split the selection panel into one card per kind of selection

src/ui/selection/SelectionContentFactory.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include <vector>
+
+#include "entt/entity/entity.hpp"
+
+#include "BuildingId.h"
+#include "SelectionContext.h"
+
+class QWidget;
+class SelectionContent;
+class Simulation;
+
+// What is currently selected, in the selection panel's terms. The two categories are
+// mutually exclusive (REQ-UI-SELECTION-CATEGORIES): either buildings is non-empty, or
+// actors and/or debris are, never both.
+struct SelectionRequest
+{
+    std::vector<BuildingId>   buildings;
+    std::vector<entt::entity> actors;
+    std::vector<entt::entity> debris;
+
+    bool isEmpty() const
+    {
+        return buildings.empty() && actors.empty() && debris.empty();
+    }
+};
+
+// One entry of the content catalog (REQ-UI-SELECTION-CONTENT). Selections that share an
+// entry get the same content and differ only in the name and symbol in the header.
+enum class SelectionContentKind
+{
+    None,              // nothing selected: the panel hides itself entirely
+    RecipeProduction,  // Miner, Assembler
+    AutoProduction,    // Smelter, Reprocessing Plant
+    Shipyard,
+    Storage,           // Salvage Bay
+    Hq,
+    Belt,              // Belt, Tunnel Entry, Tunnel Exit
+    Splitter,
+    MultiBuilding,
+    Ship,
+    Station,
+    Debris,
+    FieldMulti,
+};
+
+// Identifies the card on screen. The panel rebuilds when this changes and only refreshes
+// otherwise, so a construction site finishing swaps the card while a progress counter
+// running does not.
+struct ContentKey
+{
+    SelectionContentKind kind   = SelectionContentKind::None;
+    bool                 isSite = false;
+
+    bool operator==(const ContentKey& other) const
+    {
+        return kind == other.kind && isSite == other.isSite;
+    }
+    bool operator!=(const ContentKey& other) const { return !(*this == other); }
+};
+
+// The card this selection calls for. This is where REQ-UI-SELECTION-AGGREGATE is
+// decided: a multi-selection that aggregates resolves to the single-object kind, and
+// everything else to one of the two count summaries.
+ContentKey chooseContent(const SelectionRequest& request, Simulation& sim);
+
+// Builds the card. Returns nullptr for SelectionContentKind::None.
+SelectionContent* createContent(const ContentKey& key, const SelectionRequest& request,
+                                const SelectionContext& context, QWidget* parent);