Given 2 points and an angle, find remaining points and width/height

getRotatedRectangle.ts

type Point = {x: number; y: number};
type Rect = {
    topLeft: Point;
    topRight: Point;
    bottomLeft: Point;
    bottomRight: Point;
    width: number;
    height: number;
};

const rotateAround = (point: Point, angle: number): Point => {
    const cosA = Math.cos(angle);
    const sinA = Math.sin(angle);
    return {
        x: point.x * cosA - point.y * sinA,
        y: point.y * cosA + point.x * sinA,
    };
};

/**
 * Given 2 points and an angle, find remaining points and width/height
 *
 * @param topLeft point 1
 * @param bottomRight point 2
 * @param angle Angle in radians (counter-clockwise)
 * @returns Full rectangle with width / height
 */
const getRotatedRectangle = (
    topLeft: Point,
    bottomRight: Point,
    angle: number
): Rect => {
    // Get middle point
    const middle: Point = {
        x: bottomRight.x - topLeft.x,
        y: bottomRight.y - topLeft.y,
    };

    // Translate origin to be at middle point
    const topLeftT: Point = {
        x: topLeft.x - middle.x,
        y: topLeft.y - middle.y,
    };
    const bottomRightT: Point = {
        x: bottomRight.x - middle.x,
        y: bottomRight.y - middle.y,
    };

    // Unrotate rotated points
    const topLeftU = rotateAround(topLeftT, -angle);
    const bottomRightU = rotateAround(bottomRightT, -angle);
    // Get unknown points and width/height
    const topRightU: Point = { x: bottomRightU.x, y: topLeftU.y };
    const bottomLeftU: Point = { x: topLeftU.x, y: bottomRightU.y };
    const width = Math.abs(bottomRightU.x - topLeftU.x);
    const height = Math.abs(bottomRightU.y - topLeftU.y);
    // Rotate new points back
    const topRightT: Point = rotateAround(topRightU, angle);
    const bottomLeftT: Point = rotateAround(bottomLeftU, angle);
    // Translate new points back
    const topRight: Point = {
        x: topRightT.x + middle.x,
        y: topRightT.y + middle.y,
    };
    const bottomLeft: Point = {
        x: bottomLeftT.x + middle.x,
        y: bottomLeftT.y + middle.y,
    };

    return {
        topLeft,
        topRight,
        bottomLeft,
        bottomRight,
        width,
        height,
    };
};