// setup
Elm.Native = Elm.Native || {};
Elm.Native.Graphics = Elm.Native.Graphics || {};
Elm.Native.Graphics.Collage = Elm.Native.Graphics.Collage || {};

// definition
Elm.Native.Graphics.Collage.make = function(localRuntime) {
	'use strict';

	// attempt to short-circuit
	localRuntime.Native = localRuntime.Native || {};
	localRuntime.Native.Graphics = localRuntime.Native.Graphics || {};
	localRuntime.Native.Graphics.Collage = localRuntime.Native.Graphics.Collage || {};
	if ('values' in localRuntime.Native.Graphics.Collage)
	{
		return localRuntime.Native.Graphics.Collage.values;
	}

	// okay, we cannot short-ciruit, so now we define everything
	var Color = Elm.Native.Color.make(localRuntime);
	var List = Elm.Native.List.make(localRuntime);
	var NativeElement = Elm.Native.Graphics.Element.make(localRuntime);
	var Transform = Elm.Transform2D.make(localRuntime);
	var Utils = Elm.Native.Utils.make(localRuntime);

	function setStrokeStyle(ctx, style)
	{
		ctx.lineWidth = style.width;

		var cap = style.cap.ctor;
		ctx.lineCap = cap === 'Flat'
			? 'butt'
			: cap === 'Round'
				? 'round'
				: 'square';

		var join = style.join.ctor;
		ctx.lineJoin = join === 'Smooth'
			? 'round'
			: join === 'Sharp'
				? 'miter'
				: 'bevel';

		ctx.miterLimit = style.join._0 || 10;
		ctx.strokeStyle = Color.toCss(style.color);
	}

	function setFillStyle(ctx, style)
	{
		var sty = style.ctor;
		ctx.fillStyle = sty === 'Solid'
			? Color.toCss(style._0)
			: sty === 'Texture'
				? texture(redo, ctx, style._0)
				: gradient(ctx, style._0);
	}

	function trace(ctx, path)
	{
		var points = List.toArray(path);
		var i = points.length - 1;
		if (i <= 0)
		{
			return;
		}
		ctx.moveTo(points[i]._0, points[i]._1);
		while (i--)
		{
			ctx.lineTo(points[i]._0, points[i]._1);
		}
		if (path.closed)
		{
			i = points.length - 1;
			ctx.lineTo(points[i]._0, points[i]._1);
		}
	}

	function line(ctx,style,path)
	{
		(style.dashing.ctor === '[]')
			? trace(ctx, path)
			: customLineHelp(ctx, style, path);
		ctx.scale(1,-1);
		ctx.stroke();
	}

	function customLineHelp(ctx, style, path)
	{
		var points = List.toArray(path);
		if (path.closed)
		{
			points.push(points[0]);
		}
		var pattern = List.toArray(style.dashing);
		var i = points.length - 1;
		if (i <= 0)
		{
			return;
		}
		var x0 = points[i]._0, y0 = points[i]._1;
		var x1=0, y1=0, dx=0, dy=0, remaining=0, nx=0, ny=0;
		var pindex = 0, plen = pattern.length;
		var draw = true, segmentLength = pattern[0];
		ctx.moveTo(x0,y0);
		while (i--)
		{
			x1 = points[i]._0;
			y1 = points[i]._1;
			dx = x1 - x0;
			dy = y1 - y0;
			remaining = Math.sqrt(dx * dx + dy * dy);
			while (segmentLength <= remaining)
			{
				x0 += dx * segmentLength / remaining;
				y0 += dy * segmentLength / remaining;
				ctx[draw ? 'lineTo' : 'moveTo'](x0, y0);
				// update starting position
				dx = x1 - x0;
				dy = y1 - y0;
				remaining = Math.sqrt(dx * dx + dy * dy);
				// update pattern
				draw = !draw;
				pindex = (pindex + 1) % plen;
				segmentLength = pattern[pindex];
			}
			if (remaining > 0)
			{
				ctx[draw ? 'lineTo' : 'moveTo'](x1, y1);
				segmentLength -= remaining;
			}
			x0 = x1;
			y0 = y1;
		}
	}

	function drawLine(ctx, style, path)
	{
		setStrokeStyle(ctx, style);
		return line(ctx, style, path);
	}

