import type { MathProblem, Difficulty } from "../types";
import { randomInt, randomChoice } from "@/lib/utils";

let counter = 0;
function nextId() {
  return `int-${++counter}-${Date.now()}`;
}

/** Wrap negatives in parentheses when they follow an operator, e.g. 5 + (-3). */
function signed(n: number): string {
  return n < 0 ? `(${n})` : `${n}`;
}

export function generateIntegerAddSubtract(difficulty: Difficulty): MathProblem {
  if (difficulty === 3) {
    const a = randomInt(-12, 12);
    const b = randomInt(-12, 12);
    const c = randomInt(-12, 12);
    const op1 = randomChoice(["+", "-"] as const);
    const op2 = randomChoice(["+", "-"] as const);
    const partial = op1 === "+" ? a + b : a - b;
    const value = op2 === "+" ? partial + c : partial - c;
    return {
      id: nextId(),
      prompt: `${a} ${op1} ${signed(b)} ${op2} ${signed(c)}`,
      answer: { kind: "integer", value },
      hints: [
        "Work from left to right, one operation at a time.",
        "Subtracting a negative is the same as adding a positive.",
        `First: ${a} ${op1} ${signed(b)} = ${partial}`,
      ],
      steps: [
        { explanation: `Work left to right. First: ${a} ${op1} ${signed(b)} = ${partial}` },
        { explanation: `Then: ${partial} ${op2} ${signed(c)} = ${value}` },
      ],
    };
  }

  const range = difficulty === 1 ? 10 : 20;
  const a = randomInt(-range, range);
  const b = randomInt(-range, range);
  const op = randomChoice(["+", "-"] as const);
  const value = op === "+" ? a + b : a - b;

  const rule =
    op === "+"
      ? b < 0
        ? "Adding a negative means moving left — the same as subtracting."
        : "Adding a positive means moving right."
      : b < 0
        ? "Subtracting a negative is the same as adding a positive (move right)."
        : "Subtracting a positive means moving left.";

  return {
    id: nextId(),
    prompt: `${a} ${op} ${signed(b)}`,
    answer: { kind: "integer", value },
    hints: [
      "Picture the first number on a number line.",
      rule,
      op === "-" && b < 0 ? "Two minus signs make a plus." : "Watch the sign of the second number.",
    ],
    steps: [
      { explanation: `Start at ${a} on the number line.` },
      { explanation: rule },
      { explanation: `${a} ${op} ${signed(b)} = ${value}` },
    ],
  };
}

export function generateIntegerMultiplyDivide(difficulty: Difficulty): MathProblem {
  if (difficulty === 3) {
    // triple product, e.g. (-2) × (-3) × (-4)
    const a = randomInt(-5, 5) || 2;
    const b = randomInt(-5, 5) || 3;
    const c = randomInt(-5, 5) || 4;
    const value = a * b * c;
    const negatives = [a, b, c].filter((n) => n < 0).length;
    return {
      id: nextId(),
      prompt: `${signed(a)} \\times ${signed(b)} \\times ${signed(c)}`,
      answer: { kind: "integer", value },
      hints: [
        "Multiply two numbers at a time.",
        "Count the negative signs: an even count gives a positive result, an odd count gives a negative result.",
        `There are ${negatives} negative sign${negatives === 1 ? "" : "s"} here.`,
      ],
      steps: [
        { explanation: `Multiply the first two: ${signed(a)} × ${signed(b)} = ${a * b}` },
        { explanation: `Then multiply by the last: ${signed(a * b)} × ${signed(c)} = ${value}` },
        { explanation: `${negatives} negative signs → ${negatives % 2 === 0 ? "positive" : "negative"} answer.` },
      ],
    };
  }

  const op = randomChoice(["\\times", "\\div"] as const);
  const factorRange = difficulty === 1 ? 9 : 12;

  if (op === "\\times") {
    const a = randomInt(-factorRange, factorRange) || 3;
    const b = randomInt(-factorRange, factorRange) || 4;
    const value = a * b;
    const sameSign = a < 0 === b < 0;
    return {
      id: nextId(),
      prompt: `${signed(a)} \\times ${signed(b)}`,
      answer: { kind: "integer", value },
      hints: [
        "Multiply the numbers as normal, then decide the sign.",
        "Same signs → positive. Different signs → negative.",
        `These signs are ${sameSign ? "the same" : "different"}.`,
      ],
      steps: [
        { explanation: `Multiply the sizes: ${Math.abs(a)} × ${Math.abs(b)} = ${Math.abs(value)}` },
        { explanation: `${sameSign ? "Same signs give a positive" : "Different signs give a negative"} answer.` },
        { explanation: `${signed(a)} × ${signed(b)} = ${value}` },
      ],
    };
  }

