feat: add cross-platform PWA install prompt

src/lib/useInstallPrompt.ts

@@ -0,0 +1,65 @@
+import { useEffect, useState } from "react";
+
+export type InstallPromptState = "unsupported" | "available" | "ios-instructions" | "installed";
+
+interface BeforeInstallPromptEvent extends Event {
+  prompt: () => Promise<void>;
+  userChoice: Promise<{ outcome: "accepted" | "dismissed"; platform: string }>;
+}
+
+function isStandalone() {
+  return window.matchMedia("(display-mode: standalone)").matches ||
+    ("standalone" in navigator && Boolean((navigator as Navigator & { standalone?: boolean }).standalone));
+}
+
+function isIOSSafari() {
+  const ua = navigator.userAgent;
+  const ios = /iPad|iPhone|iPod/.test(ua) || (navigator.platform === "MacIntel" && navigator.maxTouchPoints > 1);
+  return ios && /Safari/i.test(ua) && !/CriOS|FxiOS|EdgiOS|OPiOS/i.test(ua);
+}
+
+export function useInstallPrompt() {
+  const [state, setState] = useState<InstallPromptState>(() => {
+    if (typeof window === "undefined") return "unsupported";
+    if (isStandalone()) return "installed";
+    return isIOSSafari() ? "ios-instructions" : "unsupported";
+  });
+  const [deferred, setDeferred] = useState<BeforeInstallPromptEvent | null>(null);
+  const [dismissed, setDismissed] = useState(false);
+
+  useEffect(() => {
+    if (isStandalone()) {
+      setState("installed");
+      return;
+    }
+
+    const onBeforeInstallPrompt = (event: Event) => {
+      event.preventDefault();
+      setDeferred(event as BeforeInstallPromptEvent);
+      setState("available");
+    };
+    const onInstalled = () => {
+      setDeferred(null);
+      setState("installed");
+    };
+
+    window.addEventListener("beforeinstallprompt", onBeforeInstallPrompt);
+    window.addEventListener("appinstalled", onInstalled);
+    return () => {
+      window.removeEventListener("beforeinstallprompt", onBeforeInstallPrompt);
+      window.removeEventListener("appinstalled", onInstalled);
+    };
+  }, []);
+
+  const install = async () => {
+    if (!deferred) return;
+    const event = deferred;
+    setDeferred(null);
+    await event.prompt();
+    const choice = await event.userChoice;
+    if (choice.outcome === "accepted") setState("installed");
+    else setDismissed(true);
+  };
+
+  return { state: dismissed ? "unsupported" : state, install, dismiss: () => setDismissed(true) };
+}