PKHeX/PKHeX.Core/Legality/RNG/Frame/SlotRange.cs

using System.Linq;
using static PKHeX.Core.SlotType;

namespace PKHeX.Core
{
    /// <summary>
    /// RNG Encounter Slot Ranges to convert the [0,100) value into a slot index.
    /// </summary>
    public static class SlotRange
    {
        private static readonly Range[] H_OldRod = GetRanges(70, 30);
        private static readonly Range[] H_GoodRod = GetRanges(60, 20, 20);
        private static readonly Range[] H_SuperRod = GetRanges(40, 40, 15, 4, 1);
        private static readonly Range[] H_Surf = GetRanges(60, 30, 5, 4, 1);
        private static readonly Range[] H_Regular = GetRanges(20, 20, 10, 10, 10, 10, 5, 5, 4, 4, 1, 1);

        private static readonly Range[] J_SuperRod = GetRanges(40, 40, 15, 4, 1);
        private static readonly Range[] K_SuperRod = GetRanges(40, 30, 15, 10, 5);
        private static readonly Range[] K_BCC = GetRanges(5,5,5,5, 10,10,10,10, 20,20).Reverse().ToArray();
        private static readonly Range[] K_Headbutt = GetRanges(50, 15, 15, 10, 5, 5);

        private const int Invalid = -1; // all slots are [0,X], unsigned. This will always result in a non-match.

        /// <summary>
        /// Gets the <see cref="INumberedSlot.SlotNumber"/> from the raw 16bit <see cref="rand"/> seed half.
        /// </summary>
        public static int GetSlot(SlotType type, uint rand, FrameType t) => t switch
        {
            FrameType.MethodH => HSlot(type, rand),
            FrameType.MethodJ => JSlot(type, rand),
            FrameType.MethodK => KSlot(type, rand),
            _ => Invalid,
        };

        /// <summary>
        /// Gets the <see cref="INumberedSlot.SlotNumber"/> from the raw 16bit <see cref="rand"/> seed half.
        /// </summary>
        private static int HSlot(SlotType type, uint rand)
        {
            var ESV = rand % 100;
            if ((type & Swarm) != 0)
                return ESV < 50 ? 0 : Invalid;

            return type switch
            {
                Old_Rod    => CalcSlot(ESV, H_OldRod),
                Good_Rod   => CalcSlot(ESV, H_GoodRod),
                Super_Rod  => CalcSlot(ESV, H_SuperRod),
                Rock_Smash => CalcSlot(ESV, H_Surf),
                Surf       => CalcSlot(ESV, H_Surf),
                _          => CalcSlot(ESV, H_Regular),
            };
        }

        /// <summary>
        /// Gets the <see cref="INumberedSlot.SlotNumber"/> from the raw 16bit <see cref="rand"/> seed half.
        /// </summary>
        private static int KSlot(SlotType type, uint rand)
        {
            var ESV = rand % 100;
            return type switch
            {
                Rock_Smash or Surf               => CalcSlot(ESV, H_Surf),
                Old_Rod or Good_Rod or Super_Rod => CalcSlot(ESV, K_SuperRod),
                BugContest                       => CalcSlot(ESV, K_BCC),
                Headbutt or (Headbutt | Special) => CalcSlot(ESV, K_Headbutt),
                _ => CalcSlot(ESV, H_Regular),
            };
        }

        /// <summary>
        /// Gets the <see cref="INumberedSlot.SlotNumber"/> from the raw 16bit <see cref="rand"/> seed half.
        /// </summary>
        private static int JSlot(SlotType type, uint rand)
        {
            uint ESV = rand / 656;
            return type switch
            {
                Old_Rod or Rock_Smash or Surf => CalcSlot(ESV, H_Surf),
                Good_Rod or Super_Rod         => CalcSlot(ESV, J_SuperRod),
                HoneyTree                     => 0,
                _                             => CalcSlot(ESV, H_Regular),
            };
        }

        private readonly record struct Range(uint Min, uint Max);

        private static Range[] GetRanges(params byte[] rates)
        {
            var len = rates.Length;
            var arr = new Range[len];
            uint sum = 0;
            for (int i = 0; i < len; ++i)
                arr[i] = new Range(sum, (sum += rates[i]) - 1);
            return arr;
        }

        private static int CalcSlot(uint esv, Range[] ranges)
        {
            for (int i = 0; i < ranges.Length; ++i)
            {
                var (min, max) = ranges[i];
                if (esv >= min && esv <= max)
                    return i;
            }
            return Invalid;
        }

        public static int GetLevel(EncounterSlot slot, LeadRequired lead, uint lvlrand)
        {
            if (lead == LeadRequired.PressureHustleSpirit)
                return slot.LevelMax;
            if (slot.IsFixedLevel)
                return slot.LevelMin;
            int delta = slot.LevelMax - slot.LevelMin + 1;
            var adjust = (int)(lvlrand % delta);

            return slot.LevelMin + adjust;
        }

#pragma warning disable IDE0060, RCS1163 // Unused parameter.
        public static bool GetIsEncounterable<T>(T slot, FrameType frameType, int rand, LeadRequired lead) where T : ISlotRNGType
#pragma warning restore IDE0060, RCS1163 // Unused parameter.
        {
            if (slot.Type.IsSweetScentType())
                return true;
            return true; // todo
            //return GetCanEncounter(slot, frameType, rand, lead);
        }

        // ReSharper disable once UnusedMember.Global
        public static bool GetCanEncounter<T>(T slot, FrameType frameType, int rand, LeadRequired lead) where T : ISlotRNGType
        {
            int proc = frameType == FrameType.MethodJ ? rand / 656 : rand % 100;
            var stype = slot.Type;
            if (stype == Rock_Smash)
                return proc < 60;
            if (frameType == FrameType.MethodH)
                return true; // fishing encounters are disjointed by the hooked message.
            return GetCanEncounterFish(lead, stype, proc);
        }

        private static bool GetCanEncounterFish(LeadRequired lead, SlotType stype, int proc) => stype switch
        {
            // Lead:None => can be suction cups
            Old_Rod => proc switch
            {
                < 25 => true,
                < 50 => lead == LeadRequired.None,
                _ => false,
            },
            Good_Rod => proc switch
            {
                < 50 => true,
                < 75 => lead == LeadRequired.None,
                _ => false,
            },
            Super_Rod => proc < 75 || lead == LeadRequired.None,

            _ => false,
        };

        /// <summary>
        /// Checks both Static and Magnet Pull ability type selection encounters to see if the encounter can be selected.
        /// </summary>
        /// <param name="slot">Slot Data</param>
        /// <param name="esv">Rand16 value for the call</param>
        /// <returns>Slot number from the slot data if the slot is selected on this frame, else an invalid slot value.</returns>
        internal static int GetSlotStaticMagnet<T>(T slot, uint esv) where T : EncounterSlot, IMagnetStatic, INumberedSlot
        {
            if (slot.IsStaticSlot())
            {
                var index = esv % slot.StaticCount;
                if (index == slot.StaticIndex)
                    return slot.SlotNumber;
            }
            if (slot.IsMagnetSlot())
            {
                var index = esv % slot.MagnetPullCount;
                if (index == slot.MagnetPullIndex)
                    return slot.SlotNumber;
            }
            return Invalid;
        }
    }
}