using System;
using static PKHeX.Core.LegalityCheckStrings;

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

        private static readonly string[] SuspiciousOTNames =
        {
            "PKHeX",
            "ＰＫＨｅＸ",
        };

        public override void Verify(LegalityAnalysis data)
        {
            var pkm = data.pkm;
            var enc = data.EncounterMatch;
            if (!IsPlayerOriginalTrainer(enc))
                return; // already verified

            var ot = pkm.OT_Name;
            if (ot.Length == 0)
                data.AddLine(GetInvalid(LOTShort));

            if (IsOTNameSuspicious(ot))
            {
                data.AddLine(Get(LOTSuspicious, Severity.Fishy));
            }

            if (pkm.VC)
            {
                VerifyOTG1(data);
            }
            else if (ot.Length > Legal.GetMaxLengthOT(data.Info.Generation, (LanguageID)pkm.Language))
            {
                if (!IsEdgeCaseLength(pkm, data.EncounterOriginal, ot))
                    data.AddLine(Get(LOTLong, Severity.Invalid));
            }

            if (ParseSettings.CheckWordFilter)
            {
                if (WordFilter.IsFiltered(ot, out string bad))
                    data.AddLine(GetInvalid($"Wordfilter: {bad}"));
                if (WordFilter.IsFiltered(pkm.HT_Name, out bad))
                    data.AddLine(GetInvalid($"Wordfilter: {bad}"));
                if (ContainsTooManyNumbers(ot, data.Info.Generation))
                    data.AddLine(GetInvalid("Wordfilter: Too many numbers."));
            }
        }

        /// <summary>
        /// Checks if any player (human) was the original OT.
        /// </summary>
        internal static bool IsPlayerOriginalTrainer(IEncounterable enc) => enc switch
        {
            EncounterTrade { HasTrainerName: true } => false,
            MysteryGift { IsEgg: false } => false,
            EncounterStatic5N => false,
            _ => true,
        };

        public static bool IsEdgeCaseLength(PKM pkm, IEncounterTemplate e, string ot)
        {
            if (e.EggEncounter)
            {
                if (e is WC3 wc3 && pkm.IsEgg && wc3.OT_Name == ot)
                    return true; // Fixed OT Mystery Gift Egg
                bool eggEdge = pkm.IsEgg ? pkm.IsTradedEgg || pkm.Format == 3 : pkm.WasTradedEgg;
                if (!eggEdge)
                    return false;
                var len = Legal.GetMaxLengthOT(e.Generation, LanguageID.English); // max case
                return ot.Length <= len;
            }

            if (e is EncounterTrade { HasTrainerName: true })
                return true; // already verified

            if (e is MysteryGift mg && mg.OT_Name.Length == ot.Length)
                return true; // Mattle Ho-Oh
            return false;
        }

        public void VerifyOTG1(LegalityAnalysis data)
        {
            var pkm = data.pkm;
            string tr = pkm.OT_Name;

            if (tr.Length == 0)
            {
                if (pkm is SK2 {TID: 0, IsRental: true})
                {
                    data.AddLine(Get(LOTShort, Severity.Fishy));
                }
                else
                {
                    data.AddLine(GetInvalid(LOTShort));
                    return;
                }
            }

            VerifyG1OTWithinBounds(data, tr.AsSpan());

            if (pkm.OT_Gender == 1)
            {
                if (pkm is ICaughtData2 {CaughtData:0} || (pkm.Format > 2 && pkm.VC1) || data is {EncounterOriginal: {Generation:1} or EncounterStatic2E {IsGift:true}})
                    data.AddLine(GetInvalid(LG1OTGender));
            }
        }

        private void VerifyG1OTWithinBounds(LegalityAnalysis data, ReadOnlySpan<char> str)
        {
            if (StringConverter12.GetIsG1English(str))
            {
                if (str.Length > 7 && data.EncounterOriginal is not EncounterTradeGB) // OT already verified; GER shuckle has 8 chars
                    data.AddLine(GetInvalid(LOTLong));
            }
            else if (StringConverter12.GetIsG1Japanese(str))
            {
                if (str.Length > 5)
                    data.AddLine(GetInvalid(LOTLong));
            }
            else if (data.pkm.Korean && StringConverter2KOR.GetIsG2Korean(str))
            {
                if (str.Length > 5)
                    data.AddLine(GetInvalid(LOTLong));
            }
            else if (data.EncounterOriginal is not EncounterTrade2) // OT already verified; SPA Shuckle/Voltorb transferred from French can yield 2 inaccessible chars
            {
                data.AddLine(GetInvalid(LG1CharOT));
            }
        }

        private static bool IsOTNameSuspicious(string name)
        {
            foreach (var s in SuspiciousOTNames)
            {
                if (s.StartsWith(name, StringComparison.InvariantCultureIgnoreCase))
                    return true;
            }
            return false;
        }

        public static bool ContainsTooManyNumbers(string str, int originalGeneration)
        {
            if (originalGeneration <= 3)
                return false; // no limit from these generations
            int max = originalGeneration < 6 ? 4 : 5;
            if (str.Length <= max)
                return false;
            int count = GetNumberCount(str);
            return count > max;
        }

        private static int GetNumberCount(string str)
        {
            static bool IsNumber(char c)
            {
                if ('０' <= c)
                    return c <= '９';
                return (uint)(c - '0') <= 9;
            }

            int ctr = 0;
            foreach (var c in str)
            {
                if (IsNumber(c))
                    ++ctr;
            }
            return ctr;
        }
    }
}