import { useState, useEffect } from 'react';
import type { CourseModuleV2 } from '../../types/getcertV2';
import { NapkinSpinner } from '../NapkinSpinner';
import { 
  Clock, 
  CheckCircle2, 
  ExternalLink, 
  FileText, 
  BookOpen, 
  Paperclip, 
  ListChecks, 
  Target, 
  FlaskConical, 
  Lock, 
  ArrowRight, 
  ArrowLeft,
  Tv,
  GraduationCap,
  Layers,
  Link2
} from 'lucide-react';
import { resolveCanonicalCourseTitle } from '../../utils/courseTitleResolver';

interface LearningModuleProps {
  courseName: string;
  courseSummary: string;
  modules: CourseModuleV2[];
  onTakeAssessment: () => void;
  onBackToDashboard: () => void;
  generatingAssessment?: boolean;
  completedModuleIds?: string[] | null;
  onCompletedModulesChange?: (ids: string[]) => void;
}

export function formatDurationSeconds(totalSeconds: number): string {
  if (!totalSeconds || isNaN(totalSeconds) || totalSeconds <= 0) return '';
  const hours = Math.floor(totalSeconds / 3600);
  const minutes = Math.floor((totalSeconds % 3600) / 60);
  const seconds = totalSeconds % 60;

  if (hours > 0) {
    if (minutes > 0 && seconds > 0) return `${hours}h ${minutes}m ${seconds}s`;
    if (minutes > 0) return `${hours}h ${minutes}m`;
    if (seconds > 0) return `${hours}h ${seconds}s`;
    return `${hours}h`;
  }
  if (minutes > 0) {
    return seconds > 0 ? `${minutes}m ${seconds}s` : `${minutes}m`;
  }
  return `${seconds}s`;
}

function extractYouTubeVideoId(url: string): string | null {
  const value = url.trim();
  const patterns = [
    /youtube\.com\/watch\?v=([a-zA-Z0-9_-]{11})/,
    /youtu\.be\/([a-zA-Z0-9_-]{11})/,
    /youtube\.com\/embed\/([a-zA-Z0-9_-]{11})/,
    /youtube\.com\/shorts\/([a-zA-Z0-9_-]{11})/,
  ];

  for (const pattern of patterns) {
    const match = value.match(pattern);
    if (match?.[1]) {
      return match[1];
    }
  }

  return null;
}

export function LearningModule({
  courseName,
  courseSummary,
  modules,
  onTakeAssessment,
  onBackToDashboard,
  generatingAssessment = false,
  completedModuleIds = null,
  onCompletedModulesChange,
}: LearningModuleProps) {
  const [localCompleted, setLocalCompleted] = useState<Set<string>>(new Set());

  const completedModules = new Set<string>(
    completedModuleIds !== null && completedModuleIds !== undefined ? completedModuleIds : [...localCompleted],
  );

  // Active module currently being watched/studied
  const [activeModuleId, setActiveModuleId] = useState<string>(() => {
    if (!modules || modules.length === 0) return '';
    const firstUncompleted = modules.find((m) => !completedModules.has(m.id));
    return firstUncompleted ? firstUncompleted.id : modules[0].id;
  });

  // Active tab in the lesson briefing section
  const [activeTab, setActiveTab] = useState<'notes' | 'takeaways' | 'resources' | 'syllabus'>('notes');

  const activeModule = modules.find((m) => m.id === activeModuleId) || modules[0] || null;
  const activeModuleIndex = modules.findIndex((m) => m.id === (activeModule?.id || ''));

  const markModuleComplete = (moduleId: string) => {
    if (completedModules.has(moduleId)) return;
    const next = new Set([...completedModules, moduleId]);
    if (onCompletedModulesChange) {
      onCompletedModulesChange(modules.filter((m) => next.has(m.id)).map((m) => m.id));
    } else {
      setLocalCompleted(next);
    }
  };

  const allModulesCompleted = modules.length > 0 && completedModules.size === modules.length;
  const isActiveCompleted = activeModule ? completedModules.has(activeModule.id) : false;

  // Extract video and other resources for active module
  const activeResources = activeModule?.resources || [];
  const parsedVideoResources = activeResources.map((resource) => ({
    resource,
    videoId: resource.type === 'youtube' ? extractYouTubeVideoId(resource.url) : null,
  }));

  const primaryVideo = parsedVideoResources.find((item) => !!item.videoId) || null;
  const secondaryVideos = parsedVideoResources.filter((item) => !!item.videoId && item !== primaryVideo);
  const linkedResources = parsedVideoResources.filter((item) => !item.videoId);

  const completionPercent = modules.length === 0 ? 0 : Math.round((completedModules.size / modules.length) * 100);

