Texture2D<float4> Texture : register(t0, space2);
SamplerState Sampler : register(s0, space2);

cbuffer Uniforms : register(b0, space3)
{
    float time;
    float3 viewPos;
};

// from learnopengl.com
float3 BlinnPhong(float3 normal, float3 fragPos, float3 lightPos, float3 lightColor)
{
    // diffuse  parameter
    float3 lightDir = normalize(lightPos - fragPos);
    float diff = max(dot(lightDir, normal), 0.0);
    float3 diffuse = diff * lightColor;

    // specular parameter
    float3 viewDir = normalize(fragPos - viewPos);
    float3 reflectDir = reflect(-lightDir, normal);
    float spec = 0.0;
    float3 halfwayDir = normalize(lightDir + viewDir);
    spec = pow(max(dot(normal, halfwayDir), 0.0), 30.0);
    float3 specular = spec * lightColor * 2;

    // attenuation
    float maxDist = 5;
    float cutoff1 = 2;
    float cutoff2 = 4;
    float cutoffFactor = 0.5;
    float dist = length(lightPos - fragPos);
    float attenuation = 1.0 / (dist * 2);
    if (dist > cutoff1)
    {
        attenuation *= cutoffFactor;
    }
    if (dist > cutoff2)
    {
        attenuation *= cutoffFactor;
    }
    if (dist > maxDist)
    {
        attenuation = 0;
    }
    

    diffuse *= attenuation;
    specular *= attenuation;

    return diffuse + specular;
    
    //return lightColor * 100 * attenuation;
    
}

float4 main(
    float2 UV : TEXCOORD0,
    float3 WorldPos: TEXCOORD1,
    float3 Normal: TEXCOORD2
) : SV_Target0
{

    float3 lightPos = float3(0, 20 + -4, -5);
    float3 lightColor = float3(0.8, 0.8, 0.5);

    float3 ambient = lerp(float3(0.01, 0.01, 0.003), float3(0.004, 0.004, 0.06), dot(Normal, float3(0.0,1.0,0.0)) );

    float4 s = Texture.Sample(Sampler, UV);
    float alpha = s.w;

    float3 col = s.xyz;
    float3 c2 = col * ambient + col * BlinnPhong(Normal, WorldPos, lightPos, lightColor);

    float4 rv = float4(pow(c2, 1.0 / 2.2), alpha);
    return rv;
}