adding docs subtree

docs/step2-05/exercise/src/index.tsx

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+import { reducer } from './reducers';
+import { createStore } from 'redux';
+
+const store = createStore(reducer);
+
+console.log(store.getState());

docs/step2-05/exercise/src/reducers/index.ts

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+import { Store } from '../store';
+import { addTodo, remove, complete } from './pureFunctions';
+
+export function reducer(state: Store['todos'], payload: any): Store['todos'] {
+  switch (payload.type) {
+    case 'addTodo':
+      return addTodo(state, payload.id, payload.label);
+
+    // Fill in the blanks here for:
+    // - remove
+    // - complete
+    // - clear
+  }
+
+  return state;
+}

docs/step2-05/exercise/src/reducers/pureFunctions.spec.ts

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+import { addTodo } from './pureFunctions';
+import { Store } from '../store';
+
+describe('TodoApp reducers', () => {
+  it('can add an item', () => {
+    const state = <Store['todos']>{};
+
+    const newState = addTodo(state, '0', 'item1');
+
+    const keys = Object.keys(newState);
+
+    // make sure that adding an item would not result in the same instance of state
+    // TODO: uncomment the below to get started
+    /*
+    
+    expect(newState).not.toBe(state);
+
+    expect(keys.length).toBe(1);
+    expect(newState[keys[0]].label).toBe('item1');
+    expect(newState[keys[0]].completed).toBeFalsy();
+    */
+  });
+
+  // TODO: test remove, complete and clear
+});

docs/step2-05/exercise/src/reducers/pureFunctions.ts

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+import { Store, FilterTypes } from '../store';
+
+export function addTodo(state: Store['todos'], id: string, label: string): Store['todos'] {
+  // Write code to clone the state object while inserting a new TodoItem inside
+  // - the new object must be of the type TodoItem
+  // - the new state should be cloned using the spread syntax
+  // - return the new state
+
+  return state;
+}
+
+export function remove(state: Store['todos'], id: string) {
+  // Write code:
+  // - to clone the state object into new state object
+  // - remove and item from the new state by using the "delete" keyword
+  // - return the new state
+
+  return state;
+}
+
+export function complete(state: Store['todos'], id: string) {
+  // Write code:
+  // - to clone the state object into new state object
+  // - create a clone of the state[id] into a new item object
+  // - modify new state and set the id key to the value of the new item object
+
+  return state;
+}
+
+export function clear(state: Store['todos']) {
+  // Write code:
+  // - to clone the state object into new state object
+  // - loop through the keys of the new state object
+  // - remove those items inside that new state if the item is completed using the "delete" keyword
+  // - return the new state
+
+  return state;
+}

docs/step2-05/exercise/src/store/index.ts

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+export type FilterTypes = 'all' | 'active' | 'completed';
+
+export interface TodoItem {
+  label: string;
+  completed: boolean;
+}
+
+export interface Store {
+  todos: {
+    [id: string]: TodoItem;
+  };
+
+  filter: FilterTypes;
+}