import { type ProjectStore, StaleRevisionError } from '../core/store/ProjectStore';
import type { EditorState } from './state';

/**
 * Debounced autosave: every model change schedules a save ~1 s later. Saves never run
 * during Play (`state.project` is the runtime copy then; a pending save resumes on Stop)
 * and never overlap; a change that arrives while a save is in flight triggers another save
 * afterwards.
 */
export function attachAutosave(
  state: EditorState,
  store: ProjectStore,
  delayMs = 1000,
): { flush: () => Promise<void> } {
  let timer = 0;
  let saving: Promise<void> | null = null;
  let pending = false;

  const save = async (): Promise<void> => {
    if (saving) {
      pending = true;
      return saving;
    }
    if (state.saveStatus !== 'dirty' || !state.project.id || state.mode === 'play') return;
    state.setSaveStatus('saving');
    saving = (async () => {
      try {
        state.revision = await store.save(state.project, state.revision);
        state.setSaveStatus(pending ? 'dirty' : 'saved');
      } catch (error) {
        if (error instanceof StaleRevisionError) {
          state.setSaveStatus('conflict');
          state.setNotice('This project was changed elsewhere. Reload to continue.', 'error');
        } else {
          state.setSaveStatus('error');
          state.setNotice(
            `Saving failed: ${error instanceof Error ? error.message : String(error)}`,
            'error',
          );
        }
      } finally {
        saving = null;
        if (pending) {
          pending = false;
          if (state.saveStatus === 'dirty') schedule();
        }
      }
    })();
    return saving;
  };

  const schedule = (): void => {
    window.clearTimeout(timer);
    timer = window.setTimeout(() => void save(), delayMs);
  };

  state.on('save', () => {
    if (state.saveStatus === 'dirty') schedule();
  });

  const flush = async (): Promise<void> => {
    window.clearTimeout(timer);
    await save();
  };

  window.addEventListener('beforeunload', (event) => {
    if (state.saveStatus === 'dirty' || state.saveStatus === 'saving') {
      void flush();
      event.preventDefault();
    }
  });

  return { flush };
}