How can I add the diffuse property to a vertex Shader?

Hi there!

I've been messing around with a shader that distorts the world by modifiying the vertices in the scene. Thing is, every object that I apply this shader to remains unlit. Is there a way to give it a diffuse in the script? Is that even possible with vertex shaders? How would I do it?

Here's my current shader:

 Shader "Custom/Curved" {
     Properties {
         _MainTex ("Base (RGB)", 2D) = "white" {}
         _QOffset ("Offset", Vector) = (0,0,0,0)
         _Dist ("Distance", Float) = 100.0
         _Sin ("Sin", Float) = 1
     }
     SubShader {
         Tags { "RenderType"="Opaque" }
         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
                         sampler2D _MainTex;
             float4 _QOffset;
             float _Dist;
             float _Sin;
             
             struct v2f {
                 float4 pos : SV_POSITION;
                 float4 uv : TEXCOORD0;
             };
 
             v2f vert (appdata_base v)
             {
                 v2f o;
                 float4 vPos = mul (UNITY_MATRIX_MV, v.vertex);
                 float zOff = vPos.z/_Dist;
                 _Sin = sin(zOff*1 - 3.1) * 6 + sin(zOff) * 2;
                 //_Sin = 0;
                 vPos += _QOffset*_Sin;
                 o.pos = mul (UNITY_MATRIX_P, vPos);
                 o.uv = v.texcoord;
                 return o;
             }
 
             half4 frag (v2f i) : COLOR
             {
                 half4 col = tex2D(_MainTex, i.uv.xy);
                 return col;
             }
             ENDCG
         }
     }
     FallBack "Diffuse"
 }
 

I haven't written everything by myself, found it some time ago and modified it.

Thanks in advance!