import { useEffect, useMemo, useState } from 'react';
import { Link } from 'react-router-dom';
import {
  Loader, Rocket, ArrowLeft, ChevronRight, CheckCircle2, Circle,
  Sparkles, ListChecks, PartyPopper,
} from 'lucide-react';
import Card from '../components/ui/Card';
import Button from '../components/ui/Button';
import Tag from '../components/ui/Tag';
import { useApp } from '../store/AppContext';
import {
  getOnboardingPlan,
  getCompletedThemes,
  getOrGenerateOnboardingOverview,
  markThemeCompleted,
  computeOnboardingProgress,
} from '../lib/onboardingService';

function normalizeContent(raw) {
  if (!raw) return null;
  if (typeof raw === 'string') {
    try { return JSON.parse(raw); } catch { return null; }
  }
  return raw;
}

// ── Per-theme overview view ──────────────────────────────────────────────────
function OnboardingThemeView({ theme, topics, done, onBack, onDone }) {
  const [record, setRecord] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const [marked, setMarked] = useState(done);

  useEffect(() => {
    let cancelled = false;
    setLoading(true);
    setError(null);
    getOrGenerateOnboardingOverview(theme, topics)
      .then((rec) => { if (!cancelled) setRecord(rec); })
      .catch((err) => { if (!cancelled) setError(err.message || 'Failed to load the overview.'); })
      .finally(() => { if (!cancelled) setLoading(false); });
    return () => { cancelled = true; };
  }, [theme]); // eslint-disable-line react-hooks/exhaustive-deps

  const content = normalizeContent(record?.content);

  const handleDone = async () => {
    if (marked) return;
    setMarked(true);
    await onDone(theme);
  };

  return (
    <div className="space-y-6">
      <button
        type="button"
        onClick={onBack}
        className="inline-flex items-center text-teal font-medium text-sm hover:underline"
      >
        <ArrowLeft size={16} className="mr-1" /> Back to overview
      </button>

      {loading && (
        <Card className="w-full text-center py-16">
          <Loader size={48} className="mx-auto text-teal animate-spin mb-4" />
          <p className="font-medium text-lg">Preparing this theme…</p>
          <p className="text-fg-muted text-sm mt-2">This may take 10–30 seconds the first time — the result is cached.</p>
        </Card>
      )}

      {!loading && error && (
        <Card className="w-full border border-red-200 bg-red-50 text-red-900 p-6">
          <p className="font-bold mb-1">Could not load this theme</p>
          <p className="text-sm">{error}</p>
        </Card>
      )}

      {!loading && !error && content && (
        <>
          <Card className="w-full p-6">
            <div className="flex items-center gap-2 mb-3">
              <Sparkles size={18} className="text-teal" />
              <Tag variant="dark" className="text-[10px] uppercase tracking-wide">Theme</Tag>
              {marked && <Tag variant="success" className="text-[10px]">Done</Tag>}
            </div>
            <h2 className="text-2xl md:text-3xl font-bold text-teal mb-2">{content.title}</h2>
            <p className="text-fg-muted">{content.what_it_is}</p>
          </Card>

          <Card className="w-full p-6">
            <h3 className="text-lg font-bold mb-2">Why it matters here</h3>
            <p className="text-fg-muted">{content.why_it_matters}</p>
          </Card>

          <Card className="w-full p-6">
            <h3 className="text-lg font-bold mb-3">Key points</h3>
            <ul className="list-disc pl-5 space-y-1 text-sm">
              {(content.key_points || []).map((p, i) => <li key={i}>{p}</li>)}
            </ul>
          </Card>

          {Array.isArray(content.topics_covered) && content.topics_covered.length > 0 && (
            <Card className="w-full p-6">
              <h3 className="text-lg font-bold mb-3">Topics in this theme</h3>
              <div className="flex flex-wrap gap-2">
                {content.topics_covered.map((t) => (
                  <Tag key={t.topic_id} variant="default" className="text-xs">{t.label}</Tag>
                ))}
              </div>
            </Card>
          )}

