function toQuad(p1, c1, c2, p2) {
    // Quad control point is (3*c2 - p2 + 3*c1 - p1)/4
    var x = (3 * c2.x - p2.x + 3 * c1.x - p1.x) / 4;
    var y = (3 * c2.y - p2.y + 3 * c1.y - p1.y) / 4;
    return [
        p1,
        {
            x: x,
            y: y

        },
        p2
    ];
}


/**
    * 三次贝塞尔转二次贝塞尔
    *
    * @param {Object} p1 开始点
    * @param {Object} c1 控制点1
    * @param {Object} c2 控制点2
    * @param {Object} p2 结束点
    * @return {Array} 二次贝塞尔控制点
    */
function bezierCubic2Q2(p1, c1, c2, p2, level) {
    level = level || 0;

    // 判断极端情况，控制点和起止点一样
    if (p1.x === c1.x && p1.y === c1.y && c2.x === p2.x && c2.y === p2.y) {
        return [
            [
                p1,
                {
                    x: (p1.x + p2.x) / 2,
                    y: (p1.y + p2.y) / 2
                },
                p2
            ]
        ];
    }


    var mx = p2.x - 3 * c2.x + 3 * c1.x - p1.x;
    var my = p2.y - 3 * c2.y + 3 * c1.y - p1.y;

    // control points near
    if (mx * mx + my * my <= 4 || level > 5) {
        return [
            toQuad(p1, c1, c2, p2)
        ];
    }

    // Split to 2 qubic beziers by midpoints
    // (p2 + 3*c2 + 3*c1 + p1)/8
    var mp = {
        x: (p2.x + 3 * c2.x + 3 * c1.x + p1.x) / 8,
        y: (p2.y + 3 * c2.y + 3 * c1.y + p1.y) / 8

    };

    return bezierCubic2Q2(
            p1,
            {
                x: (p1.x + c1.x) / 2,
                y: (p1.y + c1.y) / 2

            },
            {
                x: (p1.x + 2 * c1.x + c2.x) / 4,
                y: (p1.y + 2 * c1.y + c2.y) / 4
            },
            mp,
            level + 1
        ).concat(bezierCubic2Q2(
            mp,
            {
                x: (p2.x + c1.x + 2 * c2.x) / 4,
                y: (p2.y + c1.y + 2 * c2.y) / 4

            },
            {
                x: (p2.x + c2.x) / 2,
                y: (p2.y + c2.y) / 2
            },
            p2,
            level + 1
        ))
}

module.exports = bezierCubic2Q2;