using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound allegiance GameActions. Both Swear and Break carry a
/// single <c>uint32</c> target-guid payload inside the standard
/// <c>0xF7B1</c> GameAction envelope.
///
/// <para>
/// Wire layout (r11 §2.1 / §2.3):
/// <code>
///   u32 0xF7B1
///   u32 gameActionSequence
///   u32 subOpcode (0x001D or 0x001E)
///   u32 targetGuid
/// </code>
/// </para>
///
/// <para>
/// Server replies with <c>GameEventAllegianceUpdate</c> (0x0020) and
/// <c>GameEventAllegianceAllegianceUpdateDone</c> (0x01C8) on success,
/// or a <c>WeenieError</c> on failure (already sworn, already maxed
/// vassals, target not online, etc — see r11 §2.1 for the full list).
/// </para>
/// </summary>
public static class AllegianceRequests
{
    public const uint GameActionEnvelope = 0xF7B1u;
    public const uint SwearOpcode = 0x001Du;
    public const uint BreakOpcode = 0x001Eu;

    /// <summary>Pledge yourself to the given patron.</summary>
    public static byte[] BuildSwear(uint gameActionSequence, uint patronGuid)
    {
        return Build(gameActionSequence, SwearOpcode, patronGuid);
    }

    /// <summary>
    /// Break your pledge to <paramref name="targetGuid"/>. Target can be
    /// your patron (breaking from) OR your vassal (breaking them away).
    /// </summary>
    public static byte[] BuildBreak(uint gameActionSequence, uint targetGuid)
    {
        return Build(gameActionSequence, BreakOpcode, targetGuid);
    }

    private static byte[] Build(uint seq, uint sub, uint targetGuid)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  sub);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), targetGuid);
        return body;
    }
}