using System;
using static PKHeX.Core.LegalityCheckStrings;
using static PKHeX.Core.Species;

namespace PKHeX.Core;

/// <summary>
/// Verifies the <see cref="PKM.Form"/> value.
/// </summary>
public sealed class FormVerifier : Verifier
{
    protected override CheckIdentifier Identifier => CheckIdentifier.Form;

    public override void Verify(LegalityAnalysis data)
    {
        var pk = data.Entity;
        if (pk.Format < 4)
            return; // no forms exist
        var result = VerifyForm(data);
        data.AddLine(result);

        if (pk is IFormArgument f)
            data.AddLine(VerifyFormArgument(data, f));
    }

    private CheckResult VALID => GetValid(LFormValid);

    private CheckResult VerifyForm(LegalityAnalysis data)
    {
        var pk = data.Entity;
        var PersonalInfo = data.PersonalInfo;

        int count = PersonalInfo.FormCount;
        var form = pk.Form;
        if (count <= 1 && form == 0)
            return VALID; // no forms to check

        var species = pk.Species;
        var enc = data.EncounterMatch;
        var Info = data.Info;

        if (!PersonalInfo.IsFormWithinRange(form) && !FormInfo.IsValidOutOfBoundsForm(species, form, Info.Generation))
            return GetInvalid(string.Format(LFormInvalidRange, count - 1, form));

        switch ((Species)species)
        {
            case Pikachu when Info.Generation == 6: // Cosplay
                bool isStatic = enc is EncounterStatic6;
                bool validCosplay = form == (isStatic ? enc.Form : 0);
                if (!validCosplay)
                    return GetInvalid(isStatic ? LFormPikachuCosplayInvalid : LFormPikachuCosplay);
                break;

            case Pikachu when form is not 0 && ParseSettings.ActiveTrainer is SAV7b {Version:GameVersion.GE}:
            case Eevee when form is not 0 && ParseSettings.ActiveTrainer is SAV7b {Version:GameVersion.GP}:
                return GetInvalid(LFormBattle);

            case Pikachu when Info.Generation >= 7: // Cap
                bool validCap = form == (enc is EncounterInvalid or EncounterEgg ? 0 : enc.Form);
                if (!validCap)
                {
                    bool gift = enc is MysteryGift g && g.Form != form;
                    var msg = gift ? LFormPikachuEventInvalid : LFormInvalidGame;
                    return GetInvalid(msg);
                }
                break;
            case Unown when Info.Generation == 2 && form >= 26:
                return GetInvalid(string.Format(LFormInvalidRange, "Z", form == 26 ? "!" : "?"));
            case Unown when Info.Generation == 3 && form != EntityPID.GetUnownForm3(pk.EncryptionConstant):
                return GetInvalid(string.Format(LFormInvalidExpect_0, EntityPID.GetUnownForm3(pk.EncryptionConstant)));
            case Dialga or Palkia or Giratina or Arceus when form > 0 && pk is PA8: // can change forms with key items
                break;
            case Giratina when form == 1 ^ pk.HeldItem == 112: // Giratina, Origin form only with Griseous Orb
                return GetInvalid(LFormItemInvalid);

            case Arceus:
            {
                int arceus = GetArceusFormFromHeldItem(pk.HeldItem, pk.Format);
                return arceus != form ? GetInvalid(LFormItemInvalid) : GetValid(LFormItem);
            }
            case Keldeo when enc.Generation != 5 || pk.Format >= 8:
                // can mismatch in gen5 via BW tutor and transfer up
                // can mismatch in gen8+ as the form activates in battle when knowing the move; outside of battle can be either state.
                // Generation 8 patched out the mismatch; always forced to match moves.
                bool hasSword = pk.HasMove((int) Move.SecretSword);
                bool isSword = pk.Form == 1;
                if (isSword != hasSword)
                    return GetInvalid(LMoveKeldeoMismatch);
                break;
            case Genesect:
            {
                int genesect = GetGenesectFormFromHeldItem(pk.HeldItem);
                return genesect != form ? GetInvalid(LFormItemInvalid) : GetValid(LFormItem);
            }
            case Greninja:
                if (form > 1) // Ash Battle Bond active
                    return GetInvalid(LFormBattle);
                if (form != 0 && enc is not MysteryGift) // Forms are not breedable, MysteryGift already checked
                    return GetInvalid(string.Format(LFormInvalidRange, 0, form));
                break;

