Terrarium.Game.GameEngine.killOrganisms C# (CSharp) Method

        private void killOrganisms(IDictionary organismsToKill, int organismKillCount, int totalPopulation,
                                   bool killingAnimals)
        {
            const int diseaseBoundary = 10;
            int killedCount = 0;
            ArrayList largePopulationSpecies = new ArrayList();
            Random rand = new Random(DateTime.Now.Millisecond);

            if (organismsToKill == null || organismKillCount <= 0) return;

            // Find the species that have large populations on the system
            ICollection allSpeciesCollection = organismsToKill.Values;
            foreach (SortedList list in allSpeciesCollection)
            {
                // For large population species, we try to maintain their population percentages with respect to the other
                // large population species
                if (list.Count <= diseaseBoundary) continue;
                // Kill a proportional amount of this species
                int speciesKillTarget = (int) ((list.Count/(double) totalPopulation)*organismKillCount);
                while (list.Count > diseaseBoundary && speciesKillTarget > 0)
                {
                    killedCount++;
                    speciesKillTarget--;

                    // Get the oldest animal of this species
                    OrganismState state = (OrganismState) list.GetByIndex(0);
                    list.RemoveAt(0);
                    if (killingAnimals)
                    {
                        Debug.Assert(state is AnimalState);
                        state.Kill(PopulationChangeReason.Sick);
                    }
                    else
                    {
                        removeOrganism(new KilledOrganism(state.ID, PopulationChangeReason.Sick));
                    }
                }

                if (list.Count > diseaseBoundary)
                {
                    largePopulationSpecies.Add(list);
                }
            }

            organismKillCount -= killedCount;
            killedCount = 0;

            // If we still need to kill more organisms, we take it off the large populations first
            if (organismKillCount > 0)
            {
                int index = rand.Next(0, largePopulationSpecies.Count);
                while (organismKillCount > 0 && largePopulationSpecies.Count > 0)
                {
                    SortedList list = (SortedList) largePopulationSpecies[index];
                    OrganismState state = (OrganismState) list.GetByIndex(0);
                    list.RemoveAt(0);
                    if (killingAnimals)
                    {
                        Debug.Assert(state is AnimalState);
                        state.Kill(PopulationChangeReason.Sick);
                    }
                    else
                    {
                        removeOrganism(new KilledOrganism(state.ID, PopulationChangeReason.Sick));
                    }
                    organismKillCount--;
                    killedCount++;
                    if (list.Count <= diseaseBoundary)
                    {
                        largePopulationSpecies.RemoveAt(index);
                    }
                    else
                    {
                        index++;
                    }

                    if (index > largePopulationSpecies.Count - 1)
                    {
                        index = 0;
                    }
                }
            }

            killedCount = 0;

            // If we still need to kill more organisms, we take it off of anyone, one by one, randomly
            if (organismKillCount > 0)
            {
                SortedList[] allSpecies = new SortedList[organismsToKill.Count];
                allSpeciesCollection.CopyTo(allSpecies, 0);
                while (organismKillCount > 0)
                {
                    int index = rand.Next(0, allSpecies.Length);
                    SortedList list = allSpecies[index];
                    if (list.Count > 0)
                    {
                        OrganismState state = (OrganismState) list.GetByIndex(0);
                        list.RemoveAt(0);
                        if (killingAnimals)
                        {
                            Debug.Assert(state is AnimalState);
                            state.Kill(PopulationChangeReason.Sick);
                        }
                        else
                        {
                            removeOrganism(new KilledOrganism(state.ID, PopulationChangeReason.Sick));
                        }
                        organismKillCount--;
                        killedCount++;
                    }
                }
            }
        }