  // Map of videoId -> formatted duration string (e.g. '26m 52s', '20h 47m')
  const [videoDurations, setVideoDurations] = useState<Record<string, string>>({});

  // 1. Initial resolution from pre-cached or resource duration metadata
  useEffect(() => {
    const initialMap: Record<string, string> = {};
    modules.forEach((mod) => {
      mod.resources?.forEach((res) => {
        if (res.type === 'youtube') {
          const id = extractYouTubeVideoId(res.url);
          if (
            id &&
            res.duration &&
            !res.duration.includes('>20m') &&
            !res.duration.includes('Full Course')
          ) {
            initialMap[id] = res.duration;
          }
        }
      });
    });
    if (Object.keys(initialMap).length > 0) {
      setVideoDurations((prev) => ({ ...initialMap, ...prev }));
    }
  }, [modules]);

  // 2. Query /api/v2/video-info for exact server-verified duration
  useEffect(() => {
    const videoIdsToFetch = new Set<string>();
    modules.forEach((mod) => {
      mod.resources?.forEach((res) => {
        if (res.type === 'youtube') {
          const id = extractYouTubeVideoId(res.url);
          const current = videoDurations[id] || (res as any)?.duration || '';
          if (
            id &&
            (!current ||
              current.includes('>20m') ||
              current.includes('Full Course') ||
              current.includes('Loading'))
          ) {
            videoIdsToFetch.add(id);
          }
        }
      });
    });

    videoIdsToFetch.forEach((vid) => {
      fetch(`/api/v2/video-info?videoId=${encodeURIComponent(vid)}`)
        .then((res) => (res.ok ? res.json() : null))
        .then((payload) => {
          if (payload?.success && payload?.data?.durationFormatted) {
            setVideoDurations((prev) => ({
              ...prev,
              [vid]: payload.data.durationFormatted,
            }));
          }
        })
        .catch(() => {});
    });
  }, [modules, videoDurations]);

  // 3. Client-side YouTube Iframe postMessage listener (real-time zero latency)
  useEffect(() => {
    const handleMessage = (event: MessageEvent) => {
      try {
        if (
          typeof event.origin === 'string' &&
          !event.origin.includes('youtube.com') &&
          !event.origin.includes('youtube-nocookie.com')
        ) {
          return;
        }
        const data = typeof event.data === 'string' ? JSON.parse(event.data) : event.data;
        const currentVid = primaryVideo?.videoId;
        if (data?.event === 'infoDelivery' && data?.info?.duration && currentVid) {
          const seconds = Math.round(data.info.duration);
          if (seconds > 0) {
            const formatted = formatDurationSeconds(seconds);
            setVideoDurations((prev) => {
              if (prev[currentVid] === formatted) return prev;
              return { ...prev, [currentVid]: formatted };
            });
          }
        }
      } catch {}
    };

    window.addEventListener('message', handleMessage);
    return () => window.removeEventListener('message', handleMessage);
  }, [primaryVideo?.videoId]);

  const activeVideoId = primaryVideo?.videoId || null;
  const rawActiveDur = activeVideoId
    ? (videoDurations[activeVideoId] || (primaryVideo?.resource as any)?.duration || '')
    : '';
  const activeDurationFormatted =
    rawActiveDur && !rawActiveDur.includes('>20m') && !rawActiveDur.includes('Full Course')
      ? rawActiveDur
      : '';

  const displayCourseName = resolveCanonicalCourseTitle(courseName);

  return (
    <div className="bg-slate-50 min-h-screen text-slate-900 font-sans pb-28 lg:pb-16">
      
      {/* 1. Institutional Header Strip */}
      <header className="border-b border-slate-200 bg-white/95 backdrop-blur-md sticky top-0 z-40 px-3 sm:px-6 py-2.5 sm:py-3 shadow-xs">
        <div className="max-w-7xl mx-auto flex items-center justify-between gap-2">
          
          {/* Back button + Course Title */}
          <div className="flex items-center gap-2.5 sm:gap-3 min-w-0">
            <button
              onClick={onBackToDashboard}
              className="inline-flex items-center gap-1.5 text-xs font-semibold text-slate-700 hover:text-slate-900 px-2.5 sm:px-3.5 py-1.5 rounded-lg bg-slate-50 hover:bg-slate-100 border border-slate-200 transition-colors shrink-0"
              title="Return to Dashboard"
            >
              <ArrowLeft className="w-3.5 h-3.5" />
              <span className="hidden sm:inline">Back to Dashboard</span>
              <span className="sm:hidden">Exit</span>
            </button>