            case Scatterbug or Spewpa:
                if (form > Vivillon3DS.MaxWildFormID) // Fancy & Pokéball
                    return GetInvalid(LFormVivillonEventPre);
                if (pk is not IRegionOrigin tr)
                    break;
                if (!Vivillon3DS.IsPatternValid(form, tr.ConsoleRegion))
                    return GetInvalid(LFormVivillonInvalid);
                if (!Vivillon3DS.IsPatternNative(form, tr.Country, tr.Region))
                    data.AddLine(Get(LFormVivillonNonNative, Severity.Fishy));
                break;
            case Vivillon:
                if (form > Vivillon3DS.MaxWildFormID) // Fancy & Pokéball
                {
                    if (enc is not MysteryGift)
                        return GetInvalid(LFormVivillonInvalid);
                    return GetValid(LFormVivillon);
                }
                if (pk is not IRegionOrigin trv)
                    break;
                if (!Vivillon3DS.IsPatternValid(form, trv.ConsoleRegion))
                    return GetInvalid(LFormVivillonInvalid);
                if (!Vivillon3DS.IsPatternNative(form, trv.Country, trv.Region))
                    data.AddLine(Get(LFormVivillonNonNative, Severity.Fishy));
                break;

            case Floette when form == 5: // Floette Eternal Flower -- Never Released
                if (enc is not MysteryGift)
                    return GetInvalid(LFormEternalInvalid);
                return GetValid(LFormEternal);
            case Meowstic when form != pk.Gender:
                return GetInvalid(LGenderInvalidNone);

            case Silvally:
            {
                int silvally = GetSilvallyFormFromHeldItem(pk.HeldItem);
                return silvally != form ? GetInvalid(LFormItemInvalid) : GetValid(LFormItem);
            }

            // Form doesn't exist in SM; cannot originate from that game.
            case Rockruff when enc.Generation == 7 && form == 1 && pk.SM:
            case Lycanroc when enc.Generation == 7 && form == 2 && pk.SM:
                return GetInvalid(LFormInvalidGame);

            // Toxel encounters have already been checked for the nature-specific evolution criteria.
            case Toxtricity when enc.Species == (int)Toxtricity:
            {
                // The game enforces the Nature for Toxtricity encounters too!
                if (pk.Form != EvolutionMethod.GetAmpLowKeyResult(pk.Nature))
                    return GetInvalid(LFormInvalidNature);
                break;
            }

            // Impossible Egg forms
            case Rotom when pk.IsEgg && form != 0:
            case Furfrou when pk.IsEgg && form != 0:
                return GetInvalid(LEggSpecies);

            // Party Only Forms
            case Shaymin:
            case Furfrou:
            case Hoopa:
                if (form != 0 && data.SlotOrigin is not SlotOrigin.Party && pk.Format <= 6) // has form but stored in box
                    return GetInvalid(LFormParty);
                break;
        }

        var format = pk.Format;
        if (FormInfo.IsBattleOnlyForm(species, form, format))
            return GetInvalid(LFormBattle);

        if (form == 0)
            return VALID;

