/**
 * EmDash Request Context
 *
 * Uses AsyncLocalStorage to provide request-scoped state to query functions
 * without requiring explicit parameter passing. The middleware wraps next()
 * in als.run(), making the context available to all code during rendering.
 *
 * For logged-out users with no CMS signals (no edit cookie, no preview param),
 * the middleware skips ALS entirely — zero overhead for normal traffic.
 *
 * The AsyncLocalStorage instance is stored on globalThis with a Symbol key
 * to guarantee a singleton even when bundlers duplicate this module across
 * code-split chunks. Without this, Rollup/Vite may inline the module into
 * multiple chunks (e.g. middleware and page components), each with its own
 * ALS instance — breaking request-scoped state propagation.
 */

import { AsyncLocalStorage } from "node:async_hooks";

export interface EmDashRequestContext {
	/** Whether the current request is in visual editing mode */
	editMode: boolean;
	/** Preview token info, if this is a preview request */
	preview?: {
		collection: string;
		id: string;
	};
	/** Current locale from Astro's i18n routing (when configured) */
	locale?: string;
	/**
	 * Per-request database override.
	 *
	 * Set by middleware when D1 read replica sessions are enabled.
	 * The runtime's `db` getter checks this first, falling back to
	 * the singleton instance. Also used by the DO preview pattern.
	 */
	db?: unknown;
}

const ALS_KEY = Symbol.for("emdash:request-context");

const storage: AsyncLocalStorage<EmDashRequestContext> =
	// eslint-disable-next-line typescript-eslint(no-unsafe-type-assertion) -- globalThis singleton pattern
	((globalThis as Record<symbol, unknown>)[ALS_KEY] as
		| AsyncLocalStorage<EmDashRequestContext>
		| undefined) ??
	(() => {
		const als = new AsyncLocalStorage<EmDashRequestContext>();
		(globalThis as Record<symbol, unknown>)[ALS_KEY] = als;
		return als;
	})();

/**
 * Run a function within an EmDash request context.
 * Called by middleware to wrap next().
 */
export function runWithContext<T>(ctx: EmDashRequestContext, fn: () => T): T {
	return storage.run(ctx, fn);
}

/**
 * Get the current request context.
 * Returns undefined if no context is set (logged-out fast path).
 */
export function getRequestContext(): EmDashRequestContext | undefined {
	return storage.getStore();
}