decouple briefing from traitor (#19668)

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

Content.Server/Roles/RoleBriefingComponent.cs

@@ -0,0 +1,11 @@
+namespace Content.Server.Roles;
+
+/// <summary>
+/// Adds a briefing to the character info menu, does nothing else.
+/// </summary>
+[RegisterComponent]
+public sealed partial class RoleBriefingComponent : Component
+{
+    [DataField("briefing"), ViewVariables(VVAccess.ReadWrite)]
+    public string Briefing;
+}

Content.Server/Roles/RoleBriefingSystem.cs

@@ -0,0 +1,25 @@
+namespace Content.Server.Roles;
+
+public sealed class RoleBriefingSystem : EntitySystem
+{
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<RoleBriefingComponent, GetBriefingEvent>(OnGetBriefing);
+    }
+
+    private void OnGetBriefing(EntityUid uid, RoleBriefingComponent comp, ref GetBriefingEvent args)
+    {
+        if (args.Briefing == null)
+        {
+            // no previous briefing so just set it
+            args.Briefing = comp.Briefing;
+        }
+        else
+        {
+            // there is a previous briefing so append to it
+            args.Briefing += "\n" + comp.Briefing;
+        }
+    }
+}

Content.Server/Roles/RoleSystem.cs

@@ -17,7 +17,18 @@ public sealed class RoleSystem : SharedRoleSystem
 
     public string? MindGetBriefing(EntityUid? mindId)
     {
-        // TODO this should be an event
-        return CompOrNull<TraitorRoleComponent>(mindId)?.Briefing;
+        if (mindId == null)
+            return null;
+
+        var ev = new GetBriefingEvent();
+        RaiseLocalEvent(mindId.Value, ref ev);
+        return ev.Briefing;
     }
 }
+
+/// <summary>
+/// Event raised on the mind to get its briefing.
+/// Handlers can either replace or append to the briefing, whichever is more appropriate.
+/// </summary>
+[ByRefEvent]
+public record struct GetBriefingEvent(string? Briefing = null);

Content.Server/Roles/TraitorRoleComponent.cs

@@ -5,5 +5,4 @@ namespace Content.Server.Roles;
 [RegisterComponent]
 public sealed partial class TraitorRoleComponent : AntagonistRoleComponent
 {
-    public string? Briefing;
 }