import {EventEmitter} from 'events';

const STATE_CHANGE_EVENT = 'stateChange';
type StateChangeListener = (state: Record<string, any>) => void;

// Use the namespace pattern
export namespace SystemState {
  const emitter = new EventEmitter();
  let state: Record<string, any> = {};

  export function getState(): Record<string, any> {
    return {...state};
  }

  export function setState(newState: Record<string, any>): void {
    state = {...state, ...newState};
    emitter.emit(STATE_CHANGE_EVENT, getState());
  }

  export function reset(): void {
    state = {};
    emitter.emit(STATE_CHANGE_EVENT, getState());
  }

  export function getAlertResponse(): number | undefined {
    return state.alertResponse;
  }

  export function setAlertResponse(response: number | undefined): void {
    setState({alertResponse: response});
  }

  export function getTextFieldValue(fieldId: string): string | undefined {
    return state.textFieldValues?.[fieldId];
  }

  export function setTextFieldValue(fieldId: string, value: string): void {
    const textFieldValues = {...(state.textFieldValues || {})};
    textFieldValues[fieldId] = value;
    setState({textFieldValues});
  }

  export function addEventListener(event: 'stateChange', listener: StateChangeListener): void {
    if (event !== STATE_CHANGE_EVENT) {
      throw new Error(`Invalid event: ${event}`);
    }
    emitter.addListener(event, listener);
  }

  export function removeEventListener(event: 'stateChange', listener: StateChangeListener): void {
    if (event !== STATE_CHANGE_EVENT) {
      throw new Error(`Invalid event: ${event}`);
    }
    emitter.removeListener(event, listener);
  }

  export function subscribe(handler: StateChangeListener): () => void {
    addEventListener(STATE_CHANGE_EVENT, handler);
    return () => removeEventListener(STATE_CHANGE_EVENT, handler);
  }
}