feat(admin): shift-select multiple sessions in process list

apps/desktop/src/lib/database/processListSelection.ts

@@ -0,0 +1,44 @@
+import { orderedListRangeIndices, orderedListSelectionIntent } from "../selection/orderedListSelection";
+
+/** Rows are identified by the server session id, matching the process list grid. */
+export interface ProcessListSelectionRow {
+  id: number;
+}
+
+export interface ProcessListSelectionState {
+  selected: Set<number>;
+  anchorId: number | null;
+}
+
+/**
+ * Applies a row checkbox click to the current selection.
+ *
+ * A plain click toggles the clicked row and moves the anchor; Shift+click applies
+ * the clicked row's next state to every selectable row between the anchor and the
+ * clicked row, so long session lists can be selected in one gesture. Rows outside
+ * the range keep their current state, and an unknown/stale anchor degrades to a
+ * plain toggle instead of selecting an unexpected range.
+ *
+ * The next state is derived from the current selection because the grid binds
+ * `:checked` without cancelling the native checkbox activation.
+ */
+export function processListSelectionAfterClick(rows: ProcessListSelectionRow[], state: ProcessListSelectionState, id: number, event: Pick<MouseEvent, "shiftKey" | "metaKey" | "ctrlKey">): ProcessListSelectionState {
+  const targetIndex = rows.findIndex((row) => row.id === id);
+  if (targetIndex < 0) return state;
+  const checked = !state.selected.has(id);
+  const anchorIndex = state.anchorId === null ? -1 : rows.findIndex((row) => row.id === state.anchorId);
+  if (orderedListSelectionIntent(event) === "range" && anchorIndex >= 0) {
+    const selected = new Set(state.selected);
+    for (const index of orderedListRangeIndices(rows.length, anchorIndex, targetIndex)) {
+      const row = rows[index];
+      if (!row) continue;
+      if (checked) selected.add(row.id);
+      else selected.delete(row.id);
+    }
+    return { selected, anchorId: state.anchorId };
+  }
+  const selected = new Set(state.selected);
+  if (checked) selected.add(id);
+  else selected.delete(id);
+  return { selected, anchorId: id };
+}