const addButton = document.getElementById('add');
const removeButton = document.getElementById('remove');
const c0Button = document.getElementById('c0');
const c1Button = document.getElementById('c1');
const canvas = document.querySelector('canvas');
const context = canvas.getContext('2d');

let adding = false;
/** @type {number|null} */
let selected = null;
let mouseDown = false;
/** @type {number|null} */
let movePointIndex = null;

/** @type {number[][][]} */
const curves = [];

addButton.addEventListener('click', () => {
    adding = true;
    curves.push([]);
    selected = curves.length - 1;
});

removeButton.addEventListener('click', () => {
    if (selected === null) return;
    curves.splice(selected, 1);
    selected = null;
    draw();
});

c0Button.addEventListener('click', () => {
    if (curves.length <= 1 || selected === null) return;

    let p = getClosestEndPoint(curves[selected][0][0], curves[selected][0][1]);
    if (p === null) return;
    let [curveIndex, pointIndex] = p;
    curves[selected][0] = curves[curveIndex][pointIndex];

    p = getClosestEndPoint(curves[selected][3][0], curves[selected][3][1]);
    if (p === null) return;
    [curveIndex, pointIndex] = p;
    curves[selected][3] = curves[curveIndex][pointIndex];

    draw();
});

c1Button.addEventListener('click', () => {
    if (curves.length <= 1 || selected === null) return;

    let [curveIndex, pointIndex] = getClosestEndPoint(
        curves[selected][0][0],
        curves[selected][0][1],
    );
    // Move first point of selected curve to closest found point
    curves[selected][0] = curves[curveIndex][pointIndex];
    // Get control point of found point
    const h1 = curves[curveIndex][pointIndex === 0 ? 1 : 2];
    // Set control point to location mirrored over the first point
    curves[selected][1] = [
        2 * curves[selected][0][0] - h1[0],
        2 * curves[selected][0][1] - h1[1],
    ];

    [curveIndex, pointIndex] = getClosestEndPoint(
        curves[selected][3][0],
        curves[selected][3][1],
    );
    curves[selected][3] = curves[curveIndex][pointIndex];
    const h2 = curves[curveIndex][pointIndex === 0 ? 1 : 2];
    curves[selected][2] = [
        2 * curves[selected][3][0] - h2[0],
        2 * curves[selected][3][1] - h2[1],
    ];

    draw();
});

/**
 * @param {number} x
 * @param {number} y
 */
function addPoint(x, y) {
    const curve = curves[curves.length - 1];
    curve.push([x, y]);
    if (curve.length === 4) {
        adding = false;
    }
    draw();
}

/**
 * @param {number} t
 * @param {number} a
 * @param {number} b
 * @returns {number}
 */
function lerp(t, a, b) {
    return (1 - t) * a + t * b;
}

/**
 * interpolates the points
 * @param {number} t
 * @param {number[]} p array of points
 */
function lerpCurve(t, p) {
    if (p.length === 1) return p[0];
    return lerp(t, lerpCurve(t, p.slice(0, -1)), lerpCurve(t, p.slice(1)));
}

function drawCircles() {
    if (selected === null) return;
    for (const [x, y] of curves[selected]) {
        context.beginPath();
        context.ellipse(x, y, 10, 10, 0, 0, Math.PI * 2);
        context.stroke();
    }
}

function drawLines() {
    for (let i = 0; i < curves.length; i++) {
        const curve = curves[i];
        for (let j = 0; j < curve.length - 3; j += 3) {
            const p1 = curve[j];
            const p2 = curve[j + 1];
            const p3 = curve[j + 2];
            const p4 = curve[j + 3];

            context.beginPath();

            if (selected === i) {
                context.moveTo(p1[0], p1[1]);
                context.lineTo(p2[0], p2[1]);

                context.moveTo(p3[0], p3[1]);
                context.lineTo(p4[0], p4[1]);
            }

            context.moveTo(p1[0], p1[1]);
            for (let t = 0; t <= 100; t++) {
                const tt = t / 100;
                const x = lerpCurve(tt, [p1[0], p2[0], p3[0], p4[0]]);
                const y = lerpCurve(tt, [p1[1], p2[1], p3[1], p4[1]]);

                context.lineTo(x, y);
            }

            context.stroke();
        }
    }
}

function draw() {
    context.clearRect(0, 0, canvas.width, canvas.height);

    drawCircles();
    drawLines();
}

function resizeCanvas() {
    canvas.height = window.innerHeight;
    canvas.width = window.innerWidth;
    draw();
}

/**
 * Gets the index of the closest curve to the point
 * @param {number} x
 * @param {number} y
 * @returns {number|null}
 */
function getClosestCurveIndex(x, y) {
    /** @type {number|null} */
    let minDist = null;
    /** @type {number|null} */
    let minIndex = null;

    for (let i = 0; i < curves.length; i++) {
        for (const point of curves[i]) {
            const dist = Math.abs(
                Math.sqrt((x - point[0]) ** 2 + (y - point[1]) ** 2),
            );
            if (!minDist || dist < minDist) {
                minDist = dist;
                minIndex = i;
            }
        }
    }

    return minIndex;
}

/**
 * Gets the selected curve point under the mouse
 * @param {number} x
 * @param {number} y
 * @returns {number|null}
 */
function getSelectedPoint(x, y) {
    if (selected === null) return null;
    for (let i = 0; i < curves[selected].length; i++) {
        const point = curves[selected][i];
        const dist = Math.abs(
            Math.sqrt((x - point[0]) ** 2 + (y - point[1]) ** 2),
        );
        if (dist <= 10) {
            return i;
        }
    }
    return null;
}

/**
 * Gets the closest end point
 * @param {number} x
 * @param {number} y
 * @returns {number[]|null}
 */
function getClosestEndPoint(x, y) {
    /** @type {number|null} */
    let minDist = null,
        minCurveIndex = null,
        minPointIndex = null;

    for (let i = 0; i < curves.length; i++) {
        if (i === selected) continue;
        let dist = Math.abs(
            Math.sqrt((x - curves[i][0][0]) ** 2 + (y - curves[i][0][1]) ** 2),
        );
        if (minDist === null || dist < minDist) {
            minDist = dist;
            minCurveIndex = i;
            minPointIndex = 0;
        }

        dist = Math.abs(
            Math.sqrt((x - curves[i][3][0]) ** 2 + (y - curves[i][3][1]) ** 2),
        );
        if (minDist === null || dist < minDist) {
            minDist = dist;
            minCurveIndex = i;
            minPointIndex = 3;
        }
    }

    return [minCurveIndex, minPointIndex];
}

canvas.addEventListener('mousedown', (e) => {
    mouseDown = true;

    if (adding) {
        addPoint(e.pageX, e.pageY);
        return;
    }

    const point = getSelectedPoint(e.pageX, e.pageY);
    if (point !== null) {
        movePointIndex = point;
        return;
    }

    const i = getClosestCurveIndex(e.pageX, e.pageY);
    if (i === null) return;
    selected = i;
    draw();
});

canvas.addEventListener('mousemove', (e) => {
    if (!mouseDown) return;
    if (movePointIndex === null) return;
    curves[selected][movePointIndex] = [e.pageX, e.pageY];
    draw();
});

canvas.addEventListener('mouseup', () => {
    mouseDown = false;
    movePointIndex = null;
});

window.addEventListener('resize', resizeCanvas);
resizeCanvas();