import * as path from "node:path";
import type { ExtensionFactory } from "@oh-my-pi/pi-coding-agent";

export interface FieldNotesWriteBroker {
	/** Real host broker: resolve only after exact bytes are durable at the supplied destination. */
	write(destination: string, content: string): Promise<void>;
}

/** Host supplies the already-canonical allowlisted destination and a real broker. No elevated writer is bundled. */
export function createFieldNotesFallback(destination: string, broker: FieldNotesWriteBroker): ExtensionFactory {
	if (!path.isAbsolute(destination)) throw new Error("The host must supply an absolute, canonical destination.");
	return pi => {
		pi.registerFileWriteFallback(async (request, ctx) => {
			if (request.sessionId !== ctx.sessionManager.getSessionId() || request.dst !== destination) return false;
			await broker.write(request.dst, request.content);
			return true;
		});
	};
}