import type { Router } from "@suaveplan/api-router";
import type { ApolloGraphqlOptions } from "../options/options.js";

/**
 * UI plugin descriptor. The host wires a separate UI package (GraphiQL,
 * Altair, …) and hands a renderer in; the Apollo engine itself never
 * embeds Apollo's landing page (UI is opt-in — same stance as Yoga).
 */
export interface GraphqlUiPlugin {
    /** Returns the HTML body served at `/graphql/ui`. */
    render(): string;
    /** MIME type — defaults to `text/html` when omitted. */
    readonly contentType?: string;
}

/** Response envelope returned by the UI proxy handler. */
export interface UiProxyResponse {
    readonly status: 200 | 404;
    readonly body: string;
    readonly contentType: string;
}

/**
 * Mount the `/graphql/ui` proxy endpoint. When `ui` is `null` the
 * handler responds `404` with a short note explaining the UI is opt-in;
 * when supplied it returns the plugin's rendered HTML.
 */
export function mountGraphqlUiProxy(args: {
    readonly router: Router;
    readonly options: ApolloGraphqlOptions;
    readonly ui: GraphqlUiPlugin | null;
}): () => void {
    const { router, options, ui } = args;
    router.get(options.uiEndpoint, (): UiProxyResponse => {
        if (ui === null) {
            return {
                status: 404,
                body: "GraphQL UI is opt-in — wire a UI plugin to enable",
                contentType: "text/plain",
            };
        }
        return {
            status: 200,
            body: ui.render(),
            contentType: ui.contentType ?? "text/html",
        };
    });
    return () => {
        /* hot-reload teardown reserved */
    };
}