/*
	usage:
	
		base.wheel = new wheel({
			el: document.querySelector("#map"),
			update: function(val, delta){
				// do something with val
			},
		})

*/

function wheel (opt) {
	opt = defaults(opt, {
		propagate: false,
		locked: false,
		ratio: 0.02,
		val: 0,
		min: -Infinity,
		max: Infinity,
		el: document,
		fn: function(){}
	})

	el.addEventListener('mousewheel', onMouseWheel, false);
  el.addEventListener('DOMMouseScroll', onMouseWheel, false);
	function onMouseWheel (e) {
		if (opt.locked) {
			return
		}
		if (! opt.propagate) {
			e.stopPropagation()
			e.preventDefault()
		}
		
		var delta = 0;
		
		// WebKit
		if ( event.wheelDeltaY ) {
			delta -= event.wheelDeltaY * opt.ratio
		}
		// Opera / Explorer 9
		else if ( event.wheelDelta ) {
			delta -= event.wheelDelta * opt.ratio
		}
		// Firefox
		else if ( event.detail ) {
			delta += event.detail * 2
		}
		if (! opt.reversible && delta < 0) return;
		
		opt.val = clamp(opt.val + delta, opt.min, opt.max)
		
		opt.update(opt.val, delta)
	}

	return opt
}