/* global AFRAME */
AFRAME.registerShader('sky', {
  schema: {
    luminance: { type: 'number', default: 1, min: 0, max: 2, is: 'uniform' },
    turbidity: { type: 'number', default: 2, min: 0, max: 20, is: 'uniform' },
    reileigh: { type: 'number', default: 1, min: 0, max: 4, is: 'uniform' },
    mieCoefficient: { type: 'number', default: 0.005, min: 0, max: 0.1, is: 'uniform' },
    mieDirectionalG: { type: 'number', default: 0.8, min: 0, max: 1, is: 'uniform' },
    sunPosition: { type: 'vec3', default: '0 0 -1', is: 'uniform' }
  },

  vertexShader: [
    'varying vec3 vWorldPosition;',

    'void main() {',

      'vec4 worldPosition = modelMatrix * vec4( position, 1.0 );',
      'vWorldPosition = worldPosition.xyz;',

      'gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );',

    '}'

  ].join('\n'),

  fragmentShader: [

    'uniform sampler2D skySampler;',
    'uniform vec3 sunPosition;',
    'varying vec3 vWorldPosition;',

    'vec3 cameraPos = vec3(0., 0., 0.);',

    'uniform float luminance;',
    'uniform float turbidity;',
    'uniform float reileigh;',
    'uniform float mieCoefficient;',
    'uniform float mieDirectionalG;',

    '// constants for atmospheric scattering',
    'const float e = 2.71828182845904523536028747135266249775724709369995957;',
    'const float pi = 3.141592653589793238462643383279502884197169;',

    'const float n = 1.0003; // refractive index of air',
    'const float N = 2.545E25; // number of molecules per unit volume for air at',
    '// 288.15K and 1013mb (sea level -45 celsius)',
    'const float pn = 0.035;  // depolatization factor for standard air',

    '// wavelength of used primaries, according to preetham',
    'const vec3 lambda = vec3(680E-9, 550E-9, 450E-9);',

    '// mie stuff',
    '// K coefficient for the primaries',
    'const vec3 K = vec3(0.686, 0.678, 0.666);',
    'const float v = 4.0;',

    '// optical length at zenith for molecules',
    'const float rayleighZenithLength = 8.4E3;',
    'const float mieZenithLength = 1.25E3;',
    'const vec3 up = vec3(0.0, 1.0, 0.0);',

    'const float EE = 1000.0;',
    'const float sunAngularDiameterCos = 0.999956676946448443553574619906976478926848692873900859324;',
    '// 66 arc seconds -> degrees, and the cosine of that',

    '// earth shadow hack',
    'const float cutoffAngle = pi/1.95;',
    'const float steepness = 1.5;',

    'vec3 totalRayleigh(vec3 lambda)',
    '{',
      'return (8.0 * pow(pi, 3.0) * pow(pow(n, 2.0) - 1.0, 2.0) * (6.0 + 3.0 * pn)) / (3.0 * N * pow(lambda, vec3(4.0)) * (6.0 - 7.0 * pn));',
    '}',

    // see http://blenderartists.org/forum/showthread.php?321110-Shaders-and-Skybox-madness
    '// A simplied version of the total Rayleigh scattering to works on browsers that use ANGLE',
    'vec3 simplifiedRayleigh()',
    '{',
      'return 0.0005 / vec3(94, 40, 18);',
    '}',

    'float rayleighPhase(float cosTheta)',
    '{   ',
      'return (3.0 / (16.0*pi)) * (1.0 + pow(cosTheta, 2.0));',
    '}',

    'vec3 totalMie(vec3 lambda, vec3 K, float T)',
    '{',
      'float c = (0.2 * T ) * 10E-18;',
      'return 0.434 * c * pi * pow((2.0 * pi) / lambda, vec3(v - 2.0)) * K;',
    '}',

    'float hgPhase(float cosTheta, float g)',
    '{',
      'return (1.0 / (4.0*pi)) * ((1.0 - pow(g, 2.0)) / pow(1.0 - 2.0*g*cosTheta + pow(g, 2.0), 1.5));',
    '}',

    'float sunIntensity(float zenithAngleCos)',
    '{',
      'return EE * max(0.0, 1.0 - exp(-((cutoffAngle - acos(zenithAngleCos))/steepness)));',
    '}',