        // everything below here is not Form 0, so it has a form.
        if (format >= 7 && Info.Generation < 7)
        {
            if (species == 25 || Legal.AlolanOriginForms.Contains(species) || Legal.AlolanVariantEvolutions12.Contains(enc.Species))
                return GetInvalid(LFormInvalidGame);
        }
        if (format >= 8 && Info.Generation < 8)
        {
            var orig = enc.Species;
            if (Legal.GalarOriginForms.Contains(species) || Legal.GalarVariantFormEvolutions.Contains(orig))
            {
                if (species == (int)Meowth && enc.Form != 2)
                {
                    // We're okay here. There's also Alolan Meowth...
                }
                else if (((Species)orig is MrMime or MimeJr) && pk.CurrentLevel > enc.LevelMin && Info.Generation >= 4)
                {
                    // We're okay with a Mime Jr. that has evolved via level up.
                }
                else if (enc.Version != GameVersion.GO)
                {
                    return GetInvalid(LFormInvalidGame);
                }
            }
        }

        return VALID;
    }

    private static readonly ushort[] Arceus_PlateIDs = { 303, 306, 304, 305, 309, 308, 310, 313, 298, 299, 301, 300, 307, 302, 311, 312, 644 };
    private static readonly ushort[] Arceus_ZCrystal = { 782, 785, 783, 784, 788, 787, 789, 792, 777, 778, 780, 779, 786, 781, 790, 791, 793 };

    public static byte GetArceusFormFromHeldItem(int item, int format) => item switch
    {
        (>= 777 and <= 793)        => GetArceusFormFromZCrystal(item),
        (>= 298 and <= 313) or 644 => GetArceusFormFromPlate(item, format),
        _ => 0,
    };

    private static byte GetArceusFormFromZCrystal(int item)
    {
        return (byte)(Array.IndexOf(Arceus_ZCrystal, (ushort)item) + 1);
    }

    private static byte GetArceusFormFromPlate(int item, int format)
    {
        byte form = (byte)(Array.IndexOf(Arceus_PlateIDs, (ushort)item) + 1);
        if (format != 4) // No need to consider Curse type
            return form;
        if (form < 9)
            return form;
        return ++form; // ??? type Form shifts everything by 1
    }

    public static byte GetSilvallyFormFromHeldItem(int item)
    {
        if (item is >= 904 and <= 920)
            return (byte)(item - 903);
        return 0;
    }

    public static byte GetGenesectFormFromHeldItem(int item)
    {
        if (item is >= 116 and <= 119)
            return (byte)(item - 115);
        return 0;
    }

    private CheckResult VerifyFormArgument(LegalityAnalysis data, IFormArgument f)
    {
        var pk = data.Entity;
        var enc = data.EncounterMatch;
        var arg = f.FormArgument;

        var unusedMask = pk.Format == 6 ? 0xFFFF_FF00 : 0xFF00_0000;
        if ((arg & unusedMask) != 0)
            return GetInvalid(LFormArgumentHigh);

        return (Species)pk.Species switch
        {
            // Transfer Edge Cases -- Bank wipes the form but keeps old FormArgument value.
            Furfrou when pk.Format == 7 && pk.Form == 0 &&
                         ((enc.Generation == 6 && f.FormArgument <= byte.MaxValue) || IsFormArgumentDayCounterValid(f, 5, true))
                => GetValid(LFormArgumentValid),

