import {
	DataTexture,
	Matrix4,
	RepeatWrapping,
	Vector2,
	Vector3,
} from 'three';

/**
 * References:
 * - implemented algorithm - GTAO
 *   - https://iryoku.com/downloads/Practical-Realtime-Strategies-for-Accurate-Indirect-Occlusion.pdf
 *   - https://github.com/Patapom/GodComplex/blob/master/Tests/TestHBIL/2018%20Mayaux%20-%20Horizon-Based%20Indirect%20Lighting%20(HBIL).pdf
 *
 * - other AO algorithms that are not implemented here:
 *   - Screen Space Ambient Occlusion (SSAO), see also SSAOShader.js
 *	 - http://john-chapman-graphics.blogspot.com/2013/01/ssao-tutorial.html
 *	 - https://learnopengl.com/Advanced-Lighting/SSAO
 *	 - https://creativecoding.soe.ucsc.edu/courses/cmpm164/_schedule/AmbientOcclusion.pdf
 *	 - https://drive.google.com/file/d/1SyagcEVplIm2KkRD3WQYSO9O0Iyi1hfy/edit
 *   - Scalable Ambient Occlusion (SAO), see also SAOShader.js
 *	 - https://casual-effects.com/research/McGuire2012SAO/index.html
 *	   - https://research.nvidia.com/sites/default/files/pubs/2012-06_Scalable-Ambient-Obscurance/McGuire12SAO.pdf
 *   - N8HO
 *	 - https://github.com/N8python/n8ao
 *   - Horizon Based Ambient Occlusion (HBAO)
 *	 - http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.577.2286&rep=rep1&type=pdf
 *	 - https://www.derschmale.com/2013/12/20/an-alternative-implementation-for-hbao-2/
 *
 * - further reading
 * 	 - https://ceur-ws.org/Vol-3027/paper5.pdf
 *   - https://www.comp.nus.edu.sg/~lowkl/publications/mssao_visual_computer_2012.pdf
 *   - https://web.ics.purdue.edu/~tmcgraw/papers/mcgraw-ao-2008.pdf
 *   - https://www.activision.com/cdn/research/Practical_Real_Time_Strategies_for_Accurate_Indirect_Occlusion_NEW%20VERSION_COLOR.pdf
 *   - https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.390.2463&rep=rep1&type=pdf
 *   - https://www.intel.com/content/www/us/en/developer/articles/technical/adaptive-screen-space-ambient-occlusion.html
 */

const GTAOShader = {

	name: 'GTAOShader',

	defines: {
		PERSPECTIVE_CAMERA: 1,
		SAMPLES: 16,
		NORMAL_VECTOR_TYPE: 1,
		DEPTH_SWIZZLING: 'x',
		SCREEN_SPACE_RADIUS: 0,
		SCREEN_SPACE_RADIUS_SCALE: 100.0,
		SCENE_CLIP_BOX: 0,
	},

	uniforms: {
		tNormal: { value: null },
		tDepth: { value: null },
		tNoise: { value: null },
		resolution: { value: new Vector2() },
		cameraNear: { value: null },
		cameraFar: { value: null },
		cameraProjectionMatrix: { value: new Matrix4() },
		cameraProjectionMatrixInverse: { value: new Matrix4() },
		cameraWorldMatrix: { value: new Matrix4() },
		radius: { value: 0.25 },
		distanceExponent: { value: 1. },
		thickness: { value: 1. },
		distanceFallOff: { value: 1. },
		scale: { value: 1. },
		sceneBoxMin: { value: new Vector3( - 1, - 1, - 1 ) },
		sceneBoxMax: { value: new Vector3( 1, 1, 1 ) },
	},

	vertexShader: /* glsl */`

		varying vec2 vUv;

		void main() {
			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
		}`,

	fragmentShader: /* glsl */`
		varying vec2 vUv;
		uniform highp sampler2D tNormal;
		uniform highp sampler2D tDepth;
		uniform sampler2D tNoise;
		uniform vec2 resolution;
		uniform float cameraNear;
		uniform float cameraFar;
		uniform mat4 cameraProjectionMatrix;
		uniform mat4 cameraProjectionMatrixInverse;		
		uniform mat4 cameraWorldMatrix;
		uniform float radius;
		uniform float distanceExponent;
		uniform float thickness;
		uniform float distanceFallOff;
		uniform float scale;
		#if SCENE_CLIP_BOX == 1
			uniform vec3 sceneBoxMin;
			uniform vec3 sceneBoxMax;
		#endif
		
