import type { AutocompleteItem } from "@earendil-works/pi-tui";
import type { AgentConnectionCommandArgument } from "./agent-connection/types.js";

const firstToken = (value: string): string => value.trimEnd().split(" ")[0] ?? "";

/**
 * Complete an argument from the candidates a remote host published for a command.
 *
 * `value` replaces the whole typed argument, so candidates carry their own leading tokens
 * ("policy deepseek-economic"). A prefix without a space completes the first token only,
 * which keeps deeper candidates out of the first popup.
 */
export function getPublishedArgumentCompletions(
	candidates: readonly AgentConnectionCommandArgument[],
	prefix: string,
): AutocompleteItem[] | null {
	const lowered = prefix.toLowerCase();
	const completingFirstToken = !prefix.includes(" ");
	const matched = candidates.filter((candidate) => {
		const value = candidate.value.toLowerCase();
		// A candidate identical to what is already typed adds nothing.
		if (value === lowered) return false;
		if (completingFirstToken && candidate.value.trimEnd() !== firstToken(candidate.value)) return false;
		return value.startsWith(lowered);
	});
	if (matched.length === 0) return null;

	return matched.map((candidate) => ({
		value: candidate.value,
		label: candidate.label ?? candidate.value,
		...(candidate.description && { description: candidate.description }),
	}));
}