            <div className="h-4 w-px bg-slate-200 shrink-0"></div>

            <div className="min-w-0 flex-1">
              <div className="hidden sm:flex items-center gap-1.5">
                <span className="w-1.5 h-1.5 rounded-full bg-blue-600" />
                <span className="text-[10px] sm:text-[11px] font-semibold uppercase tracking-wider text-slate-500 truncate">
                  ACTIVE ACCREDITATION TRACK
                </span>
              </div>
              <div className="flex items-center gap-1.5 min-w-0">
                <h2 className="text-sm sm:text-base md:text-lg font-bold text-slate-900 leading-tight truncate tracking-tight" title={displayCourseName}>
                  {displayCourseName}
                </h2>
              </div>
            </div>
          </div>

          {/* Progress Indicator */}
          <div className="flex items-center gap-2.5 shrink-0">
            <div className="flex items-center gap-1.5 bg-blue-50 px-2.5 py-1 rounded-full border border-blue-200/80 text-xs">
              <span className="text-[11px] sm:text-xs text-[#132F50] font-semibold">
                {completionPercent}% Ready
              </span>
            </div>
          </div>

        </div>
      </header>

      {/* 2. Main Studio Workspace */}
      <main className="max-w-7xl mx-auto px-0 sm:px-4 lg:px-6 pt-0 sm:pt-6">
        <div className="grid grid-cols-1 lg:grid-cols-12 gap-0 lg:gap-6 items-start">

          {/* LEFT: Cinema Video Stage + Interactive Lesson Workbook (12 cols mobile, 8 cols desktop) */}
          <div className="lg:col-span-8 flex flex-col">

            {/* VIDEO PLAYER CHASSIS */}
            <div className="relative">
              <div className="overflow-hidden bg-slate-950 sm:p-2 sm:rounded-2xl border border-slate-800 shadow-sm relative">
                
                {/* 16:9 Video Canvas */}
                <div className="relative w-full aspect-video bg-black overflow-hidden sm:rounded-xl">
                  {primaryVideo?.videoId ? (
                    <iframe
                      id="course-video-iframe"
                      className="absolute inset-0 w-full h-full"
                      src={`https://www.youtube-nocookie.com/embed/${primaryVideo.videoId}?rel=0&modestbranding=1&enablejsapi=1`}
                      title={primaryVideo.resource.title}
                      loading="eager"
                      allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share"
                      referrerPolicy="strict-origin-when-cross-origin"
                      allowFullScreen
                    />
                  ) : (
                    <div className="absolute inset-0 flex flex-col items-center justify-center p-6 text-center text-slate-300">
                      <div className="w-12 h-12 rounded-full bg-slate-800 border border-slate-700 flex items-center justify-center text-xl mb-3 text-slate-400">
                        <Tv className="w-6 h-6" />
                      </div>
                      <h4 className="font-bold text-sm text-white mb-1">
                        Lecture Reference Available
                      </h4>
                      <p className="text-xs text-slate-400 max-w-sm mb-4">
                        {activeModule?.title || 'This module contains direct interactive reading references.'}
                      </p>
                      {activeResources[0]?.url && (
                        <a
                          href={activeResources[0].url}
                          target="_blank"
                          rel="noreferrer"
                          className="bg-[#132F50] hover:bg-[#0e233d] text-white text-xs font-semibold px-4 py-2 rounded-lg flex items-center gap-1.5 transition-colors"
                        >
                          <span>Open Resource</span>
                          <ExternalLink className="w-3.5 h-3.5" />
                        </a>
                      )}
                    </div>
                  )}
                </div>

                {/* Video Sub-Bar */}
                <div className="bg-slate-950 text-white px-3 sm:px-4 py-2 sm:py-2.5 flex items-center justify-between text-xs border-t sm:border-t-0 sm:mt-1 sm:rounded-lg border-slate-800">
                  <div className="flex items-center gap-2 truncate">
                    {activeDurationFormatted && (
                      <span className="bg-slate-800 text-blue-300 text-[10px] px-2 py-0.5 rounded font-mono font-medium shrink-0">
                        {activeDurationFormatted}
                      </span>
                    )}
                    <span className="text-xs font-medium text-slate-300 truncate">
                      {primaryVideo?.resource.title || activeModule?.title}
                    </span>
                  </div>

