statistics: support ctrl-selection for all series

Multiple selection using ctrl was only supported for
scatter series. Factor out the corresponding code and
use it in all series.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

stats/statsselection.cpp

@@ -1,2 +1,42 @@
 // SPDX-License-Identifier: GPL-2.0
 #include "statsselection.h"
+#include "core/dive.h"
+#include "core/selection.h"
+
+#include <algorithm>
+
+void processSelection(std::vector<dive *> dives, SelectionModifier modifier)
+{
+	std::vector<dive *> selected;
+
+	if (modifier.ctrl) {
+		// When shift is pressed, add the items under the mouse to the selection
+		// or, if all items under the mouse are selected, remove them.
+		selected = getDiveSelection();
+		bool allSelected = std::all_of(dives.begin(), dives.end(),
+					       [] (const dive *d) { return d->selected; });
+		if (allSelected) {
+			// Remove items under cursor from selection. This could be made more efficient.
+			for (const dive *d: dives) {
+				auto it = std::find(selected.begin(), selected.end(), d);
+				if (it != selected.end()) {
+					// Move last element to deselected element. If this already was
+					// the last element, this is a no-op. Then, chop off last element.
+					*it = selected.back();
+					selected.pop_back();
+				}
+			}
+		} else {
+			// Add items under cursor to selection
+			selected.reserve(dives.size() + selected.size());
+			for (dive *d: dives) {
+				if (std::find(selected.begin(), selected.end(), d) == selected.end())
+					selected.push_back(d);
+			}
+		}
+	} else {
+		selected = std::move(dives);
+	}
+
+	setSelection(selected, selected.empty() ? nullptr : selected.front());
+}