// Package config loads the server configuration from environment
// variables with sane defaults for local development.
package config

import (
	"fmt"
	"os"
	"strings"
)

// Config holds all runtime configuration for the API server.
type Config struct {
	// HTTPAddr is the listen address, e.g. ":8080".
	HTTPAddr string
	// StaticDir points to the built frontend (React/Vite dist).
	// Empty disables static file serving.
	StaticDir string
	// Environment is "development", "staging" or "production".
	Environment string
	// AllowedOrigins is a comma-separated list of CORS origins
	// allowed to call the API from a browser.
	AllowedOrigins []string
	// DatabaseURL is the PostgreSQL DSN.
	DatabaseURL string
	// JWTSecret signs access tokens. Must be set in production.
	JWTSecret string
	// MediaDir is the local disk location for uploaded attachments.
	MediaDir string
}

// Load reads configuration from the environment, falling back to
// development-friendly defaults. Unknown values are validated.
func Load() (*Config, error) {
	cfg := &Config{
		HTTPAddr:    fromEnv("MESSENGER_HTTP_ADDR", ":8080"),
		StaticDir:   os.Getenv("MESSENGER_STATIC_DIR"),
		Environment: fromEnv("MESSENGER_ENV", "development"),
		DatabaseURL: fromEnv("MESSENGER_DATABASE_URL", "postgres://messenger:messenger@localhost:5432/messenger?sslmode=disable"),
		JWTSecret:   fromEnv("MESSENGER_JWT_SECRET", "dev-secret-change-me"),
		MediaDir:    fromEnv("MESSENGER_MEDIA_DIR", "./media"),
	}

	for _, origin := range strings.Split(fromEnv("MESSENGER_ALLOWED_ORIGINS", ""), ",") {
		if origin = strings.TrimSpace(origin); origin != "" {
			cfg.AllowedOrigins = append(cfg.AllowedOrigins, origin)
		}
	}

	switch cfg.Environment {
	case "development", "staging", "production":
	default:
		return nil, fmt.Errorf("MESSENGER_ENV must be one of development|staging|production, got %q", cfg.Environment)
	}

	if cfg.Environment == "production" && cfg.JWTSecret == "dev-secret-change-me" {
		return nil, fmt.Errorf("MESSENGER_JWT_SECRET must be set in production")
	}

	return cfg, nil
}

// fromEnv returns the value of the environment variable name, or
// fallback if the variable is unset or empty.
func fromEnv(name, fallback string) string {
	if v := os.Getenv(name); v != "" {
		return v
	}
	return fallback
}