From 1f0e18b5555b74de4f8c1a5252cfa209d56a2d9d Mon Sep 17 00:00:00 2001
From: Pascal Welsch <pascal.welsch@grandcentrix.net>
Date: Fri, 15 Feb 2019 00:11:42 +0100
Subject: [PATCH] Add KtList.takeLast(n)

---
 .../extension/list_extension_mixin.dart       | 19 ++++++++++
 lib/src/collection/kt_list.dart               |  5 +++
 test/collection/iterable_extensions_test.dart |  7 +++-
 test/collection/list_extensions_test.dart     | 35 +++++++++++++++++++
 4 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/lib/src/collection/extension/list_extension_mixin.dart b/lib/src/collection/extension/list_extension_mixin.dart
index 51e5251e..9ff482af 100644
--- a/lib/src/collection/extension/list_extension_mixin.dart
+++ b/lib/src/collection/extension/list_extension_mixin.dart
@@ -244,4 +244,23 @@ abstract class KtListExtensionsMixin<T>
     }
     return list;
   }
+
+  @override
+  KtList<T> takeLast(int n) {
+    assert(() {
+      if (n == null) throw ArgumentError("n can't be null");
+      return true;
+    }());
+    if (n < 0) {
+      throw ArgumentError("Requested element count $n is less than zero.");
+    }
+    if (n == 0) return emptyList();
+    if (n >= size) return toList();
+    if (n == 1) return listFrom([last()]);
+    final list = mutableListOf<T>();
+    for (var i = size - n; i < size; i++) {
+      list.add(get(i));
+    }
+    return list;
+  }
 }
diff --git a/lib/src/collection/kt_list.dart b/lib/src/collection/kt_list.dart
index 3d0bf9b3..efc82a0e 100644
--- a/lib/src/collection/kt_list.dart
+++ b/lib/src/collection/kt_list.dart
@@ -202,4 +202,9 @@ abstract class KtListExtension<T> {
    * Returns a list containing elements at specified [indices].
    */
   KtList<T> slice(KtIterable<int> indices);
+
+  /**
+   * Returns a list containing last [n] elements.
+   */
+  KtList<T> takeLast(int n);
 }
diff --git a/test/collection/iterable_extensions_test.dart b/test/collection/iterable_extensions_test.dart
index 0d0a67ee..1e9cb666 100644
--- a/test/collection/iterable_extensions_test.dart
+++ b/test/collection/iterable_extensions_test.dart
@@ -1312,6 +1312,11 @@ void testIterable(KtIterable<T> Function<T>() emptyIterable,
       expect(() => emptyIterable().last((it) => it == "x"),
           throwsA(TypeMatcher<NoSuchElementException>()));
     });
+
+    test("returns null when null is the last element", () {
+      expect(listFrom([1, 2, null]).last(), null);
+      expect(listFrom([1, null, 2]).last(), 2);
+    });
   });
 
   group("lastOrNull", () {
@@ -1985,7 +1990,7 @@ void testIterable(KtIterable<T> Function<T>() emptyIterable,
       expect(iterable.take(0).toList(), emptyList());
     });
 
-    test("take negative returns empty", () {
+    test("take negative throws", () {
       final iterable = iterableOf([1, 2, 3, 4]);
       final e = catchException<ArgumentError>(() => iterable.take(-3));
       expect(e.message, allOf(contains("-3"), contains("less than zero")));
diff --git a/test/collection/list_extensions_test.dart b/test/collection/list_extensions_test.dart
index 2060ae45..5f10fb1d 100644
--- a/test/collection/list_extensions_test.dart
+++ b/test/collection/list_extensions_test.dart
@@ -267,4 +267,39 @@ void testList(
       expect(e.message, allOf(contains("size: 3"), contains("index: -1")));
     });
   });
+
+  group("takeLast", () {
+    test("takeLast zero returns empty", () {
+      final list = listOf(1, 2, 3, 4);
+      expect(list.takeLast(0).toList(), emptyList());
+    });
+
+    test("take negative throws", () {
+      final list = listOf(1, 2, 3, 4);
+      final e = catchException<ArgumentError>(() => list.takeLast(-3));
+      expect(e.message, allOf(contains("-3"), contains("less than zero")));
+    });
+
+    test("take more than size returns full list", () {
+      final list = listOf(1, 2, 3, 4);
+      expect(list.takeLast(10).toList(), list.toList());
+    });
+
+    test("take smaller list size returns last elements", () {
+      final list = listOf(1, 2, 3, 4);
+      expect(list.takeLast(2).toList(), listOf(3, 4));
+    });
+
+    test("takeLast doesn't allow null as n", () {
+      final list = emptyList<num>();
+      var e = catchException<ArgumentError>(() => list.takeLast(null));
+      expect(e.message, allOf(contains("null"), contains("n")));
+    });
+
+    test("take last element which is null", () {
+      final list = listFrom([1, null]);
+      expect(list.takeLast(1).toList(), listFrom<int>([null]));
+      expect(list.takeLast(2).toList(), listFrom([1, null]));
+    });
+  });
 }