'use strict';

/**
 *
 */
function Point(x, y, name, 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.name = name;
    this.hex = hex;
}

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

    this.a = a;
    this.b = b;
    this.c = c;
}

/**
 *
 */
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);
    },

    /**
     *
     */
    buildGradient: function(p) {
        var opp1, opp2;

        if (p === this.a) {
            opp1 = this.b;
            opp2 = this.c;
        }

        if (p === this.b) {
            opp1 = this.a;
            opp2 = this.c;
        }

        if (p === this.c) {
            opp1 = this.a;
            opp2 = this.b;
        }

        var fill = d3.select(document.createElementNS(d3.ns.prefix.svg, "linearGradient"))
            .attr("gradientUnits", "userSpaceOnUse")
            .attr("id", `fill${p.name}`)
            .attr("x1", p.x)
            .attr("y1", p.y)
            .attr("x2", this.findMidpoint(opp1, opp2).x)
            .attr("y2", this.findMidpoint(opp1, opp2).y)

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

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

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

    /**
     *
     */
    buildPath: function(p) {
        var path = d3.select(document.createElementNS(d3.ns.prefix.svg, "path"))
            .attr("d", `M${this.a.x},${this.a.y} L${this.b.x},${this.b.y} L${this.c.x},${this.c.y} Z`)
            .attr("fill", `url(#fill${p.name})`)

        return function() {
            return path.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, 'A1', '#f00'),
            new Point(200, 200, 'B1', '#0f0'),
            new Point(0, 200, 'C1', '#00f')
        ],

        [
            new Point(100, 0, 'A2', '#f00'),
            new Point(200, 200, 'B2', '#0f0'),
            new Point(300, 0, 'C2', '#00f')
        ],

        [
            new Point(300, 300, 'A3', '#f00'),
            new Point(300, 0, 'C3', '#00f'),
            new Point(200, 200, 'B3', '#0f0'),
        ],
    ];

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

        defs.append(T.buildGradient(points[i][0]));
        defs.append(T.buildGradient(points[i][1]));
        defs.append(T.buildGradient(points[i][2]));

        svg.append(T.buildPath(points[i][0]));
        svg.append(T.buildPath(points[i][1]));
        svg.append(T.buildPath(points[i][2]));
    }
}());