  // division — build from an exact product so the answer is a whole number
  const divisor = (randomInt(-factorRange, factorRange) || 3);
  const quotient = (randomInt(-factorRange, factorRange) || 2);
  const dividend = divisor * quotient;
  const sameSign = divisor < 0 === dividend < 0;
  return {
    id: nextId(),
    prompt: `${signed(dividend)} \\div ${signed(divisor)}`,
    answer: { kind: "integer", value: quotient },
    hints: [
      "Divide the numbers as normal, then decide the sign.",
      "Same signs → positive. Different signs → negative.",
      `These signs are ${sameSign ? "the same" : "different"}.`,
    ],
    steps: [
      { explanation: `Divide the sizes: ${Math.abs(dividend)} ÷ ${Math.abs(divisor)} = ${Math.abs(quotient)}` },
      { explanation: `${sameSign ? "Same signs give a positive" : "Different signs give a negative"} answer.` },
      { explanation: `${signed(dividend)} ÷ ${signed(divisor)} = ${quotient}` },
    ],
  };
}

export function generateIntegerOrderCompare(difficulty: Difficulty): MathProblem {
  const range = difficulty === 1 ? 10 : difficulty === 2 ? 20 : 30;

  if (difficulty === 3) {
    const nums: number[] = [];
    while (nums.length < 3) {
      const v = randomInt(-range, range);
      if (!nums.includes(v)) nums.push(v);
    }
    const wantLargest = Math.random() < 0.5;
    const value = wantLargest ? Math.max(...nums) : Math.min(...nums);
    return {
      id: nextId(),
      prompt: `\\text{Which is the ${wantLargest ? "largest" : "smallest"}: } ${nums.join(",\\ ")}\\text{ ?}`,
      answer: { kind: "integer", value },
      hints: ["Picture them on a number line.", "Further right is larger; further left is smaller."],
      steps: [{ explanation: `The ${wantLargest ? "largest" : "smallest"} is ${value}.` }],
    };
  }

  const a = randomInt(-range, range);
  let b = randomInt(-range, range);
  if (a === b) b = a + 1;
  const wantGreater = Math.random() < 0.5;
  const value = wantGreater ? Math.max(a, b) : Math.min(a, b);
  const dir = wantGreater ? "right" : "left";

  return {
    id: nextId(),
    prompt: `\\text{Which is ${wantGreater ? "greater" : "smaller"}, } ${a} \\text{ or } ${b}\\text{? Enter it.}`,
    answer: { kind: "integer", value },
    hints: [`On a number line, the number further ${dir} wins.`, "Negatives get smaller the further left they are."],
    steps: [{ explanation: `${value} is ${wantGreater ? "greater" : "smaller"}.` }],
  };
}

/** Add/subtract integers, occasionally as a real-world temperature word problem. */
export function generateIntegerAddSubtractMixed(difficulty: Difficulty): MathProblem {
  return Math.random() < 0.3 ? generateTemperatureProblem(difficulty) : generateIntegerAddSubtract(difficulty);
}

export function generateTemperatureProblem(difficulty: Difficulty): MathProblem {
  const cities = ["London", "Moscow", "Toronto", "Oslo", "Helsinki"];
  const days = ["Monday", "Tuesday", "Wednesday", "Thursday"];
  const city = randomChoice(cities);
  const day = randomChoice(days);
  const start = randomInt(-8, 3);
  const rose = Math.random() < 0.5;
  const change = randomInt(2, difficulty === 1 ? 6 : 12);
  const value = rose ? start + change : start - change;
  const verb = rose ? "rose" : "fell";

  return {
    id: nextId(),
    prompt: `\\begin{array}{l}\\text{In ${city} the temperature was ${start}°C on ${day}.}\\\\\\text{The next day it ${verb} by ${change}°C.}\\\\\\text{What was the temperature then?}\\end{array}`,
    answer: { kind: "integer", value },
    hints: [
      `Start at ${start}°C.`,
      `${rose ? "Rising" : "Falling"} means ${rose ? "add" : "subtract"} ${change}.`,
      `${start} ${rose ? "+" : "-"} ${change} = ${value}`,
    ],
    steps: [
      { explanation: `Start at ${start}°C.` },
      { explanation: `It ${verb}, so ${rose ? "add" : "subtract"} ${change}: ${start} ${rose ? "+" : "-"} ${change} = ${value}` },
      { explanation: `The temperature was ${value}°C.` },
    ],
  };
}