	function texture(redo, ctx, src)
	{
		var img = new Image();
		img.src = src;
		img.onload = redo;
		return ctx.createPattern(img, 'repeat');
	}

	function gradient(ctx, grad)
	{
		var g;
		var stops = [];
		if (grad.ctor === 'Linear')
		{
			var p0 = grad._0, p1 = grad._1;
			g = ctx.createLinearGradient(p0._0, -p0._1, p1._0, -p1._1);
			stops = List.toArray(grad._2);
		}
		else
		{
			var p0 = grad._0, p2 = grad._2;
			g = ctx.createRadialGradient(p0._0, -p0._1, grad._1, p2._0, -p2._1, grad._3);
			stops = List.toArray(grad._4);
		}
		var len = stops.length;
		for (var i = 0; i < len; ++i)
		{
			var stop = stops[i];
			g.addColorStop(stop._0, Color.toCss(stop._1));
		}
		return g;
	}

	function drawShape(redo, ctx, style, path)
	{
		trace(ctx, path);
		setFillStyle(ctx, style);
		ctx.scale(1,-1);
		ctx.fill();
	}


	// TEXT RENDERING

	function fillText(redo, ctx, text)
	{
		drawText(ctx, text, ctx.fillText);
	}

	function strokeText(redo, ctx, style, text)
	{
		setStrokeStyle(ctx, style);
		// Use native canvas API for dashes only for text for now
		// Degrades to non-dashed on IE 9 + 10
		if (style.dashing.ctor !== '[]' && ctx.setLineDash)
		{
			var pattern = List.toArray(style.dashing);
			ctx.setLineDash(pattern);
		}
		drawText(ctx, text, ctx.strokeText);
	}

	function drawText(ctx, text, canvasDrawFn)
	{
		var textChunks = chunkText(defaultContext, text);

		var totalWidth = 0;
		var maxHeight = 0;
		var numChunks = textChunks.length;

		ctx.scale(1,-1);

		for (var i = numChunks; i--; )
		{
			var chunk = textChunks[i];
			ctx.font = chunk.font;
			var metrics = ctx.measureText(chunk.text);
			chunk.width = metrics.width;
			totalWidth += chunk.width;
			if (chunk.height > maxHeight)
			{
				maxHeight = chunk.height;
			}
		}

		var x = -totalWidth / 2.0;
		for (var i = 0; i < numChunks; ++i)
		{
			var chunk = textChunks[i];
			ctx.font = chunk.font;
			ctx.fillStyle = chunk.color;
			canvasDrawFn.call(ctx, chunk.text, x, maxHeight / 2);
			x += chunk.width;
		}
	}

	function toFont(props)
	{
		return [
			props['font-style'],
			props['font-variant'],
			props['font-weight'],
			props['font-size'],
			props['font-family']
		].join(' ');
	}


	// Convert the object returned by the text module
	// into something we can use for styling canvas text
	function chunkText(context, text)
	{
		var tag = text.ctor;
		if (tag === 'Text:Append')
		{
			var leftChunks = chunkText(context, text._0);
			var rightChunks = chunkText(context, text._1);
			return leftChunks.concat(rightChunks);
		}
		if (tag === 'Text:Text')
		{
			return [{
				text: text._0,
				color: context.color,
				height: context['font-size'].slice(0,-2) | 0,
				font: toFont(context)
			}];
		}
		if (tag === 'Text:Meta')
		{
			var newContext = freshContext(text._0, context);
			return chunkText(newContext, text._1);
		}
	}

	function freshContext(props, ctx)
	{
		return {
			'font-style': props['font-style'] || ctx['font-style'],
			'font-variant': props['font-variant'] || ctx['font-variant'],
			'font-weight': props['font-weight'] || ctx['font-weight'],
			'font-size': props['font-size'] || ctx['font-size'],
			'font-family': props['font-family'] || ctx['font-family'],
			'color': props['color'] || ctx['color']
		};
	}

	var defaultContext = {
		'font-style': 'normal',
		'font-variant': 'normal',
		'font-weight': 'normal',
		'font-size': '12px',
		'font-family': 'sans-serif',
		'color': 'black'
	};


