/**
 * Hash routing for the demo app.
 *
 *   #/                            → empty state ("create your first session")
 *   #/s/<sessionId>               → review mode, scoped to <sessionId>
 *   #/s/<sessionId>/forms/demo    → forms mode, scoped to <sessionId>
 *
 * The hash is the single source of truth for the active session and the
 * active mode. `SessionProvider.setActive(...)` is wired as a side
 * effect of hash changes so back/forward and deep links behave
 * naturally.
 */

import type { SessionId } from "@shared/ids";

export type AppMode = "review" | "forms";

export interface AppRoute {
  readonly sessionId: SessionId | null;
  readonly mode: AppMode;
}

export const EMPTY_ROUTE: AppRoute = { sessionId: null, mode: "review" };

export function parseRoute(hash: string): AppRoute {
  // Normalise: drop leading "#", trim any trailing slashes.
  const cleaned = hash.replace(/^#/, "").replace(/^\/+|\/+$/g, "");
  if (cleaned === "") return EMPTY_ROUTE;
  const parts = cleaned.split("/");
  if (parts.length >= 2 && parts[0] === "s") {
    const sessionId = parts[1]! as SessionId;
    const mode: AppMode =
      parts[2] === "forms" && parts[3] === "demo" ? "forms" : "review";
    return { sessionId, mode };
  }
  // Legacy `#/forms/demo` (pre-CE-WP-0005) maps to the empty state — the
  // user has to pick a session first.
  return EMPTY_ROUTE;
}

export function serializeRoute(route: AppRoute): string {
  if (!route.sessionId) return "";
  const base = `#/s/${route.sessionId}`;
  return route.mode === "forms" ? `${base}/forms/demo` : base;
}

export function navigateTo(route: AppRoute): void {
  if (typeof window === "undefined") return;
  const target = serializeRoute(route);
  if (target === "") {
    // Clear the hash entirely so the URL stays clean.
    history.replaceState(null, "", window.location.pathname + window.location.search);
    // history.replaceState doesn't fire hashchange — dispatch one so
    // subscribers re-read.
    window.dispatchEvent(new HashChangeEvent("hashchange"));
    return;
  }
  if (window.location.hash !== target) {
    window.location.hash = target;
  }
}