		#include <common>
		#include <packing>

		#ifndef FRAGMENT_OUTPUT
		#define FRAGMENT_OUTPUT vec4(vec3(ao), 1.)
		#endif

		vec3 getViewPosition(const in vec2 screenPosition, const in float depth) {
			vec4 clipSpacePosition = vec4(vec3(screenPosition, depth) * 2.0 - 1.0, 1.0);
			vec4 viewSpacePosition = cameraProjectionMatrixInverse * clipSpacePosition;
			return viewSpacePosition.xyz / viewSpacePosition.w;
		}

		float getDepth(const vec2 uv) {  
			return textureLod(tDepth, uv.xy, 0.0).DEPTH_SWIZZLING;
		}

		float fetchDepth(const ivec2 uv) {   
			return texelFetch(tDepth, uv.xy, 0).DEPTH_SWIZZLING;
		}

		float getViewZ(const in float depth) {
			#if PERSPECTIVE_CAMERA == 1
				return perspectiveDepthToViewZ(depth, cameraNear, cameraFar);
			#else
				return orthographicDepthToViewZ(depth, cameraNear, cameraFar);
			#endif
		}

		vec3 computeNormalFromDepth(const vec2 uv) {
			vec2 size = vec2(textureSize(tDepth, 0));
			ivec2 p = ivec2(uv * size);
			float c0 = fetchDepth(p);
			float l2 = fetchDepth(p - ivec2(2, 0));
			float l1 = fetchDepth(p - ivec2(1, 0));
			float r1 = fetchDepth(p + ivec2(1, 0));
			float r2 = fetchDepth(p + ivec2(2, 0));
			float b2 = fetchDepth(p - ivec2(0, 2));
			float b1 = fetchDepth(p - ivec2(0, 1));
			float t1 = fetchDepth(p + ivec2(0, 1));
			float t2 = fetchDepth(p + ivec2(0, 2));
			float dl = abs((2.0 * l1 - l2) - c0);
			float dr = abs((2.0 * r1 - r2) - c0);
			float db = abs((2.0 * b1 - b2) - c0);
			float dt = abs((2.0 * t1 - t2) - c0);
			vec3 ce = getViewPosition(uv, c0).xyz;
			vec3 dpdx = (dl < dr) ? ce - getViewPosition((uv - vec2(1.0 / size.x, 0.0)), l1).xyz : -ce + getViewPosition((uv + vec2(1.0 / size.x, 0.0)), r1).xyz;
			vec3 dpdy = (db < dt) ? ce - getViewPosition((uv - vec2(0.0, 1.0 / size.y)), b1).xyz : -ce + getViewPosition((uv + vec2(0.0, 1.0 / size.y)), t1).xyz;
			return normalize(cross(dpdx, dpdy));
		}

		vec3 getViewNormal(const vec2 uv) {
			#if NORMAL_VECTOR_TYPE == 2
				return normalize(textureLod(tNormal, uv, 0.).rgb);
			#elif NORMAL_VECTOR_TYPE == 1
				return unpackRGBToNormal(textureLod(tNormal, uv, 0.).rgb);
			#else
				return computeNormalFromDepth(uv);
			#endif
		}

		vec3 getSceneUvAndDepth(vec3 sampleViewPos) {
			vec4 sampleClipPos = cameraProjectionMatrix * vec4(sampleViewPos, 1.);
			vec2 sampleUv = sampleClipPos.xy / sampleClipPos.w * 0.5 + 0.5;
			float sampleSceneDepth = getDepth(sampleUv);
			return vec3(sampleUv, sampleSceneDepth);
		}
		
		void main() {
			float depth = getDepth(vUv.xy);
			if (depth >= 1.0) {
				discard;
				return;
			}
			vec3 viewPos = getViewPosition(vUv, depth);
			vec3 viewNormal = getViewNormal(vUv);

			float radiusToUse = radius;
			float distanceFalloffToUse = thickness;
			#if SCREEN_SPACE_RADIUS == 1
				float radiusScale = getViewPosition(vec2(0.5 + float(SCREEN_SPACE_RADIUS_SCALE) / resolution.x, 0.0), depth).x;
				radiusToUse *= radiusScale;
				distanceFalloffToUse *= radiusScale;
			#endif

