MMM-HomeAssistantDisplay/node_helper.js

/* Magic Mirror
 * Node Helper: MMM-HomeAssistantDisplay
 *
 * By Brian Towles
 * MIT Licensed.
 *
 * Resilience improvements by James (2026-02-27):
 * - Circuit breaker: stops all template evals when HA is unreachable
 * - Exponential backoff on retries (no more 30 simultaneous retry timers)
 * - Coalesced health checks instead of per-section retries
 * - Graceful degradation: sections show stale data instead of freezing
 */
var backoff = require('backoff')
const NodeHelper = require("node_helper");
const HomeAssistant = require("homeassistant");
const HomeAssistantWS = require("homeassistant-ws");
const Logger = require("./helpers/Logger");
util = require('util'),


module.exports = NodeHelper.create({
	start,
	stop,
	socketNotificationReceived,
	connect,
	reconnectWebsocket,
	connectWebsocket,
	buildHttpUrl,
	onStateChangedEvent,
	evaluateTemplate,
	onWebsocketCloseEvent,
	backoffWSConnection,
	_getBreaker,
	_openCircuit,
	_closeCircuit,
	_healthCheck,
});

function start() {
	this.logger = new Logger(this.name);
	if (config.debuglogging) {
		this.logger.debug("MMM-HomeAssistantDisplay helper started...");
	}
	this.connections = {};

	// Circuit breaker state: tracks HA reachability per connection
	// When open, template evaluations are skipped entirely (no requests, no error spam)
	this._circuitBreaker = {};  // identifier -> { state: 'closed'|'open', failCount: 0, nextRetryAt: 0, retryTimer: null }
}

function stop() {
	for (const connection in this.connections) {
		this.connections[connection].websocket.unsubscribeFromEvent("state_changed");
	}
}

function socketNotificationReceived(notification, payload) {
	if (config.debuglogging) {
		this.logger.debug(`Recieved notification ${notification}`, payload);
	}
	if (notification !== "CONNECT" && (!payload.identifier || !this.connections[payload.identifier])) {
		this.logger.error(`No connection for ${payload.identifier} found`);
		return;
	}
	switch (notification) {
		case "CONNECT":
			this.connect(payload);
			break;
		case "RECONNECT_WS":
			this.reconnectWebsocket(payload);
			break;
		case "SET_WATCHED_ENTITY":
			if (!this.connections[payload.identifier].entities.includes(payload.entity)) {
				if (config.debuglogging) {
					this.logger.debug(`Registering entity ${payload.entity}`);
				}
				this.connections[payload.identifier].entities.push(payload.entity);
			}
			break;
		case "RENDER_MODULE_DISPLAY_TEMPLATE":
			this.evaluateTemplate(payload).then((ret) => {
				this.sendSocketNotification("MODULE_DISPLAY_RENDERED", ret);
			}).catch((err) => {
				// Only log if circuit is closed (avoid spam when HA is down)
				const cb = this._getBreaker(payload.identifier);
				if (cb.state === 'closed') {
					this.logger.error("Unable to evaluate template", err);
				}
			});
			break;
		case "RENDER_SECTION_DISPLAY_TEMPLATE":
			this.evaluateTemplate(payload).then((ret) => {
				this.sendSocketNotification("SECTION_DISPLAY_RENDERED", {
					...ret, 
					section: payload.section
				});
			}).catch((err) => {
				const cb = this._getBreaker(payload.identifier);
				if (cb.state === 'closed') {
					this.logger.error("unable to evaluate section template", err);
				}
			});
			break;			
	}
}

