acdream/src/AcDream.App/Combat/RuntimeCombatTargetOperationsSlot.cs

using AcDream.Runtime.Gameplay;

namespace AcDream.App.Combat;

/// <summary>
/// Early Runtime construction seam for the App-owned closest-hostile query.
/// The slot owns no target identity or selection state.
/// </summary>
internal sealed class RuntimeCombatTargetOperationsSlot
    : IRuntimeCombatTargetOperations
{
    private IRuntimeCombatTargetOperations? _owner;

    public IDisposable BindOwned(IRuntimeCombatTargetOperations owner)
    {
        ArgumentNullException.ThrowIfNull(owner);
        if (_owner is not null)
            throw new InvalidOperationException(
                "Runtime combat-target operations are already bound.");
        _owner = owner;
        return new Binding(this, owner);
    }

    private void Unbind(IRuntimeCombatTargetOperations expected)
    {
        if (ReferenceEquals(_owner, expected))
            _owner = null;
    }

    public bool AutoTarget => _owner?.AutoTarget == true;
    public uint? SelectClosestTarget() => _owner?.SelectClosestTarget();

    private sealed class Binding : IDisposable
    {
        private RuntimeCombatTargetOperationsSlot? _slot;
        private readonly IRuntimeCombatTargetOperations _expected;

        public Binding(
            RuntimeCombatTargetOperationsSlot slot,
            IRuntimeCombatTargetOperations expected)
        {
            _slot = slot;
            _expected = expected;
        }

        public void Dispose() =>
            Interlocked.Exchange(ref _slot, null)?.Unbind(_expected);
    }
}

internal sealed class LiveCombatTargetOperations(
    Func<bool> autoTarget,
    Func<uint?> selectClosestTarget)
    : IRuntimeCombatTargetOperations
{
    private readonly Func<bool> _autoTarget = autoTarget
        ?? throw new ArgumentNullException(nameof(autoTarget));
    private readonly Func<uint?> _selectClosestTarget = selectClosestTarget
        ?? throw new ArgumentNullException(nameof(selectClosestTarget));

    public bool AutoTarget => _autoTarget();
    public uint? SelectClosestTarget() => _selectClosestTarget();
}