/**
 * @desc 解决浮动运算问题，避免小数点后产生多位数和计算精度损失。
 * 问题示例：2.3 + 2.4 = 4.699999999999999，1.0 - 0.9 = 0.09999999999999998
 */

/**
 * 把错误的数据转正
 * strip(0.09999999999999998)=0.1
 */
function strip(num: number, precision = 12): number {
    return +parseFloat(num.toPrecision(precision));
}

/**
 * Return digits length of a number
 * @param num Input number
 */
function digitLength(num: number): number {
    // Get digit length of e
    const eSplit = num.toString().split(/[eE]/);
    const len = (eSplit[0].split('.')[1] || '').length - +(eSplit[1] || 0);
    return len > 0 ? len : 0;
}

/**
 * 把小数转成整数，支持科学计数法。如果是小数则放大成整数
 * @param num 输入数
 */
function float2Fixed(num: number): number {
    if (num.toString().indexOf('e') === -1) {
        return Number(num.toString().replace('.', ''));
    }
    const dLen = digitLength(num);
    return dLen > 0 ? strip(num * Math.pow(10, dLen)) : num;
}

/**
 * 检测数字是否越界，如果越界给出提示
 * @param num 输入数
 */
function checkBoundary(num: number) {
    if (_boundaryCheckingState) {
        if (num > Number.MAX_SAFE_INTEGER || num < Number.MIN_SAFE_INTEGER) {
            console.warn(
                `${num} is beyond boundary when transfer to integer, the results may not be accurate`
            );
        }
    }
}

/**
 * 精确乘法
 */
function times(num1: number, num2: number, ...others: number[]): number {
    if (others.length > 0) {
        return times(times(num1, num2), others[0], ...others.slice(1));
    }
    const num1Changed = float2Fixed(num1);
    const num2Changed = float2Fixed(num2);
    const baseNum = digitLength(num1) + digitLength(num2);
    const leftValue = num1Changed * num2Changed;

    checkBoundary(leftValue);

    return leftValue / Math.pow(10, baseNum);
}

/**
 * 精确加法
 */
function plus(num1: number, num2: number, ...others: number[]): number {
    if (others.length > 0) {
        return plus(plus(num1, num2), others[0], ...others.slice(1));
    }
    const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
    return (times(num1, baseNum) + times(num2, baseNum)) / baseNum;
}

/**
 * 精确减法
 */
function minus(num1: number, num2: number, ...others: number[]): number {
    if (others.length > 0) {
        return minus(minus(num1, num2), others[0], ...others.slice(1));
    }
    const baseNum = Math.pow(10, Math.max(digitLength(num1), digitLength(num2)));
    return (times(num1, baseNum) - times(num2, baseNum)) / baseNum;
}

/**
 * 精确除法
 */
function divide(num1: number, num2: number, ...others: number[]): number {
    if (others.length > 0) {
        return divide(divide(num1, num2), others[0], ...others.slice(1));
    }
    const num1Changed = float2Fixed(num1);
    const num2Changed = float2Fixed(num2);
    checkBoundary(num1Changed);
    checkBoundary(num2Changed);
    return times(
        num1Changed / num2Changed,
        Math.pow(10, digitLength(num2) - digitLength(num1))
    );
}

/**
 * 四舍五入
 */
function round(num: number, ratio: number): number {
    const base = Math.pow(10, ratio);
    return divide(Math.round(times(num, base)), base);
}

let _boundaryCheckingState = false;
/**
 * 是否进行边界检查，默认开启
 * @param flag 标记开关，true 为开启，false 为关闭，默认为 true
 */
function enableBoundaryChecking(flag = true) {
    _boundaryCheckingState = flag;
}
export {
    strip,
    plus,
    minus,
    times,
    divide,
    round,
    digitLength,
    float2Fixed,
    enableBoundaryChecking
};
export default {
    strip,
    plus,
    minus,
    times,
    divide,
    round,
    digitLength,
    float2Fixed,
    enableBoundaryChecking
};