const memberRegex = /[+-]?[\w\d^]+/g;
const ints = new Set(Array.from({ length: 10 }, (_, i) => i + ""));

const isNum = (s) => !isNaN(s);

const peelSpaces = (str) => str.replaceAll(" ", "");

const getDegree = (member) => {
  const units = member.split("^");
  return units[1] ? +units[1] : 1;
};

const getCoeff = (member) => {
  const match = member
    .split("^")[0]
    .split("+")
    .reduce((acc, m) => {
      m.split("").forEach((i) => {
        (i === "-" || ints.has(i)) && (acc += i);
      });
      return acc;
    }, "");
  return parseInt(match) ? match : member[0] !== "-" ? 1 : -1;
};

const getVar = (polynom) => {
  ["+", "-", "^"].forEach((s) => {
    polynom = polynom.replace(s, "");
  });
  return (polynom = polynom.split("").filter(isNaN)[0]);
};

const getMembers = (polynom) => polynom.match(memberRegex) || [polynom];

function polynomialProduct(polynom1, polynom2) {
  if (polynom1 === "1") return polynom2;
  if (polynom2 === "1") return polynom1;
  if (polynom1 === "0" || polynom2 === "0") return "0";

  polynom1 = peelSpaces(polynom1);
  polynom2 = peelSpaces(polynom2);

  if (isNum(polynom1) && isNum(polynom2)) {
    return "" + polynom1 * polynom2;
  }

  const members = [polynom1, polynom2].reduce((acc, p) => {
    let numbers = p;
    acc[p] = [
      ...getMembers(p).reduce((acc, mem) => {
        const v = getVar(mem);
        if (v) {
          numbers = numbers.replace(mem, ",");
          acc = [
            ...acc,
            {
              name: v,
              pow: getDegree(mem),
              coeff: getCoeff(mem),
            },
          ];
        }
        return acc;
      }, []),
      ...numbers
        .split(",")
        .filter(Boolean)
        .map((m) => {
          return {
            name: +m > 0 ? +m : +m * -1,
            pow: 1,
            coeff: +m,
          };
        }),
    ];
    return acc;
  }, {});

  const multiplied = members[polynom2]
    .flatMap((variable2) =>
      members[polynom1].map((variable1) => {
        const { coeff, name, pow } = variable2;
        const resultVariable = { ...variable1, coeff: variable1.coeff * coeff };
        if (isNum(resultVariable.name)) {
          resultVariable.name = name;
          resultVariable.pow = pow;
          resultVariable.isNumber = isNum(resultVariable.name);
        } else if (resultVariable.name === name) {
          resultVariable.pow += pow;
        }
        return resultVariable;
      })
    )
    .reduce((acc, variable) => {
      const { pow, name, coeff, isNumber } = variable;
      const nameWithPow = pow > 1 ? name + `^${pow}` : name;
      if (acc[nameWithPow] && acc[nameWithPow].coeff + coeff === 0) {
        delete acc[nameWithPow];
        return acc;
      }
      if (!acc[nameWithPow]) {
        acc[nameWithPow] = { coeff: 0, isNumber: false, pow: 0 };
      }
      acc[nameWithPow].pow = pow;
      acc[nameWithPow].isNumber = isNumber;
      acc[nameWithPow].coeff += coeff;
      return acc;
    }, {});

  const sorted = Object.keys(multiplied).sort((keya, keyb) => {
    return multiplied[keyb].pow > multiplied[keya].pow ? 1 : -1;
  });

  const result = sorted.reduce((acc, variable) => {
    let { coeff, isNumber } = multiplied[variable];
    if (isNumber) {
      coeff > 0 && (acc += "+");
      acc += coeff;
      return acc;
    }
    if (coeff === -1) coeff = "-";
    if (acc !== "" && coeff > 0) acc += "+";
    if (coeff === 1) coeff = "";
    acc += `${coeff}${variable}`;
    return acc;
  }, "");

  return result;
}

function perform() {
  console.log("perf");

  polynomialProduct("u^2 + 2u+1", "u + 1");
  polynomialProduct("x^2", "3x - 1");
  polynomialProduct("2", "4y - 4");
  polynomialProduct("-4r^2 + 1", "-1");
  polynomialProduct("1", "p^3");
  polynomialProduct("1", "-1");
  polynomialProduct("0", "2 - x");
  polynomialProduct("-1", "0");
  polynomialProduct("v^2 - 1+3v^3", "1+v^2");
  polynomialProduct("2x^2 + 3x + 1", "3x - 1");
  polynomialProduct("-x^3 + 3x^2 - 3x + 1", " -x + 1");
  polynomialProduct("u^2 + 3u - 1", "2u - 1");
  polynomialProduct("3u^2-4u-2", "u-7");
  polynomialProduct("u^2 - 2u + 1", "u^2 + 2u + 1");
  polynomialProduct("4", "- 2");
  polynomialProduct("-10i^13 - i + 152i^101", "-3 -98i^34 + 7i^2 - 4i");
  polynomialProduct(
    "-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48",
    "11d+20d^2-d^3+14d^11-d^13-6d^15+d^18-10d^19+16d^20-d^21+23d^23-30d^24-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-42+33d-27d^2-50d^5+15d^7+38d^8-19d^9-30d^10-3d^12+5d^15+d^21-d^22-19d^23+12d^24+12d^26-16d^27-35d^28-39d^29-18d^31-15d^32-21d^33-41d^34+43d^35+d^36+27d^38-30d^39+29d^43+40d^45+9d^46+d^47-23d^48-2d^30-27d^32-d^37-14d^38+3d^39+8d^40+11d^46"
  );
}

module.exports = polynomialProduct;