Add lib/shortcuts

ts/lib/shortcuts.ts

@@ -0,0 +1,76 @@
+const modifiers = ["Control", "Alt", "Shift", "Meta"];
+
+const platformModifiers =
+    navigator.platform === "MacIntel" ? ["Meta", "Alt", "Shift", "Control"] : modifiers;
+
+function checkKey(event: KeyboardEvent, key: string): boolean {
+    return event.code === key;
+}
+
+function checkModifiers(event: KeyboardEvent, activeModifiers: string[]): boolean {
+    return modifiers.reduce(
+        (matches: boolean, modifier: string, currentIndex: number): boolean =>
+            matches &&
+            event.getModifierState(platformModifiers[currentIndex]) ===
+                activeModifiers.includes(modifier),
+        true
+    );
+}
+
+function check(event: KeyboardEvent, modifiersAndKey: string[]): boolean {
+    return (
+        checkKey(event, modifiersAndKey[modifiersAndKey.length - 1]) &&
+        checkModifiers(event, modifiersAndKey.slice(0, -1))
+    );
+}
+
+function normalizeShortcutString(shortcutString: string): string[][] {
+    return shortcutString.split(", ").map((segment) => segment.split("+"));
+}
+
+const shortcutTimeoutMs = 350;
+
+function innerShortcut(
+    lastEvent: KeyboardEvent,
+    callback: (event: KeyboardEvent) => void,
+    ...shortcuts: string[][]
+): void {
+    if (shortcuts.length === 0) {
+        callback(lastEvent);
+    } else {
+        const [nextShortcut, ...restShortcuts] = shortcuts;
+
+        let ivl: number;
+
+        const handler = (event: KeyboardEvent): void => {
+            if (check(event, nextShortcut)) {
+                innerShortcut(event, callback, ...restShortcuts);
+                clearInterval(ivl);
+            }
+        };
+
+        ivl = setInterval(
+            (): void => document.removeEventListener("keydown", handler),
+            shortcutTimeoutMs
+        );
+
+        document.addEventListener("keydown", handler, { once: true });
+    }
+}
+
+export function shortcut(
+    callback: (event: KeyboardEvent) => void,
+    shortcutString: string
+): () => void {
+    const shortcuts = normalizeShortcutString(shortcutString);
+    const [firstShortcut, ...restShortcuts] = shortcuts;
+
+    const handler = (event: KeyboardEvent): void => {
+        if (check(event, firstShortcut)) {
+            innerShortcut(event, callback, ...restShortcuts);
+        }
+    };
+
+    document.addEventListener("keydown", handler);
+    return (): void => document.removeEventListener("keydown", handler);
+}