using System.Buffers.Binary;

namespace AcDream.Core.Net.Messages;

/// <summary>
/// Outbound character-progression + mode-change GameActions. Grouped
/// together because they share the same <c>0xF7B1</c> envelope +
/// single-opcode dispatch pattern and all target the session's player
/// (no target guid field).
///
/// <para>
/// References: r08 §3 rows 0x0044 / 0x0045 / 0x0046 / 0x0047 / 0x0053.
/// </para>
/// </summary>
public static class CharacterActions
{
    public const uint GameActionEnvelope = 0xF7B1u;

    public const uint RaiseAttributeOpcode = 0x0045u;  // u32 attr, u64 xpSpent
    public const uint RaiseVitalOpcode     = 0x0044u;  // u32 vital, u64 xpSpent
    public const uint RaiseSkillOpcode     = 0x0046u;  // u32 skillId, u64 xpSpent
    public const uint TrainSkillOpcode     = 0x0047u;  // u32 skillId, u32 credits
    public const uint ChangeCombatModeOpcode = 0x0053u; // u32 combatMode

    [Flags]
    public enum CombatMode : uint
    {
        Undef = 0,
        NonCombat = 0x01,
        Melee = 0x02,
        Missile = 0x04,
        Magic = 0x08,

        ValidCombat = NonCombat | Melee | Missile | Magic,
        CombatCombat = Melee | Missile | Magic,
    }

    /// <summary>Spend XP to raise an attribute (Strength, Endurance, etc).</summary>
    public static byte[] BuildRaiseAttribute(uint seq, uint attrId, ulong xpSpent)
        => BuildAttrOrVital(seq, RaiseAttributeOpcode, attrId, xpSpent);

    /// <summary>Spend XP to raise a vital (Health, Stamina, Mana).</summary>
    public static byte[] BuildRaiseVital(uint seq, uint vitalId, ulong xpSpent)
        => BuildAttrOrVital(seq, RaiseVitalOpcode, vitalId, xpSpent);

    /// <summary>Spend XP to raise a skill.</summary>
    public static byte[] BuildRaiseSkill(uint seq, uint skillId, ulong xpSpent)
        => BuildAttrOrVital(seq, RaiseSkillOpcode, skillId, xpSpent);

    /// <summary>Spend skill credits to train (unlock) a skill.</summary>
    public static byte[] BuildTrainSkill(uint seq, uint skillId, uint credits)
    {
        byte[] body = new byte[20];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  TrainSkillOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), skillId);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(16), credits);
        return body;
    }

    /// <summary>
    /// Change combat mode. Peace ↔ Melee / Missile / Magic toggles that
    /// switch stance + weapon ready-state. The animation + weapon
    /// wield broadcasts are server-driven from this message.
    /// </summary>
    public static byte[] BuildChangeCombatMode(uint seq, CombatMode mode)
    {
        byte[] body = new byte[16];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  ChangeCombatModeOpcode);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), (uint)mode);
        return body;
    }

    private static byte[] BuildAttrOrVital(uint seq, uint sub, uint id, ulong xp)
    {
        byte[] body = new byte[24];
        BinaryPrimitives.WriteUInt32LittleEndian(body,            GameActionEnvelope);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(4),  seq);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(8),  sub);
        BinaryPrimitives.WriteUInt32LittleEndian(body.AsSpan(12), id);
        BinaryPrimitives.WriteUInt64LittleEndian(body.AsSpan(16), xp);
        return body;
    }
}