// Circuit breaker helpers
function _getBreaker(identifier) {
	if (!this._circuitBreaker[identifier]) {
		this._circuitBreaker[identifier] = {
			state: 'closed',      // closed = healthy, open = HA unreachable
			failCount: 0,
			nextRetryAt: 0,
			retryTimer: null,
			pendingQueue: [],     // queued payloads to retry when circuit closes
		};
	}
	return this._circuitBreaker[identifier];
}

function _openCircuit(identifier) {
	const breaker = this._getBreaker(identifier);
	if (breaker.state === 'open') return; // already open

	breaker.state = 'open';
	breaker.failCount++;
	// Exponential backoff: 15s, 30s, 60s, 120s, max 300s
	const delay = Math.min(15000 * Math.pow(2, breaker.failCount - 1), 300000);
	breaker.nextRetryAt = Date.now() + delay;

	this.logger.info(`Circuit OPEN for ${identifier} — HA unreachable. Next health check in ${delay / 1000}s`);

	// Single coalesced health check timer (not per-section!)
	if (breaker.retryTimer) clearTimeout(breaker.retryTimer);
	breaker.retryTimer = setTimeout(() => {
		this._healthCheck(identifier);
	}, delay);
}

function _closeCircuit(identifier) {
	const breaker = this._getBreaker(identifier);
	if (breaker.state === 'closed') return;

	this.logger.info(`Circuit CLOSED for ${identifier} — HA is reachable again`);
	breaker.state = 'closed';
	breaker.failCount = 0;
	breaker.nextRetryAt = 0;
	if (breaker.retryTimer) {
		clearTimeout(breaker.retryTimer);
		breaker.retryTimer = null;
	}

	// Replay queued template evaluations
	const queue = breaker.pendingQueue.splice(0);
	if (queue.length > 0) {
		this.logger.info(`Replaying ${queue.length} queued template evaluations for ${identifier}`);
		for (const item of queue) {
			this.evaluateTemplate(item.payload).then((ret) => {
				if (item.payload.section !== undefined) {
					this.sendSocketNotification("SECTION_DISPLAY_RENDERED", {
						...ret,
						section: item.payload.section
					});
				} else {
					this.sendSocketNotification("MODULE_DISPLAY_RENDERED", ret);
				}
			}).catch(() => {
				// Circuit will re-open if this fails
			});
		}
	}
}

async function _healthCheck(identifier) {
	const breaker = this._getBreaker(identifier);
	const hass = this.connections[identifier] && this.connections[identifier].hass;
	if (!hass) return;

	this.logger.info(`Health check for ${identifier}...`);
	try {
		// Simple template render as health probe
		await Promise.race([
			hass.templates.render("{{ 1 }}"),
			new Promise((_, reject) =>
				setTimeout(() => reject(new Error('Health check timeout')), 10000)
			)
		]);
		// Success — close the circuit
		this._closeCircuit(identifier);
	} catch (err) {
		this.logger.info(`Health check failed for ${identifier}: ${err.message}`);
		// Re-arm with increased backoff
		breaker.state = 'closed'; // briefly close so _openCircuit fires
		this._openCircuit(identifier);
	}
}

async function evaluateTemplate(payload) {
	if (config.debuglogging) {
		this.logger.debug(`Evaluating template for ${payload.template}`);
	}

	// Circuit breaker check: if HA is known-unreachable, skip entirely
	const breaker = this._getBreaker(payload.identifier);
	if (breaker.state === 'open') {
		// Queue this request for replay when circuit closes (deduplicated by section)
		const isDuplicate = breaker.pendingQueue.some(
			(item) => item.payload.section === payload.section && item.payload.template === payload.template
		);
		if (!isDuplicate) {
			breaker.pendingQueue.push({ payload });
			// Cap queue size to prevent memory growth
			if (breaker.pendingQueue.length > 20) {
				breaker.pendingQueue.shift();
			}
		}
		throw new Error('Circuit open — HA unreachable, skipping template evaluation');
	}

	const hass = this.connections[payload.identifier].hass;

	try {
		// Wrap template call with timeout
		const response = await Promise.race([
			hass.templates.render(payload.template),
			new Promise((_, reject) =>
				setTimeout(() => reject(new Error('Template evaluation timeout')), 10000)
			)
		]);

