import { roundedRectangleDataSize } from './minimap-webgl-shapes'

export function setupWebGl(canvas: HTMLCanvasElement | null) {
	if (!canvas) throw new Error('Canvas element not found')

	const context = canvas.getContext('webgl2', {
		premultipliedAlpha: false,
	})
	if (!context) throw new Error('Failed to get webgl2 context')

	const vertexShaderSourceCode = `#version 300 es
  precision mediump float;
  
  in vec2 shapeVertexPosition;

	uniform vec4 canvasPageBounds;

	// taken (with thanks) from
	// https://webglfundamentals.org/webgl/lessons/webgl-2d-matrices.html
  void main() {
		// convert the position from pixels to 0.0 to 1.0
		vec2 zeroToOne = (shapeVertexPosition - canvasPageBounds.xy) / canvasPageBounds.zw;
	
		// convert from 0->1 to 0->2
		vec2 zeroToTwo = zeroToOne * 2.0;
	
		// convert from 0->2 to -1->+1 (clipspace)
		vec2 clipSpace = zeroToTwo - 1.0;
	
		gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);
  }`

	const vertexShader = context.createShader(context.VERTEX_SHADER)
	if (!vertexShader) {
		throw new Error('Failed to create vertex shader')
	}
	context.shaderSource(vertexShader, vertexShaderSourceCode)
	context.compileShader(vertexShader)
	if (!context.getShaderParameter(vertexShader, context.COMPILE_STATUS)) {
		throw new Error('Failed to compile vertex shader')
	}

	const fragmentShaderSourceCode = `#version 300 es
  precision mediump float;
  
	uniform vec4 fillColor;
  out vec4 outputColor;

  void main() {
	outputColor = fillColor;
  }`

	const fragmentShader = context.createShader(context.FRAGMENT_SHADER)
	if (!fragmentShader) {
		throw new Error('Failed to create fragment shader')
	}
	context.shaderSource(fragmentShader, fragmentShaderSourceCode)
	context.compileShader(fragmentShader)
	if (!context.getShaderParameter(fragmentShader, context.COMPILE_STATUS)) {
		throw new Error('Failed to compile fragment shader')
	}

	const program = context.createProgram()
	if (!program) {
		throw new Error('Failed to create program')
	}
	context.attachShader(program, vertexShader)
	context.attachShader(program, fragmentShader)
	context.linkProgram(program)
	if (!context.getProgramParameter(program, context.LINK_STATUS)) {
		throw new Error('Failed to link program')
	}
	context.useProgram(program)

	const shapeVertexPositionAttributeLocation = context.getAttribLocation(
		program,
		'shapeVertexPosition'
	)
	if (shapeVertexPositionAttributeLocation < 0) {
		throw new Error('Failed to get shapeVertexPosition attribute location')
	}
	context.enableVertexAttribArray(shapeVertexPositionAttributeLocation)

	const canvasPageBoundsLocation = context.getUniformLocation(program, 'canvasPageBounds')
	const fillColorLocation = context.getUniformLocation(program, 'fillColor')

	const selectedShapesBuffer = context.createBuffer()
	if (!selectedShapesBuffer) throw new Error('Failed to create buffer')

	const unselectedShapesBuffer = context.createBuffer()
	if (!unselectedShapesBuffer) throw new Error('Failed to create buffer')

	return {
		context,
		selectedShapes: allocateBuffer(context, 1024),
		unselectedShapes: allocateBuffer(context, 4096),
		viewport: allocateBuffer(context, roundedRectangleDataSize),
		collaborators: allocateBuffer(context, 1024),

		prepareTriangles(stuff: BufferStuff, len: number) {
			context.bindBuffer(context.ARRAY_BUFFER, stuff.buffer)
			context.bufferData(context.ARRAY_BUFFER, stuff.vertices, context.STATIC_DRAW, 0, len)
			context.enableVertexAttribArray(shapeVertexPositionAttributeLocation)
			context.vertexAttribPointer(
				shapeVertexPositionAttributeLocation,
				2,
				context.FLOAT,
				false,
				0,
				0
			)
		},

		drawTriangles(len: number) {
			context.drawArrays(context.TRIANGLES, 0, len / 2)
		},

		setFillColor(color: Float32Array) {
			context.uniform4fv(fillColorLocation, color)
		},

		setCanvasPageBounds(bounds: Float32Array) {
			context.uniform4fv(canvasPageBoundsLocation, bounds)
		},
	}
}

export type BufferStuff = ReturnType<typeof allocateBuffer>

function allocateBuffer(context: WebGL2RenderingContext, size: number) {
	const buffer = context.createBuffer()
	if (!buffer) throw new Error('Failed to create buffer')
	return { buffer, vertices: new Float32Array(size) }
}

export function appendVertices(bufferStuff: BufferStuff, offset: number, data: Float32Array) {
	let len = bufferStuff.vertices.length
	while (len < offset + data.length) {
		len *= 2
	}
	if (len != bufferStuff.vertices.length) {
		const newVertices = new Float32Array(len)
		newVertices.set(bufferStuff.vertices)
		bufferStuff.vertices = newVertices
	}

	bufferStuff.vertices.set(data, offset)
}