using System;
using System.Collections.Generic;
using DRWMotionCommand = DatReaderWriter.Enums.MotionCommand;

namespace AcDream.Core.Physics;

/// <summary>
/// Runtime-default <see cref="IMotionCommandCatalog"/>. Built from the
/// <see cref="DRWMotionCommand"/> enum (generated from the protocol XML;
/// mirrors ACE's <c>MotionCommand</c> enum and matches the values actually
/// found in the local DAT <c>MotionTable</c> records). Use this catalog
/// while talking to ACE — it is what
/// <see cref="MotionCommandResolver.ReconstructFullCommand"/> delegates to.
///
/// <para>
/// Reconstruction is a flat <c>wireLow16 -&gt; full32</c> lookup built once
/// at construction. When more than one enum value shares the same low 16
/// bits (a true class collision — class byte differs, low word doesn't),
/// the LOWER class byte wins: Action (0x10) &lt; ChatEmote (0x12/0x13)
/// &lt; Modifier (0x20) &lt; SubState (0x41/...) &lt; ... &lt; Style (0x80).
/// See <see cref="ResolveClassPriority"/>.
/// </para>
///
/// <para>
/// <b>No magic per-range override.</b> The original
/// <c>MotionCommandResolver.ApplyNamedRetailOverrides</c> force-mapped
/// wire 0x016E-0x0197 to <c>0x10000000 | lo</c> on the theory that the
/// generated DRW enum was "shifted." Verified false: building the lookup
/// straight from <see cref="DRWMotionCommand"/> (Chorizite.DatReaderWriter
/// 2.1.7, 409 distinct values, zero same-low16 collisions) already resolves
/// <c>LifestoneRecall</c> (0x0153), <c>MarketplaceRecall</c> (0x0166),
/// <c>AllegianceHometownRecall</c> (0x0171), and <c>OffhandSlashHigh</c>
/// (0x0173) to their correct Action-class full values with no override.
/// The override loop is deleted in this slice (it was masking nothing; the
/// enum was already correct). See
/// <c>docs/research/2026-06-26-ace-vs-2013-motion-command-gap.md</c>.
/// </para>
/// </summary>
public sealed class AceModernCommandCatalog : IMotionCommandCatalog
{
    private readonly Dictionary<ushort, uint> _lookup;

    public AceModernCommandCatalog()
    {
        _lookup = BuildLookup();
    }

    public uint ReconstructFullCommand(ushort wireCommand)
    {
        if (wireCommand == 0) return 0u;
        _lookup.TryGetValue(wireCommand, out var full);
        return full;
    }

    private static Dictionary<ushort, uint> BuildLookup()
    {
        var byLow = new Dictionary<ushort, List<uint>>(512);
        foreach (DRWMotionCommand v in Enum.GetValues(typeof(DRWMotionCommand)))
        {
            uint full = (uint)v;
            ushort lo = (ushort)(full & 0xFFFFu);
            if (lo == 0) continue; // Invalid / unmappable

            if (!byLow.TryGetValue(lo, out var list))
                byLow[lo] = list = new List<uint>(1);
            if (!list.Contains(full))
                list.Add(full);
        }

        var result = new Dictionary<ushort, uint>(byLow.Count);
        foreach (var (lo, candidates) in byLow)
        {
            result[lo] = candidates.Count == 1
                ? candidates[0]
                : ResolveClassPriority(candidates);
        }

        return result;
    }

    /// <summary>
    /// Given a set of full 32-bit MotionCommand values that all share the
    /// same low 16 bits, return the one whose class byte (bits 24-31) is
    /// numerically lowest — retail's class priority (Action 0x10 beats
    /// Modifier 0x20 beats SubState 0x41 beats Style 0x80, etc). Exposed
    /// as a static so it can be exercised directly by tests even when the
    /// live enum has no real collisions to exercise it through
    /// <see cref="BuildLookup"/>.
    /// </summary>
    public static uint ResolveClassPriority(IReadOnlyList<uint> candidates)
    {
        uint best = candidates[0];
        for (int i = 1; i < candidates.Count; i++)
        {
            uint candidate = candidates[i];
            if ((candidate >> 24) < (best >> 24))
                best = candidate;
        }
        return best;
    }
}