import { createHostEventSource } from './host-api';

let eventSource: EventSource | null = null;

const HOST_EVENT_TO_IPC_CHANNEL: Record<string, string> = {
  'opencode:status': 'opencode:status',
  'opencode:stderr': 'opencode:stderr',
  'oauth:code': 'oauth:code',
  'oauth:success': 'oauth:success',
  'oauth:error': 'oauth:error',
  'agent-browser:show': 'agent-browser:show',
  'agent-browser:state': 'agent-browser:state',
  'auth:session-changed': 'auth:session-changed',
};

function getEventSource(): EventSource {
  if (!eventSource) {
    eventSource = createHostEventSource();
  }
  return eventSource;
}

function allowSseFallback(): boolean {
  try {
    return window.localStorage.getItem('niancode:allow-sse-fallback') === '1';
  } catch {
    return false;
  }
}

export function subscribeHostEvent<T = unknown>(
  eventName: string,
  handler: (payload: T) => void,
): () => void {
  const ipc = window.electron?.ipcRenderer;
  const ipcChannel = HOST_EVENT_TO_IPC_CHANNEL[eventName];
  if (ipcChannel && ipc?.on && ipc?.off) {
    const listener = (payload: unknown) => {
      handler(payload as T);
    };
    // preload's `on()` wraps the callback in an internal subscription function
    // and returns a cleanup function that removes that exact wrapper.  We MUST
    // use the returned cleanup rather than calling `off(channel, listener)`,
    // because `listener` !== the internal wrapper and removeListener would be
    // a no-op, leaking the subscription.
    const unsubscribe = ipc.on(ipcChannel, listener);
    if (typeof unsubscribe === 'function') {
      return unsubscribe;
    }
    // Fallback for environments where on() doesn't return cleanup
    return () => {
      ipc.off(ipcChannel, listener);
    };
  }

  if (!allowSseFallback()) {
    console.warn(`[host-events] no IPC mapping for event "${eventName}", SSE fallback disabled`);
    return () => {};
  }

  const source = getEventSource();
  const listener = (event: Event) => {
    const payload = JSON.parse((event as MessageEvent).data) as T;
    handler(payload);
  };
  source.addEventListener(eventName, listener);
  return () => {
    source.removeEventListener(eventName, listener);
  };
}