PKHeX/PKHeX.Core/Legality/Evolutions/EvolutionLineage.cs

using System.Collections.Generic;
using System.Linq;

namespace PKHeX.Core
{
    /// <summary>
    /// Informatics pertaining to a <see cref="PKM"/>'s evolution lineage.
    /// </summary>
    public class EvolutionLineage
    {
        public readonly List<EvolutionStage> Chain = new List<EvolutionStage>();

        public void Insert(EvolutionMethod entry)
        {
            int matchChain = -1;
            for (int i = 0; i < Chain.Count; i++)
                if (Chain[i].StageEntryMethods.Any(e => e.Species == entry.Species))
                    matchChain = i;

            if (matchChain != -1)
                Chain[matchChain].StageEntryMethods.Add(entry);
            else
                Chain.Insert(0, new EvolutionStage { StageEntryMethods = new List<EvolutionMethod> {entry}});
        }
        public void Insert(EvolutionStage evo)
        {
            Chain.Insert(0, evo);
        }

        public List<DexLevel> GetExplicitLineage(PKM pkm, int maxLevel, bool skipChecks, int maxSpeciesTree, int maxSpeciesOrigin, int minLevel)
        {
            int lvl = maxLevel;
            List<DexLevel> dl = new List<DexLevel> { new DexLevel { Species = pkm.Species, Level = lvl, Form = pkm.AltForm } };
            for (int i = Chain.Count - 1; i >= 0; i--) // reverse evolution!
            {
                bool oneValid = false;
                foreach (var evo in Chain[i].StageEntryMethods)
                {
                    if (!evo.Valid(pkm, lvl, skipChecks))
                        continue;

                    if (evo.RequiresLevelUp && minLevel >= lvl)
                        break; // impossible evolution

                    oneValid = true;
                    UpdateMinValues(dl, evo);
                    int species = evo.Species;

                    // Gen7 Personal Formes -- unmap the forme personal entry ID to the actual species ID since species are consecutive
                    if (evo.Species > maxSpeciesTree)
                        species = pkm.Species - Chain.Count + i;

                    if (evo.RequiresLevelUp)
                        lvl--;
                    dl.Add(evo.GetDexLevel(species, lvl));
                    break;
                }
                if (!oneValid)
                    break;
            }

            // Remove future gen preevolutions, no munchlax in a gen3 snorlax, no pichu in a gen1 vc raichu, etc
            var last = dl[dl.Count - 1];
            if (last.Species > maxSpeciesOrigin && dl.Any(d => d.Species <= maxSpeciesOrigin))
                dl.RemoveAt(dl.Count - 1);

            // Last species is the wild/hatched species, the minimum is 1 because it has not evolved from previous species
            last = dl[dl.Count - 1];
            last.MinLevel = 1;
            last.RequiresLvlUp = false;
            return dl;
        }
        private static void UpdateMinValues(IReadOnlyList<DexLevel> dl, EvolutionMethod evo)
        {
            var last = dl[dl.Count - 1];
            if (evo.Level == 0 || !evo.RequiresLevelUp) // Evolutions like elemental stones, trade, etc
            {
                if (!evo.RequiresLevelUp)
                    last.MinLevel = 1;
                else
                {
                    // Evolutions like frienship, pichu -> pikachu, eevee -> umbreon, etc
                    last.MinLevel = 2;

                    var first = dl[0];
                    if (dl.Count > 1 && !first.RequiresLvlUp)
                        first.MinLevel = 2; // Raichu from Pikachu would have minimum level 1, but with Pichu included Raichu minimum level is 2
                }
            }
            else // level up evolutions
            {
                last.MinLevel = evo.Level;

                var first = dl[0];
                if (dl.Count > 1)
                {
                    if (first.MinLevel < evo.Level && !first.RequiresLvlUp)
                        first.MinLevel = evo.Level; // Pokemon like Nidoqueen, its minimum level is Nidorina minimum level
                    if (first.MinLevel <= evo.Level && first.RequiresLvlUp)
                        first.MinLevel = evo.Level + 1; // Pokemon like Crobat, its minimum level is Golbat minimum level + 1
                }
            }
            last.RequiresLvlUp = evo.RequiresLevelUp;
        }
    }
}