// package config manages launcher configuration and system paths.
package config

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"runtime"
)

// AppName is the canonical name for the launcher and its data directory.
const AppName = "MrixsCraft"

// Settings represents the user-configurable launcher settings stored in launcher.json.
type Settings struct {
	ServerURL    string `json:"server_url"`    // Base URL of the backend (e.g. "https://minecraft.mrixs.me")
	SelectedPack string `json:"selected_pack"` // Slug of the selected modpack
	MemoryMB     int    `json:"memory_mb"`     // Allocated RAM in MB (for -Xms / -Xmx)
	ExtraArgs    string `json:"extra_args"`    // Additional JVM flags
	Width        int    `json:"window_width"`  // Main window width
	Height       int    `json:"window_height"` // Main window height
}

// serverEnvURL is the environment variable that overrides the backend base URL.
const serverEnvURL = "MRIXSCRAFT_SERVER_URL"

// defaultServerURL is used when neither the env var nor launcher.json provide a value.
const defaultServerURL = "https://minecraft.mrixs.me"

// DefaultSettings returns sensible defaults.
func DefaultSettings() Settings {
	url := os.Getenv(serverEnvURL)
	if url == "" {
		url = defaultServerURL
	}
	return Settings{
		ServerURL:    url,
		SelectedPack: "",
		MemoryMB:     4096,
		ExtraArgs:    "",
		Width:        900,
		Height:       600,
	}
}

// RootDir returns the OS-specific data directory for the launcher.
func RootDir() (string, error) {
	switch runtime.GOOS {
	case "windows":
		appData := os.Getenv("APPDATA")
		if appData == "" {
			return "", fmt.Errorf("APPDATA environment variable is empty")
		}
		return filepath.Join(appData, AppName), nil

	case "darwin":
		home, err := os.UserHomeDir()
		if err != nil {
			return "", fmt.Errorf("resolving home directory: %w", err)
		}
		return filepath.Join(home, "Library", "Application Support", AppName), nil

	default: // linux and other unixes
		home, err := os.UserHomeDir()
		if err != nil {
			return "", fmt.Errorf("resolving home directory: %w", err)
		}
		return filepath.Join(home, "."+AppName), nil
	}
}

// EnsureRoot creates the root data directory if it does not exist.
func EnsureRoot() (string, error) {
	dir, err := RootDir()
	if err != nil {
		return "", err
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return "", fmt.Errorf("creating root directory %s: %w", dir, err)
	}
	return dir, nil
}

// Subdirectory returns (and optionally creates) a subdirectory under the root.
func Subdirectory(name string, create bool) (string, error) {
	root, err := RootDir()
	if err != nil {
		return "", err
	}
	path := filepath.Join(root, name)
	if create {
		if err := os.MkdirAll(path, 0o755); err != nil {
			return "", fmt.Errorf("creating subdirectory %s: %w", path, err)
		}
	}
	return path, nil
}

// JavaDir returns the directory for a specific Java version.
func JavaDir(version int) (string, error) {
	return Subdirectory(filepath.Join("Java", fmt.Sprintf("%d", version)), true)
}

// InstancesDir returns the directory containing modpack instances.
func InstancesDir() (string, error) {
	return Subdirectory("instances", true)
}

// InstanceDir returns the directory for a specific modpack.
func InstanceDir(slug string) (string, error) {
	return Subdirectory(filepath.Join("instances", slug), true)
}

// AssetsDir returns the assets cache directory.
func AssetsDir() (string, error) {
	return Subdirectory("assets", true)
}

// LibrariesDir returns the libraries cache directory.
func LibrariesDir() (string, error) {
	return Subdirectory("libraries", true)
}

// LauncherJSONPath returns the full path to launcher.json.
func LauncherJSONPath() (string, error) {
	root, err := RootDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(root, "launcher.json"), nil
}

// Load reads launcher.json from disk, returning defaults if the file does not exist.
func Load() (Settings, error) {
	path, err := LauncherJSONPath()
	if err != nil {
		return Settings{}, err
	}

	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return DefaultSettings(), nil
		}
		return Settings{}, fmt.Errorf("reading %s: %w", path, err)
	}

	var s Settings
	if err := json.Unmarshal(data, &s); err != nil {
		return Settings{}, fmt.Errorf("parsing %s: %w", path, err)
	}
	return s, nil
}

// Save writes the settings to launcher.json.
func Save(s Settings) error {
	path, err := LauncherJSONPath()
	if err != nil {
		return err
	}

	data, err := json.MarshalIndent(s, "", "  ")
	if err != nil {
		return fmt.Errorf("serializing settings: %w", err)
	}

	if err := os.WriteFile(path, data, 0o600); err != nil {
		return fmt.Errorf("writing %s: %w", path, err)
	}
	return nil
}