                  {primaryVideo?.resource.url && (
                    <div className="flex items-center gap-3 shrink-0 ml-2">
                      <a
                        href={primaryVideo.resource.url}
                        target="_blank"
                        rel="noreferrer"
                        className="text-[11px] text-blue-400 hover:text-blue-300 flex items-center gap-1 font-medium transition-colors"
                      >
                        <span>YouTube Source</span>
                        <ExternalLink className="w-3 h-3" />
                      </a>
                    </div>
                  )}
                </div>

              </div>
            </div>

            {/* LESSON DETAILS & ACTION RIBBON */}
            <div className="px-4 py-4 sm:px-0">
              
              <div className="flex flex-col sm:flex-row sm:items-center justify-between gap-3 pb-4 border-b border-slate-200">
                <div>
                  <div className="flex items-center gap-2 mb-1.5 flex-wrap">
                    <span className="bg-blue-50 text-[#132F50] border border-blue-200/80 font-semibold text-[10px] px-2.5 py-0.5 rounded-full uppercase tracking-wider">
                      Module {activeModuleIndex + 1} of {modules.length}
                    </span>
                    <span className="text-xs text-slate-600 font-medium inline-flex items-center gap-1 bg-slate-100 px-2 py-0.5 rounded-md">
                      <Clock className="w-3.5 h-3.5 text-slate-500 shrink-0" />
                      {activeDurationFormatted ? (
                        <span>{activeDurationFormatted}</span>
                      ) : (
                        <span className="text-slate-400 font-mono text-xs">Runtime indexing...</span>
                      )}
                    </span>
                    
                    {isActiveCompleted && (
                      <span className="bg-emerald-50 text-emerald-800 text-[10px] px-2.5 py-0.5 rounded-full border border-emerald-200 font-semibold flex items-center gap-1">
                        <CheckCircle2 className="w-3 h-3 text-emerald-600 shrink-0" />
                        <span>Completed</span>
                      </span>
                    )}
                  </div>

                  <h1 className="text-lg sm:text-xl font-extrabold text-slate-900 leading-tight">
                    {activeModule?.title}
                  </h1>
                </div>

                {/* Desktop Quick Complete Button */}
                <div className="hidden sm:flex items-center gap-2 shrink-0">
                  {activeModule && (
                    isActiveCompleted ? (
                      <div className="bg-emerald-50 text-emerald-800 border border-emerald-200 text-xs font-semibold px-3 py-1.5 rounded-lg flex items-center gap-1.5">
                        <CheckCircle2 className="w-3.5 h-3.5 text-emerald-600" />
                        <span>Module Completed</span>
                      </div>
                    ) : (
                      <button
                        onClick={() => markModuleComplete(activeModule.id)}
                        className="bg-[#132F50] hover:bg-[#0e233d] text-white font-semibold text-xs px-4 py-2 rounded-lg flex items-center gap-1.5 transition-all shadow-xs cursor-pointer active:scale-[0.98]"
                      >
                        <CheckCircle2 className="w-3.5 h-3.5" />
                        <span>Mark Module Done</span>
                      </button>
                    )
                  )}
                </div>
              </div>

              {/* SEGMENTED TABS */}
              <div className="mt-4 flex items-center gap-2 overflow-x-auto pb-1 text-xs font-semibold scrollbar-none">
                <button
                  onClick={() => setActiveTab('notes')}
                  className={`px-3.5 py-2 rounded-lg shrink-0 flex items-center gap-1.5 transition-all cursor-pointer ${
                    activeTab === 'notes'
                      ? 'bg-[#132F50] text-white shadow-2xs'
                      : 'bg-white text-slate-600 hover:bg-slate-100 border border-slate-200'
                  }`}
                >
                  <BookOpen className="w-3.5 h-3.5" />
                  <span>Lesson Notes</span>
                </button>

                <button
                  onClick={() => setActiveTab('takeaways')}
                  className={`px-3.5 py-2 rounded-lg shrink-0 flex items-center gap-1.5 transition-all cursor-pointer ${
                    activeTab === 'takeaways'
                      ? 'bg-[#132F50] text-white shadow-2xs'
                      : 'bg-white text-slate-600 hover:bg-slate-100 border border-slate-200'
                  }`}
                >
                  <Layers className="w-3.5 h-3.5" />
                  <span>Key Principles</span>
                </button>

