#include "Macros.fxh" //from FNA

static const float PI = 3.141592653589793;

// Samplers

DECLARE_TEXTURE(AlbedoTexture, 0);
DECLARE_TEXTURE(NormalTexture, 1);
DECLARE_TEXTURE(EmissionTexture, 2);
DECLARE_TEXTURE(OcclusionTexture, 3);
DECLARE_TEXTURE(MetallicRoughnessTexture, 4);
DECLARE_CUBEMAP(EnvDiffuseTexture, 8);
DECLARE_TEXTURE(BrdfLutTexture, 9);
DECLARE_CUBEMAP(EnvSpecularTexture, 10);

BEGIN_CONSTANTS

    // PBR Values
    float3 AlbedoValue                          _ps(c0)     _cb(c0);
    float MetallicValue                         _ps(c1)     _cb(c1);
    float RoughnessValue                        _ps(c2)     _cb(c2);
    float AO                                    _ps(c3)     _cb(c3);

    // Light Info
    float3 LightPositions[4]                    _ps(c4)     _cb(c4);
    float3 LightColors[4]                       _ps(c8)     _cb(c8);

    float3 EyePosition                          _ps(c12)    _cb(c12);

    float4x4 World                  _vs(c0)                 _cb(c16);
    float4x4 WorldInverseTranspose  _vs(c4)                 _cb(c20);

MATRIX_CONSTANTS

    float4x4 WorldViewProjection    _vs(c8)                _cb(c0);

END_CONSTANTS

struct VertexShaderInput
{
    float4 Position : POSITION;
    float3 Normal   : NORMAL;
    float2 TexCoord : TEXCOORD0;
};

struct PixelShaderInput
{
    float4 Position   : SV_Position;
    float2 TexCoord   : TEXCOORD0;
    float3 PositionWS : TEXCOORD1;
    float3 NormalWS   : TEXCOORD2;
};

PixelShaderInput main_vs(VertexShaderInput input)
{
    PixelShaderInput output;
   
    output.TexCoord = input.TexCoord;
    output.PositionWS = mul(input.Position, World).xyz;
    output.NormalWS = mul(input.Normal, (float3x3)WorldInverseTranspose).xyz;
    output.Position = mul(input.Position, WorldViewProjection);

    return output;
}

float3 FresnelSchlick(float cosTheta, float3 F0)
{
    return F0 + (1.0 - F0) * pow(1.0 - cosTheta, 5.0);
}

float DistributionGGX(float3 N, float3 H, float roughness)
{
    float a = roughness * roughness;
    float a2 = a * a;
    float NdotH = max(dot(N, H), 0.0);
    float NdotH2 = NdotH * NdotH;

    float num = a2;
    float denom = (NdotH2 * (a2 - 1.0) + 1.0);
    denom = PI * denom * denom;

    return num / denom;
}

float GeometrySchlickGGX(float NdotV, float roughness)
{
    float r = (roughness + 1.0);
    float k = (r * r) / 8.0;

    float num = NdotV;
    float denom = NdotV * (1.0 - k) + k;

    return num / denom;
}

float GeometrySmith(float3 N, float3 V, float3 L, float roughness)
{
    float NdotV = max(dot(N, V), 0.0);
    float NdotL = max(dot(N, L), 0.0);
    float ggx2 = GeometrySchlickGGX(NdotV, roughness);
    float ggx1 = GeometrySchlickGGX(NdotL, roughness);

    return ggx1 * ggx2;
}

// Easy trick to get tangent-normals to world-space to keep PBR code simplified.
float3 GetNormalFromMap(float3 worldPos, float2 texCoords, float3 normal)
{
    float3 tangentNormal = SAMPLE_TEXTURE(NormalTexture, texCoords).xyz * 2.0 - 1.0;

    float3 Q1  = ddx(worldPos);
    float3 Q2  = ddy(worldPos);
    float2 st1 = ddx(texCoords);
    float2 st2 = ddy(texCoords);

    float3 N   = normalize(normal);
    float3 T  = normalize(Q1*st2.y - Q2*st1.y);
    float3 B  = -normalize(cross(N, T));
    float3x3 TBN = float3x3(T, B, N);

    return normalize(mul(tangentNormal, TBN));
}

float4 ComputeColor(
    float3 worldPosition, 
    float3 worldNormal, 
    float3 albedo, 
    float metallic, 
    float roughness
) {
    float3 V = normalize(EyePosition - worldPosition);
    float3 N = worldNormal;

    float3 F0 = float3(0.04, 0.04, 0.04);
    F0 = lerp(F0, albedo, metallic);

    float3 Lo = float3(0.0, 0.0, 0.0);

    for (int i = 0; i < 4; i++)
    {
        float3 lightDir = LightPositions[i] - worldPosition;
        float3 L = normalize(lightDir);
        float3 H = normalize(V + L);

        float distance = length(lightDir);
        float attenuation = 1.0 / (distance * distance);
        float3 radiance = LightColors[i] * attenuation;

