reducers 追加

src/reducers.js

@@ -0,0 +1,68 @@
+import { combineReducers } from "redux";
+import { CLICK_SQUARE, JUMP_TO_PAST } from "./actions";
+
+const initialState = {
+  history: [
+    {
+      squares: Array(9).fill(null)
+    }
+  ],
+  stepNumber: 0,
+  xIsNext: true
+};
+
+function game(state = initialState, action) {
+  switch (action.type) {
+    case CLICK_SQUARE:
+      const history = state.history.slice(0, state.stepNumber + 1);
+      const current = history[history.length - 1];
+      const squares = current.squares.slice();
+      if (calculateWinner(squares) || squares[action.index]) {
+        return state;
+      }
+      squares[action.index] = state.xIsNext ? "X" : "O";
+      return {
+        history: history.concat([
+          {
+            squares: squares
+          }
+        ]),
+        stepNumber: history.length,
+        xIsNext: !state.xIsNext
+      };
+
+    case JUMP_TO_PAST:
+      return {
+        ...state,
+        stepNumber: action.step,
+        xIsNext: action.step % 2 === 0
+      };
+
+    default:
+      return state;
+  }
+}
+
+export const app = combineReducers({ game });
+
+// ========================================
+
+function calculateWinner(squares) {
+  const lines = [
+    [0, 1, 2],
+    [3, 4, 5],
+    [6, 7, 8],
+    [0, 3, 6],
+    [1, 4, 7],
+    [2, 5, 8],
+    [0, 4, 8],
+    [2, 4, 6]
+  ];
+  for (let i = 0; i < lines.length; i++) {
+    const [a, b, c] = lines[i];
+    if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
+      return squares[a];
+    }
+  }
+  return null;
+}