using System;
using System.Collections.Generic;
using System.Linq;
using static PKHeX.Core.LegalityCheckStrings;
using static PKHeX.Core.LanguageID;

namespace PKHeX.Core
{
    /// <summary>
    /// Verifies the <see cref="PKM.Nickname"/>.
    /// </summary>
    public sealed class NicknameVerifier : Verifier
    {
        protected override CheckIdentifier Identifier => CheckIdentifier.Nickname;

        public override void Verify(LegalityAnalysis data)
        {
            var pkm = data.pkm;

            // If the Pokémon is not nicknamed, it should match one of the language strings.
            var nickname = pkm.Nickname;
            if (nickname.Length == 0)
            {
                data.AddLine(GetInvalid(LNickLengthShort));
                return;
            }
            if (pkm.Species > SpeciesName.SpeciesLang[0].Count)
            {
                data.AddLine(Get(LNickLengthShort, Severity.Indeterminate));
                return;
            }

            var enc = data.EncounterOriginal;
            if (enc is ILangNicknamedTemplate n)
            {
                VerifyFixedNicknameEncounter(data, n, enc, pkm, nickname);
                if (pkm.IsEgg)
                    VerifyNicknameEgg(data);
                return;
            }

            if (pkm.Format <= 7 && pkm.IsNicknamed) // can nickname afterwards
            {
                if (pkm.VC)
                    VerifyG1NicknameWithinBounds(data, nickname.AsSpan());
                else if (enc is MysteryGift {IsEgg: false})
                    data.AddLine(Get(LEncGiftNicknamed, ParseSettings.NicknamedMysteryGift));
            }

            if (enc is EncounterTrade t)
            {
                VerifyNicknameTrade(data, t);
                if (t.HasNickname)
                    return;
            }

            if (pkm.IsEgg)
            {
                VerifyNicknameEgg(data);
                return;
            }

            if (VerifyUnNicknamedEncounter(data, pkm, nickname))
                return;

            // Non-nicknamed strings have already been checked.
            if (ParseSettings.CheckWordFilter && pkm.IsNicknamed)
            {
                if (WordFilter.IsFiltered(nickname, out string bad))
                    data.AddLine(GetInvalid($"Word Filter: {bad}"));
                if (TrainerNameVerifier.ContainsTooManyNumbers(nickname, data.Info.Generation))
                    data.AddLine(GetInvalid("Word Filter: Too many numbers."));
            }
        }

        private void VerifyFixedNicknameEncounter(LegalityAnalysis data, ILangNicknamedTemplate n, IEncounterTemplate enc, PKM pkm, string nickname)
        {
            var nick = n.GetNickname(pkm.Language);

            if (string.IsNullOrWhiteSpace(nick))
            {
                if (n is WC8 {IsHOMEGift: true})
                {
                    VerifyHomeGiftNickname(data, enc, pkm, nickname);
                    return;
                }

                if (n.CanHandleOT(pkm.Language))
                    return;

                if (n is WC3 && pkm.Format != 3)
                {
                    // Gen3 gifts transferred to Generation 4 from another language can set the nickname flag.
                    var evos = data.Info.EvoChainsAllGens.Gen3;
                    bool matchAny = evos.Any(evo => !SpeciesName.IsNicknamedAnyLanguage(evo.Species, nickname, 3));
                    if (matchAny)
                        return;
                }

                if (pkm.IsNicknamed)
                    data.AddLine(Get(LEncGiftNicknamed, Severity.Invalid));
                return;
            }

            if (!pkm.IsNicknamed)
            {
                // Check if it had a nickname at all
                var orig = SpeciesName.GetSpeciesNameGeneration(enc.Species, pkm.Language, enc.Generation);
                if (orig == nick)
                {
                    // Didn't have a nickname. Ensure that the language matches the current nickname string.
                    if (!SpeciesName.IsNicknamed(pkm.Species, nickname, pkm.Language, pkm.Format))
                        return;
                }

                // Should have a nickname present.
                data.AddLine(GetInvalid(LNickMatchLanguageFail));
                return;
            }

            // Encounter has a nickname, and PKM should have it.
            var severity = nick != nickname || !pkm.IsNicknamed ? Severity.Invalid : Severity.Valid;
            data.AddLine(Get(LEncGiftNicknamed, severity));
        }

        private void VerifyHomeGiftNickname(LegalityAnalysis data, IEncounterTemplate enc, ILangNick pkm, string nickname)
        {
            // can nickname on redemption
            if (!pkm.IsNicknamed)
                return;

