import { ShaderPass } from './ShaderPass.js';

const LUTShader = {

	defines: {
		USE_3DTEXTURE: 1,
	},

	uniforms: {
		lut3d: { value: null },

		lut: { value: null },
		lutSize: { value: 0 },

		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 lutSize;
		#if USE_3DTEXTURE
		precision highp sampler3D;
		uniform sampler3D lut3d;
		#else
		uniform sampler2D lut;

		vec3 lutLookup( sampler2D tex, float size, vec3 rgb ) {

			float sliceHeight = 1.0 / size;
			float yPixelHeight = 1.0 / ( size * size );

			// Get the slices on either side of the sample
			float slice = rgb.b * size;
			float interp = fract( slice );
			float slice0 = slice - interp;
			float centeredInterp = interp - 0.5;

			float slice1 = slice0 + sign( centeredInterp );

			// Pull y sample in by half a pixel in each direction to avoid color
			// bleeding from adjacent slices.
			float greenOffset = clamp( rgb.g * sliceHeight, yPixelHeight * 0.5, sliceHeight - yPixelHeight * 0.5 );

			vec2 uv0 = vec2(
				rgb.r,
				slice0 * sliceHeight + greenOffset
			);
			vec2 uv1 = vec2(
				rgb.r,
				slice1 * sliceHeight + greenOffset
			);

			vec3 sample0 = texture2D( tex, uv0 ).rgb;
			vec3 sample1 = texture2D( tex, uv1 ).rgb;

			return mix( sample0, sample1, abs( centeredInterp ) );

		}
		#endif

		varying vec2 vUv;
		uniform float intensity;
		uniform sampler2D tDiffuse;
		void main() {

			vec4 val = texture2D( tDiffuse, vUv );
			vec4 lutVal;

			// pull the sample in by half a pixel so the sample begins
			// at the center of the edge pixels.
			float pixelWidth = 1.0 / lutSize;
			float halfPixelWidth = 0.5 / lutSize;
			vec3 uvw = vec3( halfPixelWidth ) + val.rgb * ( 1.0 - pixelWidth );

			#if USE_3DTEXTURE

			lutVal = vec4( texture( lut3d, uvw ).rgb, val.a );

			#else

			lutVal = vec4( lutLookup( lut, lutSize, uvw ), val.a );

			#endif

			gl_FragColor = vec4( mix( val, lutVal, intensity ) );

		}

	`,

};

class LUTPass extends ShaderPass {

	set lut( v ) {

		const material = this.material;
		if ( v !== this.lut ) {

			material.uniforms.lut3d.value = null;
			material.uniforms.lut.value = null;

			if ( v ) {

				const is3dTextureDefine = v.isDataTexture3D ? 1 : 0;
				if ( is3dTextureDefine !== material.defines.USE_3DTEXTURE ) {

					material.defines.USE_3DTEXTURE = is3dTextureDefine;
					material.needsUpdate = true;

				}

				material.uniforms.lutSize.value = v.image.width;
				if ( v.isDataTexture3D ) {

					material.uniforms.lut3d.value = v;

				} else {

					material.uniforms.lut.value = v;

				}

			}

		}

	}

	get lut() {

		return this.material.uniforms.lut.value || this.material.uniforms.lut3d.value;

	}

	set intensity( v ) {

		this.material.uniforms.intensity.value = v;

	}

	get intensity() {

		return this.material.uniforms.intensity.value;

	}

	constructor( options = {} ) {

		super( LUTShader );
		this.lut = options.lut || null;
		this.intensity = 'intensity' in options ? options.intensity : 1;

	}

}

export { LUTPass };
