feat: implement ltrim command (stipsan#709)

compat.md

@@ -75,7 +75,7 @@
 | [lrange](http://redis.io/commands/LRANGE)                             | :white_check_mark: | :white_check_mark: |
 | [lrem](http://redis.io/commands/LREM)                                 | :white_check_mark: | :white_check_mark: |
 | [lset](http://redis.io/commands/LSET)                                 | :white_check_mark: | :white_check_mark: |
-| [ltrim](http://redis.io/commands/LTRIM)                               | :white_check_mark: |        :x:         |
+| [ltrim](http://redis.io/commands/LTRIM)                               | :white_check_mark: | :white_check_mark: |
 | [memory](http://redis.io/commands/MEMORY)                             | :white_check_mark: |        :x:         |
 | [mget](http://redis.io/commands/MGET)                                 | :white_check_mark: | :white_check_mark: |
 | [migrate](http://redis.io/commands/MIGRATE)                           | :white_check_mark: |        :x:         |

src/commands/index.js

@@ -51,6 +51,7 @@ export * from './lpushx';
 export * from './lrange';
 export * from './lrem';
 export * from './lset';
+export * from './ltrim';
 export * from './mget';
 export * from './mset';
 export * from './msetnx';

src/commands/ltrim.js

@@ -0,0 +1,19 @@
+export function ltrim(key, s, e) {
+  if (this.data.has(key) && !(this.data.get(key) instanceof Array)) {
+    throw new Error(`Key ${key} does not contain a list`);
+  }
+  let start = parseInt(s, 10);
+  let end = parseInt(e, 10);
+
+  const list = this.data.get(key) || [];
+
+  if (start < 0) {
+    start = list.length + start;
+  }
+  if (end < 0) {
+    end = list.length + end;
+  }
+
+  this.data.set(key, list.slice(start, end + 1));
+  return 'OK';
+}

test/commands/ltrim.js

@@ -0,0 +1,77 @@
+import expect from 'expect';
+
+import MockRedis from '../../src';
+
+describe('ltrim', () => {
+  it('should return first 3 items', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return Promise.all([
+      redis.ltrim('foo', 0, 2).then(res => expect(res).toEqual('OK')),
+      redis
+        .lrange('foo', 0, -1)
+        .then(res => expect(res).toEqual(['1', '2', '3'])),
+    ]);
+  });
+
+  it('should return last 3 items', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return Promise.all([
+      redis.ltrim('foo', -3, -1).then(res => expect(res).toEqual('OK')),
+      redis
+        .lrange('foo', 0, -1)
+        .then(res => expect(res).toEqual(['3', '4', '5'])),
+    ]);
+  });
+
+  it('should return last all items on larger numbers', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return Promise.all([
+      redis.ltrim('foo', 0, 100).then(res => expect(res).toEqual('OK')),
+      redis
+        .lrange('foo', 0, -1)
+        .then(res => expect(res).toEqual(['1', '2', '3', '4', '5'])),
+    ]);
+  });
+
+  it('should return empty array if out-of-range', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: ['1', '2', '3', '4', '5'],
+      },
+    });
+
+    return Promise.all([
+      redis.ltrim('foo', 10, 100).then(res => expect(res).toEqual('OK')),
+      redis.lrange('foo', 0, -1).then(res => expect(res).toEqual([])),
+    ]);
+  });
+
+  it('should throw an exception if the key contains something other than a list', () => {
+    const redis = new MockRedis({
+      data: {
+        foo: 'not a list',
+      },
+    });
+
+    return redis
+      .ltrim('foo', 0, 2)
+      .catch(err =>
+        expect(err.message).toBe('Key foo does not contain a list')
+      );
+  });
+});