acdream/src/AcDream.Core.Net/Messages/MoveToState.cs

using System.Numerics;
using AcDream.Core.Net.Packets;
using AcDream.Core.Physics;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound <c>GameAction(MoveToState)</c> message — opcode <c>0xF61C</c>.
/// Sent whenever the client's motion state changes: starting or stopping
/// walking, switching direction, changing speed, entering or leaving combat
/// stance. The server uses this to update the player's authoritative motion
/// state and to drive interpolated position for other nearby clients.
///
/// <para>
/// Wire layout — ports retail's <c>MoveToStatePack::Pack</c> verbatim
/// (<c>0x005168f0</c>, decomp lines ~284694-284722). Confirmed against the
/// Ghidra decompile-by-address bridge during this slice (2026-06-30):
/// </para>
/// <list type="bullet">
///   <item><b>GameAction envelope</b>: u32 0xF7B1, u32 sequence, u32 0xF61C</item>
///   <item><b>RawMotionState::Pack</b>: see <see cref="RawMotionStatePacker"/>
///         — default-difference flags dword + conditional fields + actions.</item>
///   <item><b>Position::Pack</b>: u32 cellId, f32 x, f32 y, f32 z,
///         f32 qw, f32 qx, f32 qy, f32 qz (32 bytes)</item>
///   <item><b>Sequences</b>: u16 instance, u16 serverControl,
///         u16 teleport, u16 forcePosition</item>
///   <item><b>Trailing byte</b>: <c>(standingLongjump ? 0x02 : 0) |
///         (contact ? 0x01 : 0)</c> — <c>MoveToStatePack::Pack</c> trailing
///         byte expression <c>(longjump_mode == 0) - 1U &amp; 2 |
///         contact != 0</c>.</item>
///   <item><b>Align to 4 bytes</b></item>
/// </list>
/// </summary>
public static class MoveToState
{
    public const uint GameActionOpcode  = 0xF7B1u;
    public const uint MoveToStateAction = 0xF61Cu;

    /// <summary>
    /// Build a MoveToState GameAction body.
    /// </summary>
    /// <param name="gameActionSequence">Monotonically increasing counter from
    ///   <see cref="WorldSession.NextGameActionSequence"/>.</param>
    /// <param name="rawMotionState">Complete raw-motion snapshot, matching
    ///   retail's <c>CPhysicsObj::InqRawMotionState()</c>. Fields equal to
    ///   <see cref="RawMotionState.Default"/> are omitted from the wire
    ///   (see <see cref="RawMotionStatePacker"/>).</param>
    /// <param name="cellId">Landblock cell ID (u32).</param>
    /// <param name="position">World-space position relative to the landblock.</param>
    /// <param name="rotation">Rotation quaternion. AC wire order is W, X, Y, Z.</param>
    /// <param name="instanceSequence">Instance sequence number from the server.</param>
    /// <param name="serverControlSequence">Server-control sequence number.</param>
    /// <param name="teleportSequence">Teleport sequence number.</param>
    /// <param name="forcePositionSequence">Force-position sequence number.</param>
    /// <param name="contact">True if the character is on the ground.</param>
    /// <param name="standingLongjump">True during a standing (charged,
    ///   stationary) longjump wind-up. Not yet implemented in acdream —
    ///   callers pass <c>false</c> honestly until that feature lands.</param>
    public static byte[] Build(
        uint           gameActionSequence,
        RawMotionState rawMotionState,
        uint           cellId,
        Vector3        position,
        Quaternion     rotation,
        ushort         instanceSequence,
        ushort         serverControlSequence,
        ushort         teleportSequence,
        ushort         forcePositionSequence,
        bool           contact = true,
        bool           standingLongjump = false)
    {
        var w = new PacketWriter(128);

        // --- GameAction envelope ---
        w.WriteUInt32(GameActionOpcode);
        w.WriteUInt32(gameActionSequence);
        w.WriteUInt32(MoveToStateAction);

        // --- RawMotionState::Pack (0x0051ed10) ---
        RawMotionStatePacker.Pack(w, rawMotionState);

        // --- Position::Pack (0x005a9640): cellId + Frame::Pack (32 bytes) ---
        w.WriteUInt32(cellId);
        w.WriteFloat(position.X);
        w.WriteFloat(position.Y);
        w.WriteFloat(position.Z);
        // Quaternion wire order: W, X, Y, Z
        w.WriteFloat(rotation.W);
        w.WriteFloat(rotation.X);
        w.WriteFloat(rotation.Y);
        w.WriteFloat(rotation.Z);

        // --- Sequence numbers ---
        w.WriteUInt16(instanceSequence);
        w.WriteUInt16(serverControlSequence);
        w.WriteUInt16(teleportSequence);
        w.WriteUInt16(forcePositionSequence);

        // --- Trailing byte (MoveToStatePack::Pack, 0x005168f0): ---
        //   ((longjump_mode != 0) ? 0x02 : 0) | (contact != 0 ? 0x01 : 0)
        byte trailing = (byte)((standingLongjump ? 0x02 : 0) | (contact ? 0x01 : 0));
        w.WriteByte(trailing);
        w.AlignTo4();

        return w.ToArray();
    }
}