index.js

"use strict";

var Service, Characteristic;
var request = require('request');

module.exports = function (homebridge) {
	Service = homebridge.hap.Service;
	Characteristic = homebridge.hap.Characteristic;
	homebridge.registerAccessory("@timjwilkinson/homebridge-purpleair", "PurpleAir", PurpleAirAccessory);
};


/**
 * PurpleAir Accessory
 */
function PurpleAirAccessory(log, config) {
	this.log = log;

	this.purpleID = config.purpleID;
	switch (config.adjust) {
		case 'NONE':
		case 'EPA':
		case 'LRAPA':
		case 'AQANDU':
			this.adjust = config.adjust;
			break;
		default:
			this.adjust = 'NONE';
			break;
	}
	switch (config.statsKey) {
		case 'v':
		case 'v1':
		case 'v2':
		case 'v3':
		case 'v4':
		case 'v5':
		case 'v6':
			this.statsKey = config.statsKey;
			break;
		default:
			this.statsKey = 'v';
			break;
	}
	this.lastupdate = 0;
	this.allowFlaggedData = config.allowFlaggedData;

	this.updateFreq = config.updateFreq;
	if (!this.updateFreq) {
		this.updateFreq = 300		// default 5 minutes
	}
	this.updateMsecs = this.updateFreq * 1000;
	this.includePM10 = config.includePM10 || false;

	this.log.info("PurpleAir is working");

	// Update the air data at the requested frequency.
	var self = this;
	setInterval(function () {
		self.getPurpleAirData();
	}, this.updateMsecs);
	this.getPurpleAirData();
}

PurpleAirAccessory.prototype = {
	/**
	 * Get all Air data from PurpleAir
	 */
	getPurpleAirData: function () {
		// Make request every updateFreq seconds (PurpleAir actual update frequency is around 40 seconds, but we really don't need that precision here}
		// this.log("getPurpleAirData called... lastupdate: %s, now: %s, freq: %s", this.lastupdate.toString(), timenow.toString(), this.updateMsecs.toString());
		var self = this;
		request({
			url: 'https://www.purpleair.com/json?show=' + this.purpleID,
			json: true,
		}, function (err, response, data) {
			// If no errors
			if (!err && response.statusCode === 200) {
				self.updateData(data);
				// If error
			}
			else {
				self.airQuality.updateCharacteristic(Characteristic.StatusFault, 1);
				self.log.error("PurpleAir Network or Unknown Error.");
			};
		});
	},

	/**
	 * Update data
	 */
	updateData: function (data) {
		this.airQuality.updateCharacteristic(Characteristic.StatusFault, 0);

		// PurpleAir outdoor sensors send data from two internal sensors, but indoor sensors only have one
		// We have to verify exterior/interior, and if exterior, whether both sensors are working or only 1
		var dataA;
		var dataB;

		// Basic sanity check
		if (!data.results || !data.results[0] || !data.results[0].Stats) {
			return;
		}

		// Copy over environ in case the rest of dataA is faulty
		if (dataA && dataB) {
			dataB.humidity = dataA.humidity;
			dataB.temp_f = dataA.temp_f;
		}

		dataA = data.results[0];
		if (data.results[1] && data.results[1].Stats && data.results[0].DEVICE_LOCATIONTYPE !== 'inside') {
			dataB = data.results[1];
		}

		// Select only valid data unless explicitly allowed
		if (!this.allowFlaggedData) {
			if (dataA.Flag == 1) {
				dataA = undefined;
			}
			if (dataB && dataB.Flag == 1) {
				dataB = undefined;
			}
		}

		// No valid data
		if (!dataA && !dataB) {
			return;
		}
		// Make sure dataA and dataB are both valid (but can be copies)
		if (!dataA) {
			dataA = dataB;
		}
		if (!dataB) {
			dataB = dataA;
		}

		var statsA = JSON.parse(dataA.Stats);
		var statsB = JSON.parse(dataB.Stats);

		var newest = Math.max(statsA.lastModified, statsB.lastModified);
		if (newest <= this.lastupdate) {
			return;
		}
		this.lastupdate = newest;

		var va = (statsA[this.statsKey] + statsB[this.statsKey]) / 2;
		var pm10 = (parseFloat(dataA.pm10_0_atm) + parseFloat(dataB.pm10_0_atm)) / 2;

		var tempC = (parseFloat(dataA.temp_f) - 32) * 5 / 9;
		var hum = parseFloat(dataA.humidity);

		var pm2_5 = isNaN(hum) ? va : this.adjustPM(va, hum);
		var aqi = this.calculateAQI2_5(pm2_5);
		if (this.includePM10) {
			// If we include PM10 measurements in the AQI, we select the highest of the two
			aqi = Math.max(aqi, this.calculateAQI10(pm10));
		}

		this.airQuality.updateCharacteristic(Characteristic.PM2_5Density, pm2_5.toFixed(2));
		this.airQuality.updateCharacteristic(Characteristic.PM10Density, pm10.toFixed(2));
		this.airQuality.updateCharacteristic(Characteristic.AirQuality, this.transformAQI(aqi));

		this.temperature.updateCharacteristic(Characteristic.CurrentTemperature, tempC);
		this.humidity.updateCharacteristic(Characteristic.CurrentRelativeHumidity, hum);

		this.log.debug("PurpleAir %s pm2_5 is %s, pm10 is %s, AQI is %s, Air Quality is %s. Temperature is %sC. Humidity is %s%%",
			this.statsKey, pm2_5.toString(), pm10.toFixed(2), aqi.toString(), this.airQualityString(aqi), tempC.toFixed(1), hum.toFixed(1));
	},

