1 files changed, 177 insertions, 0 deletions
diff --git a/src/main/java/au/id/zancanaro/javacheck/Iterators.java b/src/main/java/au/id/zancanaro/javacheck/Iterators.java
new file mode 100644
index 0000000..347a927
--- /dev/null
+++ b/src/main/java/au/id/zancanaro/javacheck/Iterators.java
@@ -0,0 +1,177 @@
+package au.id.zancanaro.javacheck;
+
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+import java.util.function.Predicate;
+
+public final class Iterators {
+    private Iterators() {
+    }
+
+    public static <T> RangeIterator<T> rangeIterator(int countTo, Function<Integer,T> fn) {
+        return new RangeIterator<T>(countTo, fn);
+    }
+
+    private static class RangeIterator<T> implements Iterator<T> {
+        private final Function<Integer, T> action;
+        private final int countTo;
+        private int index = 0;
+
+        public RangeIterator(int countTo, Function<Integer, T> action) {
+            this.countTo = countTo;
+            this.action = action;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return index < countTo;
+        }
+
+        @Override
+        public T next() {
+            return action.apply(index++);
+        }
+    }
+
+    public static <T> FlattenIterator<T> flatten(Iterator<Iterator<T>> iterators) {
+        return new FlattenIterator<>(iterators);
+    }
+    public static class FlattenIterator<T> implements Iterator<T> {
+        private Iterator<T> current;
+
+        private Iterator<Iterator<T>> iterators;
+
+        public FlattenIterator(Iterator<Iterator<T>> iterators) {
+            this.current = Iterators.emptyIterator();
+            this.iterators = iterators;
+        }
+
+        private Iterator<T> getCurrent() {
+            while (!current.hasNext() && iterators.hasNext()) {
+                current = iterators.next();
+            }
+            return current;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return getCurrent().hasNext();
+        }
+        @Override
+        public T next() {
+            return getCurrent().next();
+        }
+
+    }
+
+    public static <T> ConcatIterator<T> concat(Iterator<T> left, Iterator<T> right) {
+        return new ConcatIterator<>(left, right);
+    }
+    public static class ConcatIterator<T> implements Iterator<T> {
+        private final Iterator<T> left;
+
+        private final Iterator<T> right;
+
+        public ConcatIterator(Iterator<T> left, Iterator<T> right) {
+            this.left = left;
+            this.right = right;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return left.hasNext() || right.hasNext();
+        }
+        @Override
+        public T next() {
+            if (left.hasNext()) {
+                return left.next();
+            } else {
+                return right.next();
+            }
+        }
+
+    }
+
+    public static <T> EmptyIterator<T> emptyIterator() {
+        return new EmptyIterator<>();
+    }
+    public static class EmptyIterator<T> implements Iterator<T> {
+
+        @Override
+        public boolean hasNext() {
+            return false;
+        }
+        @Override
+        public T next() {
+            return null;
+        }
+
+    }
+
+    public static <T,R> MappingIterator<T,R> mappingIterator(Function<T,R> f, Iterator<T> iterator) {
+        return new MappingIterator<>(f, iterator);
+    }
+    private static class MappingIterator<T, R> implements Iterator<R> {
+        private final Function<T, R> mapping;
+
+        private final Iterator<T> iterator;
+
+        public MappingIterator(Function<T, R> mapping, Iterator<T> iterator) {
+            this.mapping = mapping;
+            this.iterator = iterator;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return iterator.hasNext();
+        }
+        @Override
+        public R next() {
+            return mapping.apply(iterator.next());
+        }
+
+    }
+
+    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;
+        }
+    }
+}