                <button
                  onClick={() => setActiveTab('resources')}
                  className={`px-3.5 py-2 rounded-lg shrink-0 flex items-center gap-1.5 transition-all cursor-pointer ${
                    activeTab === 'resources'
                      ? 'bg-[#132F50] text-white shadow-2xs'
                      : 'bg-white text-slate-600 hover:bg-slate-100 border border-slate-200'
                  }`}
                >
                  <Paperclip className="w-3.5 h-3.5" />
                  <span>Documentation & References ({linkedResources.length})</span>
                </button>

                {/* Full Syllabus Tab for mobile/tablets */}
                <button
                  onClick={() => setActiveTab('syllabus')}
                  className={`lg:hidden px-3.5 py-2 rounded-lg shrink-0 flex items-center gap-1.5 transition-all cursor-pointer ${
                    activeTab === 'syllabus'
                      ? 'bg-blue-600 text-white shadow-2xs'
                      : 'bg-blue-50 text-blue-900 border border-blue-200'
                  }`}
                >
                  <ListChecks className="w-3.5 h-3.5" />
                  <span>Syllabus Playlist ({modules.length})</span>
                </button>
              </div>

              {/* TAB CONTENT PANELS */}
              <div className="mt-4 space-y-4">
                
                {/* 1. LESSON NOTES TAB */}
                {activeTab === 'notes' && (
                  <div className="bg-white rounded-2xl border border-slate-200/90 p-5 sm:p-6 shadow-xs space-y-4">
                    <div>
                      <div className="flex items-center gap-2 mb-2">
                        <span className="text-sm font-bold text-slate-900 uppercase tracking-wider">
                          Session Learning Objectives:
                        </span>
                      </div>
                      <p className="text-xs sm:text-sm text-slate-600 leading-relaxed font-normal">
                        {activeModule?.description || courseSummary}
                      </p>
                    </div>

                    {/* Certification Exam Intel Callout */}
                    <div className="p-4 bg-blue-50/70 border border-blue-200/80 rounded-xl">
                      <div className="flex items-start gap-3">
                        <Target className="w-4 h-4 text-blue-700 shrink-0 mt-0.5" />
                        <div>
                          <span className="text-xs font-bold text-blue-950 uppercase tracking-wider block">
                            Certification Exam Telemetry:
                          </span>
                          <p className="text-xs text-blue-900/90 mt-1 leading-relaxed font-normal">
                            Pay close attention to practical syntax and underlying logic in this video. The final proctored evaluation creates dynamic scenario questions derived directly from this module's technical audio transcripts.
                          </p>
                        </div>
                      </div>
                    </div>

                    {/* Secondary video embeds if module has more than one */}
                    {secondaryVideos.length > 0 && (
                      <div className="mt-4 pt-4 border-t border-slate-100 space-y-3">
                        <span className="text-xs font-semibold uppercase text-slate-500 tracking-wider">
                          Supplemental Video Exercises:
                        </span>
                        {secondaryVideos.map(({ resource, videoId }, idx) => (
                          <div key={idx} className="rounded-xl border border-slate-200 p-3 bg-slate-50">
                            <div className="aspect-video rounded-lg overflow-hidden bg-black mb-2">
                              <iframe
                                src={`https://www.youtube-nocookie.com/embed/${videoId}?rel=0`}
                                title={resource.title}
                                className="w-full h-full"
                                allowFullScreen
                              />
                            </div>
                            <div className="text-xs font-semibold text-slate-800">{resource.title}</div>
                          </div>
                        ))}
                      </div>
                    )}
                  </div>
                )}

                {/* 2. ARCHITECTURE TAKEAWAYS TAB */}
                {activeTab === 'takeaways' && (
                  <div className="bg-white rounded-2xl border border-slate-200/90 p-5 sm:p-6 shadow-xs space-y-4">
                    <h3 className="text-sm font-bold text-slate-900 uppercase tracking-wider mb-2">
                      Core Engineering Principles & Best Practices:
                    </h3>

                    <div className="grid grid-cols-1 sm:grid-cols-2 gap-3 text-xs">
                      <div className="bg-slate-50 border border-slate-200 rounded-xl p-3.5">
                        <span className="font-semibold text-slate-900 mb-1 flex items-center gap-1.5">
                          <Target className="w-3.5 h-3.5 text-blue-600" /> Core Objective
                        </span>
                        <p className="text-slate-600 leading-relaxed font-normal mt-1">
                          Build deep mental models rather than memorizing syntax. Understand failure modes and debugging strategies.
                        </p>
                      </div>

