improve rotate

spec/core/array/operator/rotate.spec.ts

@@ -7,7 +7,29 @@ describe('rotate', () => {
     const array = [1, 2, 3, 4, 5];
     const fn = rotate(2);
     expect(fn(array)).to.eql([3, 4, 5, 1, 2,]);
-
+  });
+  it('should rotate negative', () => {
+    const array = [1, 2, 3, 4, 5];
+    const fn = rotate(-2);
+    expect(fn(array)).to.eql([4, 5, 1, 2, 3,]);
+  });
+  it('should rotate negative twice', () => {
+    const array = [1, 2, 3, 4, 5];
+    expect(rotate(-2)(array)).to.eql(rotate(-12)(array));
+  });
+  it('should rotate another test case', () => {
+    const array = [1, 2, 3, 4, 5, 6, 7];
+    expect(rotate(-2)(array)).to.eql([6, 7, 1, 2, 3, 4, 5,]);
+    expect(rotate(2)(array)).to.eql([3, 4, 5, 6, 7, 1, 2,]);
+  });
+  it('should rotate mod length', () => {
+    const array = [1, 2, 3, 4, 5];
+    const offset = Math.floor(Math.random() * array.length);
+    const n = Math.round(Math.random() * 10) - 5;
+    const fn = rotate(offset);
+    expect(fn(array)).to.eql(rotate(offset + array.length)(array));
+    expect(fn(array)).to.eql(rotate(offset - array.length)(array));
+    expect(fn(array)).to.eql(rotate(offset + array.length * n)(array));
   });
 
   it('should rotate negative', () => {
@@ -17,7 +39,7 @@ describe('rotate', () => {
 
   it('should rotate modulo', () => {
     const array = [1, 2, 3, 4, 5];
-    expect(rotate(6)(array)).to.eql(rotate(6%array.length)(array));
+    expect(rotate(6)(array)).to.eql(rotate(6 % array.length)(array));
 
   });
 
@@ -28,11 +50,11 @@ describe('rotate', () => {
 
   it('should rotate early', () => {
     const fn = rotate(2);
-    expect(fn([1])).to.eql([1,]);
+    expect(fn([1])).to.eql([1]);
   });
   it('should rotate last', () => {
     const fn = rotate(2);
-    expect(fn([1, 2])).to.eql([1, 2,]);
+    expect(fn([1, 2])).to.eql([1, 2]);
   });
 
   it('should rotate 0', () => {

src/array/operator/rotate.ts

@@ -1,7 +1,6 @@
 export function rotate(offset: number) {
-  return <S>(array: S[]): S[] => {
-    const length = array.length;
-    const index = ((offset % length) + length) % length;
+  return <T>(array: T[]): T[] => {
+    const index = offset % array.length;
     return array.slice(index).concat(array.slice(0, index));
   };
 }

src/array/operator/rotateBack.ts

@@ -1,3 +1,3 @@
 import {rotate} from './rotate';
 
-export const rotateBack = (offset: number) => rotate(-offset)
+export const rotateBack = (offset: number) => rotate(-offset);