'use client';
import { usePathname, useRouter, useSearchParams } from 'next/navigation';
import { useCallback, useMemo, useRef } from 'react';

/**
 * URL state for the analytical views (explore, trajectories, scatter, finder, extremes…): every meaningful
 * piece of view state lives in the query string so a view is shareable and survives a reload. `replace`
 * batches rapid updates (a dragged slider) with `router.replace` and never scrolls.
 *
 *   const { get, set, url } = useUrlState();
 *   set({ year: 1990, indicator: 'gdp-per-capita' })   // null/undefined/'' remove the key
 */
import { applyPatch, type UrlPatch } from './url-params';
export { applyPatch, parseList, parseYear, type UrlPatch } from './url-params';

export function useUrlState(defaults: Record<string, string> = {}) {
  const router = useRouter();
  const pathname = usePathname();
  const params = useSearchParams();
  const pending = useRef<UrlPatch>({});
  const timer = useRef<ReturnType<typeof setTimeout> | null>(null);

  const get = useCallback((key: string): string | null => params.get(key) ?? defaults[key] ?? null, [params, defaults]);
  const getNum = useCallback(
    (key: string): number | null => {
      const v = params.get(key) ?? defaults[key];
      if (v == null || v === '') return null;
      const n = Number(v);
      return Number.isFinite(n) ? n : null;
    },
    [params, defaults],
  );

  const flush = useCallback(() => {
    const patch = pending.current;
    pending.current = {};
    timer.current = null;
    const next = applyPatch(new URLSearchParams(window.location.search), patch);
    // Drop keys equal to their default so canonical URLs stay short.
    for (const [k, v] of Object.entries(defaults)) if (next.get(k) === v) next.delete(k);
    const s = next.toString();
    router.replace(`${pathname}${s ? `?${s}` : ''}`, { scroll: false });
  }, [router, pathname, defaults]);

  /** Merge a patch into the URL; coalesces updates within `delay` ms (default 120 — slider friendly). */
  const set = useCallback(
    (patch: UrlPatch, delay = 120) => {
      pending.current = { ...pending.current, ...patch };
      if (timer.current) clearTimeout(timer.current);
      if (delay <= 0) flush();
      else timer.current = setTimeout(flush, delay);
    },
    [flush],
  );

  const url = useMemo(() => `${pathname}${params.toString() ? `?${params.toString()}` : ''}`, [pathname, params]);
  return { get, getNum, set, params, url } as const;
}