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/*
 * this is a modified recreation of @jackrugile's awesomepen:
 * Rainbow Grid http://codepen.io/jackrugile/details/bdwvMo/
 *
 * I have no credit over the idea, but the code is original and side option comes from this pen
 */

var w = c.width = window.innerWidth,
    h = c.height = window.innerHeight,
    ctx = c.getContext( '2d' ),
    
    opts = {
      lineMaxCount: 40,
      lineSpawnProb: .1,
      lineMaxLength: 10,
      lineIncrementProb: .5,
      lineDecrementProb: .7,
      lineSafeTime: 150,
      lineMidJitter: 7,
      lineMidPoints: 3,
      lineHueVariation: 30,
      lineAlpha: 1,

gridSideNum: 6,
      gridSide: 30,
      gridRotationVel: .002,
      gridScalingInputMultiplier: .01,
      gridScalingMultiplier: .3,
      gridHueChange: .6,
      gridRepaintAlpha: .1,
      gridCenterX: w/2,
      gridCenterY: h/2
    },
    
    tick = ( Math.random() * 360 ),
    lines = [],
    linePart, s,
    radPart = Math.PI * 2 / opts.gridSideNum;

function loop() {
  
  window.requestAnimationFrame( loop );
  
  loop.step();
  loop.draw();
}

loop.step = function() {
  
  loop.step.spawn();
  loop.step.updateTick();
  
  lines.map( function( line ) { line.step(); } );
}
loop.draw = function() {
  
  linePart = 1 / opts.lineMidPoints;
  s = opts.gridSide;
  
  loop.draw.repaint();
  loop.draw.transform();
  
  lines.map( function( line ) { line.draw(); } );
  
  ctx.restore();
}

loop.step.spawn = function() {
  
  if( lines.length < opts.lineMaxCount && Math.random() < opts.lineSpawnProb )
    lines.push( new Line );
}
loop.step.updateTick = function() {
  
  ++tick;
}
loop.draw.repaint = function() {
  
  ctx.globalCompositeOperation = 'destination-out';
  ctx.fillStyle = 'rgba(0,0,0,alp)'.replace( 'alp', opts.gridRepaintAlpha );
  ctx.fillRect( 0, 0, w, h );
  ctx.globalCompositeOperation = 'lighter';
}
loop.draw.transform = function() {
  
  ctx.save();
  var scaleFactor = 1 + Math.sin( tick * opts.gridScalingInputMultiplier ) * opts.gridScalingMultiplier;
  
  ctx.translate( opts.gridCenterX, opts.gridCenterY );
  ctx.rotate( tick * opts.gridRotationVel );
  ctx.scale( scaleFactor, scaleFactor );
  
  ctx.lineWidth = .2;
}

function Line() {
  
  this.reset();
}
Line.prototype.reset = function() {
  
  this.head = new Vec( 0, 0 );
  this.path = [ this.head ];
  
  this.life = 0;
  this.hue = ( ( tick * opts.gridHueChange ) % 360 ) |0;
}

Line.prototype.step = function() {
  
  ++this.life;
  
  this.step_increment();
  this.step_decrement();
}
Line.prototype.draw = function() {
  
  if( this.path.length === 0 ) return;
  
  var	x1 = this.path[ 0 ].x,
      y1 = this.path[ 0 ].y,
      x2, y2, dx, dy;
  
  for( var i = 1; i < this.path.length; ++i ) {
    // I start from 1 intentionally, so that I don't have to do any checkings
    
    ctx.strokeStyle = 'hsla(hue, 80%, 50%, alp)'
      .replace( 'hue', this.hue + ( Math.random() * opts.lineHueVariation ) |0 )
      .replace( 'alp', opts.lineAlpha / ( this.life / 80 ) );
    
    x2 = this.path[ i ].x;
    y2 = this.path[ i ].y;
    
    dx = ( x2 - x1 ) / opts.lineMidPoints;
    dy = ( y2 - y1 ) / opts.lineMidPoints;
    
    ctx.beginPath();
    ctx.moveTo( x1 * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2, y1 * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2 );
    
    for( var j = 1; j < opts.lineMidPoints - 1; ++j )
      ctx.lineTo(
     // initial + step portion + jitter
        ( x1 + dx * j ) * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2,
        ( y1 + dy * j ) * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2
      );
    
    ctx.lineTo( x2 * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2, y2 * s + Math.random() * opts.lineMidJitter - opts.lineMidJitter / 2 );
    ctx.stroke();
    
    x1 = x2;
    y1 = y2;
  }
}
Line.prototype.step_increment = function() {
  
  if( Math.random() > opts.lineIncrementProb ) return;
  
  var vec,
      lastHead = this.path[ this.path.length - 2 ];
  
  do {
    
    vec = randomPos( this.head );
  } while ( lastHead && vec.x === lastHead.x && vec.y === lastHead.y );
  
  this.head = vec;
  this.path.push( vec );
  
  if( this.path.length >= opts.lineMaxLength ) this.path.shift();
}
Line.prototype.step_decrement = function() {
  
  if( this.life < opts.lineSafeTime || Math.random() > opts.lineDecrementProb ) return;
  
  this.path.length > 0 ?
  	this.path.shift()
  	:
  	this.reset();
  
}

function Vec( x, y ) {
  
  this.x = x;
  this.y = y;
}

function randomPos( previous ) {
  
  var rad = radPart * ( ( Math.random() * opts.gridSideNum ) |0 );
  
  return new Vec( Math.cos( rad ) + previous.x, Math.sin( rad ) + previous.y );
}

loop();

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