Update P1Service.js

- Add accessory for Capacity tariff, see #69.

lib/P1Service.js

@@ -33,6 +33,7 @@ class P1Service extends homebridgeLib.ServiceDelegate {
   }
 
   static get Electricity () { return Electricity }
+  static get ElectricityCapacity () { return ElectricityCapacity }
   static get Phase () { return Phase }
   static get Gas () { return Gas }
   static get Water () { return Water }
@@ -110,6 +111,34 @@ class Electricity extends P1Service {
   }
 }
 
+class ElectricityCapacity extends P1Service {
+  constructor (p1Accessory, data) {
+    super(p1Accessory, data)
+    this.addCharacteristicDelegate({
+      key: 'consumption',
+      Characteristic: this.Characteristics.eve.TotalConsumption
+    })
+    this.addCharacteristicDelegate({
+      key: 'power',
+      Characteristic: this.Characteristics.eve.CurrentConsumption
+    })
+    this.addCharacteristicDelegate({
+      key: 'lastUpdated',
+      Characteristic: this.Characteristics.my.LastUpdated,
+      silent: true
+    })
+    this.check(data)
+  }
+
+  check (data) {
+    this.values.consumption =
+      Math.round(1000 * (data.consumption.low + data.consumption.normal)) / 1000
+    this.values.power = data.avg_power
+    const date = data.lastupdated == null ? new Date() : new Date(data.lastupdated)
+    this.values.lastUpdated = String(date).slice(0, 24)
+  }
+}
+
 class Phase extends P1Service {
   constructor (p1Accessory, data, subtype) {
     super(p1Accessory, data, subtype)