            Furfrou when pk.Form != 0 => !IsFormArgumentDayCounterValid(f, 5, true) ? GetInvalid(LFormArgumentInvalid) :GetValid(LFormArgumentValid),
            Hoopa when pk.Form == 1 => !IsFormArgumentDayCounterValid(f, 3) ? GetInvalid(LFormArgumentInvalid) : GetValid(LFormArgumentValid),
            Yamask when pk.Form == 1 => arg switch
            {
                not 0 when pk.IsEgg => GetInvalid(LFormArgumentNotAllowed),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Runerigus when enc.Species == (int)Runerigus => arg switch
            {
                not 0 => GetInvalid(LFormArgumentNotAllowed),
                _ => GetValid(LFormArgumentValid),
            },
            Runerigus => arg switch // From Yamask-1
            {
                < 49 => GetInvalid(LFormArgumentLow),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Alcremie when enc.Species == (int)Alcremie => arg switch
            {
                not 0 => GetInvalid(LFormArgumentNotAllowed),
                _ => GetValid(LFormArgumentValid),
            },
            Alcremie => arg switch // From Milcery
            {
                > (uint) AlcremieDecoration.Ribbon => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Overqwil when enc.Species == (int)Overqwil => arg switch
            {
                not 0 => GetInvalid(LFormArgumentNotAllowed),
                _ => GetValid(LFormArgumentValid),
            },
            Wyrdeer when enc.Species == (int)Wyrdeer => arg switch
            {
                not 0 => GetInvalid(LFormArgumentNotAllowed),
                _ => GetValid(LFormArgumentValid),
            },
            Basculegion when enc.Species == (int)Basculegion => arg switch
            {
                not 0 => GetInvalid(LFormArgumentNotAllowed),
                _ => GetValid(LFormArgumentValid),
            },
            Basculin when pk.Form is 2 => arg switch
            {
                not 0 when pk.IsEgg => GetInvalid(LFormArgumentNotAllowed),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Qwilfish when pk.Form is 1 => arg switch
            {
                not 0 when pk.IsEgg => GetInvalid(LFormArgumentNotAllowed),
                not 0 when pk.CurrentLevel < 25 => GetInvalid(LFormArgumentHigh),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Stantler when pk is PA8 || data.Info.EvoChainsAllGens.HasVisitedPLA => arg switch
            {
                not 0 when pk.IsEgg => GetInvalid(LFormArgumentNotAllowed),
                not 0 when pk.CurrentLevel < 31 => GetInvalid(LFormArgumentHigh),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Wyrdeer => arg switch // From Stantler
            {
                < 20 => GetInvalid(LFormArgumentLow),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Overqwil => arg switch // From Qwilfish-1
            {
                < 20 => GetInvalid(LFormArgumentLow),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            Basculegion => arg switch // From Basculin-2
            {
                < 294 => GetInvalid(LFormArgumentLow),
                > 9_999 => GetInvalid(LFormArgumentHigh),
                _ => GetValid(LFormArgumentValid),
            },
            _ => VerifyFormArgumentNone(pk, f),
        };
    }

    private CheckResult VerifyFormArgumentNone(PKM pk, IFormArgument f)
    {
        if (pk is not PK6 pk6)
        {
            if (f.FormArgument != 0)
            {
                if (pk.Species == (int)Furfrou && pk.Form == 0 && (f.FormArgument & ~0xFF_00_00u) == 0)
                    return GetValid(LFormArgumentValid);
                return GetInvalid(LFormArgumentNotAllowed);
            }
            return GetValid(LFormArgumentValid);
        }

        if (f.FormArgument != 0)
        {
            if (pk.Species == (int)Furfrou && pk.Form == 0 && (f.FormArgument & ~0xFFu) == 0)
                return GetValid(LFormArgumentValid);
            return GetInvalid(LFormArgumentNotAllowed);
        }

        // Stored separately from main form argument value
        if (pk6.FormArgumentRemain != 0)
            return GetInvalid(LFormArgumentNotAllowed);
        if (pk6.FormArgumentElapsed != 0)
            return GetInvalid(LFormArgumentNotAllowed);

        return GetValid(LFormArgumentValid);
    }

    private static bool IsFormArgumentDayCounterValid(IFormArgument f, uint maxSeed, bool canRefresh = false)
    {
        var remain = f.FormArgumentRemain;
        var elapsed = f.FormArgumentElapsed;
        var maxElapsed = f.FormArgumentMaximum;
        if (canRefresh)
        {
            if (maxElapsed < elapsed)
                return false;

            if (remain + elapsed < maxSeed)
                return false;
        }
        else
        {
            if (maxElapsed != 0)
                return false;

            if (remain + elapsed != maxSeed)
                return false;
        }
        if (remain > maxSeed)
            return false;
        return remain != 0;
    }
}