	adjustPM(pm, rh) {
		switch (this.adjust) {
			case 'EPA':
				pm = 0.534 * pm - 0.0844 * rh + 5.604;
				break;
			case 'LRAPA':
				pm = 0.5 * pm - 0.66;
				break;
			case 'AQANDU':
				pm = 0.778 * pm + 2.65;
				break;
			case 'NONE':
			default:
				break;
		}
		return pm;
	},

	calculateAQI2_5: function (pm) {
		var aqi;
		if (pm > 500) {
			aqi = 500;
		}
		else if (pm > 350.5) {
			aqi = this.remap(pm, 350.5, 500.5, 400, 500);
		}
		else if (pm > 250.5) {
			aqi = this.remap(pm, 250.5, 350.5, 300, 400);
		}
		else if (pm > 150.5) {
			aqi = this.remap(pm, 150.5, 250.5, 200, 300);
		}
		else if (pm > 55.5) {
			aqi = this.remap(pm, 55.5, 150.5, 150, 200);
		}
		else if (pm > 35.5) {
			aqi = this.remap(pm, 35.5, 55.5, 100, 150);
		}
		else if (pm > 12) {
			aqi = this.remap(pm, 12, 35.5, 50, 100);
		}
		else if (pm > 0) {
			aqi = this.remap(pm, 0, 12, 0, 50);
		}
		else {
			aqi = 0
		}
		return Math.round(aqi);
	},

	calculateAQI10: function(pm) {
		var aqi;
		if (pm >= 605) {
			aqi = 500;
		}
		else if (pm >= 505) {
			aqi = this.remap(pm, 505, 605, 400, 500);
		}
		else if (pm >= 425) {
			aqi = this.remap(pm, 425, 505, 300, 400);
		}
		else if (pm >= 355) {
			aqi = this.remap(pm, 355, 425, 200, 300);
		}
		else if (pm >= 255) {
			aqi = this.remap(pm, 255, 355, 150, 200);
		}
		else if (pm >= 155) {
			aqi = this.remap(pm, 155, 255, 100, 150)
		}
		else if (pm >= 55) {
			aqi = this.remap(pm, 55, 155, 50, 100);
		}
		else {
			aqi = this.remap(pm, 0, 55, 0, 50);
		}
		return Math.round(aqi);
	},

	/**
	 * Return Air Quality Index
	 * @param aqi
	 * @returns {number}
	 */
	transformAQI: function (aqi) {
		// this.log("Transforming %s.", aqi.toString())
		if (aqi == undefined) {
			return 0; // Error or unknown response
		}
		else if (aqi <= 50) {
			return 1; // Return EXCELLENT
		}
		else if (aqi <= 100) {
			return 2; // Return GOOD
		}
		else if (aqi <= 150) {
			return 3; // Return FAIR
		}
		else if (aqi <= 200) {
			return 4; // Return INFERIOR
		}
		else if (aqi > 200) {
			return 5; // Return POOR (Homekit only goes to cat 5, so combined the last two AQI cats of Very Unhealty and Hazardous.
		}
	},

	airQualityString: function (aqi) {
		if (aqi == undefined) {
			return "Unknown"; // Error or unknown response
		}
		else if (aqi <= 50) {
			return "Excellent"; // Return EXCELLENT
		}
		else if (aqi <= 100) {
			return "Good"; // Return GOOD
		}
		else if (aqi <= 150) {
			return "Fair"; // Return FAIR
		}
		else if (aqi <= 200) {
			return "Inferior"; // Return INFERIOR
		}
		else if (aqi > 200) {
			return "Poor"; // Return POOR (Homekit only goes to cat 5, so combined the last two AQI cats of Very Unhealty and Hazardous.
		}
	},

	remap: function (value, fromLow, fromHigh, toLow, toHigh) {
		var fromRange = fromHigh - fromLow;
		var toRange = toHigh - toLow;
		var scaleFactor = toRange / fromRange;

		// Re-zero the value within the from range
		var tmpValue = value - fromLow;
		// Rescale the value to the to range
		tmpValue *= scaleFactor;
		// Re-zero back to the to range
		return tmpValue + toLow;
	},


	identify: function (callback) {
		this.log("Identify requested!");
		callback(); // success
	},

	getServices: function () {
		/**
		 * Informations
		 */
		var informationService = new Service.AccessoryInformation();
		informationService
			.updateCharacteristic(Characteristic.Manufacturer, "PurpleAir")
			.updateCharacteristic(Characteristic.Model, "JSON_API")
			.updateCharacteristic(Characteristic.SerialNumber, this.purpleID);

		/**
		 * airQuality, temperature and humidity
		 */
		this.airQuality = new Service.AirQualitySensor('Air Quality');
		this.airQuality.getCharacteristic(Characteristic.AirQuality);
		this.airQuality.getCharacteristic(Characteristic.StatusFault);
		this.airQuality.getCharacteristic(Characteristic.PM2_5Density);
		this.airQuality.getCharacteristic(Characteristic.PM10Density);

		this.temperature = new Service.TemperatureSensor('Temperature');
		this.temperature.getCharacteristic(Characteristic.CurrentTemperature).setProps({ minValue: -40, maxValue: 125 });

		this.humidity = new Service.HumiditySensor('Humidity');
		this.humidity.getCharacteristic(Characteristic.CurrentRelativeHumidity);

		this.airQuality.isPrimaryService = true;
		this.airQuality.linkedServices = [ this.temperature, this.humidity ];

		return [ informationService, this.airQuality, this.temperature, this.humidity ];
	}
};