import { parseNumber, removeLeadingZeros, removeTrailingZeros } from "./utils";

/**

* Multiplies two numbers represented as strings.

* @param left

* @param right

* @returns

*/

export function multiply(left: string, right: string): string {

let num1 = parseNumber(left);

let num2 = parseNumber(right);

// Calculate total decimal places

let totalDecimalPlaces =

num1.fractionalPart.length + num2.fractionalPart.length;

// Combine integer and fractional parts to convert to whole numbers

let wholeNum1 = num1.integerPart + num1.fractionalPart;

let wholeNum2 = num2.integerPart + num2.fractionalPart;

// Remove leading zeros

wholeNum1 = removeLeadingZeros(wholeNum1);

wholeNum2 = removeLeadingZeros(wholeNum2);

// If either number is 0, the result is 0

if (wholeNum1 === "0" || wholeNum2 === "0") {

return "0";

}

// Initialize array to store the result

let result = Array(wholeNum1.length + wholeNum2.length).fill(0);

// Perform multiplication (as if calculating by hand)

for (let i = wholeNum1.length - 1; i >= 0; i--) {

for (let j = wholeNum2.length - 1; j >= 0; j--) {

let mul = parseInt(wholeNum1[i]) * parseInt(wholeNum2[j]);

let p1 = i + j;

let p2 = i + j + 1;

let sum = mul + result[p2];

result[p2] = sum % 10;

result[p1] += Math.floor(sum / 10);

}

}

// Convert result array to string

let resultStr = result.join("");

// Remove leading zeros

resultStr = removeLeadingZeros(resultStr);

// Adjust decimal point position

if (totalDecimalPlaces > 0) {

// Add leading '0' if result string is shorter than total decimal places

if (resultStr.length <= totalDecimalPlaces) {

resultStr = resultStr.padStart(totalDecimalPlaces + 1, "0");

}

let integerPart = resultStr.slice(0, -totalDecimalPlaces);

let fractionalPart = resultStr.slice(-totalDecimalPlaces);

// Remove trailing zeros

fractionalPart = removeTrailingZeros(fractionalPart);

if (fractionalPart !== "0") {

resultStr = integerPart + "." + fractionalPart;

} else {

resultStr = integerPart;

}

}

// Determine the sign of the result

let resultSign = num1.sign * num2.sign;

if (resultSign === -1 && resultStr !== "0") {

resultStr = "-" + resultStr;

}

return resultStr;

}

export default multiply;