Draft for Genetic Diseases

Source/Genes/Diseases/Defs/GeneticDiseaseExtension.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Verse;
+
+namespace RJW_Genes
+{
+    public class GeneticDiseaseExtension : DefModExtension
+    {
+        /// <summary>
+        /// The chance for this gene to spread upon (finished) sex. 
+        /// </summary>
+        public float infectionChance;
+    }
+
+}

Source/Genes/Diseases/Genes/DiseaseGene.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Verse;
+
+namespace RJW_Genes
+{
+    public class DiseaseGene : Gene
+    {
+
+    }
+}

Source/Genes/Diseases/Patches/Patch_AftersexUtility_TransferGeneticDiseases.cs

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+using HarmonyLib;
+using rjw;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Verse;
+
+namespace RJW_Genes.Genes.Diseases.Patches
+{
+    [HarmonyPatch(typeof(SexUtility), "Aftersex")]
+    public class Patch_AftersexUtility_TransferGeneticDiseases
+    {
+
+        public static void Postfix(SexProps props)
+        {
+            if (props == null || props.pawn == null || props.partner == null) return;
+
+            Pawn pawn = props.pawn;
+            Pawn partner = props.partner;
+
+            if (pawn == partner) return;
+            if (pawn.IsAnimal() || partner.IsAnimal()) return;
+            if (pawn.genes == null || partner.genes == null) return;
+            // No Infections on Condom Use
+            if (props.usedCondom) return;
+
+            ModLog.Debug($"Firing Patch_TransferGeneticDiseases for {pawn} and {partner}");
+            TryTransferGeneticDiseases(pawn, partner, props);
+            TryTransferGeneticDiseases(partner, pawn, props);
+        }
+
+        private static void TryTransferGeneticDiseases(Pawn infector, Pawn infected, SexProps props)
+        {
+            if (infected.genes.HasActiveGene(GeneDefOf.rjw_genes_genetic_disease_immunity))
+            {
+                ModLog.Debug($"{infected} is immune to genetic diseases");
+                return;
+            }
+
+            foreach (GeneDef disease in GetGeneticDiseaseGenes(infector)) {
+                ModLog.Debug($"Found genetic disease {disease} in {infector}, trying to infect {infected}");
+
+                if (infected.genes.HasActiveGene(disease))
+                    continue;
+
+                if ((new Random()).NextDouble() <= LookupDiseaseInfectionChance(disease))
+                {
+                    infected.genes.AddGene(disease, false);
+                }
+            }
+        }
+
+        private static List<GeneDef> GetGeneticDiseaseGenes(Pawn pawn)
+        {
+            if (pawn != null && pawn.genes != null)
+            {
+                return pawn.genes
+                    .GenesListForReading
+                    .ConvertAll(gene => gene.def)
+                    .Where(genedef => pawn.genes.HasActiveGene(genedef))
+                    .Where(IsGeneticDiseaseGene)
+                    .ToList();
+            }
+
+            return new List<GeneDef>() { };
+        }
+
+        private static bool IsGeneticDiseaseGene(GeneDef geneDef)
+        {
+            return geneDef.geneClass.FullName.Contains("DiseaseGene");
+        }
+
+        private static float LookupDiseaseInfectionChance(GeneDef geneDef)
+        {
+            if (IsGeneticDiseaseGene(geneDef))
+            {
+                GeneticDiseaseExtension diseaseExt = geneDef.GetModExtension<GeneticDiseaseExtension>();
+                return diseaseExt != null ? diseaseExt.infectionChance : 0.0f;
+            } 
+            else 
+                return 0.0f;
+        }
+    }
+}