          <div className="flex justify-end">
            <Button onClick={handleDone} disabled={marked}>
              {marked
                ? <span className="flex items-center"><CheckCircle2 size={16} className="mr-2" /> Marked as done</span>
                : 'Mark as done'}
            </Button>
          </div>
        </>
      )}
    </div>
  );
}

// ── Progress ring ─────────────────────────────────────────────────────────────
function ProgressRing({ percentage }) {
  return (
    <div className="relative w-20 h-20 shrink-0">
      <svg viewBox="0 0 36 36" className="w-20 h-20 -rotate-90">
        <circle cx="18" cy="18" r="15.9155" fill="none" stroke="var(--bg-warm)" strokeWidth="3" />
        <circle
          cx="18" cy="18" r="15.9155" fill="none" stroke="var(--teal)" strokeWidth="3"
          strokeDasharray={`${percentage} 100`} strokeLinecap="round"
        />
      </svg>
      <div className="absolute inset-0 flex items-center justify-center text-sm font-bold">{percentage}%</div>
    </div>
  );
}

// ── Page ──────────────────────────────────────────────────────────────────────
export default function OnboardingTrack() {
  const { state } = useApp();
  const { currentUser } = state;

  const [plan, setPlan] = useState(null);
  const [completed, setCompleted] = useState(new Set());
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const [selectedTheme, setSelectedTheme] = useState(null);

  useEffect(() => {
    if (!currentUser) return;
    let cancelled = false;
    setLoading(true);
    Promise.all([getOnboardingPlan(), getCompletedThemes(currentUser.id)])
      .then(([p, done]) => { if (!cancelled) { setPlan(p); setCompleted(done); } })
      .catch((err) => { if (!cancelled) setError(err.message || 'Failed to load the onboarding track.'); })
      .finally(() => { if (!cancelled) setLoading(false); });
    return () => { cancelled = true; };
  }, [currentUser]);

  const progress = useMemo(
    () => computeOnboardingProgress(plan?.days || [], completed),
    [plan, completed],
  );

  const handleThemeDone = async (theme) => {
    await markThemeCompleted(currentUser.id, theme);
    setCompleted((prev) => new Set(prev).add(theme));
    setSelectedTheme(null);
  };

  if (loading) {
    return (
      <div className="p-6 md:p-10">
        <Card className="w-full text-center py-16">
          <Loader size={48} className="mx-auto text-teal animate-spin mb-4" />
          <p className="font-medium text-lg">Loading your onboarding track…</p>
        </Card>
      </div>
    );
  }

  if (error) {
    return (
      <div className="p-6 md:p-10">
        <Card className="w-full border border-red-200 bg-red-50 text-red-900 p-6">
          <p className="font-bold mb-1">Could not load the onboarding track</p>
          <p className="text-sm">{error}</p>
        </Card>
      </div>
    );
  }

  // Empty KB → friendly empty state.
  if (!plan || plan.themes.length === 0) {
    return (
      <div className="p-6 md:p-10 space-y-6">
        <header>
          <h1 className="text-3xl md:text-4xl font-bold mb-2 flex items-center gap-3"><Rocket size={28} className="text-teal" /> Onboarding</h1>
        </header>
        <Card className="w-full p-8 text-center">
          <p className="text-fg-muted">There are no themes to introduce yet. Once the knowledge base has content, your 5-day onboarding track will appear here.</p>
          <div className="mt-4"><Link to="/"><Button variant="outline">Back to dashboard</Button></Link></div>
        </Card>
      </div>
    );
  }

  const themeTopics = (theme) => plan.themeTopicMap.get(theme) || [];

  if (selectedTheme) {
    return (
      <div className="p-6 md:p-10 animate-in fade-in slide-in-from-bottom-4 duration-500">
        <OnboardingThemeView
          theme={selectedTheme}
          topics={themeTopics(selectedTheme)}
          done={completed.has(selectedTheme)}
          onBack={() => setSelectedTheme(null)}
          onDone={handleThemeDone}
        />
      </div>
    );
  }

