'use strict';

/**
 *
 */
function Point(x, y, hex) {
    if (typeof x !== typeof 1) {
        throw new Error("x = " + x + " must be of type 'number'; it is currently of type '" + (typeof x) + "'.");
    }

    if (typeof y !== typeof 1) {
        throw new Error("y = " + y + " must be of type 'number'; it is currently of type '" + (typeof y) + "'.");
    }

    if (x < 0 || y < 0) {
        throw new Error("X and Y must be greater than 0.");
    }

    this.x = x;
    this.y = y;
    this.hex = hex;
}

/**
 *
 */
function Triangle(p1, p2, p3) {
    if (!(p1 instanceof Point) || !(p2 instanceof Point) || !(p3 instanceof Point)) {
        throw new Error("All three arguments must be of type Point.");
    }

    this.vertexA = p1;
    this.vertexB = p2;
    this.vertexC = p3;

    // Midpoints on each edge.
    this.midpointAB = this.findMidpoint(this.vertexA, this.vertexB);
    this.midpointAC = this.findMidpoint(this.vertexA, this.vertexC);
    this.midpointBC = this.findMidpoint(this.vertexB, this.vertexC);

    // Midpoints of segments between midpoints.
    this.midpointABAC = this.findMidpoint(this.midpointAB, this.midpointAC);
    this.midpointABBC = this.findMidpoint(this.midpointAB, this.midpointBC);
    this.midpointACBC = this.findMidpoint(this.midpointAC, this.midpointBC);

    // Paths created from a vertex and the midpoints on its two adjacent edges.
    this.subpathA = [this.vertexA, this.midpointAB, this.midpointAC];
    this.subpathB = [this.vertexB, this.midpointAB, this.midpointBC];
    this.subpathC = [this.vertexC, this.midpointAC, this.midpointBC];
}

/**
 *
 */
Triangle.prototype = {
    /**
     *
     */
    findMidpoint: function(p1, p2) {
        var minX = Math.min(p1.x, p2.x);
        var maxX = Math.max(p1.x, p2.x);
        var minY = Math.min(p1.y, p2.y);
        var maxY = Math.max(p1.y, p2.y);

        var midX = minX + ((maxX - minX) / 2);
        var midY = minY + ((maxY - minY) / 2);

        return new Point(midX, midY);
    },


    /**
     *
     */
    buildPath: function(p1, p2, p3, fill) {
        var path = d3.select(document.createElementNS(d3.ns.prefix.svg, "path"))
            .attr("d", `M${p1.x},${p1.y} L${p2.x},${p2.y} L${p3.x},${p3.y} Z`)
            // .attr("stroke", "#000")

        var hex = /^#[\da-f]{3}$|^#[\da-f]{6}$/i;

        if (fill !== undefined) {
            if (fill.match(hex)) {
                path.attr("fill", fill).attr("stroke", fill);
            }
            else {
                path.attr("fill", `url(#${fill})`)
                // .attr("stroke", `url(#${fill})`);
            }
        }

        return function() {
            return path.node();
        };
    },

    /**
     *
     */
    buildGradient: function(p1, p2, id, hex) {
        var fill = d3.select(document.createElementNS(d3.ns.prefix.svg, "linearGradient"))
            .attr("gradientUnits", "userSpaceOnUse")
            .attr("id", id)
            .attr("x1", p1.x)
            .attr("y1", p1.y)
            .attr("x2", p2.x)
            .attr("y2", p2.y)

        fill.append("stop")
            .attr("offset", "0%")
            .attr("stop-color", hex)

        fill.append("stop")
            .attr("offset", "100%")
            .attr("stop-color", "#fff")
            .attr("stop-opacity", "0")

        return function() {
            return fill.node();
        };
    },
};

/**
 *
 */
(function() {
    var svg = d3.select("body").append("svg")
        .attr("width", 500)
        .attr("height", 500);

    var defs = svg.append("defs");

    var points = [
        [
            new Point(100, 0, '#f00'),
            new Point(200, 200, '#0f0'),
            new Point(0, 300, '#00f')
        ]

        // [
        //     new Point(100, 0, '#f00'),
        //     new Point(200, 200, '#0f0'),
        //     new Point(300, 0, '#00f')
        // ],

        // [
        //     new Point(300, 300, '#f00'),
        //     new Point(200, 200, '#0f0'),
        //     new Point(300, 0, '#00f')
        // ],
    ];

    var subpathA;
    var subpathB;
    var subpathC;
    var subpathM1;
    var subpathM2;
    var subpathM3;

    for (var i = 0, len = points.length; i < len; i++) {
        var T = new Triangle(points[i][0], points[i][1], points[i][2]);

        subpathA = T.buildPath(T.subpathA[0], T.subpathA[1], T.subpathA[2], points[i][0].hex);
        subpathB = T.buildPath(T.subpathB[0], T.subpathB[1], T.subpathB[2], points[i][1].hex);
        subpathC = T.buildPath(T.subpathC[0], T.subpathC[1], T.subpathC[2], points[i][2].hex);

        defs.append(T.buildGradient(T.midpointACBC, T.midpointBC, `fill-${i}-0`, points[i][0].hex));
        defs.append(T.buildGradient(T.midpointABBC, T.midpointAC, `fill-${i}-1`, points[i][1].hex));
        defs.append(T.buildGradient(T.midpointABAC, T.midpointAB, `fill-${i}-2`, points[i][2].hex));

        subpathM1 = T.buildPath(T.midpointAB, T.midpointAC, T.midpointBC, `fill-${i}-0`);
        subpathM2 = T.buildPath(T.midpointAB, T.midpointAC, T.midpointBC, `fill-${i}-1`);
        subpathM3 = T.buildPath(T.midpointAB, T.midpointAC, T.midpointBC, `fill-${i}-2`);

        svg.append(subpathA);
        svg.append(subpathB);
        svg.append(subpathC);

        svg.append(subpathM1);
        svg.append(subpathM2);
        svg.append(subpathM3);
    }
}());