react_demo/calc/src/redux/reducer.js

import ACTIONS from "./action";


const evaluate = state => {
    let { currentValue, lastValue, operator } = state;
    currentValue = parseFloat(currentValue);
    lastValue = parseFloat(lastValue);
    let ans = "";
    switch (operator) {
        case "+": {
            ans = lastValue + currentValue;
            break;
        }

        case "-": {
            ans = lastValue - currentValue;
            break;
        }

        case "×": {
            ans = lastValue * currentValue;
            break;
        }

        case "÷": {
            ans = lastValue / currentValue;
            break;
        }
        default:
            break;
    }
    return ans.toString();
}

const reducer = (
    state = {
        lastValue: "",
        currentValue: "",
        operator: "",
        overWrite: false,
    }, action) => {
    switch (action.type) {
        case ACTIONS.ADD_DIGIT: {
            if (state.overWrite) {
                state.currentValue = "";
                state.overWrite = false;
            }

            if (state.currentValue === '0' && action.digit === '0')
                return state;
            if (state.currentValue === '0' && action.digit !== '.')
                return {
                    ...state,
                    currentValue: action.digit,
                }
            if (action.digit === '.' && state.currentValue.includes('.')) {
                return state;
            }
            if (action.digit === '.' && state.currentValue === "") {
                return {
                    ...state,
                    currentValue: "0.",
                }
            }
            return {
                ...state,
                currentValue: state.currentValue + action.digit,
            }
        }

        case ACTIONS.DELETE_DIGIT:
            {
                if (state.overWrite) {
                    return {
                        ...state,
                        currentValue: "",
                        overWrite: false,
                    }
                }
                if (state.currentValue === '') {
                    return state;
                }

                return {
                    ...state,
                    currentValue: state.currentValue.slice(0, -1), // 删除最后一个元素
                }
            }

        case ACTIONS.CHOOSE_OPERATION:
            {
                if (state.currentValue === "" && state.lastValue === "") {
                    return state;
                }
                if (state.lastValue === "") {
                    return {
                        ...state,
                        lastValue: state.currentValue,
                        operator: action.operator,
                        currentValue: ""
                    }
                }

                if (state.currentValue === "") {
                    return {
                        ...state,
                        operator: action.operator,
                    }
                }
                let ans = evaluate(state);
                if (ans === "Infinity") {
                    return {
                        ...state,
                        lastValue: "",
                        operator: "",
                        currentValue: "除数不能为0",
                        overWrite: true
                    }
                }

                return {
                    ...state,
                    lastValue: ans,
                    operator: action.operator,
                    currentValue: "",
                }
            }

        case ACTIONS.EVALUATE:
            {
                if (state.currentValue === ""
                    || state.lastValue === ""
                    || state.operator === "")
                    return state;

                let ans = evaluate(state);
                if (ans === "Infinity") {
                    return {
                        ...state,
                        lastValue: "",
                        operator: "",
                        currentValue: "除数不能为0",
                        overWrite: true
                    }
                }

                return {
                    ...state,
                    currentValue: ans,
                    operator: "",
                    lastValue: "",
                    overWrite: true,
                }
            }

        case ACTIONS.CLEAR:
            {
                return {
                    currentValue: "",
                    lastValue: "",
                    operator: "",
                }
            }
        default:
            return state;
    }

}

export default reducer;