package config

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"time"
)

// Config holds runtime configuration for the alexa-bridge process.
type Config struct {
	HTTPPort              string        // HTTP_PORT, default "8080"
	AlexaSkillID          string        // ALEXA_SKILL_ID — verified against the request envelope's application ID (required)
	HAGatewayAddr         string        // HA_GATEWAY_ADDR, default "ha-gateway.home-services.svc.cluster.local:50051"
	HAGatewayServerName   string        // HA_GATEWAY_SERVER_NAME, default "ha-gateway.home-services.svc.cluster.local"
	TLSDir                string        // TLS_DIR, default "/tls" — unlike ai-gateway/discord-bot, mTLS is on by default here since alexa-bridge is internet-facing; set empty to disable for local dev
	EntityRefreshInterval time.Duration // ENTITY_REFRESH_INTERVAL, default 5m
	OTELEndpoint          string        // OTEL_ENDPOINT, empty disables telemetry
	LogLevel              string        // LOG_LEVEL, default "info"
	LogFormat             string        // LOG_FORMAT, default "json"
}

// Load reads configuration from environment variables and applies defaults.
func Load() (*Config, error) {
	skillID := os.Getenv("ALEXA_SKILL_ID")
	if skillID == "" {
		return nil, errors.New("ALEXA_SKILL_ID is required but not set")
	}

	refreshInterval, err := parseDurationEnv("ENTITY_REFRESH_INTERVAL", 5*time.Minute)
	if err != nil {
		return nil, err
	}

	cfg := &Config{
		HTTPPort:              getenvDefault("HTTP_PORT", "8080"),
		AlexaSkillID:          skillID,
		HAGatewayAddr:         getenvDefault("HA_GATEWAY_ADDR", "ha-gateway.home-services.svc.cluster.local:50051"),
		HAGatewayServerName:   getenvDefault("HA_GATEWAY_SERVER_NAME", "ha-gateway.home-services.svc.cluster.local"),
		TLSDir:                getenvDefault("TLS_DIR", "/tls"),
		EntityRefreshInterval: refreshInterval,
		OTELEndpoint:          os.Getenv("OTEL_ENDPOINT"),
		LogLevel:              getenvDefault("LOG_LEVEL", "info"),
		LogFormat:             getenvDefault("LOG_FORMAT", "json"),
	}
	if cfg.TLSDir != "" {
		if err := validateTLSDir(cfg.TLSDir); err != nil {
			return nil, err
		}
	}
	return cfg, nil
}

func getenvDefault(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}

func parseDurationEnv(key string, fallback time.Duration) (time.Duration, error) {
	if v := os.Getenv(key); v != "" {
		d, err := time.ParseDuration(v)
		if err != nil {
			return 0, fmt.Errorf("parse %s: %w", key, err)
		}
		return d, nil
	}
	return fallback, nil
}

func validateTLSDir(dir string) error {
	required := []string{"tls.crt", "tls.key", "ca.crt"}
	for _, name := range required {
		path := filepath.Join(dir, name)
		info, err := os.Stat(path)
		if err != nil {
			return fmt.Errorf("tls dir validation failed for %s: %w", path, err)
		}
		if info.IsDir() {
			return fmt.Errorf("tls dir validation failed for %s: %w", path, errors.New("expected file"))
		}
	}
	return nil
}