            // Can't nickname everything.
            if (enc.Species == (int) Species.Melmetal)
            {
                data.AddLine(GetInvalid(LEncGiftNicknamed));
                return;
            }

            // Ensure the nickname does not match species name
            var orig = SpeciesName.GetSpeciesNameGeneration(enc.Species, pkm.Language, enc.Generation);
            if (nickname == orig)
                data.AddLine(GetInvalid(LNickMatchLanguageFlag));
        }

        private bool VerifyUnNicknamedEncounter(LegalityAnalysis data, PKM pkm, string nickname)
        {
            if (pkm.IsNicknamed)
            {
                if (data.Info.Generation >= 8)
                {
                    // Can only nickname if it matches your language.
                    // Setting the nickname to the same as the species name does not set the Nickname flag (equals unmodified, no flag)
                    if (!SpeciesName.IsNicknamed(pkm.Species, nickname, pkm.Language, pkm.Format))
                    {
                        data.AddLine(Get(LNickMatchLanguageFlag, Severity.Invalid));
                        return true;
                    }
                }
                for (int i = 0; i < SpeciesName.SpeciesDict.Count; i++)
                {
                    if (!SpeciesName.SpeciesDict[i].TryGetValue(nickname, out int species))
                        continue;
                    var msg = species == pkm.Species && i != pkm.Language ? LNickMatchNoOthersFail : LNickMatchLanguageFlag;
                    data.AddLine(Get(msg, ParseSettings.NicknamedAnotherSpecies));
                    return true;
                }
                if (pkm.Format <= 7 && StringConverter.HasEastAsianScriptCharacters(nickname.AsSpan()) && pkm is not PB7) // East Asian Scripts
                {
                    data.AddLine(GetInvalid(LNickInvalidChar));
                    return true;
                }
                if (nickname.Length > Legal.GetMaxLengthNickname(data.Info.Generation, (LanguageID)pkm.Language))
                {
                    int length = GetForeignNicknameLength(pkm, data.Info.EncounterOriginal, data.Info.Generation);
                    var severe = (length != 0 && nickname.Length <= length) ? Severity.Fishy : Severity.Invalid;
                    data.AddLine(Get(LNickLengthLong, severe));
                    return true;
                }
                data.AddLine(GetValid(LNickMatchNoOthers));
            }
            else if (pkm.Format < 3)
            {
                // pk1/pk2 IsNicknamed getter checks for match, logic should only reach here if matches.
                data.AddLine(GetValid(LNickMatchLanguage));
            }
            else
            {
                var enc = data.EncounterOriginal;
                bool valid = IsNicknameValid(pkm, enc, nickname);
                var result = valid ? GetValid(LNickMatchLanguage) : GetInvalid(LNickMatchLanguageFail);
                data.AddLine(result);
            }
            return false;
        }

        private static int GetForeignNicknameLength(PKM pkm, IEncounterTemplate match, int origin)
        {
            // HOME gifts already verified prior to reaching here.
            System.Diagnostics.Debug.Assert(match is not WC8 {IsHOMEGift:true});

            int length = 0;
            if (origin is (4 or 5 or 6 or 7) && match.EggEncounter && pkm.WasTradedEgg)
                length = Legal.GetMaxLengthNickname(origin, English);

            if (pkm.FatefulEncounter)
                return length;

            if (pkm.Format < 8 || pkm.BDSP)
                return length;

            // Can only nickname if the language matches.
            var future = Legal.GetMaxLengthNickname(pkm.Format, (LanguageID)pkm.Language);
            return Math.Max(length, future);
        }

        private static bool IsNicknameValid(PKM pkm, IEncounterTemplate enc, string nickname)
        {
            int species = pkm.Species;
            int format = pkm.Format;
            int language = pkm.Language;
            if (SpeciesName.GetSpeciesNameGeneration(species, language, format) == nickname)
                return true;