        float NDF = DistributionGGX(N, H, roughness);
        float G = GeometrySmith(N, V, L, roughness);
        float3 F = FresnelSchlick(max(dot(H, V), 0.0), F0);

        float3 numerator = NDF * G * F;
        float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0);
        float3 specular = numerator / max(denominator, 0.001);

        float3 kS = F;
        float3 kD = float3(1.0, 1.0, 1.0) - kS;

        kD *= 1.0 - metallic;

        float NdotL = max(dot(N, L), 0.0);
        Lo += (kD * albedo / PI + specular) * radiance * NdotL;
    }

    float3 ambient = float3(0.03, 0.03, 0.03) * albedo * AO;
    float3 color = ambient + Lo;

    color = color / (color + float3(1.0, 1.0, 1.0));
    float exposureConstant = 1.0 / 2.2;
    color = pow(color, float3(exposureConstant, exposureConstant, exposureConstant));

    return float4(color, 1.0);
}

// The case where we have no texture maps for any PBR data
float4 None(PixelShaderInput input) : SV_TARGET0
{
    return ComputeColor(
        input.PositionWS,
        input.NormalWS, 
        AlbedoValue,
        MetallicValue,
        RoughnessValue
    );
}

float4 AlbedoMapPS(PixelShaderInput input) : SV_TARGET
{
    float3 albedo = pow(SAMPLE_TEXTURE(AlbedoTexture, input.TexCoord), 2.2).rgb;

    return ComputeColor(
        input.PositionWS,
        input.NormalWS,
        albedo,
        MetallicValue,
        RoughnessValue
    );
}

float4 MetallicRoughnessPS(PixelShaderInput input) : SV_TARGET
{
    float2 metallicRoughness = SAMPLE_TEXTURE(MetallicRoughnessTexture, input.TexCoord).rg;

    return ComputeColor(
        input.PositionWS,
        input.NormalWS,
        AlbedoValue,
        metallicRoughness.r,
        metallicRoughness.g
    );
}

float4 NormalPS(PixelShaderInput input) : SV_TARGET
{
    float3 normal = GetNormalFromMap(input.PositionWS, input.TexCoord, input.NormalWS);

    return ComputeColor(
        input.PositionWS,
        normal,
        AlbedoValue,
        MetallicValue,
        RoughnessValue
    );
}

float4 AlbedoMetallicRoughnessMapPS(PixelShaderInput input) : SV_TARGET
{
    float3 albedo = pow(SAMPLE_TEXTURE(AlbedoTexture, input.TexCoord), 2.2).rgb;
    float2 metallicRoughness = SAMPLE_TEXTURE(MetallicRoughnessTexture, input.TexCoord).rg;

    return ComputeColor(
        input.PositionWS,
        input.NormalWS,
        albedo,
        metallicRoughness.r,
        metallicRoughness.g
    );
}

float4 AlbedoNormalPS(PixelShaderInput input) : SV_TARGET
{
    float3 albedo = pow(SAMPLE_TEXTURE(AlbedoTexture, input.TexCoord), 2.2).rgb;
    float3 normal = GetNormalFromMap(input.PositionWS, input.TexCoord, input.NormalWS);

    return ComputeColor(
        input.PositionWS,
        normal,
        albedo,
        MetallicValue,
        RoughnessValue
    );
}

float4 MetallicRoughnessNormalPS(PixelShaderInput input) : SV_TARGET
{
    float2 metallicRoughness = SAMPLE_TEXTURE(MetallicRoughnessTexture, input.TexCoord).rg;
    float3 normal = GetNormalFromMap(input.PositionWS, input.TexCoord, input.NormalWS);

    return ComputeColor(
        input.PositionWS,
        normal,
        AlbedoValue,
        metallicRoughness.r,
        metallicRoughness.g
    );
}

float4 AlbedoMetallicRoughnessNormalMapPS(PixelShaderInput input) : SV_TARGET
{
    float3 albedo = pow(SAMPLE_TEXTURE(AlbedoTexture, input.TexCoord), 2.2).rgb;
    float2 metallicRoughness = SAMPLE_TEXTURE(MetallicRoughnessTexture, input.TexCoord).rg;
    float3 normal = GetNormalFromMap(input.PositionWS, input.TexCoord, input.NormalWS);

    return ComputeColor(
        input.PositionWS,
        normal,
        albedo,
        metallicRoughness.r,
        metallicRoughness.g
    );
}

PixelShader PSArray[8] =
{
    compile ps_3_0 None(),

    compile ps_3_0 AlbedoMapPS(),
    compile ps_3_0 MetallicRoughnessPS(),
    compile ps_3_0 NormalPS(),

    compile ps_3_0 AlbedoMetallicRoughnessMapPS(),
    compile ps_3_0 AlbedoNormalPS(),
    compile ps_3_0 MetallicRoughnessNormalPS(),

    compile ps_3_0 AlbedoMetallicRoughnessNormalMapPS()
};

int ShaderIndex = 0;

Technique PBR
{
    Pass
    {
        VertexShader = compile vs_3_0 main_vs();
        PixelShader = (PSArray[ShaderIndex]);
    }
}