// Export → Earlier versions: the copies the server kept of this study as you worked. Look at what is different
// from now, and put one back. The version you replace is kept, so putting one back can be undone too.
import { useCallback, useEffect, useState } from 'react';
import { getStudyVersion, listStudyVersions } from '../syncService.js';
import { describeDiff, diffProjects } from '../utils/projectDiff.js';

const btn = 'rounded-lg border border-[var(--r-line)] px-3 py-1.5 text-xs hover:bg-black/5 disabled:opacity-50';

export default function VersionHistory({ project, onRestore }) {
  const [state, setState] = useState({ status: 'loading', versions: [] });
  const [open, setOpen] = useState(null); // { id, lines } the version being looked at
  const [busy, setBusy] = useState(false);
  const [error, setError] = useState('');

  const load = useCallback(async () => {
    if (!project?.id) return;
    const r = await listStudyVersions(project.id);
    setState(r.ok ? { status: 'ready', versions: r.data.versions } : { status: 'unavailable', versions: [] });
  }, [project?.id]);
  useEffect(() => { load(); }, [load]);

  const preview = async (v) => {
    if (open?.id === v.id) { setOpen(null); return; }
    setError('');
    const r = await getStudyVersion(project.id, v.id);
    if (!r.ok) { setError(r.error ?? 'Could not open that version.'); return; }
    setOpen({ id: v.id, lines: describeDiff(diffProjects(project, r.data)) });
  };
  const restore = async (v) => {
    if (!window.confirm(`Put back the version from ${new Date(v.savedAt).toLocaleString()}? What you have now is kept in this list, so you can undo it.`)) return;
    setBusy(true); setError('');
    const ok = await onRestore(v.id);
    setBusy(false);
    if (ok) { setOpen(null); load(); } else setError('Could not restore that version. Check your connection and try again.');
  };

  return (
    <section className="rounded-2xl border border-[var(--r-line)] bg-[var(--r-bar)] p-5" aria-label="Earlier versions">
      <h2 className="text-sm font-medium">Earlier versions</h2>
      <p className="mb-3 mt-1 text-xs text-[var(--r-sub)]">As you work, your account keeps earlier copies of this study (about one for every ten minutes of editing, the latest 30). Use one to undo a bad merge or a deletion.</p>
      {state.status === 'loading' && <p className="text-xs text-[var(--r-sub)]">Loading…</p>}
      {state.status === 'unavailable' && <p className="text-xs text-[var(--r-sub)]">Earlier versions need your account and a connection, and the study has to have synced once.</p>}
      {state.status === 'ready' && state.versions.length === 0 && <p className="text-xs text-[var(--r-sub)]">Nothing kept yet. The first earlier version appears after you’ve changed the study a couple of times.</p>}
      {state.versions.length > 0 && (
        <ul className="divide-y divide-[var(--r-line)] text-sm">
          {state.versions.map((v) => (
            <li key={v.id} className="py-2">
              <div className="flex flex-wrap items-center justify-between gap-2">
                <span><span className="font-medium">{new Date(v.savedAt).toLocaleString()}</span> <span className="text-xs text-[var(--r-sub)]">{v.chunks} chunk{v.chunks === 1 ? '' : 's'} · {v.words} words</span></span>
                <span className="flex gap-2">
                  <button type="button" onClick={() => preview(v)} aria-expanded={open?.id === v.id} className={btn}>{open?.id === v.id ? 'Hide' : 'What’s different'}</button>
                  <button type="button" onClick={() => restore(v)} disabled={busy} className={btn}>Put this back</button>
                </span>
              </div>
              {open?.id === v.id && (
                <ul className="mt-2 list-disc space-y-0.5 rounded-lg bg-[var(--r-bg)] py-2 pl-7 pr-3 text-xs text-[var(--r-sub)]">
                  {open.lines.map((line) => <li key={line}>{line}</li>)}
                </ul>
              )}
            </li>
          ))}
        </ul>
      )}
      {error && <p role="alert" className="mt-2 text-xs text-[var(--r-danger,#b42318)]">{error}</p>}
    </section>
  );
}