#include "Macros.fxh" //from FNA

static const float PI = 3.141592653589793;
static const int MAX_POINT_LIGHTS = 64;
static const int NUM_SHADOW_CASCADES = 4;

DECLARE_TEXTURE(gPosition, 0);
DECLARE_TEXTURE(gAlbedo, 1);
DECLARE_TEXTURE(gNormal, 2);
DECLARE_TEXTURE(gMetallicRoughness, 3);
DECLARE_TEXTURE(shadowMapOne, 4);
DECLARE_TEXTURE(shadowMapTwo, 5);
DECLARE_TEXTURE(shadowMapThree, 6);
DECLARE_TEXTURE(shadowMapFour, 7);

BEGIN_CONSTANTS

    float3 EyePosition                                         _ps(c0)      _cb(c0);
    
    float3 PointLightPositions[MAX_POINT_LIGHTS]               _ps(c1)      _cb(c1);
    float3 PointLightColors[MAX_POINT_LIGHTS]                  _ps(c65)     _cb(c65);

    float3 DirectionalLightDirection                           _ps(c129)   _cb(c129);
    float3 DirectionalLightColor                               _ps(c130)   _cb(c130);

    float CascadeFarPlanes[NUM_SHADOW_CASCADES]                _ps(c131)   _cb(c131);

MATRIX_CONSTANTS

    float4x4 LightSpaceMatrixOne                               _ps(c135)   _cb(c135);
    float4x4 LightSpaceMatrixTwo                               _ps(c139)   _cb(c139);
    float4x4 LightSpaceMatrixThree                             _ps(c143)   _cb(c143);
    float4x4 LightSpaceMatrixFour                              _ps(c147)   _cb(c147);

    // used to select shadow cascade
    float4x4 ViewMatrix                                        _ps(c151)   _cb(c151);

END_CONSTANTS

struct VertexInput
{
    float4 Position : POSITION;
    float2 TexCoord : TEXCOORD;
};

struct PixelInput
{
    float4 Position : SV_POSITION;
    float2 TexCoord : TEXCOORD0;
};

PixelInput main_vs(VertexInput input)
{
    PixelInput output;

    output.Position = input.Position;
    output.TexCoord = input.TexCoord;

    return output;
}

// Pixel Shader

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;
}

float ComputeShadow(float3 positionWorldSpace, float3 N, float L)
{
    float bias = 0.005 * tan(acos(dot(N, L)));
    bias = clamp(bias, 0, 0.01);

    float4 positionCameraSpace = mul(float4(positionWorldSpace, 1.0), ViewMatrix);

    int shadowCascadeIndex = 0; // 0 is closest
    for (int i = 0; i < NUM_SHADOW_CASCADES; i++)
    {
        if (positionCameraSpace.z < CascadeFarPlanes[i])
        {
            shadowCascadeIndex = i;
            break;
        }
    }

    float4x4 lightSpaceMatrix;

    if (shadowCascadeIndex == 0)
    {
        lightSpaceMatrix = LightSpaceMatrixOne;
    }
    else if (shadowCascadeIndex == 1)
    {
        lightSpaceMatrix = LightSpaceMatrixTwo;
    }
    else if (shadowCascadeIndex == 2)
    {
        lightSpaceMatrix = LightSpaceMatrixThree;
    }
    else
    {
        lightSpaceMatrix = LightSpaceMatrixFour;
    }

    float4 positionLightSpace = mul(float4(positionWorldSpace, 1.0), lightSpaceMatrix);
   
    // maps to [-1, 1]
    float3 projectionCoords = positionLightSpace.xyz / positionLightSpace.w;

    // maps to [0, 1]
    projectionCoords.x = (projectionCoords.x * 0.5) + 0.5;
    projectionCoords.y = (projectionCoords.y * 0.5) + 0.5;
    projectionCoords.y *= -1;

    float closestDepth;
    if (shadowCascadeIndex == 0)
    {
        closestDepth = SAMPLE_TEXTURE(shadowMapOne, projectionCoords.xy).r;
    }
    else if (shadowCascadeIndex == 1)
    {
        closestDepth = SAMPLE_TEXTURE(shadowMapTwo, projectionCoords.xy).r;
    }
    else if (shadowCascadeIndex == 2)
    {
        closestDepth = SAMPLE_TEXTURE(shadowMapThree, projectionCoords.xy).r;
    }
    else
    {
        closestDepth = SAMPLE_TEXTURE(shadowMapFour, projectionCoords.xy).r;
    }

    float currentDepth = projectionCoords.z;

    if (currentDepth - bias > closestDepth)
    {
        return 1.0;
    }
    else
    {
        return 0.0;
    }
}

float3 ComputeLight(
    float3 L,
    float3 radiance,
    float3 F0,
    float3 V,
    float3 N,
    float3 albedo,
    float metallic,
    float roughness,
    float shadow
) {
    float3 H = normalize(V + L);

    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);
    return (kD * albedo / PI + specular) * radiance * NdotL * shadow;
}

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

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

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

    // point light
    for (int i = 0; i < MAX_POINT_LIGHTS; i++)
    {
        float3 lightDir = PointLightPositions[i] - worldPosition;
        float3 L = normalize(lightDir);
        float distance = length(lightDir);
        float attenuation = 1.0 / (distance * distance);
        float3 radiance = PointLightColors[i] * attenuation;

        Lo += ComputeLight(L, radiance, F0, V, N, albedo, metallic, roughness, 1.0);
    }

    // directional light
    float3 L = normalize(DirectionalLightDirection);
    float3 radiance = DirectionalLightColor;

    float shadow = ComputeShadow(worldPosition, N, L);

    Lo += ComputeLight(L, radiance, F0, V, N, albedo, metallic, roughness, (1.0 - shadow));

    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);
}

float4 main_ps(PixelInput input) : SV_TARGET0
{
    float3 worldPosition = SAMPLE_TEXTURE(gPosition, input.TexCoord).rgb;
    float3 normal = SAMPLE_TEXTURE(gNormal, input.TexCoord).xyz;
    float3 albedo = SAMPLE_TEXTURE(gAlbedo, input.TexCoord).rgb;
    float2 metallicRoughness = SAMPLE_TEXTURE(gMetallicRoughness, input.TexCoord).rg;

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

Technique DeferredPBR
{
    Pass
    {
        VertexShader = compile vs_3_0 main_vs();
        PixelShader = compile ps_3_0 main_ps();
    }
}