using System;
using static PKHeX.Core.LegalityCheckStrings;

namespace PKHeX.Core;

/// <summary>
/// Verifies the <see cref="PKM.CurrentLevel"/>.
/// </summary>
public sealed class LevelVerifier : Verifier
{
    protected override CheckIdentifier Identifier => CheckIdentifier.Level;

    public override void Verify(LegalityAnalysis data)
    {
        var pk = data.Entity;
        var enc = data.EncounterOriginal;
        if (enc is MysteryGift gift)
        {
            if (gift.Level != pk.Met_Level && pk.HasOriginalMetLocation)
            {
                switch (gift)
                {
                    case WC3 wc3 when wc3.Met_Level == pk.Met_Level || wc3.IsEgg:
                        break;
                    case WC7 wc7 when wc7.MetLevel == pk.Met_Level:
                        break;
                    case PGT {IsManaphyEgg: true} when pk.Met_Level == 0:
                        break;
                    default:
                        data.AddLine(GetInvalid(LLevelMetGift));
                        return;
                }
            }
            if (gift.Level > pk.CurrentLevel)
            {
                data.AddLine(GetInvalid(LLevelMetGiftFail));
                return;
            }
        }

        if (pk.IsEgg)
        {
            int elvl = enc.LevelMin;
            if (elvl != pk.CurrentLevel)
            {
                data.AddLine(GetInvalid(string.Format(LEggFMetLevel_0, elvl)));
                return;
            }

            var reqEXP = enc is EncounterStatic2Odd
                ? 125 // Gen2 Dizzy Punch gifts always have 125 EXP, even if it's more than the Lv5 exp required.
                : Experience.GetEXP(elvl, pk.PersonalInfo.EXPGrowth);
            if (reqEXP != pk.EXP)
                data.AddLine(GetInvalid(LEggEXP));
            return;
        }

        int lvl = pk.CurrentLevel;
        if (lvl >= 100)
        {
            var expect = Experience.GetEXP(100, pk.PersonalInfo.EXPGrowth);
            if (pk.EXP != expect)
                data.AddLine(GetInvalid(LLevelEXPTooHigh));
        }

        if (lvl < pk.Met_Level)
            data.AddLine(GetInvalid(LLevelMetBelow));
        else if (!enc.IsWithinEncounterRange(pk) && lvl != 100 && pk.EXP == Experience.GetEXP(lvl, pk.PersonalInfo.EXPGrowth))
            data.AddLine(Get(LLevelEXPThreshold, Severity.Fishy));
        else
            data.AddLine(GetValid(LLevelMetSane));
    }

    public void VerifyG1(LegalityAnalysis data)
    {
        var pk = data.Entity;
        var enc = data.EncounterMatch;
        if (pk.IsEgg)
        {
            const int elvl = 5;
            if (elvl != pk.CurrentLevel)
                data.AddLine(GetInvalid(string.Format(LEggFMetLevel_0, elvl)));
            return;
        }
        if (pk.Met_Location != 0) // crystal
        {
            int lvl = pk.CurrentLevel;
            if (lvl < pk.Met_Level)
                data.AddLine(GetInvalid(LLevelMetBelow));
        }

        if (IsTradeEvolutionRequired(data, enc))
        {
            // Pokemon has been traded illegally between games without evolving.
            // Trade evolution species IDs for Gen1 are sequential dex numbers.
            var species = enc.Species;
            var evolved = ParseSettings.SpeciesStrings[species + 1];
            var unevolved = ParseSettings.SpeciesStrings[species];
            data.AddLine(GetInvalid(string.Format(LEvoTradeReqOutsider, unevolved, evolved)));
        }
    }

    /// <summary>
    /// Checks if a Gen1 trade evolution must have occurred.
    /// </summary>
    private static bool IsTradeEvolutionRequired(LegalityAnalysis data, IEncounterTemplate enc)
    {
        // There is no way to prevent a Gen1 trade evolution, as held items (Everstone) did not exist.
        // Machoke, Graveler, Haunter and Kadabra captured in the second phase evolution, excluding in-game trades, are already checked
        var pk = data.Entity;
        var species = pk.Species;

        // This check is only applicable if it's a trade evolution that has not been evolved.
        if (!GBRestrictions.Trade_Evolution1.Contains((byte)enc.Species) || enc.Species != species)
            return false;

        // Context check is only applicable to gen1/2; transferring to Gen2 is a trade.
        // Stadium 2 can transfer across game/generation boundaries without initiating a trade.
        // Ignore this check if the environment's loaded trainer is not from Gen1/2 or is from GB Era.
        if (ParseSettings.ActiveTrainer.Generation >= 3 || ParseSettings.AllowGBCartEra)
            return false;

        var moves = data.Info.Moves;
        // Gen2 stuff can be traded between Gen2 games holding an Everstone, assuming it hasn't been transferred to Gen1 for special moves.
        if (enc.Generation == 2)
            return Array.Exists(moves, z => z.Generation != 2);
        // Gen1 stuff can only be un-evolved if it was never traded from the OT.
        if (Array.Exists(moves, z => z.Generation != 1))
            return true; // traded to Gen2 for special moves
        if (pk.Format != 1)
            return true; // traded to Gen2 (current state)
        return !ParseSettings.IsFromActiveTrainer(pk); // not with OT
    }
}