		// Success — ensure circuit is closed (resets fail count)
		if (breaker.failCount > 0) {
			this._closeCircuit(payload.identifier);
		}

		return {
			identifier: payload.identifier,
			render: response
		};
	} catch (err) {
		// Check if this is a connectivity error (not a template syntax error)
		const isConnectivityError = /ENETUNREACH|ECONNREFUSED|ECONNRESET|ETIMEDOUT|EHOSTUNREACH|timeout/i.test(err.message);

		if (isConnectivityError) {
			this.logger.error(`Template evaluation failed (connectivity): ${err.message}`);
			this._openCircuit(payload.identifier);
		} else {
			// Template/logic error — log but don't trip the breaker
			this.logger.error(`Template evaluation failed: ${err.message}`);
		}

		throw err;
	}
}

function buildHttpUrl(config) {
	if (config.useTLS){
		schema = "https"
	}
	else {
		schema = "http"
	}
	var url = `${schema}://${config.host}`;
	return url;
}


async function connect(payload) {
	const connectionConfig = {
		host: payload.host,
		port: payload.port,
		token: payload.token,
		ignoreCert: payload.ignoreCert,
		useTLS: payload.useTLS,
	};
	const hass = new HomeAssistant({...connectionConfig, host: this.buildHttpUrl(connectionConfig)});
	this.logger.info(`HomeAssistant connected for ${payload.identifier}`);
	this.connections[payload.identifier] = {
		hass,
		entities: []
	};

	await this.backoffWSConnection(payload.identifier, connectionConfig)
}

async function backoffWSConnection(identifier, connectionConfig) {
	self = this;
	var call = backoff.call(this.connectWebsocket, this, identifier, connectionConfig, function(err, res) {		
		if (err) {
			self.logger.info(`Unable to connect to Home Assistant for ${identifier}: ` + err.message);
		} else {
			self.logger.info(`Conected to Home Assistant for ${identifier} after ${call.getNumRetries()} retries`);	
		}
	});

	call.retryIf(function(err) {
		 return true; 
	});

	call.setStrategy(new backoff.ExponentialStrategy({
		initialDelay: 10,
		maxDelay: 10000
	}));

	call.start();
}

function connectWebsocket(obj, identifier, connectionConfig, callback) {
	var self = obj;
	HomeAssistantWS.default({
		...connectionConfig,
		protocol: ((connectionConfig.useTLS) ? "wss" : "ws")
	})
		.then((hassWs) => {
			self.connections[identifier].websocket = hassWs;
			hassWs.on("state_changed", onStateChangedEvent.bind(self));
			hassWs.on("ws_close", onWebsocketCloseEvent.bind(self));
			callback(null, hassWs);
		})
		.catch((err) => {
			self.logger.error(
				`Unable to connect to Home Assistant for module ${identifier} failed with message: `,
				err.message
			);
			callback(err, null);
		});
	return;
}

async function reconnectWebsocket(payload) {
	const connectionConfig = {
		host: payload.host,
		port: payload.port,
		token: payload.token,
		useTLS: payload.useTLS,
		ignoreCert: payload.ignoreCert
	};
	for (const connection in this.connections) {
		if (connection == payload.identifier){
			this.logger.info(`Reconnecting to Home Assistant websocket for ${payload.identifier}`);		
			await this.backoffWSConnection(payload.identifier, connectionConfig)
		}		
	}
}

function onStateChangedEvent(event) {
	for (const connection in this.connections) {
		if (this.connections[connection].entities.includes(event.data.entity_id)) {
			this.sendSocketNotification("CHANGED_STATE", {
				identifier: connection,
				cause: event.data.entity_id,
			});
		}
	}
}

function onWebsocketCloseEvent(event) {
	for (const connection in this.connections) {
		if (event.target == this.connections[connection].websocket.rawClient.ws) {
			this.logger.info(`Hass WS Disconnected (${connection})`);
			this.sendSocketNotification("HASSWS_DISCONNECTED", {
				identifier: connection,
			});
		}
	}
}