experimental welder fuel regeneration (#15475)

* solution regeneration system

* experimental welding tool regenerates 1u of fuel every second

* pro

* use a solution

* added -> generated

---------

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

Content.Server/Chemistry/EntitySystems/SolutionRegenerationSystem.cs

@@ -0,0 +1,40 @@
+using Content.Server.Chemistry.Components;
+using Content.Server.Chemistry.Components.SolutionManager;
+using Robust.Shared.Timing;
+
+namespace Content.Server.Chemistry.EntitySystems;
+
+public sealed class SolutionRegenerationSystem : EntitySystem
+{
+    [Dependency] private readonly SolutionContainerSystem _solutionContainer = default!;
+    [Dependency] private readonly IGameTiming _timing = default!;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<SolutionRegenerationComponent, EntityUnpausedEvent>(OnUnpaused);
+    }
+
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+
+        var query = EntityQueryEnumerator<SolutionRegenerationComponent, SolutionContainerManagerComponent>();
+        while (query.MoveNext(out var uid, out var regen, out var manager))
+        {
+            if (_timing.CurTime < regen.NextRegenTime)
+                continue;
+
+            // timer ignores if its full, it's just a fixed cycle
+            regen.NextRegenTime = _timing.CurTime + regen.Duration;
+            if (_solutionContainer.TryGetSolution(uid, regen.Solution, out var solution, manager))
+                _solutionContainer.TryAddSolution(uid, solution, regen.Generated);
+        }
+    }
+
+    private void OnUnpaused(EntityUid uid, SolutionRegenerationComponent comp, ref EntityUnpausedEvent args)
+    {
+        comp.NextRegenTime += args.PausedTime;
+    }
+}