            // Can't have another language name if it hasn't evolved or wasn't a language-traded egg.
            // Starting in Generation 8, hatched language-traded eggs will take the Language from the trainer that hatched it.
            // Also in Generation 8, evolving in a foreign language game will retain the original language as the source for the newly evolved species name.
            // Transferring from Gen7->Gen8 realigns the Nickname string to the Language, if not nicknamed.
            bool canHaveAnyLanguage = format <= 7 && (enc.Species != species || pkm.WasTradedEgg) && !pkm.GG;
            if (canHaveAnyLanguage && !SpeciesName.IsNicknamedAnyLanguage(species, nickname, format))
                return true;

            switch (enc)
            {
                case WC7 wc7 when wc7.IsAshGreninjaWC7(pkm):
                    return true;
                case ILangNick loc:
                    if (loc.Language != 0 && !loc.IsNicknamed && !SpeciesName.IsNicknamedAnyLanguage(species, nickname, format))
                        return true; // fixed language without nickname, nice job event maker!
                    break;
            }

            if (format == 5 && !pkm.IsNative) // transfer
            {
                if (canHaveAnyLanguage)
                   return !SpeciesName.IsNicknamedAnyLanguage(species, nickname, 4);
                return SpeciesName.GetSpeciesNameGeneration(species, language, 4) == nickname;
            }

            return false;
        }

        private static void VerifyNicknameEgg(LegalityAnalysis data)
        {
            var Info = data.Info;
            var pkm = data.pkm;

            bool flagState = EggStateLegality.IsNicknameFlagSet(Info.EncounterMatch, pkm);
            if (pkm.IsNicknamed != flagState)
                data.AddLine(GetInvalid(flagState ? LNickFlagEggYes : LNickFlagEggNo, CheckIdentifier.Egg));

            var nick = pkm.Nickname;
            if (pkm.Format == 2 && !SpeciesName.IsNicknamedAnyLanguage(0, nick, 2))
                data.AddLine(GetValid(LNickMatchLanguageEgg, CheckIdentifier.Egg));
            else if (nick != SpeciesName.GetSpeciesNameGeneration(0, pkm.Language, Info.Generation))
                data.AddLine(GetInvalid(LNickMatchLanguageEggFail, CheckIdentifier.Egg));
            else
                data.AddLine(GetValid(LNickMatchLanguageEgg, CheckIdentifier.Egg));
        }

        private static void VerifyNicknameTrade(LegalityAnalysis data, EncounterTrade t)
        {
            switch (data.Info.Generation)
            {
                case 8 when t is EncounterTrade8b b: VerifyTrade8b(data, b); return;

                case 1: VerifyTrade12(data, t); return;
                case 2: return; // already checked all relevant properties when fetching with getValidEncounterTradeVC2
                case 3: VerifyTrade3(data, t); return;
                case 4: VerifyTrade4(data, t); return;
                case 5: VerifyTrade5(data, t); return;
                case 6:
                case 7:
                case 8:
                    VerifyTrade(data, t, data.pkm.Language); return;
            }
        }

        private void VerifyG1NicknameWithinBounds(LegalityAnalysis data, ReadOnlySpan<char> str)
        {
            var pkm = data.pkm;
            if (StringConverter12.GetIsG1English(str))
            {
                if (str.Length > 10)
                    data.AddLine(GetInvalid(LNickLengthLong));
            }
            else if (StringConverter12.GetIsG1Japanese(str))
            {
                if (str.Length > 5)
                    data.AddLine(GetInvalid(LNickLengthLong));
            }
            else if (pkm.Korean && StringConverter2KOR.GetIsG2Korean(str))
            {
                if (str.Length > 5)
                    data.AddLine(GetInvalid(LNickLengthLong));
            }
            else
            {
                data.AddLine(GetInvalid(LG1CharNick));
            }
        }

        private static void VerifyTrade12(LegalityAnalysis data, EncounterTrade t)
        {
            var t1 = (EncounterTrade1)t;
            if (!t1.IsNicknameValid(data.pkm))
                data.AddLine(GetInvalid(LEncTradeChangedNickname, CheckIdentifier.Nickname));
            if (!t1.IsTrainerNameValid(data.pkm))
                data.AddLine(GetInvalid(LEncTradeChangedOT, CheckIdentifier.Trainer));
        }

        private static void VerifyTrade3(LegalityAnalysis data, EncounterTrade t)
        {
            var pkm = data.pkm;
            int lang = pkm.Language;
            if (t.Species == (int)Species.Jynx) // FRLG Jynx
                lang = DetectTradeLanguageG3DANTAEJynx(pkm, lang);
            VerifyTrade(data, t, lang);
        }

