systant/src/mqtt.ts

import mqtt, { type MqttClient, type IClientOptions } from "mqtt";
import type { Config, EntityConfig } from "./config";

export interface MqttConnection {
  client: MqttClient;
  publish(topic: string, payload: string | object, retain?: boolean): Promise<void>;
  subscribe(topic: string, handler: (topic: string, payload: Buffer) => void): Promise<void>;
  disconnect(): Promise<void>;
}

export async function connect(config: Config, hostname: string): Promise<MqttConnection> {
  const options: IClientOptions = {
    clientId: config.mqtt.clientId || `systant-${hostname}`,
    username: config.mqtt.username,
    password: config.mqtt.password,
    will: {
      topic: `${config.mqtt.topicPrefix}/${hostname}/status`,
      payload: Buffer.from("offline"),
      qos: 1,
      retain: true,
    },
  };

  const client = mqtt.connect(config.mqtt.broker, options);
  const handlers = new Map<string, (topic: string, payload: Buffer) => void>();

  await new Promise<void>((resolve, reject) => {
    client.on("connect", () => {
      console.log(`Connected to MQTT broker: ${config.mqtt.broker}`);
      resolve();
    });
    client.on("error", reject);
  });

  client.on("message", (topic, payload) => {
    for (const [pattern, handler] of handlers) {
      if (topicMatches(pattern, topic)) {
        handler(topic, payload);
      }
    }
  });

  // Publish online status
  await publishAsync(client, `${config.mqtt.topicPrefix}/${hostname}/status`, "online", true);

  // Publish HA discovery if enabled
  if (config.homeassistant.discovery) {
    await publishDiscovery(client, config, hostname);
  }

  return {
    client,

    async publish(topic: string, payload: string | object, retain = false): Promise<void> {
      const fullTopic = `${config.mqtt.topicPrefix}/${hostname}/${topic}`;
      const data = typeof payload === "object" ? JSON.stringify(payload) : payload;
      await publishAsync(client, fullTopic, data, retain);
    },

    async subscribe(topic: string, handler: (topic: string, payload: Buffer) => void): Promise<void> {
      const fullTopic = `${config.mqtt.topicPrefix}/${hostname}/${topic}`;
      handlers.set(fullTopic, handler);
      await new Promise<void>((resolve, reject) => {
        client.subscribe(fullTopic, { qos: 1 }, (err) => {
          if (err) reject(err);
          else resolve();
        });
      });
      console.log(`Subscribed to: ${fullTopic}`);
    },

    async disconnect(): Promise<void> {
      await publishAsync(client, `${config.mqtt.topicPrefix}/${hostname}/status`, "offline", true);
      await new Promise<void>((resolve) => client.end(false, {}, () => resolve()));
    },
  };
}

function publishAsync(client: MqttClient, topic: string, payload: string, retain: boolean): Promise<void> {
  return new Promise((resolve, reject) => {
    client.publish(topic, payload, { qos: 1, retain }, (err) => {
      if (err) reject(err);
      else resolve();
    });
  });
}

function topicMatches(pattern: string, topic: string): boolean {
  if (pattern === topic) return true;
  if (pattern.endsWith("#")) {
    return topic.startsWith(pattern.slice(0, -1));
  }
  return false;
}

async function publishDiscovery(client: MqttClient, config: Config, hostname: string): Promise<void> {
  const prefix = config.homeassistant.discoveryPrefix;
  const topicPrefix = config.mqtt.topicPrefix;

  const entityCount = Object.keys(config.entities).length;
  if (entityCount === 0) {
    console.log("No entities configured, skipping HA discovery");
    return;
  }

  for (const [id, entity] of Object.entries(config.entities)) {
    const payload = buildDiscoveryPayload(id, entity, hostname, topicPrefix);
    const discoveryTopic = `${prefix}/${entity.type}/${hostname}_${id}/config`;
    await publishAsync(client, discoveryTopic, JSON.stringify(payload), true);
  }

  console.log(`Published Home Assistant discovery for ${entityCount} entity/entities`);
}

function buildDiscoveryPayload(
  id: string,
  entity: EntityConfig,
  hostname: string,
  topicPrefix: string
): Record<string, unknown> {
  const displayName = entity.name || id.replace(/_/g, " ");

  const payload: Record<string, unknown> = {
    name: displayName,
    unique_id: `systant_${hostname}_${id}`,
    device: {
      identifiers: [`systant_${hostname}`],
      name: `${hostname}`,
      manufacturer: "Systant",
    },
  };

  // Stateful entities have a state_topic (buttons don't)
  if (entity.type !== "button") {
    payload.state_topic = `${topicPrefix}/${hostname}/${id}/state`;
  }

  // Add availability tracking unless explicitly disabled
  if (entity.availability !== false) {
    payload.availability_topic = `${topicPrefix}/${hostname}/status`;
    payload.payload_available = "online";
    payload.payload_not_available = "offline";
  }

  // Common optional fields
  if (entity.icon) payload.icon = entity.icon;

  // Type-specific fields
  switch (entity.type) {
    case "sensor":
      if (entity.unit) payload.unit_of_measurement = entity.unit;
      if (entity.device_class) payload.device_class = entity.device_class;
      break;

    case "binary_sensor":
      payload.payload_on = "ON";
      payload.payload_off = "OFF";
      if (entity.device_class) payload.device_class = entity.device_class;
      break;

    case "light":
    case "switch":
      payload.command_topic = `${topicPrefix}/${hostname}/${id}/set`;
      payload.payload_on = "ON";
      payload.payload_off = "OFF";
      payload.state_on = "ON";
      payload.state_off = "OFF";
      break;

    case "button":
      payload.command_topic = `${topicPrefix}/${hostname}/${id}/press`;
      payload.payload_press = "PRESS";
      break;
  }

  return payload;
}