/*
 * Veskslop — minimal Chrome DevTools Protocol client.
 *
 * Connects to the Discord page target exposed by Vesktop's
 * --remote-debugging-port, evaluates expressions in the page, and receives
 * pushed events through a CDP binding. This is the entire integration surface:
 * Vesktop itself is unmodified.
 */

import WebSocket from "ws";

export type CdpListener = (event: any) => void;

interface PendingRequest {
    resolve: (value: any) => void;
    reject: (error: Error) => void;
}

export class CdpClient {
    private ws!: WebSocket;
    private nextId = 0;
    private readonly pending = new Map<number, PendingRequest>();
    private readonly listeners = new Set<CdpListener>();

    static async connect(cdpUrl = process.env.CDP_URL ?? "http://127.0.0.1:9222"): Promise<CdpClient> {
        const targets = (await (await fetch(`${cdpUrl}/json`)).json()) as any[];
        const page = targets.find(target => target.type === "page" && target.url.includes("discord.com"));
        if (!page) throw new Error(`No Discord page target at ${cdpUrl}`);

        const client = new CdpClient();
        client.ws = new WebSocket(page.webSocketDebuggerUrl);

        await new Promise<void>((resolve, reject) => {
            client.ws.once("open", resolve);
            client.ws.once("error", reject);
        });

        client.ws.on("message", (raw: WebSocket.RawData) => client.onMessage(raw));

        await client.send("Runtime.enable");
        await client.send("Runtime.addBinding", { name: "veskslopEmit" });

        return client;
    }

    private onMessage(raw: WebSocket.RawData) {
        const message = JSON.parse(raw.toString());

        if (message.id && this.pending.has(message.id)) {
            const request = this.pending.get(message.id)!;
            this.pending.delete(message.id);

            if (message.error) request.reject(new Error(message.error.message));
            else request.resolve(message.result);

            return;
        }

        if (message.method === "Runtime.bindingCalled" && message.params?.name === "veskslopEmit") {
            try {
                const event = JSON.parse(message.params.payload);
                for (const listener of this.listeners) listener(event);
            } catch {
                // ignore malformed payloads
            }
        }
    }

    send(method: string, params?: unknown): Promise<any> {
        const id = ++this.nextId;

        return new Promise((resolve, reject) => {
            this.pending.set(id, { resolve, reject });
            this.ws.send(JSON.stringify({ id, method, params }));
        });
    }

    async evaluate<T = unknown>(expression: string): Promise<T> {
        const result = await this.send("Runtime.evaluate", {
            expression,
            returnByValue: true,
            awaitPromise: true
        });

        if (result.exceptionDetails) {
            const description =
                result.exceptionDetails.exception?.description ?? result.exceptionDetails.text ?? "evaluation failed";
            throw new Error(description);
        }

        return result.result?.value as T;
    }

    onEvent(listener: CdpListener): () => void {
        this.listeners.add(listener);
        return () => this.listeners.delete(listener);
    }

    close() {
        this.ws.close();
    }
}