RenderDistance = 12
	c.Client.Language = "zh_cn"
	c.Client.Graphics.SmoothLighting = true
	c.Client.Graphics.Mipmap = true
	c.Client.Graphics.Anisotropic = 4
	c.Client.Audio.Volume = 1.0
	c.Client.Audio.Music = true
	return c
}

// ServerConfig 服务器配置（设计.md §14.1）。
type ServerConfig struct {
	Server struct {
		Port         int `yaml:"port"`
		MaxPlayers   int `yaml:"max_players"`
		ViewDistance int `yaml:"view_distance"`
		TickRate     int `yaml:"tick_rate"`
	} `yaml:"server"`
	World struct {
		Seed      int64  `yaml:"seed"`
		Name      string `yaml:"name"`
		Generator struct {
			BiomeScale  float64 `yaml:"biome_scale"`
			HeightScale float64 `yaml:"height_scale"`
			CaveDensity float64 `yaml:"cave_density"`
		} `yaml:"generator"`
	} `yaml:"world"`
	Mods struct {
		Enabled         bool   `yaml:"enabled"`
		Directory       string `yaml:"directory"`
		AllowScripts    bool   `yaml:"allow_scripts"`
		ScriptTimeoutMS int    `yaml:"script_timeout_ms"`
		HotReload       bool   `yaml:"hot_reload"`
	} `yaml:"mods"`
}

// DefaultServer 服务器默认配置。
func DefaultServer() *ServerConfig {
	c := &ServerConfig{}
	c.Server.Port = 25565
	c.Server.MaxPlayers = 20
	c.Server.ViewDistance = 10
	c.Server.TickRate = 20
	c.World.Seed = 123456789
	c.World.Name = "NewWorld"
	c.World.Generator.BiomeScale = 0.005
	c.World.Generator.HeightScale = 0.01
	c.World.Generator.CaveDensity = 0.1
	c.Mods.Enabled = true
	c.Mods.Directory = "mods"
	c.Mods.AllowScripts = true
	c.Mods.ScriptTimeoutMS = 5
	return c
}

// Load 读取 YAML 配置；文件不存在时返回 defaults（零拷贝不可行则回退默认构造）。
func Load[T any](path string, defaults *T) (*T, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return defaults, nil
		}
		return nil, fmt.Errorf("config.Load %s: %w", path, err)
	}
	out := new(T)
	if defaults != nil {
		*out = *defaults
	}
	if err := yaml.Unmarshal(b, out); err != nil {
		return nil, fmt.Errorf("config.Load %s: %w", path, err)
	}
	return out, nil
}