	// IMAGES

	function drawImage(redo, ctx, form)
	{
		var img = new Image();
		img.onload = redo;
		img.src = form._3;
		var w = form._0,
			h = form._1,
			pos = form._2,
			srcX = pos._0,
			srcY = pos._1,
			srcW = w,
			srcH = h,
			destX = -w/2,
			destY = -h/2,
			destW = w,
			destH = h;

		ctx.scale(1,-1);
		ctx.drawImage(img, srcX, srcY, srcW, srcH, destX, destY, destW, destH);
	}

	function renderForm(redo, ctx, form)
	{
		ctx.save();

		var x = form.x,
			y = form.y,
			theta = form.theta,
			scale = form.scale;

		if (x !== 0 || y !== 0)
		{
			ctx.translate(x, y);
		}
		if (theta !== 0)
		{
			ctx.rotate(theta);
		}
		if (scale !== 1)
		{
			ctx.scale(scale,scale);
		}
		if (form.alpha !== 1)
		{
			ctx.globalAlpha = ctx.globalAlpha * form.alpha;
		}

		ctx.beginPath();
		var f = form.form;
		switch (f.ctor)
		{
			case 'FPath':
				drawLine(ctx, f._0, f._1);
				break;

			case 'FImage':
				drawImage(redo, ctx, f);
				break;

			case 'FShape':
				if (f._0.ctor === 'Line')
				{
					f._1.closed = true;
					drawLine(ctx, f._0._0, f._1);
				}
				else
				{
					drawShape(redo, ctx, f._0._0, f._1);
				}
				break;

			case 'FText':
				fillText(redo, ctx, f._0);
				break;

			case 'FOutlinedText':
				strokeText(redo, ctx, f._0, f._1);
				break;
		}
		ctx.restore();
	}

	function formToMatrix(form)
	{
	   var scale = form.scale;
	   var matrix = A6( Transform.matrix, scale, 0, 0, scale, form.x, form.y );

	   var theta = form.theta
	   if (theta !== 0)
	   {
		   matrix = A2( Transform.multiply, matrix, Transform.rotation(theta) );
	   }

	   return matrix;
	}

	function str(n)
	{
		if (n < 0.00001 && n > -0.00001)
		{
			return 0;
		}
		return n;
	}

	function makeTransform(w, h, form, matrices)
	{
		var props = form.form._0.props;
		var m = A6( Transform.matrix, 1, 0, 0, -1,
					(w - props.width ) / 2,
					(h - props.height) / 2 );
		var len = matrices.length;
		for (var i = 0; i < len; ++i)
		{
			m = A2( Transform.multiply, m, matrices[i] );
		}
		m = A2( Transform.multiply, m, formToMatrix(form) );

		return 'matrix(' +
			str( m[0]) + ', ' + str( m[3]) + ', ' +
			str(-m[1]) + ', ' + str(-m[4]) + ', ' +
			str( m[2]) + ', ' + str( m[5]) + ')';
	}

	function stepperHelp(list)
	{
		var arr = List.toArray(list);
		var i = 0;
		function peekNext()
		{
			return i < arr.length ? arr[i].form.ctor : '';
		}
		// assumes that there is a next element
		function next()
		{
			var out = arr[i];
			++i;
			return out;
		}
		return {
			peekNext: peekNext,
			next: next
		};
	}

	function formStepper(forms)
	{
		var ps = [stepperHelp(forms)];
		var matrices = [];
		var alphas = [];
		function peekNext()
		{
			var len = ps.length;
			var formType = '';
			for (var i = 0; i < len; ++i )
			{
				if (formType = ps[i].peekNext()) return formType;
			}
			return '';
		}
		// assumes that there is a next element
		function next(ctx)
		{
			while (!ps[0].peekNext())
			{
				ps.shift();
				matrices.pop();
				alphas.shift();
				if (ctx)
				{
					ctx.restore();
				}
			}
			var out = ps[0].next();
			var f = out.form;
			if (f.ctor === 'FGroup')
			{
				ps.unshift(stepperHelp(f._1));
				var m = A2(Transform.multiply, f._0, formToMatrix(out));
				ctx.save();
				ctx.transform(m[0], m[3], m[1], m[4], m[2], m[5]);
				matrices.push(m);

				var alpha = (alphas[0] || 1) * out.alpha;
				alphas.unshift(alpha);
				ctx.globalAlpha = alpha;
			}
			return out;
		}
		function transforms()
		{
			return matrices;
		}
		function alpha()
		{
			return alphas[0] || 1;
		}
		return {
			peekNext: peekNext,
			next: next,
			transforms: transforms,
			alpha: alpha
		};
	}