			#if SCENE_CLIP_BOX == 1
				vec3 worldPos = (cameraWorldMatrix * vec4(viewPos, 1.0)).xyz;
				float boxDistance = length(max(vec3(0.0), max(sceneBoxMin - worldPos, worldPos - sceneBoxMax)));
				if (boxDistance > radiusToUse) {
					discard;
					return;
				}
			#endif
			
			vec2 noiseResolution = vec2(textureSize(tNoise, 0));
			vec2 noiseUv = vUv * resolution / noiseResolution;
			vec4 noiseTexel = textureLod(tNoise, noiseUv, 0.0);
			vec3 randomVec = noiseTexel.xyz * 2.0 - 1.0;
			vec3 tangent = normalize(vec3(randomVec.xy, 0.));
			vec3 bitangent = vec3(-tangent.y, tangent.x, 0.);
			mat3 kernelMatrix = mat3(tangent, bitangent, vec3(0., 0., 1.));

			const int DIRECTIONS = SAMPLES < 30 ? 3 : 5;
			const int STEPS = (SAMPLES + DIRECTIONS - 1) / DIRECTIONS;
			float ao = 0.0, totalWeight = 0.0;
			for (int i = 0; i < DIRECTIONS; ++i) {
				
				float angle = float(i) / float(DIRECTIONS) * PI;
				vec4 sampleDir = vec4(cos(angle), sin(angle), 0., 0.5 + 0.5 * noiseTexel.w); 
				sampleDir.xyz = normalize(kernelMatrix * sampleDir.xyz);

				vec3 viewDir = normalize(-viewPos.xyz);
				vec3 sliceBitangent = normalize(cross(sampleDir.xyz, viewDir));
				vec3 sliceTangent = cross(sliceBitangent, viewDir);
				vec3 normalInSlice = normalize(viewNormal - sliceBitangent * dot(viewNormal, sliceBitangent));
				
				vec3 tangentToNormalInSlice = cross(normalInSlice, sliceBitangent);
				vec2 cosHorizons = vec2(dot(viewDir, tangentToNormalInSlice), dot(viewDir, -tangentToNormalInSlice));
				
				for (int j = 0; j < STEPS; ++j) {
					vec3 sampleViewOffset = sampleDir.xyz * radiusToUse * sampleDir.w * pow(float(j + 1) / float(STEPS), distanceExponent);	

					vec3 sampleSceneUvDepth = getSceneUvAndDepth(viewPos + sampleViewOffset);
					vec3 sampleSceneViewPos = getViewPosition(sampleSceneUvDepth.xy, sampleSceneUvDepth.z);
					vec3 viewDelta = sampleSceneViewPos - viewPos;
					if (abs(viewDelta.z) < thickness) {
						float sampleCosHorizon = dot(viewDir, normalize(viewDelta));
						cosHorizons.x += max(0., (sampleCosHorizon - cosHorizons.x) * mix(1., 2. / float(j + 2), distanceFallOff));
					}		

					sampleSceneUvDepth = getSceneUvAndDepth(viewPos - sampleViewOffset);
					sampleSceneViewPos = getViewPosition(sampleSceneUvDepth.xy, sampleSceneUvDepth.z);
					viewDelta = sampleSceneViewPos - viewPos;
					if (abs(viewDelta.z) < thickness) {
						float sampleCosHorizon = dot(viewDir, normalize(viewDelta));
						cosHorizons.y += max(0., (sampleCosHorizon - cosHorizons.y) * mix(1., 2. / float(j + 2), distanceFallOff));
					}
				}

				vec2 sinHorizons = sqrt(1. - cosHorizons * cosHorizons);
				float nx = dot(normalInSlice, sliceTangent);
				float ny = dot(normalInSlice, viewDir);
				float nxb = 1. / 2. * (acos(cosHorizons.y) - acos(cosHorizons.x) + sinHorizons.x * cosHorizons.x - sinHorizons.y * cosHorizons.y);
				float nyb = 1. / 2. * (2. - cosHorizons.x * cosHorizons.x - cosHorizons.y * cosHorizons.y);
				float occlusion = nx * nxb + ny * nyb;
				ao += occlusion;
			}

			ao = clamp(ao / float(DIRECTIONS), 0., 1.);		
		#if SCENE_CLIP_BOX == 1
			ao = mix(ao, 1., smoothstep(0., radiusToUse, boxDistance));
		#endif
			ao = pow(ao, scale);

