/**
 * History adapter — the injected browser effect for client-side routing.
 *
 * A thin wrapper over `window.history` + the `popstate` event that exposes the
 * current pathname, a `navigate` (pushState) that updates the URL without a
 * reload, and a `subscribe` for path changes (back/forward buttons + programmatic
 * navigation). The route SEMANTICS (path → workspace/home) live in the
 * `workspaces` feature's pure `parsePath`; this adapter deals only in path
 * strings, so it stays generic + reusable.
 *
 * The browser edge (`window`/`history`) is INJECTED (defaults to the global) so
 * it is testable without the DOM and degrades to a no-op when absent (SSR / no
 * `window`).
 */

/** The minimal browser-history surface this adapter needs. */
export interface HistoryWindow {
  readonly location: { readonly pathname: string };
  readonly history: {
    pushState(data: unknown, unused: string, url?: string | URL | null): void;
    replaceState(data: unknown, unused: string, url?: string | URL | null): void;
  };
  addEventListener(type: "popstate", listener: () => void): void;
  removeEventListener(type: "popstate", listener: () => void): void;
}

export interface HistoryAdapter {
  /** The current pathname. */
  readonly path: string;
  /** Push a new path (updates the URL without a reload) + notifies subscribers. */
  navigate(path: string): void;
  /** Replace the current path without adding a history entry (no notify). */
  replace(path: string): void;
  /** Subscribe to path changes (back/forward + navigate). Returns unsubscribe. */
  subscribe(cb: (path: string) => void): () => void;
}

export interface CreateHistoryOptions {
  /** The browser window; defaults to `globalThis`. Inject for tests. */
  readonly window?: HistoryWindow;
}

function noop(): void {}

/** A no-op adapter for when there is no `window` (SSR). */
function createNoopHistory(): HistoryAdapter {
  return {
    get path() {
      return "/";
    },
    navigate: noop,
    replace: noop,
    subscribe() {
      return noop;
    },
  };
}

export function createHistoryAdapter(opts?: CreateHistoryOptions): HistoryAdapter {
  const w = opts?.window ?? (globalThis as unknown as HistoryWindow);
  if (w === undefined || w === null || w.location === undefined) {
    return createNoopHistory();
  }

  const listeners = new Set<(path: string) => void>();
  const current = (): string => w.location.pathname;
  const emit = (): void => {
    const p = current();
    for (const cb of listeners) cb(p);
  };

  return {
    get path() {
      return current();
    },
    navigate(path: string): void {
      w.history.pushState(null, "", path);
      emit();
    },
    replace(path: string): void {
      w.history.replaceState(null, "", path);
    },
    subscribe(cb: (path: string) => void): () => void {
      listeners.add(cb);
      const onPop = (): void => cb(current());
      w.addEventListener("popstate", onPop);
      return () => {
        listeners.delete(cb);
        w.removeEventListener("popstate", onPop);
      };
    },
  };
}