// Insights: your studies seen together — this week's own work, themes (tags), words you keep studying,
// what slipped in recalls, and follow-ups still open.
import { useMemo } from 'react';
import { useApp } from '../context/AppContext.js';
import PageShell from '../components/study/PageShell.jsx';
import { loadProjectById } from '../utils/projectStorage.js';
import { followUpList, slippedList, themeIndex, weeklySummary, wordIndex } from '../utils/insights.js';

const card = 'rounded-2xl border border-[var(--r-line)] bg-[var(--r-bar)] p-5';
const open = 'text-xs text-[var(--r-accent)] hover:underline';

function Stat({ label, value }) {
  return (
    <div className="rounded-xl border border-[var(--r-line)] bg-[var(--r-bg)] px-4 py-3">
      <p className="text-2xl font-medium tabular-nums">{value}</p>
      <p className="text-xs text-[var(--r-sub)]">{label}</p>
    </div>
  );
}

export default function InsightsPage() {
  const { projectIndex, openStudyChunk, goHome } = useApp();
  const data = useMemo(() => {
    const projects = projectIndex.map((e) => loadProjectById(e.id)).filter(Boolean);
    return { week: weeklySummary(projects), themes: themeIndex(projects), words: wordIndex(projects), slipped: slippedList(projects), followUps: followUpList(projects) };
  }, [projectIndex]);
  const { week, themes, words, slipped, followUps } = data;
  const link = (item) => <button type="button" onClick={() => openStudyChunk(item.projectId, item.chunkId)} className={open}>{item.reference} · {item.projectTitle}</button>;

  return (
    <PageShell title="Insights" active="studies" onBack={goHome} maxWidth="max-w-4xl">
      <main className="mx-auto max-w-4xl space-y-5 px-4 pb-10">
        <section aria-label="This week" className={card}>
          <h2 className="text-sm font-medium">This week</h2>
          <p className="mb-3 mt-0.5 text-xs text-[var(--r-sub)]">Counted over the chunks you edited in the last 7 days. Pasted text isn’t counted as yours.</p>
          <div className="grid grid-cols-2 gap-3 sm:grid-cols-4">
            <Stat label="Chunks worked on" value={week.chunksTouched} />
            <Stat label="Words of your own" value={week.ownWords} />
            <Stat label="Your own words" value={week.ownShare === null ? '–' : `${week.ownShare}%`} />
            <Stat label="Recalls done" value={week.recalls} />
          </div>
          {(week.teachBacks > 0 || week.fiveMinutes > 0) && <p className="mt-2 text-xs text-[var(--r-sub)]">{[week.fiveMinutes > 0 && `${week.fiveMinutes} five-minute session${week.fiveMinutes === 1 ? '' : 's'}`, week.teachBacks > 0 && `${week.teachBacks} teach-it-back summar${week.teachBacks === 1 ? 'y' : 'ies'}`].filter(Boolean).join(' · ')} this week.</p>}
        </section>

        <section aria-label="Open follow-ups" className={card}>
          <h2 className="text-sm font-medium">Follow-ups</h2>
          {followUps.length === 0 ? <p className="mt-1 text-xs text-[var(--r-sub)]">None yet. Add them under “More” in the Study stage.</p> : (
            <ul className="mt-2 space-y-1.5 text-sm">
              {followUps.map((f) => (
                <li key={f.id} className="flex flex-wrap items-baseline gap-x-3">
                  <span className={f.done ? 'text-[var(--r-sub)] line-through' : ''}>{f.text}</span>
                  {link(f)}
                </li>
              ))}
            </ul>
          )}
        </section>

        <section aria-label="What slipped" className={card}>
          <h2 className="text-sm font-medium">What slipped in recalls</h2>
          {slipped.length === 0 ? <p className="mt-1 text-xs text-[var(--r-sub)]">Nothing yet. After a weekly recall, note what you missed.</p> : (
            <ul className="mt-2 space-y-3 text-sm">
              {slipped.map((r) => (
                <li key={`${r.chunkId}-${r.at}`}>
                  <p className="text-xs text-[var(--r-sub)]">{new Date(r.at).toLocaleDateString()} · {link(r)}</p>
                  <ul className="ml-4 list-disc">{r.items.map((i) => <li key={i}>{i}</li>)}</ul>
                </li>
              ))}
            </ul>
          )}
        </section>

        <section aria-label="Themes" className={card}>
          <h2 className="text-sm font-medium">Themes</h2>
          {themes.length === 0 ? <p className="mt-1 text-xs text-[var(--r-sub)]">Tag a chunk (under “More”) and it appears here with every other chunk on the same theme.</p> : (
            <div className="mt-2 space-y-3">
              {themes.map((t) => (
                <details key={t.tag} className="rounded-xl border border-[var(--r-line)] bg-[var(--r-bg)] px-3 py-2">
                  <summary className="cursor-pointer text-sm"><span className="font-medium">{t.tag}</span> <span className="text-xs text-[var(--r-sub)]">· {t.count} chunk{t.count === 1 ? '' : 's'}</span></summary>
                  <ul className="mt-2 space-y-2">
                    {t.items.map((i) => (
                      <li key={`${i.chunkId}`} className="text-sm">{link(i)}{i.snippet && <p className="font-serif text-[13px] text-[var(--r-sub)]">{i.snippet}</p>}</li>
                    ))}
                  </ul>
                </details>
              ))}
            </div>
          )}
        </section>

        <section aria-label="Words you keep studying" className={card}>
          <h2 className="text-sm font-medium">Words you keep studying</h2>
          {words.length === 0 ? <p className="mt-1 text-xs text-[var(--r-sub)]">Words you study in two or more places show up here.</p> : (
            <ul className="mt-2 space-y-2 text-sm">
              {words.map((w) => (
                <li key={w.key}>
                  <span className="font-serif text-base">{w.lexeme}</span> <span className="text-xs text-[var(--r-sub)]">{[w.transliteration, w.strong, w.gloss].filter(Boolean).join(' · ')} · {w.count} places</span>
                  <span className="mt-0.5 flex flex-wrap gap-x-3">{w.places.map((p) => <span key={p.chunkId}>{link(p)}</span>)}</span>
                </li>
              ))}
            </ul>
          )}
        </section>
      </main>
    </PageShell>
  );
}