import { createImpl } from './create-impl';
import type { SharedImpl } from './shared-impl';

export const STATE_KEY = Symbol.for('@servicetitan/datadog-rum');

export interface GlobalSlot {
    [STATE_KEY]?: SharedImpl;
}

function slot(): GlobalSlot {
    return globalThis as unknown as GlobalSlot;
}

/** Returns the shared impl, creating it if it doesn't exist yet. Only called by `init`. */
export function getOrCreateSharedImpl(): SharedImpl {
    const s = slot();
    s[STATE_KEY] ??= createImpl();
    return s[STATE_KEY];
}

/** Returns the shared impl if it already exists, or `undefined`. */
export function getSharedImpl(): SharedImpl | undefined {
    return slot()[STATE_KEY];
}