using AcDream.Core.Net.Packets;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound GameMessages for the character-select → in-world transition.
/// The client sends two messages in order after receiving
/// <see cref="CharacterList"/>:
///
/// <list type="number">
///   <item><c>CharacterEnterWorldRequest</c> (opcode <c>0xF7C8</c>) —
///         empty body beyond the 4-byte opcode. "Hi server, I'm about
///         to try to enter the world, anything I should know?"</item>
///   <item>Server replies with
///         <c>CharacterEnterWorldServerReady</c> (0xF7DF).</item>
///   <item><c>CharacterEnterWorld</c> (opcode <c>0xF657</c>) — u32 GUID
///         of the chosen character + String16L account name. Server
///         validates ownership and begins spawning the player + world
///         entities into our session, which is where the CreateObject
///         flood starts.</item>
/// </list>
///
/// Both messages are tiny enough to fit in one fragment each. They go on
/// the <see cref="GameMessageGroup.UIQueue"/> queue per ACE's
/// <c>CharacterHandler</c> annotations.
/// </summary>
public static class CharacterEnterWorld
{
    public const uint EnterWorldRequestOpcode = 0xF7C8u;
    public const uint EnterWorldOpcode        = 0xF657u;

    /// <summary>
    /// Build the body bytes for an outbound <c>CharacterEnterWorldRequest</c>.
    /// Just the 4-byte opcode, nothing else.
    /// </summary>
    public static byte[] BuildEnterWorldRequestBody()
    {
        var w = new PacketWriter(8);
        w.WriteUInt32(EnterWorldRequestOpcode);
        return w.ToArray();
    }

    /// <summary>
    /// Build the body bytes for an outbound <c>CharacterEnterWorld</c>.
    /// Layout: opcode(4) + characterGuid(4) + String16L(accountName).
    /// </summary>
    public static byte[] BuildEnterWorldBody(uint characterGuid, string accountName)
    {
        ArgumentNullException.ThrowIfNull(accountName);
        var w = new PacketWriter(32);
        w.WriteUInt32(EnterWorldOpcode);
        w.WriteUInt32(characterGuid);
        w.WriteString16L(accountName);
        return w.ToArray();
    }
}