	function makeCanvas(w,h)
	{
		var canvas = NativeElement.createNode('canvas');
		canvas.style.width  = w + 'px';
		canvas.style.height = h + 'px';
		canvas.style.display = "block";
		canvas.style.position = "absolute";
		var ratio = window.devicePixelRatio || 1;
		canvas.width  = w * ratio;
		canvas.height = h * ratio;
		return canvas;
	}

	function render(model)
	{
		var div = NativeElement.createNode('div');
		div.style.overflow = 'hidden';
		div.style.position = 'relative';
		update(div, model, model);
		return div;
	}

	function nodeStepper(w,h,div)
	{
		var kids = div.childNodes;
		var i = 0;
		var ratio = window.devicePixelRatio || 1;

		function transform(transforms, ctx)
		{
			ctx.translate( w / 2 * ratio, h / 2 * ratio );
			ctx.scale( ratio, -ratio );
			var len = transforms.length;
			for (var i = 0; i < len; ++i)
			{
				var m = transforms[i];
				ctx.save();
				ctx.transform(m[0], m[3], m[1], m[4], m[2], m[5]);
			}
			return ctx;
		}
		function nextContext(transforms)
		{
			while (i < kids.length)
			{
				var node = kids[i];
				if (node.getContext)
				{
					node.width = w * ratio;
					node.height = h * ratio;
					node.style.width = w + 'px';
					node.style.height = h + 'px';
					++i;
					return transform(transforms, node.getContext('2d'));
				}
				div.removeChild(node);
			}
			var canvas = makeCanvas(w,h);
			div.appendChild(canvas);
			// we have added a new node, so we must step our position
			++i;
			return transform(transforms, canvas.getContext('2d'));
		}
		function addElement(matrices, alpha, form)
		{
			var kid = kids[i];
			var elem = form.form._0;

			var node = (!kid || kid.getContext)
				? NativeElement.render(elem)
				: NativeElement.update(kid, kid.oldElement, elem);

			node.style.position = 'absolute';
			node.style.opacity = alpha * form.alpha * elem.props.opacity;
			NativeElement.addTransform(node.style, makeTransform(w, h, form, matrices));
			node.oldElement = elem;
			++i;
			if (!kid)
			{
				div.appendChild(node);
			}
			else
			{
				div.insertBefore(node, kid);
			}
		}
		function clearRest()
		{
			while (i < kids.length)
			{
				div.removeChild(kids[i]);
			}
		}
		return {
			nextContext: nextContext,
			addElement: addElement,
			clearRest: clearRest
		};
	}


	function update(div, _, model)
	{
		var w = model.w;
		var h = model.h;

		var forms = formStepper(model.forms);
		var nodes = nodeStepper(w,h,div);
		var ctx = null;
		var formType = '';

		while (formType = forms.peekNext())
		{
			// make sure we have context if we need it
			if (ctx === null && formType !== 'FElement')
			{
				ctx = nodes.nextContext(forms.transforms());
				ctx.globalAlpha = forms.alpha();
			}

			var form = forms.next(ctx);
			// if it is FGroup, all updates are made within formStepper when next is called.
			if (formType === 'FElement')
			{
				// update or insert an element, get a new context
				nodes.addElement(forms.transforms(), forms.alpha(), form);
				ctx = null;
			}
			else if (formType !== 'FGroup')
			{
				renderForm(function() { update(div, model, model); }, ctx, form);
			}
		}
		nodes.clearRest();
		return div;
	}


	function collage(w,h,forms)
	{
		return A3(NativeElement.newElement, w, h, {
			ctor: 'Custom',
			type: 'Collage',
			render: render,
			update: update,
			model: {w:w, h:h, forms:forms}
		});
	}

	function getAt(pair, bbuf)
	{
		var canvas = bbuf._0.element.render(bbuf._0.element.model).children[0];
		var context = canvas.getContext('2d');
		var rgba = context.getImageData(pair._0, pair._1, 1, 1).data;
		if (rgba[0] === 0)
		{
			return {ctor: "Nothing"}
		}else{
			return {ctor: "Just", _0: rgba[1]*256 + rgba[2]}
		}
	}

	return localRuntime.Native.Graphics.Collage.values = {
		collage: F3(collage),
		getAt: F2(getAt)
	};

};