Add functions for creation selection commands

Author: robertbrignull

extensions/ql-vscode/src/common/selection-commands.ts

@@ -0,0 +1,51 @@
+import { showAndLogErrorMessage } from "../helpers";
+import {
+  ExplorerSelectionCommandFunction,
+  TreeViewContextMultiSelectionCommandFunction,
+  TreeViewContextSingleSelectionCommandFunction,
+} from "./commands";
+
+// A hack to match types that are not an array, which is useful to help avoid
+// misusing createSingleSelectionCommand, e.g. where T accidentally gets instantiated
+// as DatabaseItem[] instead of DatabaseItem.
+type NotArray = object & { length?: never };
+
+// A way to get the type system to help assert that one type is a supertype of another.
+type CreateSupertypeOf<Super, Sub extends Super> = Sub;
+
+// This asserts that SelectionCommand is assignable to all of the different types of
+// SelectionCommand defined in commands.ts. The intention is the output from the helpers
+// in this file can be used with any of the select command types and cna handle any of
+// the inputs.
+type SelectionCommand<T extends NotArray> = CreateSupertypeOf<
+  TreeViewContextMultiSelectionCommandFunction<T> &
+    TreeViewContextSingleSelectionCommandFunction<T> &
+    ExplorerSelectionCommandFunction<T>,
+  (singleItem: T, multiSelect?: T[] | undefined) => Promise<void>
+>;
+
+export function createSingleSelectionCommand<T extends NotArray>(
+  f: (argument: T) => Promise<void>,
+  itemName: string,
+): SelectionCommand<T> {
+  return async (singleItem, multiSelect) => {
+    if (multiSelect === undefined || multiSelect.length === 1) {
+      return f(singleItem);
+    } else {
+      void showAndLogErrorMessage(`Please select a single ${itemName}.`);
+      return;
+    }
+  };
+}
+
+export function createMultiSelectionCommand<T extends NotArray>(
+  f: (argument: T[]) => Promise<void>,
+): SelectionCommand<T> {
+  return async (singleItem, multiSelect) => {
+    if (multiSelect !== undefined && multiSelect.length > 0) {
+      return f(multiSelect);
+    } else {
+      return f([singleItem]);
+    }
+  };
+}