Enabling lighting/shadow receiving on custom shader.

Hello, I've recently obtained a shader that I'm trying to modify to allow light/shadows. At the moment it renders unlit (I'm also using Universal Render Pipeline, if it helps)

I'm fairly competent in Shader Graph, but when it comes to shader code I'm unfortunately useless.

Is there something I'm missing here? I've tried a few things already, but nothing seems to be working. If someone could help point me in the right direction, I'd greatly appreciate it. Or, if someone can break this down into something I can recreate in Shader Graph, that would also be extremely helpful.

 Shader "LGPE/GroundTexture"
 {
     Properties
     {
         _TexA("TexA", 2D) = "white" {}
         _TexB("TexB", 2D) = "white" {}
         _TexC("TexC", 2D) = "white" {}
         _TexD("TexD", 2D) = "white" {}
         _TexNoise("TexNoise", 2D) = "white" {}
         _TexTransition("TexTransition", 2D) = "white" {}
     }
     SubShader
     {
         Tags { "RenderType"="Opaque" }
         LOD 100
 
         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             
             #include "UnityCG.cginc"
 
             struct appdata
             {
                 float4 vertex : POSITION;
                 float2 uv : TEXCOORD0;
                 float2 uv1 : TEXCOORD1;
             };
 
             struct v2f
             {
                 float2 uv_a : TEXCOORD0;
                 float2 uv_b : TEXCOORD1;
                 float2 uv_c : TEXCOORD2;
                 float2 uv_d : TEXCOORD3;
                 float2 uv_n : TEXCOORD4;
                 float2 uv_t : TEXCOORD5;
                 UNITY_FOG_COORDS(1)
                 float4 vertex : SV_POSITION;
             };
 
             sampler2D _TexA;
             sampler2D _TexB;
             sampler2D _TexC;
             sampler2D _TexD;
             sampler2D _TexNoise;
             sampler2D _TexTransition;
             float4 _TexA_ST;
             float4 _TexB_ST;
             float4 _TexC_ST;
             float4 _TexD_ST;
             float4 _TexNoise_ST;
             float4 _TexTransition_ST;
             
             v2f vert (appdata v)
             {
                 v2f o;
                 o.vertex = UnityObjectToClipPos(v.vertex);
                 o.uv_a = TRANSFORM_TEX(v.uv, _TexA);
                 o.uv_b = TRANSFORM_TEX(v.uv, _TexB);
                 o.uv_c = TRANSFORM_TEX(v.uv, _TexC);
                 o.uv_d = TRANSFORM_TEX(v.uv, _TexD);
                 o.uv_n = TRANSFORM_TEX(v.uv, _TexNoise);
                 o.uv_t = TRANSFORM_TEX(v.uv1, _TexTransition);
                 return o;
             }
             
             fixed4 func(fixed4 a, fixed4 b, fixed4 c)
             {
                 return a * (b - c) + c;
             }
 
             fixed4 frag (v2f i) : SV_Target
             {
                 fixed4 tex_a = tex2D(_TexA, i.uv_a);
                 fixed4 tex_b = tex2D(_TexB, i.uv_b);
                 fixed4 tex_c = tex2D(_TexC, i.uv_c);
                 fixed4 tex_d = tex2D(_TexD, i.uv_d);
                 fixed4 tex_noise = tex2D(_TexNoise, i.uv_n);
                 fixed4 tex_transition = tex2D(_TexTransition, i.uv_t);
                 float trans_alpha = tex_transition.w;
                 fixed4 col = tex_transition * func(trans_alpha,
                     func(tex_noise, tex_a, tex_b),
                     func(tex_noise, tex_c, tex_d));
                 return col;
             }
             ENDCG
         }
     }
 }