  return (
    <div className="p-6 md:p-10 space-y-8 animate-in fade-in slide-in-from-bottom-4 duration-500">
      <header className="flex items-start justify-between gap-4">
        <div>
          <h1 className="text-3xl md:text-4xl font-bold mb-2 flex items-center gap-3"><Rocket size={28} className="text-teal" /> Onboarding</h1>
          <p className="text-fg-muted text-lg max-w-2xl">
            A light, self-paced tour of every theme at Respellion, spread over about five days.
            It gives you the breadth you need to understand how we work day to day and week to week —
            you can go faster if you like.
          </p>
        </div>
      </header>

      <Card className="border border-bg-warm">
        <div className="flex items-center gap-5">
          <ProgressRing percentage={progress.percentage} />
          <div className="flex-1">
            <p className="font-bold text-lg">
              {progress.allDone
                ? 'Onboarding complete'
                : `${progress.daysCompleted}/${progress.dayCount} days complete`}
            </p>
            <p className="text-fg-muted text-sm">{progress.themesDone} of {progress.themesTotal} themes done</p>
            <div className="flex gap-1.5 mt-3">
              {plan.days.map((d) => {
                const dayDone = d.themes.every((t) => completed.has(t));
                return (
                  <div
                    key={d.day}
                    title={`Day ${d.day}`}
                    className={`h-2 flex-1 rounded-full ${dayDone ? 'bg-teal' : 'bg-bg-warm'}`}
                  />
                );
              })}
            </div>
          </div>
        </div>
      </Card>

      {progress.allDone && (
        <Card className="w-full p-6 border border-teal/30 bg-sage/40">
          <div className="flex items-start gap-3">
            <PartyPopper size={24} className="text-teal shrink-0 mt-0.5" />
            <div>
              <h3 className="text-lg font-bold">You've completed the onboarding track 🎉</h3>
              <p className="text-fg-muted text-sm mt-1">
                You've been introduced to every theme. You're ready to pick up a first assignment —
                and you can revisit any theme below whenever you want a refresher.
              </p>
              <div className="mt-3"><Link to="/"><Button>Back to dashboard</Button></Link></div>
            </div>
          </div>
        </Card>
      )}

      <div className="space-y-6">
        {plan.days.map((d) => {
          const doneCount = d.themes.filter((t) => completed.has(t)).length;
          return (
            <Card key={d.day} className="p-0 border border-bg-warm overflow-hidden">
              <div className="flex items-center justify-between px-5 py-3 bg-bg-warm/40 border-b border-bg-warm">
                <div className="flex items-center gap-2">
                  <Tag variant="dark" className="text-[10px] uppercase tracking-wide">Day {d.day}</Tag>
                  <ListChecks size={16} className="text-fg-muted" />
                </div>
                <span className="text-sm text-fg-muted">{doneCount}/{d.themes.length} done</span>
              </div>
              <div className="divide-y divide-bg-warm">
                {d.themes.map((theme) => {
                  const isDone = completed.has(theme);
                  const count = themeTopics(theme).length;
                  return (
                    <button
                      key={theme}
                      type="button"
                      onClick={() => setSelectedTheme(theme)}
                      className="w-full flex items-center justify-between p-4 text-left hover:bg-bg-warm/30 transition-colors"
                    >
                      <div className="flex items-center gap-3">
                        {isDone
                          ? <CheckCircle2 size={20} className="text-teal shrink-0" />
                          : <Circle size={20} className="text-fg-muted/40 shrink-0" />}
                        <div>
                          <p className="font-medium">{theme}</p>
                          <p className="text-sm text-fg-muted">{count} {count === 1 ? 'topic' : 'topics'}</p>
                        </div>
                      </div>
                      <ChevronRight size={18} className="text-fg-muted" />
                    </button>
                  );
                })}
              </div>
            </Card>
          );
        })}
      </div>
    </div>
  );
}