        private static void VerifyTrade4(LegalityAnalysis data, EncounterTrade t)
        {
            var pkm = data.pkm;
            if (pkm.TID == 1000)
            {
                VerifyTradeOTOnly(data, t);
                return;
            }
            int lang = pkm.Language;
            switch (t.Species)
            {
                case (int)Species.Pikachu: // HGSS Pikachu
                    lang = DetectTradeLanguageG4SurgePikachu(pkm, t, lang);
                    // flag korean on gen4 saves since the pkm.Language is German
                    FlagKoreanIncompatibleSameGenTrade(data, pkm, lang);
                    break;
                case (int)Species.Magikarp: // DPPt Magikarp
                    lang = DetectTradeLanguageG4MeisterMagikarp(pkm, t, lang);
                    // flag korean on gen4 saves since the pkm.Language is German
                    FlagKoreanIncompatibleSameGenTrade(data, pkm, lang);
                    break;

                default:
                    if (t is EncounterTrade4PID && pkm.Version is ((int)GameVersion.D or (int)GameVersion.P)) // mainline DP
                    {
                        // DP English origin are Japanese lang. Can't have LanguageID 2
                        if (lang == 2)
                        {
                            data.AddLine(GetInvalid(string.Format(LOTLanguage, Japanese, English), CheckIdentifier.Language));
                            break;
                        }

                        // Since two locales (JPN/ENG) can have the same LanguageID, check which we should be validating with.
                        if (lang == 1 && pkm.OT_Name != t.GetOT(1)) // not Japanese
                            lang = 2; // verify strings with English locale instead.
                    }
                    break;
            }
            VerifyTrade(data, t, lang);
        }

        private static void VerifyTrade8b(LegalityAnalysis data, EncounterTrade8b t)
        {
            var pkm = data.pkm;
            int lang = pkm.Language;
            if (t.Species == (int)Species.Magikarp)
            {
                // Japanese 
                if (pkm.Language == (int)Japanese && pkm.OT_Name is "Diamond." or "Pearl.")
                {
                    // Traded between players, the original OT is replaced with the above OT (version dependent) as the original OT is >6 chars in length.
                    VerifyTradeNickname(data, t, t.Nicknames[(int)German], pkm);
                    return;
                }

                lang = DetectTradeLanguageG8MeisterMagikarp(pkm, t, lang);
                if (lang == 0) // err
                    data.AddLine(GetInvalid(string.Format(LOTLanguage, $"{Japanese}/{German}", $"{(LanguageID)pkm.Language}"), CheckIdentifier.Language));
            }
            VerifyTrade(data, t, lang);
        }

        private static int DetectTradeLanguageG8MeisterMagikarp(PKM pkm, EncounterTrade8b t, int currentLanguageID)
        {
            // Receiving the trade on a German game -> Japanese LanguageID.
            // Receiving the trade on any other language -> German LanguageID.
            if (currentLanguageID is not ((int)Japanese or (int)German))
                return 0;

            var nick = pkm.Nickname;
            var ot = pkm.OT_Name;
            for (int i = 1; i < (int)ChineseT; i++)
            {
                if (t.Nicknames[i] != nick)
                    continue;
                if (t.TrainerNames[i] != ot)
                    continue;

                // Language gets flipped to another language ID; can't be equal.
                var shouldNotBe = currentLanguageID == (int)German ? German : Japanese;
                return i != (int)shouldNotBe ? i : 0;
            }
            return 0;
        }

        private static void FlagKoreanIncompatibleSameGenTrade(LegalityAnalysis data, PKM pkm, int lang)
        {
            if (pkm.Format != 4 || lang != (int)Korean)
                return; // transferred or not appropriate
            if (ParseSettings.ActiveTrainer.Language != (int)Korean && ParseSettings.ActiveTrainer.Language >= 0)
                data.AddLine(GetInvalid(string.Format(LTransferOriginFInvalid0_1, L_XKorean, L_XKoreanNon), CheckIdentifier.Language));
        }

        private static int DetectTradeLanguage(string OT, EncounterTrade t, int currentLanguageID)
        {
            var names = t.TrainerNames;
            for (int lang = 1; lang < names.Count; lang++)
            {
                if (names[lang] != OT)
                    continue;
                return lang;
            }
            return currentLanguageID;
        }

        private static int DetectTradeLanguageG3DANTAEJynx(PKM pk, int currentLanguageID)
        {
            if (currentLanguageID != (int)Italian)
                return currentLanguageID;

            if (pk.Version == (int)GameVersion.LG)
                currentLanguageID = (int)English; // translation error; OT was not localized => same as English
            return currentLanguageID;
        }

        private static int DetectTradeLanguageG4MeisterMagikarp(PKM pkm, EncounterTrade t, int currentLanguageID)
        {
            if (currentLanguageID == (int)English)
                return (int)German;

