package config

import (
	"os"
	"path/filepath"
	"sync"

	"gopkg.in/yaml.v3"
)

// Config holds all client configuration.
type Config struct {
	EngineURL     string `yaml:"engine_url"`
	APIKey        string `yaml:"api_key"`
	DefaultFormat string `yaml:"default_format"`
}

var (
	cfg  Config
	once sync.Once
)

// Load reads configuration from ~/.kb/client.yaml, then applies environment
// variable overrides. Defaults are applied first.
func Load() error {
	var loadErr error
	once.Do(func() {
		// Defaults
		cfg = Config{
			EngineURL:     "http://localhost:8000",
			DefaultFormat: "human",
		}

		// Read config file if it exists
		home, err := os.UserHomeDir()
		if err == nil {
			path := filepath.Join(home, ".kb", "client.yaml")
			data, err := os.ReadFile(path)
			if err == nil {
				var fileCfg Config
				if err := yaml.Unmarshal(data, &fileCfg); err == nil {
					if fileCfg.EngineURL != "" {
						cfg.EngineURL = fileCfg.EngineURL
					}
					if fileCfg.APIKey != "" {
						cfg.APIKey = fileCfg.APIKey
					}
					if fileCfg.DefaultFormat != "" {
						cfg.DefaultFormat = fileCfg.DefaultFormat
					}
				}
			}
		}

		// Environment variable overrides
		if v := os.Getenv("KB_ENGINE_URL"); v != "" {
			cfg.EngineURL = v
		}
		if v := os.Getenv("KB_API_KEY"); v != "" {
			cfg.APIKey = v
		}
	})
	return loadErr
}

// Get returns the loaded configuration singleton.
func Get() *Config {
	return &cfg
}

// ApplyFlags overrides configuration with CLI flag values (only if non-empty).
func ApplyFlags(engine, format, apiKey string) {
	if engine != "" {
		cfg.EngineURL = engine
	}
	if format != "" {
		cfg.DefaultFormat = format
	}
	if apiKey != "" {
		cfg.APIKey = apiKey
	}
}