File-based motion or contact sensor

This module creates a motion sensor accessory based on watching a
directory or file.

accessories/FileSensor.js

@@ -0,0 +1,76 @@
+var Service = require("HAP-NodeJS").Service;
+var Characteristic = require("HAP-NodeJS").Characteristic;
+var chokidar = require("chokidar");
+var debug = require("debug")("FileSensorAccessory");
+var crypto = require("crypto");
+
+module.exports = {
+  accessory: FileSensorAccessory
+}
+
+function FileSensorAccessory(log, config) {
+  this.log = log;
+
+  // url info
+  this.name = config["name"];
+  this.path = config["path"];
+  this.window_seconds = config["window_seconds"] || 5;
+  this.sensor_type = config["sensor_type"] || "m";
+  this.inverse = config["inverse"] || false;
+  
+  if(config["sn"]){
+      this.sn = config["sn"];
+  } else {
+      var shasum = crypto.createHash('sha1');
+      shasum.update(this.path);
+      this.sn = shasum.digest('base64');
+      debug('Computed SN ' + this.sn);
+  }
+}
+
+FileSensorAccessory.prototype = {
+
+  getServices: function() {
+
+    // you can OPTIONALLY create an information service if you wish to override
+    // the default values for things like serial number, model, etc.
+    var informationService = new Service.AccessoryInformation();
+    
+    informationService
+      .setCharacteristic(Characteristic.Name, this.name)
+      .setCharacteristic(Characteristic.Manufacturer, "Homebridge")
+      .setCharacteristic(Characteristic.Model, "File Sensor")
+      .setCharacteristic(Characteristic.SerialNumber, this.sn);
+    
+    var service, changeAction;
+    if(this.sensor_type === "c"){
+        service = new Service.ContactSensor();
+        changeAction = function(newState){
+            service.getCharacteristic(Characteristic.ContactSensorState)
+                    .setValue(newState ? Characteristic.ContactSensorState.CONTACT_DETECTED : Characteristic.ContactSensorState.CONTACT_NOT_DETECTED);
+        };
+    } else {
+        service = new Service.MotionSensor();
+        changeAction = function(newState){
+            service.getCharacteristic(Characteristic.MotionDetected)
+                    .setValue(newState);
+        };
+    }
+    
+    var changeHandler = function(path, stats){
+        var d = new Date();
+        if(d.getTime() - stats.mtime.getTime() <= (this.window_seconds * 1000)){
+            var newState = this.inverse ? false : true;
+            changeAction(newState);
+            if(this.timer !== undefined) clearTimeout(this.timer);
+            this.timer = setTimeout(function(){changeAction(!newState);}, this.window_seconds * 1000);
+        }
+    }.bind(this);
+    
+    var watcher = chokidar.watch(this.path, {alwaysStat: true});
+    watcher.on('add', changeHandler);
+    watcher.on('change', changeHandler);
+    
+    return [informationService, service];
+  }
+};