			gl_FragColor = FRAGMENT_OUTPUT;
		}`

};

const GTAODepthShader = {

	name: 'GTAODepthShader',

	defines: {
		PERSPECTIVE_CAMERA: 1
	},

	uniforms: {
		tDepth: { value: null },
		cameraNear: { value: null },
		cameraFar: { value: null },
	},

	vertexShader: /* glsl */`
		varying vec2 vUv;

		void main() {
			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
		}`,

	fragmentShader: /* glsl */`
		uniform sampler2D tDepth;
		uniform float cameraNear;
		uniform float cameraFar;
		varying vec2 vUv;

		#include <packing>

		float getLinearDepth( const in vec2 screenPosition ) {
			#if PERSPECTIVE_CAMERA == 1
				float fragCoordZ = texture2D( tDepth, screenPosition ).x;
				float viewZ = perspectiveDepthToViewZ( fragCoordZ, cameraNear, cameraFar );
				return viewZToOrthographicDepth( viewZ, cameraNear, cameraFar );
			#else
				return texture2D( tDepth, screenPosition ).x;
			#endif
		}

		void main() {
			float depth = getLinearDepth( vUv );
			gl_FragColor = vec4( vec3( 1.0 - depth ), 1.0 );

		}`

};

const GTAOBlendShader = {

	name: 'GTAOBlendShader',

	uniforms: {
		tDiffuse: { value: null },
		intensity: { value: 1.0 }
	},

	vertexShader: /* glsl */`
		varying vec2 vUv;

		void main() {
			vUv = uv;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );
		}`,

	fragmentShader: /* glsl */`
		uniform float intensity;
		uniform sampler2D tDiffuse;
		varying vec2 vUv;

		void main() {
			vec4 texel = texture2D( tDiffuse, vUv );
			gl_FragColor = vec4(mix(vec3(1.), texel.rgb, intensity), texel.a);
		}`

};


function generateMagicSquareNoise( size = 5 ) {

	const noiseSize = Math.floor( size ) % 2 === 0 ? Math.floor( size ) + 1 : Math.floor( size );
	const magicSquare = generateMagicSquare( noiseSize );
	const noiseSquareSize = magicSquare.length;
	const data = new Uint8Array( noiseSquareSize * 4 );

	for ( let inx = 0; inx < noiseSquareSize; ++ inx ) {

		const iAng = magicSquare[ inx ];
		const angle = ( 2 * Math.PI * iAng ) / noiseSquareSize;
		const randomVec = new Vector3(
			Math.cos( angle ),
			Math.sin( angle ),
			0
		).normalize();
		data[ inx * 4 ] = ( randomVec.x * 0.5 + 0.5 ) * 255;
		data[ inx * 4 + 1 ] = ( randomVec.y * 0.5 + 0.5 ) * 255;
		data[ inx * 4 + 2 ] = 127;
		data[ inx * 4 + 3 ] = 255;

	}

	const noiseTexture = new DataTexture( data, noiseSize, noiseSize );
	noiseTexture.wrapS = RepeatWrapping;
	noiseTexture.wrapT = RepeatWrapping;
	noiseTexture.needsUpdate = true;

	return noiseTexture;

}

function generateMagicSquare( size ) {

	const noiseSize = Math.floor( size ) % 2 === 0 ? Math.floor( size ) + 1 : Math.floor( size );
	const noiseSquareSize = noiseSize * noiseSize;
	const magicSquare = Array( noiseSquareSize ).fill( 0 );
	let i = Math.floor( noiseSize / 2 );
	let j = noiseSize - 1;

	for ( let num = 1; num <= noiseSquareSize; ) {

		if ( i === - 1 && j === noiseSize ) {

			j = noiseSize - 2;
			i = 0;

		} else {

			if ( j === noiseSize ) {

				j = 0;

			}

			if ( i < 0 ) {

				i = noiseSize - 1;

			}

		}

		if ( magicSquare[ i * noiseSize + j ] !== 0 ) {

			j -= 2;
			i ++;
			continue;

		} else {

			magicSquare[ i * noiseSize + j ] = num ++;

		}

		j ++;
		i --;

	}

	return magicSquare;

}


export { generateMagicSquareNoise, GTAOShader, GTAODepthShader, GTAOBlendShader };