ninja 2 electric boogaloo (#15534)

Co-authored-by: deltanedas <@deltanedas:kde.org>

Content.Shared/Ninja/Systems/SharedBatteryDrainerSystem.cs

@@ -0,0 +1,69 @@
+using Content.Shared.Ninja.Components;
+using Content.Shared.DoAfter;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Ninja.Systems;
+
+/// <summary>
+/// Basic draining prediction and API, all real logic is handled serverside.
+/// </summary>
+public abstract class SharedBatteryDrainerSystem : EntitySystem
+{
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<BatteryDrainerComponent, DoAfterAttemptEvent<DrainDoAfterEvent>>(OnDoAfterAttempt);
+        SubscribeLocalEvent<BatteryDrainerComponent, DrainDoAfterEvent>(OnDoAfter);
+    }
+
+    /// <summary>
+    /// Cancel any drain doafters if the battery is removed or gets filled.
+    /// </summary>
+    protected virtual void OnDoAfterAttempt(EntityUid uid, BatteryDrainerComponent comp, DoAfterAttemptEvent<DrainDoAfterEvent> args)
+    {
+        if (comp.BatteryUid == null)
+        {
+            args.Cancel();
+        }
+    }
+
+    /// <summary>
+    /// Drain power from a power source (on server) and repeat if it succeeded.
+    /// Client will predict always succeeding since power is serverside.
+    /// </summary>
+    private void OnDoAfter(EntityUid uid, BatteryDrainerComponent comp, DrainDoAfterEvent args)
+    {
+        if (args.Cancelled || args.Handled || args.Target == null)
+            return;
+
+        // repeat if there is still power to drain
+        args.Repeat = TryDrainPower(uid, comp, args.Target.Value);
+    }
+
+    /// <summary>
+    /// Attempt to drain as much power as possible into the powercell.
+    /// Client always predicts this as succeeding since power is serverside and it can only fail once, when the powercell is filled or the target is emptied.
+    /// </summary>
+    protected virtual bool TryDrainPower(EntityUid uid, BatteryDrainerComponent comp, EntityUid target)
+    {
+        return true;
+    }
+
+    /// <summary>
+    /// Sets the battery field on the drainer.
+    /// </summary>
+    public void SetBattery(EntityUid uid, EntityUid? battery, BatteryDrainerComponent? comp = null)
+    {
+        if (!Resolve(uid, ref comp))
+            return;
+
+        comp.BatteryUid = battery;
+    }
+}
+
+/// <summary>
+/// DoAfter event for <see cref="BatteryDrainerComponent"/>.
+/// </summary>
+[Serializable, NetSerializable]
+public sealed partial class DrainDoAfterEvent : SimpleDoAfterEvent { }