                      <div className="bg-slate-50 border border-slate-200 rounded-xl p-3.5">
                        <span className="font-semibold text-slate-900 mb-1 flex items-center gap-1.5">
                          <FlaskConical className="w-3.5 h-3.5 text-blue-600" /> Verification Focus
                        </span>
                        <p className="text-slate-600 leading-relaxed font-normal mt-1">
                          Recruiter-verifiable diplomas grade candidates on situational problem solving, architecture design, and code safety.
                        </p>
                      </div>
                    </div>

                    <div className="pt-3 border-t border-slate-100">
                      <h4 className="text-xs font-semibold uppercase text-slate-500 mb-1.5 tracking-wider">Course Synopsis:</h4>
                      <p className="text-xs text-slate-600 leading-relaxed font-normal">{courseSummary}</p>
                    </div>
                  </div>
                )}

                {/* 3. CHEATSHEETS & ATTACHMENTS TAB */}
                {activeTab === 'resources' && (
                  <div className="bg-white rounded-2xl border border-slate-200/90 p-5 sm:p-6 shadow-xs space-y-3">
                    <h3 className="text-xs uppercase tracking-wider text-slate-500 font-semibold mb-3 flex items-center gap-1.5">
                      <Paperclip className="w-3.5 h-3.5" />
                      <span>Documentation, Code & Official References</span>
                    </h3>

                    {linkedResources.length === 0 ? (
                      <p className="text-xs text-slate-500 italic py-2 font-normal">
                        All study materials for this module are incorporated directly in the primary video lecture above.
                      </p>
                    ) : (
                      <div className="space-y-2.5">
                        {linkedResources.map(({ resource }, idx) => (
                          <a
                            key={idx}
                            href={resource.url}
                            target="_blank"
                            rel="noreferrer"
                            className="flex items-center justify-between p-3.5 rounded-xl border border-slate-200 hover:border-[#132F50] bg-slate-50/50 hover:bg-blue-50/30 transition-all text-xs group"
                          >
                            <div className="flex items-center gap-2.5">
                              <span className="text-[#132F50] text-sm">
                                {resource.type === 'documentation' ? (
                                  <FileText className="w-4 h-4" />
                                ) : (
                                  <Link2 className="w-4 h-4" />
                                )}
                              </span>
                              <div>
                                <div className="font-semibold text-slate-800 group-hover:text-blue-700 transition-colors">
                                  {resource.title}
                                </div>
                                <div className="text-[10px] text-slate-400 font-mono">
                                  Type: {resource.type}
                                </div>
                              </div>
                            </div>
                            <span className="text-xs font-semibold text-[#132F50] group-hover:text-blue-700 flex items-center gap-1">
                              <span>Open</span>
                              <ExternalLink className="w-3 h-3" />
                            </span>
                          </a>
                        ))}
                      </div>
                    )}
                  </div>
                )}

                {/* 4. FULL SYLLABUS TAB (MOBILE / TABLET) */}
                {activeTab === 'syllabus' && (
                  <div className="bg-white rounded-2xl border border-slate-200/90 p-5 sm:p-6 shadow-xs space-y-3 lg:hidden">
                    <h3 className="text-xs uppercase tracking-wider text-slate-500 font-semibold mb-2">
                      Tap any module to switch video:
                    </h3>

                    <div className="space-y-2.5">
                      {modules.map((module, idx) => {
                        const isDone = completedModules.has(module.id);
                        const isCurrent = module.id === activeModuleId;
                        const modYt = module.resources?.find((r) => r.type === 'youtube');
                        const modVid = modYt ? extractYouTubeVideoId(modYt.url) : null;
                        const modDur = modVid ? (videoDurations[modVid] || (modYt as any)?.duration || '') : '';

                        return (
                          <div
                            key={module.id}
                            onClick={() => {
                              setActiveModuleId(module.id);
                              setActiveTab('notes');
                              window.scrollTo({ top: 0, behavior: 'smooth' });
                            }}
                            className={`p-3.5 rounded-xl border transition-all cursor-pointer ${
                              isCurrent
                                ? 'border-[#132F50] bg-blue-50/70 shadow-xs'
                                : 'border-slate-200 hover:border-slate-300 bg-white'
                            }`}
                          >
                            <div className="flex items-center justify-between text-[10px] font-mono mb-1">
                              <span className={isCurrent ? 'text-blue-700 font-bold' : 'text-slate-400'}>
                                {isCurrent ? 'NOW PLAYING' : `MODULE ${idx + 1}`}
                              </span>
                              <div className="flex items-center gap-1.5">
                                <span className="text-slate-500 font-mono text-[10px] font-medium flex items-center gap-1">
                                  <Clock className="w-2.5 h-2.5 text-slate-400 shrink-0" />
                                  <span>{modDur || (isCurrent && activeDurationFormatted) || 'Loading...'}</span>
                                </span>
                                {isDone && (
                                  <span className="text-emerald-700 font-semibold bg-emerald-50 px-1.5 py-0.5 rounded border border-emerald-200 flex items-center gap-0.5">
                                    <CheckCircle2 className="w-2.5 h-2.5 text-emerald-600" />
                                    <span>Done</span>
                                  </span>
                                )}
                              </div>
                            </div>
                            <h4 className="text-xs font-bold text-slate-900">{module.title}</h4>
                            <p className="text-[11px] text-slate-500 mt-1 line-clamp-2">{module.description}</p>
                          </div>
                        );
                      })}
                    </div>
                  </div>
                )}

