import { useCallback, useEffect, useState } from 'react';
import { decodeState, encodeState } from './url-state';
import { reduceProject } from './project-state';
import type { ProjectAction } from './project-state';

export const PROJECT_STORAGE_KEY = 'floor-planner.project';

function readLocation() {
  const link = window.location.search;
  if (link && link !== '?' && link !== '?planner') return decodeState(link);
  try {
    const saved = decodeState(window.localStorage.getItem(PROJECT_STORAGE_KEY) ?? '');
    if (!saved.error) return saved;
  } catch {
    /* Storage may be unavailable. */
  }
  return decodeState('');
}

/** React owns live state. Persistence is an output between navigations. */
export function useProject() {
  const [loaded, setLoaded] = useState(() => ({ ...readLocation(), milestone: false }));
  useEffect(() => {
    const restore = () => setLoaded({ ...readLocation(), milestone: false });
    window.addEventListener('popstate', restore);
    return () => window.removeEventListener('popstate', restore);
  }, []);
  useEffect(() => {
    if (loaded.error) return;
    try {
      const query = encodeState(loaded.state);
      if (query !== window.location.search || window.location.hash)
        window.history[loaded.milestone ? 'pushState' : 'replaceState'](
          null,
          '',
          `${window.location.pathname}${query}`,
        );
      try {
        window.localStorage.setItem(PROJECT_STORAGE_KEY, query);
      } catch {
        /* The URL remains available if storage is blocked or full. */
      }
    } catch (error) {
      // Keep edits usable even if the browser cannot save this link.
      setLoaded((current) =>
        current === loaded
          ? {
              ...current,
              error: error instanceof Error ? error.message : 'This plan could not be saved.',
            }
          : current,
      );
    }
  }, [loaded]);
  const dispatch = useCallback((action: ProjectAction) => {
    setLoaded((current) => ({
      state: reduceProject(current.state, action),
      error: null,
      milestone:
        action.type === 'addRoom' || action.type === 'removeRoom' || action.type === 'visitRoom',
    }));
  }, []);
  return { ...loaded, dispatch };
}