package config

import (
	"encoding/base64"
	"encoding/json"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

// saveMu serializes Saves: the UI thread (path browse, Dalamud toggle) and the
// login worker (credentials after a successful login) can both Save, and they
// would otherwise interleave on the same .tmp file.
var saveMu sync.Mutex

type Config struct {
	GamePath string `json:"game_path"`
	User     string `json:"user"`
	Pass     string `json:"pass"`
	Dalamud  bool   `json:"dalamud"` // launch with the Dalamud plugin framework
}

func Path() (string, error) {
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(dir, "ffxiv-tiny-launcher", "config"), nil
}

// Load reads the config file if present. Missing file yields an empty config.
func Load() (Config, error) {
	var cfg Config
	p, err := Path()
	if err != nil {
		return cfg, err
	}
	data, err := os.ReadFile(p)
	if err != nil {
		if os.IsNotExist(err) {
			return cfg, nil
		}
		return cfg, err
	}
	raw, err := base64.StdEncoding.DecodeString(string(data))
	if err != nil {
		return Config{}, nil // corrupted; start fresh rather than crash
	}
	for i := range raw {
		raw[i] ^= key[i%len(key)]
	}
	// A mangled file (e.g. a torn write on older builds) can contain invalid
	// UTF-8, which json.Unmarshal rejects outright — replace such bytes before
	// parsing so the rest of the config still loads and nothing raw ever
	// reaches the UI or the login request. (SE passwords are ASCII in
	// practice, so this only ever triggers on corruption.)
	raw = []byte(strings.ToValidUTF8(string(raw), "\uFFFD"))
	if err := json.Unmarshal(raw, &cfg); err != nil {
		return Config{}, nil
	}
	return cfg, nil
}

// Save writes the config obfuscated (XOR+base64). This is hiding from
// casual eyes only, not real protection. Callers must pass a snapshot of the
// config, never a struct they may still be mutating on another goroutine.
func Save(cfg Config) error {
	saveMu.Lock()
	defer saveMu.Unlock()

	p, err := Path()
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(p), 0o700); err != nil {
		return err
	}
	raw, err := json.Marshal(cfg)
	if err != nil {
		return err
	}
	for i := range raw {
		raw[i] ^= key[i%len(key)]
	}
	// Write atomically (temp file + rename) so a crash mid-write can never
	// leave a truncated config behind.
	tmp := p + ".tmp"
	if err := os.WriteFile(tmp, []byte(base64.StdEncoding.EncodeToString(raw)), 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, p)
}

var key = []byte("ffxiv-tiny-launcher-key")