import { credentials } from './authStorage';

/**
 * WHEN ANOTHER TAB SIGNS OUT, THIS ONE IS NEVER TOLD.
 *
 * A front desk keeps several tabs open. The idle timer is per-tab and in-memory - it watches document
 * events on its own tab - so whichever tab goes quiet first is the one that signs everybody out. It calls
 * logout(), which clears the shared localStorage keys and then navigates ITSELF back to the portal page.
 *
 * Every other tab keeps rendering. Its React state still says signed in, so the nav, the clinician's name
 * and any open patient dialog stay on the monitor with the session already gone underneath them. Nothing
 * in the app listened for `storage`, so there was no path by which those tabs could find out.
 */

// It watches the credential record: the committed epoch is the session and its retirement is the event. A wakeup
// also arrives when someone signs in again elsewhere, so it is only the prompt to look; the epoch read back answers.

/** Whether the shared session is gone right now, as the last committed read says. */
export const sessionTokenIsGone = (): boolean =>
    // Storage that cannot be read cannot tell us the session ended, and claiming it did would cover a working
    // screen. Silence is the safe direction here, unlike everywhere else in this file.
    credentials().current().state === 'signed-out';

/** The committed epoch of the shared session, or null when there is none. */
export const storedSessionId = (): string | null => credentials().epoch();

/** A view signed in under a session that predates ids is judged by its token alone. */
export const UNNUMBERED_SESSION = '';

// The session this tab is ending itself. Its own sweep and the moments before its reload are not another tab's.
let endingHere: string | null | undefined;

/** Called by logout with the epoch it ends: this tab's own sign-out never covers this tab. */
export const noteSessionEndingHere = (epoch: string | null = storedSessionId()): void => {
    endingHere = epoch ?? UNNUMBERED_SESSION;
};

/** Check the displayed session on storage changes and tab return; a different session cannot restore this view. */
export function watchForSessionEndedElsewhere(
    onEnded: () => void,
    viewSession: () => string | undefined,
): () => void {
    if (typeof window === 'undefined') return () => undefined;

    const check = () => {
        const shown = viewSession();
        if (shown === undefined || shown === endingHere) return;
        // Nothing read yet, or nothing readable, says nothing about whether the session ended.
        const state = credentials().current().state;
        if (state === 'loading' || state === 'unavailable') return;
        if (sessionTokenIsGone() || (shown !== UNNUMBERED_SESSION && storedSessionId() !== shown)) onEnded();
    };

    const onVisible = () => {
        if (document.visibilityState === 'visible') check();
    };

    const stopRecord = credentials().onChange(check);
    window.addEventListener('pageshow', check);
    window.addEventListener('focus', check);
    document.addEventListener('visibilitychange', onVisible);
    check();
    return () => {
        stopRecord();
        window.removeEventListener('pageshow', check);
        window.removeEventListener('focus', check);
        document.removeEventListener('visibilitychange', onVisible);
    };
}