package main

import (
	_ "embed"
	"encoding/json"
	"fmt"
	"log"
	"net"
	"net/url"
	"regexp"
	"strconv"
	"time"
)

const (
	MQTT_BROKER_REGEX       = `^tcp://127\.0\.0\.1:\d+$`
	MQTT_CLIENT_ID_REGEX    = `^[0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ]{1,23}$`
	MQTT_TOPIC_PREFIX_REGEX = `^[a-zA-Z0-9]{1,20}$`
)

var (
	mqttBrokerRegexp      *regexp.Regexp
	mqttClientIDRegexp    *regexp.Regexp
	mqttTopicPrefixRegexp *regexp.Regexp
)

func init() {
	mqttBrokerRegexp = regexp.MustCompile(MQTT_BROKER_REGEX)
	mqttClientIDRegexp = regexp.MustCompile(MQTT_CLIENT_ID_REGEX)
	mqttTopicPrefixRegexp = regexp.MustCompile(MQTT_TOPIC_PREFIX_REGEX)
}

//go:embed configs/default.json
var defaultConfig []byte

type MQTTConfig struct {
	Broker      string `json:"broker"`
	ClientID    string `json:"client-id"`
	TopicPrefix string `json:"topic-prefix"`
}

type HomematicConfig struct {
	CCU           string `json:"ccu"`
	PollingPeriod string `json:"polling-period"`
}

type StartupConfig struct {
	MQTT      MQTTConfig      `json:"mqtt"`
	Homematic HomematicConfig `json:"homematic"`
}

func (sc StartupConfig) Validate() error {
	if !mqttBrokerRegexp.MatchString(sc.MQTT.Broker) {
		return fmt.Errorf(
			"mqtt/broker configuration '%s' does not match regular expression '%s'.",
			sc.MQTT.Broker,
			MQTT_BROKER_REGEX,
		)
	}

	if !mqttClientIDRegexp.MatchString(sc.MQTT.ClientID) {
		return fmt.Errorf(
			"mqtt/client-id configuration '%s' does not match regular expression '%s'.",
			sc.MQTT.ClientID,
			MQTT_CLIENT_ID_REGEX,
		)
	}

	if !mqttTopicPrefixRegexp.MatchString(sc.MQTT.TopicPrefix) {
		return fmt.Errorf(
			"mqtt/topic-prefix configuration '%s' does not match regular expression '%s'.",
			sc.MQTT.TopicPrefix,
			MQTT_TOPIC_PREFIX_REGEX,
		)
	}

	cu, err := url.Parse(sc.Homematic.CCU)
	if err != nil {
		return fmt.Errorf("homematic/ccu configuration '%s' cannot be parsed as URL: %v", sc.Homematic.CCU, err)
	}

	if cu.Scheme != `http` {
		return fmt.Errorf("homematic/ccu configuration '%s' must use scheme 'http'.", sc.Homematic.CCU)
	}

	host, portstring, err := net.SplitHostPort(cu.Host)
	if err != nil {
		return fmt.Errorf("homematic/ccu configuration '%s' can't be split into hostname and port: %v", sc.Homematic.CCU, err)
	}

	ip := net.ParseIP(host)
	if ip == nil {
		return fmt.Errorf("homematic/ccu configuration '%s' must use a plain IP address as host.", sc.Homematic.CCU)
	}

	_, err = strconv.Atoi(portstring)
	if err != nil {
		return fmt.Errorf("homematic/ccu configuration '%s' must use a numeric port: %v", sc.Homematic.CCU, err)
	}

	_, err = time.ParseDuration(sc.Homematic.PollingPeriod)
	if err != nil {
		return fmt.Errorf("homematic/polling-period configuration '%s' could not be parsed to duration: %v", sc.Homematic.PollingPeriod, err)
	}

	return nil
}

func (sc *StartupConfig) FromJSON(data []byte) error {
	err := json.Unmarshal(data, sc)
	if err != nil {
		return fmt.Errorf("Failed to unmarshal configuration: %w", err)
	}

	err = sc.Validate()
	if err != nil {
		return fmt.Errorf("Could not validate configuration: %w", err)
	}

	return nil
}

func GetStartupConfig() StartupConfig {
	config := StartupConfig{}

	err := config.FromJSON(defaultConfig)
	if err != nil {
		log.Fatalf("Could not parse default config: %v", err)
	}

	return config
}