package config

import (
	"fmt"
	"os"

	"github.com/joho/godotenv"
)

// Config holds all application configuration
type Config struct {
	// Server
	Port        string
	FrontendURL string

	// Database
	DBHost     string
	DBPort     string
	DBUser     string
	DBPassword string
	DBName     string

	// Firebase
	FirebaseProjectID       string
	FirebaseStorageBucket   string
	FirebaseCredentialsFile string
}

// LoadConfig loads configuration from environment variables
// Loading order (later files override earlier ones):
// 1. .env (base/default values)
// 2. .env.local (local development overrides - takes precedence)
// Note: OS environment variables take highest precedence (godotenv won't override them)
func LoadConfig() (*Config, error) {
	// Load .env file if it exists (optional, won't error if missing)
	_ = godotenv.Load(".env")

	// Load .env.local if it exists (overrides .env values)
	// This allows local development overrides without modifying .env
	_ = godotenv.Load(".env.local")

	cfg := &Config{
		// Server
		Port:        getEnv("PORT", "8080"),
		FrontendURL: getEnv("FRONTEND_URL", "http://localhost:5173"),

		// Database
		DBHost:     getEnv("DB_HOST", "localhost"),
		DBPort:     getEnv("DB_PORT", "5432"),
		DBUser:     getEnv("DB_USER", ""),
		DBPassword: getEnv("DB_PASSWORD", ""),
		DBName:     getEnv("DB_NAME", ""),

		// Firebase
		FirebaseProjectID:       getEnv("FIREBASE_PROJECT_ID", ""),
		FirebaseStorageBucket:   getEnv("FIREBASE_STORAGE_BUCKET", ""),
		FirebaseCredentialsFile: getEnv("FIREBASE_CREDENTIALS_FILE", ""),
	}

	// Validate required fields
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("config validation failed: %w", err)
	}

	return cfg, nil
}

// Validate checks that all required configuration values are set
func (c *Config) Validate() error {
	var missing []string

	if c.DBUser == "" {
		missing = append(missing, "DB_USER")
	}
	if c.DBPassword == "" {
		missing = append(missing, "DB_PASSWORD")
	}
	if c.DBName == "" {
		missing = append(missing, "DB_NAME")
	}
	if c.FirebaseProjectID == "" {
		missing = append(missing, "FIREBASE_PROJECT_ID")
	}
	if c.FirebaseStorageBucket == "" {
		missing = append(missing, "FIREBASE_STORAGE_BUCKET")
	}
	if c.FirebaseCredentialsFile == "" {
		// Check if GOOGLE_APPLICATION_CREDENTIALS is set as fallback
		if os.Getenv("GOOGLE_APPLICATION_CREDENTIALS") == "" {
			missing = append(missing, "FIREBASE_CREDENTIALS_FILE (or GOOGLE_APPLICATION_CREDENTIALS)")
		}
	}

	if len(missing) > 0 {
		return fmt.Errorf("missing required environment variables: %v", missing)
	}

	return nil
}

// getEnv gets an environment variable or returns a default value
func getEnv(key, defaultValue string) string {
	if value := os.Getenv(key); value != "" {
		return value
	}
	return defaultValue
}