using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound <c>Magic_CastSpell</c> GameActions — targeted and untargeted
/// variants. From r01 §2 + r08 §3 opcodes 0x0048 / 0x004A.
///
/// <para>
/// Wire layouts (inside the <c>0xF7B1</c> GameAction envelope):
/// </para>
///
/// <para>
/// Untargeted (<c>0x0048</c>):
/// <code>
///   u32 0xF7B1
///   u32 gameActionSequence
///   u32 0x0048
///   u32 spellId
/// </code>
/// </para>
///
/// <para>
/// Targeted (<c>0x004A</c>):
/// <code>
///   u32 0xF7B1
///   u32 gameActionSequence
///   u32 0x004A
///   u32 targetGuid
///   u32 spellId
/// </code>
/// </para>
/// </summary>
public static class CastSpellRequest
{
    public const uint GameActionEnvelope = 0xF7B1u;
    public const uint UntargetedSubOpcode = 0x0048u;
    public const uint TargetedSubOpcode   = 0x004Au;

    /// <summary>Build an untargeted cast (buff self, recall, self-heal, etc).</summary>
    public static byte[] BuildUntargeted(uint gameActionSequence, uint spellId)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  gameActionSequence);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  UntargetedSubOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), spellId);
        return body;
    }

    /// <summary>
    /// Build a targeted cast (projectile attacks, target buffs, debuffs).
    /// </summary>
    public static byte[] BuildTargeted(uint gameActionSequence, uint targetGuid, uint spellId)
    {
        byte[] body = new byte[20];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  gameActionSequence);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  TargetedSubOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), targetGuid);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(16), spellId);
        return body;
    }
}