/**
 * This method converts a base-10 or scientific E-notation value to
 * a decimal form string. Javascript's IEE 754 double-precision numbers
 * give the same precision as `number.toString()`.
 *
 * @param {number|string} value - The value to be converted.
 * @throws {TypeError} If value is not a valid format.
 * @throws {TypeError} If value is a Symbol or not coercible.
 * @returns {string} The value converted to a decimal form string.
 */
export default function toFixed(value: number | string): string {
  // 判断是否是正规数字
  if (!/^-?(?:(?:\d|[1-9]\d*)(?:\.\d+)?)(?:e[+-]?\d+)?$/i.test(value + "")) {
    return value + "";
  }
  //-0 ? + 0
  if (value === 0) {
    if (1 / value < 0) {
      return "-0";
    } else if (1 / value > 0) {
      return "0";
    }
    return "0";
  }

  let workingValue = value + "";

  let sign;
  if (workingValue.charAt(0) === "-") {
    workingValue = workingValue.slice(1);
    sign = -1;
  } else {
    sign = 1;
  }

  // 小数点
  const pointIndex = workingValue.indexOf(".");

  if (pointIndex > -1) {
    workingValue = workingValue.replace(".", "");
  }

  let exponentIndex = pointIndex;
  // 科学计数法 e
  let index = workingValue.search(/e/i);
  if (index > 0) {
    // 12e3
    if (exponentIndex < 0) {
      // exponentIndex = 2
      exponentIndex = index;
    }
    //  exponentIndex = 2 + 3
    exponentIndex += Number(workingValue.slice(index + 1));
    //workingValue=12
    workingValue = workingValue.slice(0, index);
  } else if (exponentIndex < 0) {
    // 整数
    exponentIndex = workingValue.length;
  }

  let leadingZeroIndex = workingValue.length;
  // Determine leading zeros.
  index = 0;
  while (index < leadingZeroIndex && workingValue.charAt(index) === "0") {
    index += 1;
  }

  let coefficient;
  let exponent;

  if (index === leadingZeroIndex) {
    // Zero.
    exponent = 0;
    coefficient = [0];
  } else {
    // Determine trailing zeros.
    if (leadingZeroIndex > 0) {
      do {
        leadingZeroIndex -= 1;
      } while (
        workingValue.charAt(leadingZeroIndex) === "0"
        && leadingZeroIndex > 0
      );
    }

    exponent = exponentIndex - index - 1;
    coefficient = [];
    coefficient.length = leadingZeroIndex + 1;

    // Convert string to array of digits without leading/trailing zeros.
    let position = 0;
    while (index <= leadingZeroIndex) {
      coefficient[position] = Number(workingValue.charAt(index));
      position += 1;
      index += 1;
    }
  }

  let decimalForm = coefficient.join("");
  const decimalFormLength = decimalForm.length;

  if (exponent < 0) {
    exponent += 1;
    while (exponent) {
      decimalForm = "0" + decimalForm;
      exponent += 1;
    }

    decimalForm = "0" + "." + decimalForm;
  } else if (exponent > 0) {
    exponent += 1;

    if (exponent > decimalFormLength) {
      exponent -= decimalFormLength;
      while (exponent) {
        decimalForm += "0";
        exponent -= 1;
      }
    } else if (exponent < decimalFormLength) {
      decimalForm
        = decimalForm.slice(0, exponent) + "." + decimalForm.slice(exponent);
    }

    // Exponent is zero.
  } else if (decimalFormLength > 1) {
    decimalForm = decimalForm.charAt(0) + "." + decimalForm.slice(1);
  }

  return sign < 0 ? "-" + decimalForm : decimalForm;
}