괄호 앞 음수 분배 스테이지 추가

lib/engine/parenthesis-sign.ts

@@ -0,0 +1,118 @@
+import type {
+  GradeResult,
+  ParenthesisSignProblem,
+  UserAnswer,
+} from "./types";
+
+const MIN_MULTIPLIER = -9;
+const MAX_MULTIPLIER = -1;
+const MIN_TERM = 1;
+const MAX_TERM = 9;
+const MAX_PROBLEM_COUNT = 9 * 8 * 2;
+
+type ProblemSeed = Pick<
+  ParenthesisSignProblem,
+  "multiplier" | "a" | "operator" | "b"
+>;
+
+function randomInt(min: number, max: number) {
+  return Math.floor(Math.random() * (max - min + 1)) + min;
+}
+
+function formatLatexTermPair(first: number, second: number) {
+  const operator = second < 0 ? "-" : "+";
+
+  return `${first} ${operator} ${Math.abs(second)}`;
+}
+
+function createProblem({ multiplier, a, operator, b }: ProblemSeed) {
+  const distributedA = multiplier * a;
+  const distributedB = operator === "-" ? multiplier * -b : multiplier * b;
+  const key = `${multiplier}:${a}:${operator}:${b}`;
+
+  return {
+    id: `parenthesis-sign:${key}`,
+    key,
+    multiplier,
+    a,
+    operator,
+    b,
+    distributedA,
+    distributedB,
+    latexBefore: `${multiplier}\\left(${a} ${operator} ${b}\\right)`,
+    latexAfter: formatLatexTermPair(distributedA, distributedB),
+  };
+}
+
+function createAllProblemSeeds() {
+  const seeds: ProblemSeed[] = [];
+
+  for (
+    let multiplier = MIN_MULTIPLIER;
+    multiplier <= MAX_MULTIPLIER;
+    multiplier += 1
+  ) {
+    for (let a = MIN_TERM; a <= MAX_TERM; a += 1) {
+      for (let b = MIN_TERM; b <= MAX_TERM; b += 1) {
+        if (a === b) continue;
+
+        seeds.push({ multiplier, a, operator: "+", b });
+        seeds.push({ multiplier, a, operator: "-", b });
+      }
+    }
+  }
+
+  return seeds;
+}
+
+function shuffle<T>(items: T[]) {
+  const shuffled = [...items];
+
+  for (let index = shuffled.length - 1; index > 0; index -= 1) {
+    const targetIndex = randomInt(0, index);
+    const current = shuffled[index];
+    shuffled[index] = shuffled[targetIndex];
+    shuffled[targetIndex] = current;
+  }
+
+  return shuffled;
+}
+
+export function generateProblem(): ParenthesisSignProblem {
+  const a = randomInt(MIN_TERM, MAX_TERM);
+  let b = randomInt(MIN_TERM, MAX_TERM);
+
+  while (a === b) {
+    b = randomInt(MIN_TERM, MAX_TERM);
+  }
+
+  return createProblem({
+    multiplier: randomInt(MIN_MULTIPLIER, MAX_MULTIPLIER),
+    a,
+    operator: Math.random() < 0.5 ? "+" : "-",
+    b,
+  });
+}
+
+export function generateSession(count = 10): ParenthesisSignProblem[] {
+  if (!Number.isInteger(count) || count < 1) {
+    throw new Error("count must be a positive integer.");
+  }
+
+  if (count > MAX_PROBLEM_COUNT) {
+    throw new Error(`count cannot exceed ${MAX_PROBLEM_COUNT}.`);
+  }
+
+  return shuffle(createAllProblemSeeds()).slice(0, count).map(createProblem);
+}
+
+export function gradeAnswer(
+  problem: ParenthesisSignProblem,
+  answer: UserAnswer,
+): GradeResult {
+  return {
+    correct:
+      answer.a === problem.distributedA && answer.b === problem.distributedB,
+    correctAnswer: [problem.distributedA, problem.distributedB],
+  };
+}