move ninja objectives code into generic antag system (#20186)

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

Content.Server/GenericAntag/GenericAntagComponent.cs

@@ -0,0 +1,30 @@
+using Content.Server.GameTicking.Rules.Components;
+using Robust.Shared.Prototypes;
+using Robust.Shared.Serialization.TypeSerializers.Implementations.Custom.Prototype;
+
+namespace Content.Server.GenericAntag;
+
+/// <summary>
+/// Added to a mob to make it a generic antagonist where all its objectives are fixed.
+/// This is unlike say traitor where it gets objectives picked randomly using difficulty.
+/// </summary>
+/// <remarks>
+/// A GenericAntag is not necessarily an antagonist, that depends on the roles you do or do not add after.
+/// </remarks>
+[RegisterComponent, Access(typeof(GenericAntagSystem))]
+public sealed partial class GenericAntagComponent : Component
+{
+    /// <summary>
+    /// Gamerule to start when a mind is added.
+    /// This must have <see cref="GenericAntagRuleComponent"/> or it will not work.
+    /// </summary>
+    [DataField(required: true), ViewVariables(VVAccess.ReadWrite)]
+    public EntProtoId Rule = string.Empty;
+
+    /// <summary>
+    /// The rule that's been spawned.
+    /// Used to prevent spawning multiple rules.
+    /// </summary>
+    [DataField, ViewVariables(VVAccess.ReadWrite)]
+    public EntityUid? RuleEntity;
+}

Content.Server/GenericAntag/GenericAntagSystem.cs

@@ -0,0 +1,67 @@
+using Content.Server.GameTicking.Rules;
+using Content.Shared.Mind;
+using Content.Shared.Mind.Components;
+
+namespace Content.Server.GenericAntag;
+
+/// <summary>
+/// Handles adding objectives to <see cref="GenericAntagComponent"/>s.
+/// Roundend summary is handled by <see cref="GenericAntagRuleSystem"/>.
+/// </summary>
+public sealed class GenericAntagSystem : EntitySystem
+{
+    [Dependency] private readonly SharedMindSystem _mind = default!;
+    [Dependency] private readonly GenericAntagRuleSystem _genericAntagRule = default!;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<GenericAntagComponent, MindAddedMessage>(OnMindAdded);
+    }
+
+    private void OnMindAdded(EntityUid uid, GenericAntagComponent comp, MindAddedMessage args)
+    {
+        if (!TryComp<MindContainerComponent>(uid, out var mindContainer) || mindContainer.Mind == null)
+            return;
+
+        var mindId = mindContainer.Mind.Value;
+        MakeAntag(uid, mindId, comp);
+    }
+
+    /// <summary>
+    /// Turns a player into this antagonist.
+    /// Does the same thing that having a mind added does, use for antag ctrl.
+    /// </summary>
+    public void MakeAntag(EntityUid uid, EntityUid mindId, GenericAntagComponent? comp = null, MindComponent? mind = null)
+    {
+        if (!Resolve(uid, ref comp) || !Resolve(mindId, ref mind))
+            return;
+
+        // only add the rule once
+        if (comp.RuleEntity != null)
+            return;
+
+        // start the rule
+        if (!_genericAntagRule.StartRule(comp.Rule, mindId, out comp.RuleEntity, out var rule))
+            return;
+
+        // let other systems know the antag was created so they can add briefing, roles, etc.
+        // its important that this is before objectives are added since they may depend on roles added here
+        var ev = new GenericAntagCreatedEvent(mindId, mind);
+        RaiseLocalEvent(uid, ref ev);
+
+        // add the objectives from the rule
+        foreach (var id in rule.Objectives)
+        {
+            _mind.TryAddObjective(mindId, mind, id);
+        }
+    }
+}
+
+/// <summary>
+/// Event raised on a player's entity after its simple antag rule is started and objectives get added.
+/// Use this to add a briefing, roles, etc.
+/// </summary>
+[ByRefEvent]
+public record struct GenericAntagCreatedEvent(EntityUid MindId, MindComponent Mind);