/*
Author: Oliver Steele
Copyright: Copyright 2006 Oliver Steele.  All rights reserved.
License: MIT License (Open Source)
Homepage: http://osteele.com/sources/javascript
Docs: http://osteele.com/sources/javascript/docs/path
Download: http://osteele.com/sources/javascript/path.js
Example: http://osteele.com/sources/javascript/bezier-demo.php
Created: 2006-02-20
Modified: 2006-03-21

Usage:
var path = new Path();
path.addBezier([{x:0,y:0}, {x:50,y:50}, {x:100,y:25}]);
path.addLine([{x:100,y:25}, {x:150,y:50}]);
path.draw(context);
var midpoint = path.atT(0.5);
var length = 0.5 * path.measureLength();

== Related
Also see {<tt>path.js</tt>}[http://osteele.com/sources/javascript/docs/path].
*/

function Path(segments) {
    this.segments = segments || [];
}

Path.prototype.resetMetrics = function() {
    this.measureLength = Path.prototype.measureLength;
};

Path.prototype.measureLength = function () {
    var s = 0;
    for (var i = 0, segment; segment = this.segments[i++]; )
    s += segment.measureLength();
    return (this.measureLength = function() {return s})();
};

Path.prototype.atT = function (t) {
    // The comments are true if 0 <= t <= 1.
    // The function works in any case; it simply extrapolates the first
    // or last segment.
    var s = t * this.measureLength();
    // 0 <= s <= sum i {segment_i.length}
    var i = 0;
    var segment = this.segments[i++];
    while (s > segment.measureLength() && i < this.segments.length) {
        s -= segment.measureLength();
        segment = this.segments[i++];
    }
    // 0 <= s <= segment.measureLength()
    return segment.atT(s / segment.measureLength());
};

Path.prototype.draw = function (ctx) {
    for (var i = 0, segment; segment = this.segments[i++]; )
    segment.draw(ctx);
};

Path.prototype.addBezier = function (pointsOrBezier) {
    this.segments.push(new Path.Bezier(pointsOrBezier));
    this.resetMetrics();
};

Path.Bezier = function(pointsOrBezier) {
    this.bezier = (pointsOrBezier instanceof Array
    ? new Bezier(pointsOrBezier)
    : pointsOrBezier);
};

Path.Bezier.prototype.atT = function (t) {
    return this.bezier.atT(t);
};

Path.Bezier.prototype.measureLength = function () {
    var s = this.bezier.measureLength();
    return (this.measureLength = function() {return s})();
};

Path.Bezier.prototype.draw = function (ctx) {
    this.bezier.draw(ctx);
};

// A line could be represented as an order-2 bezier, but I wrote this
// before the Bezier library could support arbitrary orders, and I
// don't have the heart to take it out...
Path.prototype.addLine = function (p0, p1) {
    this.segments.push(new Path.Line([p0, p1]));
    this.resetMetrics();
};

Path.Line = function (points) {
    this.points = points;
};

Path.Line.prototype.measureLength = function () {
    var s = distance.apply(null, this.points);
    return (this.measureLength = function() {return s})();
};

Path.Line.prototype.atT = function (t) {
    var p0 = this.points[0], p1 = this.points[1];
    return {x: p0.x + (p1.x-p0.x)*t,
    y: p0.y + (p1.y-p0.y)*t};
};

Path.Line.prototype.draw = function (ctx) {
    var points = this.points;
    ctx.moveTo(points[0].x, points[0].y);
    ctx.lineTo(points[1].x, points[1].y);
};