              </div>
            </div>

          </div>

          {/* RIGHT: Syllabus Workbook & Exam Gate (Desktop 4 cols, Sticky) */}
          <div className="hidden lg:flex lg:col-span-4 flex-col gap-5 sticky top-20">

            {/* Syllabus Playlist Box */}
            <div className="bg-white rounded-2xl border border-slate-200/90 p-5 shadow-xs">
              <div className="flex items-center justify-between pb-3 border-b border-slate-100 mb-3">
                <div>
                  <span className="text-[10px] uppercase tracking-wider text-slate-500 font-semibold block">
                    Curriculum Playlist
                  </span>
                  <h3 className="text-sm font-bold text-slate-900">Module Lessons</h3>
                </div>
                <span className="bg-blue-50 text-[#132F50] border border-blue-200/80 text-[10px] px-2.5 py-0.5 rounded-full font-semibold">
                  {completedModules.size} / {modules.length} Completed
                </span>
              </div>

              {/* Modules List */}
              <div className="space-y-2.5 max-h-[420px] overflow-y-auto pr-1">
                {modules.map((module, idx) => {
                  const isDone = completedModules.has(module.id);
                  const isCurrent = module.id === activeModuleId;
                  const modYt = module.resources?.find((r) => r.type === 'youtube');
                  const modVid = modYt ? extractYouTubeVideoId(modYt.url) : null;
                  const modDur = modVid ? (videoDurations[modVid] || (modYt as any)?.duration || '') : '';

                  return (
                    <div
                      key={module.id}
                      onClick={() => setActiveModuleId(module.id)}
                      className={`p-3 rounded-xl border transition-all cursor-pointer ${
                        isCurrent
                          ? 'border-[#132F50] bg-blue-50/50 shadow-xs ring-1 ring-[#132F50]/20'
                          : 'border-slate-200/80 hover:border-slate-300 bg-white'
                      }`}
                    >
                      <div className="flex items-center justify-between text-[10px] font-mono mb-1">
                        <span className={`flex items-center gap-1.5 ${isCurrent ? 'text-blue-700 font-semibold' : 'text-slate-400'}`}>
                          {isCurrent ? (
                            <>
                              <span className="w-1.5 h-1.5 rounded-full bg-blue-600 animate-pulse"></span>
                              <span>NOW PLAYING</span>
                            </>
                          ) : (
                            <span>MODULE {idx + 1}</span>
                          )}
                        </span>
                        
                        {isDone ? (
                          <span className="text-emerald-700 font-semibold bg-emerald-50 px-1.5 py-0.5 rounded border border-emerald-200 text-[9px] flex items-center gap-0.5">
                            <CheckCircle2 className="w-2.5 h-2.5 text-emerald-600" />
                            <span>Done</span>
                          </span>
                        ) : (
                          <span className="text-slate-500 font-mono text-[10px] font-medium flex items-center gap-1">
                            <Clock className="w-2.5 h-2.5 text-slate-400 shrink-0" />
                            <span>{modDur || (isCurrent && activeDurationFormatted) || 'Loading...'}</span>
                          </span>
                        )}
                      </div>

                      <h4 className={`text-xs font-bold leading-snug ${isCurrent ? 'text-slate-900' : 'text-slate-700'}`}>
                        {idx + 1}. {module.title}
                      </h4>
                      <p className="text-[11px] text-slate-500 mt-1 leading-tight line-clamp-2">
                        {module.description}
                      </p>
                    </div>
                  );
                })}
              </div>
            </div>

