/**
 * Catmull-Rom spline 插值折线
 * @module zrender/shape/util/smoothSpline
 * @author pissang (https://www.github.com/pissang)
 *         Kener (@Kener-林峰, kener.linfeng@gmail.com)
 *         errorrik (errorrik@gmail.com)
 */
define(function (require) {
    var vec2 = require('../../core/vector');

    /**
     * @inner
     */
    function interpolate(p0, p1, p2, p3, t, t2, t3) {
        var v0 = (p2 - p0) * 0.5;
        var v1 = (p3 - p1) * 0.5;
        return (2 * (p1 - p2) + v0 + v1) * t3
                + (-3 * (p1 - p2) - 2 * v0 - v1) * t2
                + v0 * t + p1;
    }

    /**
     * @alias module:zrender/shape/util/smoothSpline
     * @param {Array} points 线段顶点数组
     * @param {boolean} isLoop
     * @return {Array}
     */
    return function (points, isLoop) {
        var len = points.length;
        var ret = [];

        var distance = 0;
        for (var i = 1; i < len; i++) {
            distance += vec2.distance(points[i - 1], points[i]);
        }

        var segs = distance / 2;
        segs = segs < len ? len : segs;
        for (var i = 0; i < segs; i++) {
            var pos = i / (segs - 1) * (isLoop ? len : len - 1);
            var idx = Math.floor(pos);

            var w = pos - idx;

            var p0;
            var p1 = points[idx % len];
            var p2;
            var p3;
            if (!isLoop) {
                p0 = points[idx === 0 ? idx : idx - 1];
                p2 = points[idx > len - 2 ? len - 1 : idx + 1];
                p3 = points[idx > len - 3 ? len - 1 : idx + 2];
            }
            else {
                p0 = points[(idx - 1 + len) % len];
                p2 = points[(idx + 1) % len];
                p3 = points[(idx + 2) % len];
            }

            var w2 = w * w;
            var w3 = w * w2;

            ret.push([
                interpolate(p0[0], p1[0], p2[0], p3[0], w, w2, w3),
                interpolate(p0[1], p1[1], p2[1], p3[1], w, w2, w3)
            ]);
        }
        return ret;
    };
});
