feat(frontend): useDrawerUrlState hook for ?claim= sync

src/hooks/useDrawerUrlState.ts

@@ -0,0 +1,104 @@
+import { useCallback, useEffect, useState } from "react";
+
+/**
+ * Read the current `?claim=…` query param off `window.location.search`.
+ * Returns `null` when the param is absent or empty.
+ *
+ * `URLSearchParams` is the standard, locale-free way to parse query
+ * strings in the browser. Using it (rather than hand-rolled string
+ * slicing) means we correctly handle multiple params and percent-encoded
+ * characters in claim IDs without surprises.
+ */
+function readClaimId(): string | null {
+  const params = new URLSearchParams(window.location.search);
+  return params.get("claim");
+}
+
+/**
+ * Build the URL we want to push/replace into history.
+ *
+ * - `claimId === null`  →  drop the `?claim=` param, preserving any
+ *   other params (e.g. `?foo=bar` stays).
+ * - `claimId !== null`  →  set the param to the new id, also preserving
+ *   any other params.
+ *
+ * We return `pathname + search + hash` (a relative URL) rather than the
+ * full href — `history.pushState` accepts a relative URL and rewriting
+ * only the relative form keeps the document's origin stable. `hash` is
+ * appended so a `#section` anchor survives navigation, matching what
+ * the browser would do natively.
+ */
+function buildUrl(claimId: string | null): string {
+  const url = new URL(window.location.href);
+  if (claimId === null) {
+    url.searchParams.delete("claim");
+  } else {
+    url.searchParams.set("claim", claimId);
+  }
+  return url.pathname + url.search + url.hash;
+}
+
+/**
+ * Per-claim detail drawer URL state (SP4).
+ *
+ * Reads `?claim=` from the URL on mount and keeps the value in sync with
+ * history as the drawer is opened, navigated (j/k), and closed. The
+ * drawer parent uses this hook as the single source of truth for "is a
+ * claim open and which one" — the URL is the durable record so that
+ * deep links (`/claims?claim=CLM-1`) restore the drawer state on reload.
+ *
+ *   - `claimId`: the id parsed from the URL (or `null` when the param
+ *     is absent). React state so consumers re-render on changes.
+ *   - `open(id)`: pushes a NEW history entry with `?claim={id}` — so the
+ *     browser Back button returns to the previous page (e.g. the claims
+ *     list) and not just to the previously-open claim.
+ *   - `setClaimId(id)`: REPLACES the current history entry — used by the
+ *     j/k nav handler so j/k moves through the list without polluting
+ *     history with one entry per keystroke.
+ *   - `close()`: pushes a NEW entry that strips the param, so Back from
+ *     the closed drawer returns to whatever page the user was on before
+ *     opening the drawer.
+ *
+ * The hook subscribes to `popstate` so that browser Back/Forward
+ * (which fire popstate rather than our own pushState) propagate into
+ * the React state. Without this, hitting Back would change the URL but
+ * leave the drawer open on the stale id.
+ *
+ * Implementation note: this is a single-operator local-only tool, so we
+ * call `history.pushState` / `replaceState` directly without try/catch
+ * wrappers — the only way they throw in modern browsers is when the URL
+ * is malformed, which we control.
+ */
+export function useDrawerUrlState(): {
+  claimId: string | null;
+  open: (id: string) => void;
+  close: () => void;
+  setClaimId: (id: string) => void;
+} {
+  const [claimId, setClaimIdState] = useState<string | null>(() => readClaimId());
+
+  const open = useCallback((id: string) => {
+    window.history.pushState(null, "", buildUrl(id));
+    setClaimIdState(id);
+  }, []);
+
+  const setClaimId = useCallback((id: string) => {
+    window.history.replaceState(null, "", buildUrl(id));
+    setClaimIdState(id);
+  }, []);
+
+  const close = useCallback(() => {
+    window.history.pushState(null, "", buildUrl(null));
+    setClaimIdState(null);
+  }, []);
+
+  useEffect(() => {
+    const onPopState = () => {
+      setClaimIdState(readClaimId());
+    };
+    window.addEventListener("popstate", onPopState);
+    return () => window.removeEventListener("popstate", onPopState);
+  }, []);
+
+  return { claimId, open, close, setClaimId };
+}