From c25450f6288748782ad60cc7c4b8e0e0bdc52c1c Mon Sep 17 00:00:00 2001
From: Carlo Zancanaro <carlo@zancanaro.id.au>
Date: Sun, 31 May 2015 13:53:08 +1000
Subject: Better code, based off ParentRunner among other things

---
 src/main/java/au/id/zancanaro/Iterators.java | 45 ++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

(limited to 'src/main/java/au/id/zancanaro/Iterators.java')

diff --git a/src/main/java/au/id/zancanaro/Iterators.java b/src/main/java/au/id/zancanaro/Iterators.java
index b879c76..08cc37e 100644
--- a/src/main/java/au/id/zancanaro/Iterators.java
+++ b/src/main/java/au/id/zancanaro/Iterators.java
@@ -1,7 +1,11 @@
 package au.id.zancanaro;
 
+import java.util.Collections;
 import java.util.Iterator;
+import java.util.List;
+import java.util.Optional;
 import java.util.function.Function;
+import java.util.function.Predicate;
 
 public final class Iterators {
     public static <T> RangeIterator<T> rangeIterator(int countTo, Function<Integer,T> fn) {
@@ -127,4 +131,45 @@ public final class Iterators {
         }
 
     }
+
+    public static <T> FilteringIterator<T> filteringIterator(Predicate<T> pred, Iterator<T> iterator) {
+        return new FilteringIterator<>(pred, iterator);
+    }
+
+    private static class FilteringIterator<T> implements Iterator<T> {
+        private final Predicate<T> predicate;
+        private final Iterator<T> iterator;
+        private List<T> nextValue;
+
+        public FilteringIterator(Predicate<T> pred, Iterator<T> iterator) {
+            this.predicate = pred;
+            this.iterator = iterator;
+            this.nextValue = null;
+        }
+
+        private void populateNext() {
+            while (nextValue == null && iterator.hasNext()) {
+                T value = iterator.next();
+                if (predicate.test(value)) {
+                    nextValue = Collections.singletonList(value);
+                } else {
+                    nextValue = null;
+                }
+            }
+        }
+
+        @Override
+        public boolean hasNext() {
+            populateNext();
+            return nextValue != null;
+        }
+
+        @Override
+        public T next() {
+            populateNext();
+            T result = nextValue.get(0);
+            nextValue = null;
+            return result;
+        }
+    }
 }
-- 
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