using System;
using System.Collections.Generic;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Types;

namespace AcDream.Core.Physics.Motion;

/// <summary>
/// #175: the motion table's DEFAULT-STATE part pose — the pose an idle
/// entity's parts hold (retail: <c>CMotionTable::SetDefaultState</c>
/// 0x005230a0 installs <c>StyleDefaults[DefaultStyle]</c>'s cycle; the parts
/// then sit at that animation's frames — the live <c>CPhysicsPart</c> pose
/// collision tests against). Used as the BSP shadow-shape part-pose override
/// at server-entity registration (doors: the CLOSED pose).
///
/// <para>
/// Cycle key arithmetic mirrors <see cref="CMotionTable"/>'s
/// <c>LookupCycle</c> (CMotionTable.cs:683): <c>(style &lt;&lt; 16) |
/// (substate &amp; 0xFFFFFF)</c> — the raw dat <c>Cycles</c> dictionary is
/// keyed by the COMBINED word, not the bare style (the first cut of this
/// helper looked up the bare style, always missed, and silently fell back
/// to placement frames — the #175 "not fixed" report).
/// </para>
/// </summary>
public static class MotionTablePose
{
    /// <summary>
    /// Resolve the default-state pose frames. Returns null (callers fall
    /// back to placement frames) when the table has no default-style
    /// substate, no matching cycle, or no animation. A pose covering FEWER
    /// parts than the Setup is returned as-is —
    /// <see cref="ShadowShapeBuilder"/> falls back to the placement frame
    /// PER PART beyond the override's length (e.g. a door anim that poses
    /// only the panel parts, not the BSP-less frame header).
    /// </summary>
    /// <param name="mt">The raw dat motion table (wire MotionTableId).</param>
    /// <param name="loadAnimation">Animation loader (production:
    /// <c>id => dats.Get&lt;Animation&gt;(id)</c>).</param>
    public static IReadOnlyList<Frame>? DefaultStatePartFrames(
        MotionTable mt,
        Func<uint, Animation?> loadAnimation)
    {
        if (mt is null) return null;

        // SetDefaultState: StyleDefaults[DefaultStyle] → the default substate.
        if (!mt.StyleDefaults.TryGetValue(mt.DefaultStyle, out var defaultSubstateCmd))
            return null;

        // LookupCycle key (CMotionTable.cs:683 — same wrap semantics).
        uint style = (uint)mt.DefaultStyle;
        uint substate = (uint)defaultSubstateCmd;
        int key = (int)((style << 16) | (substate & 0xFFFFFFu));

        if (!mt.Cycles.TryGetValue(key, out var cycle) || cycle.Anims.Count == 0)
            return null;

        var animRef = cycle.Anims[0];
        var anim = loadAnimation(animRef.AnimId);
        if (anim is null || anim.PartFrames.Count == 0) return null;

        int idx = Math.Clamp((int)animRef.LowFrame, 0, anim.PartFrames.Count - 1);
        var frames = anim.PartFrames[idx].Frames;
        return frames.Count > 0 ? frames : null;
    }
}