// Package config loads and validates the Sense process configuration.
package config

import (
	"fmt"
	"net"
	"net/url"
	"os"
	"strconv"
	"time"
)

const (
	defaultHTTPAddress     = "127.0.0.1:8080"
	defaultDatabaseDSN     = "file:data/sense.db"
	defaultMediaMTXURL     = "http://127.0.0.1:9997"
	defaultReconcilePeriod = 5 * time.Second
	defaultProbePeriod     = 10 * time.Second
)

type Config struct {
	HTTPAddress       string
	AllowNonLoopback  bool
	DatabaseDSN       string
	MediaMTXURL       string
	ReconcileInterval time.Duration
	ProbeInterval     time.Duration
}

func Load() (Config, error) {
	allow, err := boolEnv("SENSE_ALLOW_NON_LOOPBACK", false)
	if err != nil {
		return Config{}, err
	}
	reconcilePeriod, err := durationEnv("SENSE_RECONCILE_INTERVAL", defaultReconcilePeriod)
	if err != nil {
		return Config{}, err
	}
	probePeriod, err := durationEnv("SENSE_PROBE_INTERVAL", defaultProbePeriod)
	if err != nil {
		return Config{}, err
	}

	cfg := Config{
		HTTPAddress:       stringEnv("SENSE_HTTP_ADDR", defaultHTTPAddress),
		AllowNonLoopback:  allow,
		DatabaseDSN:       stringEnv("SENSE_DB_DSN", defaultDatabaseDSN),
		MediaMTXURL:       stringEnv("SENSE_MEDIAMTX_URL", defaultMediaMTXURL),
		ReconcileInterval: reconcilePeriod,
		ProbeInterval:     probePeriod,
	}
	if err := cfg.Validate(); err != nil {
		return Config{}, err
	}
	return cfg, nil
}

func (c Config) Validate() error {
	host, _, err := net.SplitHostPort(c.HTTPAddress)
	if err != nil {
		return fmt.Errorf("invalid SENSE_HTTP_ADDR: %w", err)
	}
	ip := net.ParseIP(host)
	isLoopback := host == "localhost" || (ip != nil && ip.IsLoopback())
	if !isLoopback && !c.AllowNonLoopback {
		return fmt.Errorf("non-loopback HTTP bind requires SENSE_ALLOW_NON_LOOPBACK=true")
	}
	if c.DatabaseDSN == "" {
		return fmt.Errorf("SENSE_DB_DSN must not be empty")
	}
	mediaURL, err := url.Parse(c.MediaMTXURL)
	if err != nil || mediaURL.Scheme == "" || mediaURL.Host == "" {
		return fmt.Errorf("invalid SENSE_MEDIAMTX_URL")
	}
	if mediaURL.User != nil {
		return fmt.Errorf("SENSE_MEDIAMTX_URL must not contain credentials")
	}
	if c.ReconcileInterval <= 0 || c.ProbeInterval <= 0 {
		return fmt.Errorf("loop intervals must be positive")
	}
	return nil
}

func stringEnv(name, fallback string) string {
	if value, ok := os.LookupEnv(name); ok {
		return value
	}
	return fallback
}

func boolEnv(name string, fallback bool) (bool, error) {
	value, ok := os.LookupEnv(name)
	if !ok {
		return fallback, nil
	}
	parsed, err := strconv.ParseBool(value)
	if err != nil {
		return false, fmt.Errorf("invalid %s: %w", name, err)
	}
	return parsed, nil
}

func durationEnv(name string, fallback time.Duration) (time.Duration, error) {
	value, ok := os.LookupEnv(name)
	if !ok {
		return fallback, nil
	}
	parsed, err := time.ParseDuration(value)
	if err != nil {
		return 0, fmt.Errorf("invalid %s: %w", name, err)
	}
	return parsed, nil
}