State refactored using reducer

utils/languages.json

@@ -121,6 +121,7 @@
   },
   "mappings": {
     "target": {
+      "zh": "zh-CN",
       "zh_HANT": "zh-TW"
     }
   }

utils/reducer.ts

@@ -0,0 +1,37 @@
+export enum Actions {
+    "SET_FIELD",
+    "SET_ALL"
+}
+
+export const initialState = {
+    source: "auto",
+    target: "en",
+    query: ""
+}
+
+type Action = {
+    type: Actions.SET_FIELD,
+    payload: {
+        key: string,
+        value: string
+    }
+} | {
+    type: Actions.SET_ALL,
+    payload: {
+        state: {
+            [key: string]: string
+        }
+    }
+}
+
+export default function reducer(state: typeof initialState, action: Action) {
+    switch (action.type) {
+        case Actions.SET_FIELD:
+            const { key, value } = action.payload;
+            return { ...state, [key]: value };
+        case Actions.SET_ALL:
+            return { ...state, ...action.payload.state };
+        default:
+            return state;
+    }
+}