"use client";
import { useEffect, useRef, useState } from "react";

export type SseEvent<T = unknown> = { type: string; data: T[]; received_at: number };

/** Subscribe to the market-data SSE relay. Handlers are kept in a ref so re-renders don't reconnect. */
export function useMarketStream(symbols: string[], channels: string[], handlers: Partial<Record<string, (ev: SseEvent<Record<string, unknown>>) => void>>) {
  const [connected, setConnected] = useState(false);
  const ref = useRef(handlers);
  useEffect(() => {
    ref.current = handlers;
  });
  const key = `${symbols.join(",")}|${channels.join(",")}`;
  useEffect(() => {
    if (!symbols.length) return;
    const url = `/api/market/stream?symbols=${encodeURIComponent(symbols.join(","))}&channels=${encodeURIComponent(channels.join(","))}`;
    const es = new EventSource(url, { withCredentials: true });
    es.onopen = () => setConnected(true);
    es.onerror = () => setConnected(false);
    const listeners: [string, (e: MessageEvent) => void][] = [];
    for (const ch of channels) {
      const fn = (e: MessageEvent) => {
        try {
          const parsed = JSON.parse(e.data) as SseEvent<Record<string, unknown>>;
          ref.current[ch]?.(parsed);
        } catch {
          /* ignore malformed */
        }
      };
      es.addEventListener(ch, fn);
      listeners.push([ch, fn]);
    }
    return () => {
      for (const [ch, fn] of listeners) es.removeEventListener(ch, fn);
      es.close();
      setConnected(false);
    };
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [key]);
  return connected;
}