            {/* Certification Exam Gate Card */}
            <div id="milestone-gate" className="bg-white rounded-2xl border border-slate-200/90 p-5 shadow-xs">
              <h3 className="text-sm font-bold text-slate-900">
                Certification Exam Gate
              </h3>
              <p className="text-xs text-slate-500 mt-1 leading-relaxed font-normal">
                Pass mark: 60% or higher. Complete all curriculum modules to unlock your live dynamic proctored assessment.
              </p>

              <div className="mt-4 pt-3 border-t border-slate-100">
                <div className="flex justify-between text-xs mb-1.5">
                  <span className="text-slate-500 font-medium">Readiness Threshold</span>
                  <span className="text-[#132F50] font-bold">{completionPercent}%</span>
                </div>
                <div className="w-full bg-slate-100 rounded-full h-2 overflow-hidden">
                  <div
                    className="bg-[#132F50] h-full rounded-full transition-all duration-500"
                    style={{ width: `${completionPercent}%` }}
                  />
                </div>
              </div>

              {allModulesCompleted ? (
                <button
                  onClick={onTakeAssessment}
                  disabled={generatingAssessment}
                  className="mt-4 w-full bg-emerald-600 hover:bg-emerald-700 disabled:opacity-50 text-white rounded-xl font-semibold text-xs py-3 transition-all flex items-center justify-center gap-2 shadow-xs cursor-pointer active:scale-[0.98]"
                >
                  {generatingAssessment ? (
                    <>
                      <NapkinSpinner size="sm" />
                      <span>Synthesizing examination sheet...</span>
                    </>
                  ) : (
                    <span className="flex items-center gap-1.5">
                      <GraduationCap className="w-4 h-4" />
                      <span>Start Certification Exam Now</span>
                    </span>
                  )}
                </button>
              ) : (
                <button
                  disabled
                  className="mt-4 w-full bg-slate-100 text-slate-400 border border-slate-200 rounded-xl py-2.5 text-xs font-medium cursor-not-allowed flex items-center justify-center gap-1.5"
                >
                  <Lock className="w-3.5 h-3.5" />
                  <span>Complete {modules.length - completedModules.size} More {modules.length - completedModules.size === 1 ? 'Module' : 'Modules'} to Unlock</span>
                </button>
              )}
            </div>

          </div>

        </div>
      </main>

      {/* 3. Mobile Docked Bottom Bar */}
      <div className="lg:hidden fixed bottom-0 inset-x-0 bg-white/95 backdrop-blur-md border-t border-slate-200 px-4 py-3 z-50 flex items-center justify-between shadow-lg">
        <div>
          <div className="text-[10px] font-semibold text-slate-500 uppercase">
            Module {activeModuleIndex + 1} of {modules.length}
          </div>
          <div className="text-xs font-bold text-slate-900 truncate max-w-[190px]">
            {activeModule?.title}
          </div>
        </div>

        {allModulesCompleted ? (
          <button
            onClick={onTakeAssessment}
            disabled={generatingAssessment}
            className="bg-emerald-600 hover:bg-emerald-700 text-white text-xs font-semibold px-4 py-2 rounded-lg flex items-center gap-1.5 shadow-xs cursor-pointer active:scale-[0.98]"
          >
            {generatingAssessment ? (
              <span>Preparing...</span>
            ) : (
              <>
                <GraduationCap className="w-3.5 h-3.5" />
                <span>Take Exam</span>
                <ArrowRight className="w-3.5 h-3.5" />
              </>
            )}
          </button>
        ) : activeModule && !isActiveCompleted ? (
          <button
            onClick={() => markModuleComplete(activeModule.id)}
            className="bg-[#132F50] hover:bg-[#0e233d] text-white text-xs font-semibold px-4 py-2 rounded-lg flex items-center gap-1.5 shadow-xs cursor-pointer active:scale-[0.98]"
          >
            <CheckCircle2 className="w-3.5 h-3.5" />
            <span>Mark Complete</span>
          </button>
        ) : (
          <button
            onClick={() => {
              // Jump to next uncompleted module
              const nextMod = modules.find((m) => !completedModules.has(m.id));
              if (nextMod) {
                setActiveModuleId(nextMod.id);
                window.scrollTo({ top: 0, behavior: 'smooth' });
              }
            }}
            className="bg-blue-600 hover:bg-blue-700 text-white text-xs font-semibold px-4 py-2 rounded-lg flex items-center gap-1.5 shadow-xs cursor-pointer active:scale-[0.98]"
          >
            <span>Next Module</span>
            <ArrowRight className="w-3.5 h-3.5" />
          </button>
        )}
      </div>

    </div>
  );
}