            // All have German, regardless of origin version.
            var lang = DetectTradeLanguage(pkm.OT_Name, t, currentLanguageID);
            if (lang == (int)English) // possible collision with FR/ES/DE. Check nickname
                return pkm.Nickname == t.Nicknames[(int)French] ? (int)French : (int)Spanish; // Spanish is same as English

            return lang;
        }

        private static int DetectTradeLanguageG4SurgePikachu(PKM pkm, EncounterTrade t, int currentLanguageID)
        {
            if (currentLanguageID == (int)French)
                return (int)English;

            // All have English, regardless of origin version.
            var lang = DetectTradeLanguage(pkm.OT_Name, t, currentLanguageID);
            if (lang == 2) // possible collision with ES/IT. Check nickname
                return pkm.Nickname == t.Nicknames[(int)Italian] ? (int)Italian : (int)Spanish;

            return lang;
        }

        private static void VerifyTrade5(LegalityAnalysis data, EncounterTrade t)
        {
            var pkm = data.pkm;
            int lang = pkm.Language;
            // Trades for JPN games have language ID of 0, not 1.
            if (pkm.BW)
            {
                if (pkm.Format == 5 && lang == (int)Japanese)
                    data.AddLine(GetInvalid(string.Format(LOTLanguage, 0, Japanese), CheckIdentifier.Language));

                lang = Math.Max(lang, 1);
                VerifyTrade(data, t, lang);
            }
            else // B2W2
            {
                if (t.TID is Encounters5.YancyTID or Encounters5.CurtisTID)
                    VerifyTradeOTOnly(data, t);
                else
                    VerifyTrade(data, t, lang);
            }
        }

        private static void VerifyTradeOTOnly(LegalityAnalysis data, EncounterTrade t)
        {
            var result = CheckTradeOTOnly(data, t.TrainerNames);
            data.AddLine(result);
        }

        private static CheckResult CheckTradeOTOnly(LegalityAnalysis data, IReadOnlyList<string> validOT)
        {
            var pkm = data.pkm;
            if (pkm.IsNicknamed && (pkm.Format < 8 || pkm.FatefulEncounter))
                return GetInvalid(LEncTradeChangedNickname, CheckIdentifier.Nickname);
            int lang = pkm.Language;
            if (validOT.Count <= lang)
                return GetInvalid(LEncTradeIndexBad, CheckIdentifier.Trainer);
            if (validOT[lang] != pkm.OT_Name)
                return GetInvalid(LEncTradeChangedOT, CheckIdentifier.Trainer);
            return GetValid(LEncTradeUnchanged, CheckIdentifier.Nickname);
        }

        private static void VerifyTrade(LegalityAnalysis data, EncounterTrade t, int language)
        {
            var ot = t.GetOT(language);
            var nick = t.GetNickname(language);
            if (string.IsNullOrEmpty(nick))
                VerifyTradeOTOnly(data, t);
            else
                VerifyTradeOTNick(data, t, nick, ot);
        }

        private static void VerifyTradeOTNick(LegalityAnalysis data, EncounterTrade t, string nick, string OT)
        {
            var pkm = data.pkm;
            // trades that are not nicknamed (but are present in a table with others being named)
            VerifyTradeNickname(data, t, nick, pkm);

            if (OT != pkm.OT_Name)
                data.AddLine(GetInvalid(LEncTradeChangedOT, CheckIdentifier.Trainer));
        }

        private static void VerifyTradeNickname(LegalityAnalysis data, EncounterTrade t, string expectedNickname, PKM pkm)
        {
            var result = IsNicknameMatch(expectedNickname, pkm, t)
                ? GetValid(LEncTradeUnchanged, CheckIdentifier.Nickname)
                : Get(LEncTradeChangedNickname, ParseSettings.NicknamedTrade, CheckIdentifier.Nickname);
            data.AddLine(result);
        }

        private static bool IsNicknameMatch(string nick, ILangNick pkm, EncounterTrade enc)
        {
            if (nick == "Quacklin’" && pkm.Nickname == "Quacklin'")
                return true;
            if (enc.IsNicknamed != pkm.IsNicknamed)
                return false;
            if (nick != pkm.Nickname) // if not match, must not be a nicknamed trade && not currently named
                return !enc.IsNicknamed && !pkm.IsNicknamed;
            return true;
        }
    }
}