Shader "Custom/Snake"
{
  Properties
  {
    _Base ("Base", Color) = (0.4, 1, 0.25, 1)
    _Delta ("Delta", Vector) = (-0.1, 0, 0.05, 1)

    _Backup ("Backup", Color) = (0.4, 1, 0.25, 1)

    _DirectionA ("Direction A", Vector) = (0.8, 1, 0.9)
    _DirectionB ("Direction B", Vector) = (-0.8, -0.7, -0.9)
  }
  SubShader
  {
    Pass
    {
      CGPROGRAM

      #pragma vertex VertexProgram
      #pragma fragment FragmentProgram
      #pragma multi_compile_instancing
      #pragma target 3.5

      // #include "UnityCG.cginc"
      #include "UnityStandardBRDF.cginc"

      struct VertexData
      {
        fixed4 position : POSITION;
        fixed3 normal : NORMAL;
        UNITY_VERTEX_INPUT_INSTANCE_ID
        fixed4 color : COLOR;
      };

      struct Interpolators
      {
        fixed4 position : SV_POSITION;
        fixed3 normal : TEXCOORD1;
        fixed4 color : COLOR0;
      };

      int _JustAte, _Flash;
      fixed4 _Base, _Delta;
      fixed3 _DirectionA, _DirectionB;

      Interpolators VertexProgram (VertexData v)
      {
        Interpolators i;

        UNITY_SETUP_INSTANCE_ID(v);
        
        int id = 0;
        #ifdef UNITY_INSTANCING_ENABLED
          id = unity_InstanceID;
        #endif

        i.position = UnityObjectToClipPos(v.position);
        i.normal = UnityObjectToWorldNormal(v.normal);
        i.color = v.color;

        if (_Flash > 0)
        {
          i.color = fixed4(1, 1, 1, 1);
          return i;
        }

        // if mesh = snake green (for snake head)
        if (i.color.g > 0.5 && i.color.r < 0.5)
        {
          // Base Color
          i.color = fixed4(0, 0, 0, 1);

          // Complimentary Lights
          i.color += _Base * clamp(dot(i.normal, _DirectionA), 0, 1);
          i.color += (_Base + _Delta) * clamp(dot(i.normal, _DirectionB), 0, 1);

          // Rings
          if ((id / 1.5) % 2 == 0)
          {
            i.color.r *= 1 + 0.8 * (1 - clamp((half)id / 27, 0, 1));
          }

          // Decay
          i.color *= 1 - ((half)id / 729);

          if (id == _JustAte)
          {
            i.color += fixed4(1,1,1,1) * (1 - clamp((half)id / 27, 0, 1));
          }
          
          // Alpha Fix
          i.color.a = 1;
        }


        return i;
      }

      fixed4 FragmentProgram (Interpolators i) : SV_TARGET
      {
        return i.color;
      }

      ENDCG
    }
  }
}