feat: Support Dark mode for the widget (#4137)

Co-authored-by: Pranav Raj S <pranav@chatwoot.com>

app/javascript/widget/mixins/darkModeMixin.js

@@ -0,0 +1,15 @@
+import { mapGetters } from 'vuex';
+
+export default {
+  computed: {
+    ...mapGetters({ darkMode: 'appConfig/darkMode' }),
+  },
+  methods: {
+    $dm(light, dark) {
+      if (this.darkMode === 'light') {
+        return light;
+      }
+      return light + ' ' + dark;
+    },
+  },
+};

app/javascript/widget/mixins/specs/darkModeMixin.spec.js

@@ -0,0 +1,41 @@
+import { shallowMount, createLocalVue } from '@vue/test-utils';
+import darkModeMixin from '../darkModeMixin';
+import Vuex from 'vuex';
+const localVue = createLocalVue();
+localVue.use(Vuex);
+
+const darkModeValues = ['light', 'auto'];
+
+describe('darkModeMixin', () => {
+  let getters;
+  let store;
+  beforeEach(() => {
+    getters = {
+      'appConfig/darkMode': () => darkModeValues[0],
+    };
+    store = new Vuex.Store({ getters });
+  });
+
+  it('if light theme', () => {
+    const Component = {
+      render() {},
+      mixins: [darkModeMixin],
+    };
+    const wrapper = shallowMount(Component, { store, localVue });
+    expect(wrapper.vm.$dm('bg-100', 'bg-600')).toBe('bg-100');
+  });
+
+  it('if auto theme', () => {
+    getters = {
+      'appConfig/darkMode': () => darkModeValues[2],
+    };
+    store = new Vuex.Store({ getters });
+
+    const Component = {
+      render() {},
+      mixins: [darkModeMixin],
+    };
+    const wrapper = shallowMount(Component, { store, localVue });
+    expect(wrapper.vm.$dm('bg-100', 'bg-600')).toBe('bg-100 bg-600');
+  });
+});