1 files changed, 105 insertions, 0 deletions
diff --git a/packages/web/src/math/Ratio.ts b/packages/web/src/math/Ratio.ts
new file mode 100644
index 0000000..e2a1fbf
--- /dev/null
+++ b/packages/web/src/math/Ratio.ts
@@ -0,0 +1,105 @@
+import { gcd } from ".";
+
+/** Serializable representation of a ratio. */
+export type RatioData = [numerator: number, denominator: number];
+
+/** Representation of a ratio for performing fractional artithmetic. */
+export default class Ratio {
+  readonly #numerator: number;
+  readonly #denominator: number;
+
+  get numerator(): number {
+    return this.#numerator;
+  }
+
+  get denominator(): number {
+    return this.#denominator;
+  }
+
+  constructor(numerator: number, denominator: number) {
+    if (!Number.isInteger(numerator) || !Number.isInteger(denominator)) {
+      throw new TypeError(
+        `Ratio must have integer parts: ${numerator} / ${denominator}`,
+      );
+    }
+
+    if (denominator === 0) {
+      throw new RangeError("Ratio demnominator cannot be zero");
+    }
+
+    const divisor = gcd(numerator, denominator);
+
+    this.#numerator = numerator / divisor;
+    this.#denominator = denominator / divisor;
+  }
+
+  multiplyRatio(other: Ratio): Ratio {
+    return new Ratio(
+      this.numerator * other.numerator,
+      this.denominator * other.denominator,
+    );
+  }
+
+  divideRatio(other: Ratio): Ratio {
+    return new Ratio(
+      this.numerator * other.denominator,
+      this.denominator * other.numerator,
+    );
+  }
+
+  add(other: Ratio): Ratio {
+    return new Ratio(
+      this.numerator * other.denominator + other.numerator * this.denominator,
+      this.denominator * other.denominator,
+    );
+  }
+
+  subtract(other: Ratio): Ratio {
+    return new Ratio(
+      this.numerator * other.denominator - other.numerator * this.denominator,
+      this.denominator * other.denominator,
+    );
+  }
+
+  compare(other: Ratio): number {
+    const left = this.numerator * other.denominator;
+    const right = other.numerator * this.denominator;
+    return left < right ? -1 : left > right ? 1 : 0;
+  }
+
+  equals(other: Ratio): boolean {
+    return this.compare(other) === 0;
+  }
+
+  toNumber(): number {
+    return this.numerator / this.denominator;
+  }
+
+  toString(): string {
+    return `${this.numerator}/${this.denominator}`;
+  }
+
+  [Symbol.for("nodejs.util.inspect.custom")](): string {
+    return `Ratio { ${this.numerator}/${this.denominator} }`;
+  }
+
+  static fromInteger(n: number): Ratio {
+    return new Ratio(n, 1);
+  }
+
+  toData(): RatioData {
+    return [this.numerator, this.denominator];
+  }
+
+  static fromData(ratio: RatioData): Ratio {
+    return new Ratio(ratio[0], ratio[1]);
+  }
+
+  static min(...ratios: Ratio[]): Ratio {
+    return ratios.reduce((a, b) => (a.compare(b) <= 0 ? a : b));
+  }
+
+  static max(...ratios: Ratio[]): Ratio {
+    return ratios.reduce((a, b) => (a.compare(b) >= 0 ? a : b));
+  }
+}