    '// Filmic ToneMapping http://filmicgames.com/archives/75',
    'float A = 0.15;',
    'float B = 0.50;',
    'float C = 0.10;',
    'float D = 0.20;',
    'float E = 0.02;',
    'float F = 0.30;',
    'float W = 1000.0;',

    'vec3 Uncharted2Tonemap(vec3 x)',
    '{',
       'return ((x*(A*x+C*B)+D*E)/(x*(A*x+B)+D*F))-E/F;',
    '}',

    'void main() ',
    '{',
      'float sunfade = 1.0-clamp(1.0-exp((sunPosition.y/450000.0)),0.0,1.0);',

      'float reileighCoefficient = reileigh - (1.0* (1.0-sunfade));',

      'vec3 sunDirection = normalize(sunPosition);',

      'float sunE = sunIntensity(dot(sunDirection, up));',

      '// extinction (absorbtion + out scattering) ',
      '// rayleigh coefficients',

      'vec3 betaR = simplifiedRayleigh() * reileighCoefficient;',

      '// mie coefficients',
      'vec3 betaM = totalMie(lambda, K, turbidity) * mieCoefficient;',

      '// optical length',
      '// cutoff angle at 90 to avoid singularity in next formula.',
      'float zenithAngle = acos(max(0.0, dot(up, normalize(vWorldPosition - cameraPos))));',
      'float sR = rayleighZenithLength / (cos(zenithAngle) + 0.15 * pow(93.885 - ((zenithAngle * 180.0) / pi), -1.253));',
      'float sM = mieZenithLength / (cos(zenithAngle) + 0.15 * pow(93.885 - ((zenithAngle * 180.0) / pi), -1.253));',

      '// combined extinction factor  ',
      'vec3 Fex = exp(-(betaR * sR + betaM * sM));',

      '// in scattering',
      'float cosTheta = dot(normalize(vWorldPosition - cameraPos), sunDirection);',

      'float rPhase = rayleighPhase(cosTheta*0.5+0.5);',
      'vec3 betaRTheta = betaR * rPhase;',

      'float mPhase = hgPhase(cosTheta, mieDirectionalG);',
      'vec3 betaMTheta = betaM * mPhase;',

      'vec3 Lin = pow(sunE * ((betaRTheta + betaMTheta) / (betaR + betaM)) * (1.0 - Fex),vec3(1.5));',
      'Lin *= mix(vec3(1.0),pow(sunE * ((betaRTheta + betaMTheta) / (betaR + betaM)) * Fex,vec3(1.0/2.0)),clamp(pow(1.0-dot(up, sunDirection),5.0),0.0,1.0));',

      '//nightsky',
      'vec3 direction = normalize(vWorldPosition - cameraPos);',
      'float theta = acos(direction.y); // elevation --> y-axis, [-pi/2, pi/2]',
      'float phi = atan(direction.z, direction.x); // azimuth --> x-axis [-pi/2, pi/2]',
      'vec2 uv = vec2(phi, theta) / vec2(2.0*pi, pi) + vec2(0.5, 0.0);',
      '// vec3 L0 = texture2D(skySampler, uv).rgb+0.1 * Fex;',
      'vec3 L0 = vec3(0.1) * Fex;',

      '// composition + solar disc',
      'float sundisk = smoothstep(sunAngularDiameterCos,sunAngularDiameterCos+0.00002,cosTheta);',
      'L0 += (sunE * 19000.0 * Fex)*sundisk;',

      'vec3 whiteScale = 1.0/Uncharted2Tonemap(vec3(W));',

      'vec3 texColor = (Lin+L0);   ',
      'texColor *= 0.04 ;',
      'texColor += vec3(0.0,0.001,0.0025)*0.3;',

      'float g_fMaxLuminance = 1.0;',
      'float fLumScaled = 0.1 / luminance;     ',
      'float fLumCompressed = (fLumScaled * (1.0 + (fLumScaled / (g_fMaxLuminance * g_fMaxLuminance)))) / (1.0 + fLumScaled); ',

      'float ExposureBias = fLumCompressed;',

      'vec3 curr = Uncharted2Tonemap((log2(2.0/pow(luminance,4.0)))*texColor);',
      'vec3 color = curr*whiteScale;',

      'vec3 retColor = pow(color,vec3(1.0/(1.2+(1.2*sunfade))));',

      'gl_FragColor.rgb = retColor;',

      'gl_FragColor.a = 1.0;',
    '}'
  ].join('\n')
});