using System;
using System.Collections.Generic;
using static PKHeX.Core.LegalityCheckStrings;
using static PKHeX.Core.ParseSettings;

namespace PKHeX.Core
{
    /// <summary>
    /// Logic to verify the current <see cref="PKM.RelearnMoves"/>.
    /// </summary>
    public static class VerifyRelearnMoves
    {
        internal static void DummyValid(CheckMoveResult p) => p.Set(MoveSource.Relearn, 0, Severity.Valid, L_AValid, CheckIdentifier.RelearnMove);

        public static CheckMoveResult[] VerifyRelearn(PKM pkm, IEncounterTemplate enc, CheckMoveResult[] result)
        {
            if (ShouldNotHaveRelearnMoves(enc, pkm))
                return VerifyRelearnNone(pkm, result);

            return enc switch
            {
                IRelearn s when s.Relearn.Count != 0 => VerifyRelearnSpecifiedMoveset(pkm, s.Relearn, result),
                EncounterEgg e => VerifyEggMoveset(e, result, pkm.RelearnMoves),
                EncounterSlot6AO {CanDexNav:true} z when pkm.RelearnMove1 != 0 => VerifyRelearnDexNav(pkm, result, z),
                EncounterSlot8b {IsUnderground:true} u => VerifyRelearnUnderground(pkm, result, u),
                _ => VerifyRelearnNone(pkm, result),
            };
        }

        public static bool ShouldNotHaveRelearnMoves(IGeneration enc, PKM pkm) => enc.Generation < 6 || pkm is IBattleVersion {BattleVersion: not 0};

        private static CheckMoveResult[] VerifyRelearnSpecifiedMoveset(PKM pkm, IReadOnlyList<int> required, CheckMoveResult[] result)
        {
            CheckResult(pkm.RelearnMove4, required[3], result[3]);
            CheckResult(pkm.RelearnMove3, required[2], result[2]);
            CheckResult(pkm.RelearnMove2, required[1], result[1]);
            CheckResult(pkm.RelearnMove1, required[0], result[0]);
            return result;

            static void CheckResult(int move, int require, CheckMoveResult p)
            {
                if (move == require)
                {
                    DummyValid(p);
                    return;
                }
                var c = string.Format(LMoveFExpect_0, MoveStrings[require]);
                p.Set(MoveSource.Relearn, 0, Severity.Invalid, c, CheckIdentifier.RelearnMove);
            }
        }

        private static void ParseExpectEmpty(CheckMoveResult p, int move)
        {
            if (move == 0)
                DummyValid(p);
            else
                p.Set(MoveSource.Relearn, 0, Severity.Invalid, LMoveRelearnNone, CheckIdentifier.RelearnMove);
        }

        private static CheckMoveResult[] VerifyRelearnDexNav(PKM pkm, CheckMoveResult[] result, EncounterSlot6AO slot)
        {
            // All other relearn moves must be empty.
            ParseExpectEmpty(result[3], pkm.RelearnMove4);
            ParseExpectEmpty(result[2], pkm.RelearnMove3);
            ParseExpectEmpty(result[1], pkm.RelearnMove2);

            // DexNav Pokémon can have 1 random egg move as a relearn move.
            var p = result[0];
            if (!slot.CanBeDexNavMove(pkm.RelearnMove1)) // not found
                p.Set(MoveSource.Relearn, 6, Severity.Invalid, LMoveRelearnDexNav, CheckIdentifier.RelearnMove);
            else
                DummyValid(p);

            return result;
        }

        private static CheckMoveResult[] VerifyRelearnUnderground(PKM pkm, CheckMoveResult[] result, EncounterSlot8b slot)
        {
            // All other relearn moves must be empty.
            ParseExpectEmpty(result[3], pkm.RelearnMove4);
            ParseExpectEmpty(result[2], pkm.RelearnMove3);
            ParseExpectEmpty(result[1], pkm.RelearnMove2);

            // Underground Pokémon can have 1 random egg move as a relearn move.
            var p = result[0];
            if (!slot.CanBeUndergroundMove(pkm.RelearnMove1)) // not found
                p.Set(MoveSource.Relearn, 0, Severity.Invalid, LMoveRelearnUnderground, CheckIdentifier.RelearnMove);
            else
                DummyValid(p);

            return result;
        }

        private static CheckMoveResult[] VerifyRelearnNone(PKM pkm, CheckMoveResult[] result)
        {
            // No relearn moves should be present.
            ParseExpectEmpty(result[3], pkm.RelearnMove4);
            ParseExpectEmpty(result[2], pkm.RelearnMove3);
            ParseExpectEmpty(result[1], pkm.RelearnMove2);
            ParseExpectEmpty(result[0], pkm.RelearnMove1);
            return result;
        }

        internal static CheckMoveResult[] VerifyEggMoveset(EncounterEgg e, CheckMoveResult[] result, int[] moves, CheckIdentifier type = CheckIdentifier.RelearnMove)
        {
            int gen = e.Generation;
            var origins = MoveBreed.Process(gen, e.Species, e.Form, e.Version, moves, out var valid);
            if (valid)
            {
                for (int i = 0; i < result.Length; i++)
                {
                    var msg = EggSourceUtil.GetSource(origins, gen, i);
                    result[i].Set(MoveSource.EggMove, gen, Severity.Valid, msg, type);
                }
            }
            else
            {
                var expected = MoveBreed.GetExpectedMoves(moves, e);
                origins = MoveBreed.Process(gen, e.Species, e.Form, e.Version, expected, out _);
                for (int i = 0; i < moves.Length; i++)
                {
                    var msg = EggSourceUtil.GetSource(origins, gen, i);
                    var expect = expected[i];
                    var p = result[i];
                    if (moves[i] == expect)
                    {
                        p.Set(MoveSource.EggMove, gen, Severity.Valid, msg, type);
                    }
                    else
                    {
                        msg = string.Format(LMoveRelearnFExpect_0, MoveStrings[expect], msg);
                        p.Set(MoveSource.EggMove, gen, Severity.Invalid, msg, type);
                    }
                }
            }

            var dupe = IsAnyMoveDuplicate(moves);
            if (dupe != NO_DUPE)
                result[dupe].Set(MoveSource.EggMove, gen, Severity.Invalid, LMoveSourceDuplicate, type);
            return result;
        }

        private const int NO_DUPE = -1;

        private static int IsAnyMoveDuplicate(ReadOnlySpan<int> move)
        {
            int m1 = move[0];
            int m2 = move[1];

            if (m1 != 0 && m1 == m2)
                return 1;
            int m3 = move[2];
            if (m3 != 0 && (m1 == m3 || m2 == m3))
                return 2;
            int m4 = move[3];
            if (m4 != 0 && (m1 == m4 || m2 == m4 || m3 == m4))
                return 3;
            return NO_DUPE;
        }
    }
}