From fc6df79b6582407afe9f1d0762774bc7ea63b239 Mon Sep 17 00:00:00 2001
From: henryw374 <henryw374@gmail.com>
Date: Thu, 12 Jul 2018 07:44:52 +0100
Subject: [PATCH] add OffsetClock

---
 src/Clock.js      | 68 +++++++++++++++++++++++++++++++++++++++++++++++
 test/ClockTest.js | 13 +++++++++
 2 files changed, 81 insertions(+)

diff --git a/src/Clock.js b/src/Clock.js
index 57cb36670..dbf96d68c 100644
--- a/src/Clock.js
+++ b/src/Clock.js
@@ -104,6 +104,29 @@ export class Clock {
     static fixed(fixedInstant, zoneOffset) {
         return new FixedClock(fixedInstant, zoneOffset);
     }
+    
+    /**
+     * Obtains a clock that returns instants from the specified clock with the
+     * specified duration added
+     * <p>
+     * This clock wraps another clock, returning instants that are later by the
+     * specified duration. If the duration is negative, the instants will be
+     * earlier than the current date and time.
+     * The main use case for this is to simulate running in the future or in the past.
+     * <p>
+     * A duration of zero would have no offsetting effect.
+     * Passing zero will return the underlying clock.
+     * <p>
+     * The returned implementation is immutable, thread-safe and {@code Serializable}
+     * providing that the base clock is.
+     *
+     * @param baseClock  the base clock to add the duration to, not null
+     * @param offsetDuration  the duration to add, not null
+     * @return a clock based on the base clock with the duration added, not null
+     */
+    static offset(baseClock, duration) {
+        return new OffsetClock(baseClock, duration);   
+    }
 
     /**
       * Gets the current millisecond instant of the clock.
@@ -220,3 +243,48 @@ class FixedClock extends Clock{
         return 'FixedClock[]';
     }
 }
+
+
+/**
+ * Implementation of a clock that adds an offset to an underlying clock.
+ */
+class OffsetClock extends Clock {
+    constructor(baseClock, offset) {
+        super();
+        this._baseClock = baseClock;
+        this._offset = offset;
+    }
+   
+    zone() {
+        return this._baseClock.zone();
+    }
+    
+    
+    withZone(zone) {
+        if (zone.equals(this._baseClock.zone())) {  // intentional NPE
+            return this;
+        }
+        return new OffsetClock(this._baseClock.withZone(zone), this._offset);
+    }
+    
+    millis() {
+        return this._baseClock.millis() + this._offset.toMillis();
+    }
+    
+    instant() {
+        return this._baseClock.instant().plus(this._offset);
+    }
+    
+    
+    equals(obj) {
+        if (obj instanceof OffsetClock) {
+            
+            return this._baseClock.equals(obj.baseClock) && this._offset.equals(obj.offset);
+        }
+        return false;
+    }
+    
+    toString() {
+        return 'OffsetClock[' + this._baseClock + ',' + this._offset + ']';
+    }
+}
\ No newline at end of file
diff --git a/test/ClockTest.js b/test/ClockTest.js
index c7fa6df43..86b16af70 100644
--- a/test/ClockTest.js
+++ b/test/ClockTest.js
@@ -7,6 +7,9 @@ import {expect} from 'chai';
 import './_init';
 
 import {Clock} from '../src/Clock';
+import {Duration} from  '../src/Duration';
+import {Instant} from '../src/Instant';
+import {ZoneId} from '../src/ZoneId';
 
 describe('Clock', () => {
     describe('should deny calling an instant method of pseudo abstract class Clock', () => {
@@ -38,5 +41,15 @@ describe('Clock', () => {
             expect(Clock.fixed().toString()).to.contain('FixedClock');
         });
     });
+    
+    describe('offset clock', () => {
+        it('is offset', () => {
+            const duration = Duration.parse('PT0H3M');
+            const base = Clock.fixed(Instant.now(), ZoneId.systemDefault());
+            const offset = Clock.offset(base, duration);
+            expect(base.millis() === offset.millis() + duration.toMillis()); 
+        });
+    
+    });
 });