[EXILED::Events] BeingObserved event stolen (#91)

* Scp173 Observing, Stolen from https://github.com/ExMod-Team/EXILED/pull/72/files

* Remove old comment

EXILED/Exiled.Events/EventArgs/Scp173/BeingObservedEventArgs.cs

@@ -0,0 +1,57 @@
+// -----------------------------------------------------------------------
+// <copyright file="BeingObservedEventArgs.cs" company="Exiled Team">
+// Copyright (c) Exiled Team. All rights reserved.
+// Licensed under the CC BY-SA 3.0 license.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Exiled.Events.EventArgs.Scp173
+{
+    using Exiled.API.Features;
+    using Exiled.API.Features.Roles;
+    using Exiled.Events.EventArgs.Interfaces;
+
+    /// <summary>
+    /// Contains all the information before SCP-173 is observed.
+    /// </summary>
+    public class BeingObservedEventArgs : IScp173Event, IDeniableEvent
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="BeingObservedEventArgs" /> class.
+        /// </summary>
+        /// <param name="target">
+        /// The <see cref="Exiled.API.Features.Player"/> instance of the target.
+        /// </param>
+        /// <param name="scp173">
+        /// The <see cref="Exiled.API.Features.Player"/> instance of the SCP-173.
+        /// </param>
+        /// <param name="isAllowed">
+        /// Whether or not the target will be counted as observing the SCP-173.
+        /// </param>
+        public BeingObservedEventArgs(API.Features.Player target, API.Features.Player scp173, bool isAllowed = true)
+        {
+            Target = target;
+            Player = scp173;
+            Scp173 = scp173.Role.As<Scp173Role>();
+            IsAllowed = isAllowed;
+        }
+
+        /// <summary>
+        /// Gets the player who's observing the SCP-173.
+        /// </summary>
+        public Player Target { get; }
+
+        /// <summary>
+        /// Gets the player who's being observed.
+        /// </summary>
+        public Player Player { get; }
+
+        /// <inheritdoc/>
+        public Scp173Role Scp173 { get; }
+
+        /// <summary>
+        /// Gets or sets a value indicating whether or not the player can be counted as observing.
+        /// </summary>
+        public bool IsAllowed { get; set; }
+    }
+}

EXILED/Exiled.Events/Handlers/Scp173.cs

@@ -37,6 +37,11 @@ public static class Scp173
         /// </summary>
         public static Event<UsingBreakneckSpeedsEventArgs> UsingBreakneckSpeeds { get; set; } = new();
 
+        /// <summary>
+        /// Invoked before SCP-173 is observed.
+        /// </summary>
+        public static Event<BeingObservedEventArgs> BeingObserved { get; set; } = new();
+
         /// <summary>
         /// Called before players near SCP-173 blink.
         /// </summary>
@@ -60,5 +65,11 @@ public static class Scp173
         /// </summary>
         /// <param name="ev">The <see cref="UsingBreakneckSpeedsEventArgs" /> instance.</param>
         public static void OnUsingBreakneckSpeeds(UsingBreakneckSpeedsEventArgs ev) => UsingBreakneckSpeeds.InvokeSafely(ev);
+
+        /// <summary>
+        /// Called before Scp 173 is observed.
+        /// </summary>
+        /// <param name="ev">The <see cref="BeingObservedEventArgs" /> instance.</param>
+        public static void OnBeingObserved(BeingObservedEventArgs ev) => BeingObserved.InvokeSafely(ev);
     }
-}
+}

EXILED/Exiled.Events/Patches/Events/Scp173/BeingObserved.cs

@@ -0,0 +1,89 @@
+// -----------------------------------------------------------------------
+// <copyright file="BeingObserved.cs" company="Exiled Team">
+// Copyright (c) Exiled Team. All rights reserved.
+// Licensed under the CC BY-SA 3.0 license.
+// </copyright>
+// -----------------------------------------------------------------------
+
+namespace Exiled.Events.Patches.Events.Scp173
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using System.Reflection;
+    using System.Reflection.Emit;
+
+    using Exiled.API.Features.Pools;
+    using Exiled.Events.Attributes;
+    using Exiled.Events.EventArgs.Scp173;
+    using HarmonyLib;
+    using PlayerRoles.PlayableScps.Scp173;
+    using PlayerRoles.Subroutines;
+    using PluginAPI.Events;
+
+    using static HarmonyLib.AccessTools;
+
+    /// <summary>
+    /// Patches <see cref="Scp173ObserversTracker.IsObservedBy" />.
+    /// Adds the <see cref="Handlers.Scp173.BeingObserved" /> event.
+    /// </summary>
+    [EventPatch(typeof(Handlers.Scp173), nameof(Handlers.Scp173.BeingObserved))]
+    [HarmonyPatch(typeof(Scp173ObserversTracker), nameof(Scp173ObserversTracker.IsObservedBy), typeof(ReferenceHub), typeof(float))]
+    internal static class BeingObserved
+    {
+        private static IEnumerable<CodeInstruction> Transpiler(IEnumerable<CodeInstruction> instructions, ILGenerator generator)
+        {
+            List<CodeInstruction> newInstructions = ListPool<CodeInstruction>.Pool.Get(instructions);
+
+            Label continueLabel = generator.DefineLabel();
+
+            const int offset = -4;
+            var scp173ExecuteEvent = typeof(EventManager)
+                .GetMethods(BindingFlags.Public | BindingFlags.Static)
+                .FirstOrDefault(m => m.Name == nameof(EventManager.ExecuteEvent)
+                                     && !m.IsGenericMethod);
+            int index = newInstructions.FindLastIndex(i => i.Calls(scp173ExecuteEvent)) + offset;
+
+            newInstructions.InsertRange(
+                index,
+                new CodeInstruction[]
+            {
+                // Player.Get(target)
+                new(OpCodes.Ldarg_1),
+                new(OpCodes.Call, Method(typeof(API.Features.Player), nameof(API.Features.Player.Get), new[] { typeof(ReferenceHub) })),
+
+                // Player.Get(base.Owner)
+                new(OpCodes.Ldarg_0),
+                new(OpCodes.Call, PropertyGetter(typeof(StandardSubroutine<Scp173Role>), nameof(StandardSubroutine<Scp173Role>.Owner))),
+                new(OpCodes.Call, Method(typeof(API.Features.Player), nameof(API.Features.Player.Get), new[] { typeof(ReferenceHub) })),
+
+                // true
+                new(OpCodes.Ldc_I4_1),
+
+                // BeingObservedEventArgs ev = new(Player, Player, bool)
+                new(OpCodes.Newobj, GetDeclaredConstructors(typeof(BeingObservedEventArgs))[0]),
+                new(OpCodes.Dup),
+
+                // Handlers.Scp173.OnBeingObserved(ev)
+                new(OpCodes.Call, Method(typeof(Handlers.Scp173), nameof(Handlers.Scp173.OnBeingObserved))),
+
+                // if (ev.IsAllowed)
+                //   goto continueLabel
+                new(OpCodes.Callvirt, PropertyGetter(typeof(BeingObservedEventArgs), nameof(BeingObservedEventArgs.IsAllowed))),
+                new(OpCodes.Brtrue, continueLabel),
+
+                // return false
+                new(OpCodes.Ldc_I4_0),
+                new(OpCodes.Ret),
+
+                // continueLabel:
+                new CodeInstruction(OpCodes.Nop).WithLabels(continueLabel),
+            });
+
+            for (int z = 0; z < newInstructions.Count; z++)
+                yield return newInstructions[z];
+
+            ListPool<CodeInstruction>.Pool.Return(newInstructions);
+        }
+    }
+}