import React, { useEffect, useState, useRef } from 'react';
import { BlogSection as BlogSectionType, PaperStructure } from '../types';
import BlogSectionComponent from './BlogSection';
import Sidebar from './Sidebar';
import { Clock, BookOpen, FileText, Share2, Download, Sparkles, CheckCircle2, Loader2, AlertCircle, RefreshCw } from 'lucide-react';

// Loading placeholder for sections being generated
const SectionLoadingPlaceholder: React.FC<{ title: string; index: number; isCurrentlyGenerating: boolean }> = ({ 
  title, 
  index, 
  isCurrentlyGenerating 
}) => (
  <section className="relative scroll-mt-32 animate-in fade-in duration-500">
    <div className="flex gap-8">
      <article className="flex-1 min-w-0">
        <header className="mb-8">
          <div className="flex items-center gap-4 mb-4">
            <span className={`
              flex-shrink-0 w-10 h-10 rounded-xl flex items-center justify-center text-white font-bold text-lg shadow-lg
              ${isCurrentlyGenerating 
                ? 'bg-gradient-to-br from-brand-500 to-purple-600 animate-pulse' 
                : 'bg-gray-300 dark:bg-gray-700'
              }
            `}>
              {isCurrentlyGenerating ? (
                <Loader2 size={20} className="animate-spin" />
              ) : (
                index + 1
              )}
            </span>
            <h2 className={`text-2xl md:text-3xl font-display font-bold leading-tight ${
              isCurrentlyGenerating ? 'text-gray-900 dark:text-gray-50' : 'text-gray-400 dark:text-gray-600'
            }`}>
              {title}
            </h2>
          </div>
          <div className={`w-20 h-1 rounded-full ${
            isCurrentlyGenerating 
              ? 'bg-gradient-to-r from-brand-500 to-purple-500 animate-pulse' 
              : 'bg-gray-200 dark:bg-gray-800'
          }`} />
        </header>

        {/* Loading skeleton */}
        <div className="space-y-4">
          {isCurrentlyGenerating ? (
            <>
              <div className="flex items-center gap-2 text-sm text-brand-600 dark:text-brand-400 mb-4">
                <Loader2 size={14} className="animate-spin" />
                <span>Generating content...</span>
              </div>
              <div className="space-y-3">
                <div className="h-4 bg-gray-200 dark:bg-gray-800 rounded-lg w-full animate-pulse" />
                <div className="h-4 bg-gray-200 dark:bg-gray-800 rounded-lg w-11/12 animate-pulse delay-75" />
                <div className="h-4 bg-gray-200 dark:bg-gray-800 rounded-lg w-4/5 animate-pulse delay-100" />
                <div className="h-4 bg-gray-200 dark:bg-gray-800 rounded-lg w-full animate-pulse delay-150" />
                <div className="h-4 bg-gray-200 dark:bg-gray-800 rounded-lg w-3/4 animate-pulse delay-200" />
              </div>
              <div className="mt-6 p-4 rounded-xl bg-gray-100 dark:bg-gray-800/50 border border-gray-200 dark:border-gray-700">
                <div className="h-32 bg-gray-200 dark:bg-gray-700 rounded-lg animate-pulse" />
              </div>
            </>
          ) : (
            <div className="p-8 rounded-xl border-2 border-dashed border-gray-200 dark:border-gray-800 text-center">
              <p className="text-gray-400 dark:text-gray-600 text-sm">
                Waiting to be generated...
              </p>
            </div>
          )}
        </div>
      </article>
    </div>

    {/* Section Divider */}
    <div className="my-16 flex items-center gap-4">
      <div className="flex-1 h-px bg-gradient-to-r from-transparent via-gray-200 dark:via-gray-800 to-transparent" />
    </div>
  </section>
);

// Error state for failed sections
const SectionErrorState: React.FC<{ title: string; error: string; index: number }> = ({ title, error, index }) => (
  <section className="relative scroll-mt-32">
    <div className="flex gap-8">
      <article className="flex-1 min-w-0">
        <header className="mb-8">
          <div className="flex items-center gap-4 mb-4">
            <span className="flex-shrink-0 w-10 h-10 rounded-xl bg-red-500 flex items-center justify-center text-white font-bold text-lg shadow-lg">
              <AlertCircle size={20} />
            </span>
            <h2 className="text-2xl md:text-3xl font-display font-bold text-gray-900 dark:text-gray-50 leading-tight">
              {title}
            </h2>
          </div>
        </header>

        <div className="p-6 rounded-xl bg-red-50 dark:bg-red-900/20 border border-red-200 dark:border-red-800">
          <div className="flex items-start gap-3">
            <AlertCircle size={20} className="text-red-500 flex-shrink-0 mt-0.5" />
            <div>
              <p className="font-semibold text-red-700 dark:text-red-300">
                Failed to generate this section
              </p>
              <p className="mt-1 text-sm text-red-600 dark:text-red-400">
                {error}
              </p>
            </div>
          </div>
        </div>
      </article>
    </div>

    <div className="my-16 flex items-center gap-4">
      <div className="flex-1 h-px bg-gradient-to-r from-transparent via-gray-300 dark:via-gray-700 to-transparent" />
    </div>
  </section>
);

interface Props {
  sections: BlogSectionType[];
  paperTitle: string;
  theme: 'light' | 'dark';
  onExport: () => void;
  onShare: () => void;
  isLoading?: boolean;
  loadingStage?: 'idle' | 'analyzing' | 'generating';
  currentSection?: number;
  paperStructure?: PaperStructure | null;
}

const BlogView: React.FC<Props> = ({ 
  sections, 
  paperTitle, 
  theme, 
  onExport, 
  onShare,
  isLoading = false,
  loadingStage = 'idle',
  currentSection = -1,
  paperStructure = null
}) => {
  const [activeSection, setActiveSection] = useState<string>(sections[0]?.id || '');
  const [readProgress, setReadProgress] = useState(0);
  const contentRef = useRef<HTMLDivElement>(null);

  // Calculate reading time (rough estimate: 200 words per minute)
  const completedSections = sections.filter(s => !s.isLoading && s.content);
  const totalWords = completedSections.reduce((acc, section) => {
    return acc + (section.content?.split(/\s+/).length || 0);
  }, 0);
  const readingTime = Math.max(1, Math.ceil(totalWords / 200));
  
  // Count completed sections
  const completedCount = sections.filter(s => !s.isLoading && !s.error).length;

  // Intersection Observer for active section tracking
  useEffect(() => {
    const options = {
      root: null,
      rootMargin: '-20% 0px -60% 0px',
      threshold: 0
    };

    const observer = new IntersectionObserver((entries) => {
      entries.forEach((entry) => {
        if (entry.isIntersecting) {
          const id = entry.target.id.replace('section-', '');
          setActiveSection(id);
        }
      });
    }, options);

    sections.forEach((section) => {
      const element = document.getElementById(`section-${section.id}`);
      if (element) observer.observe(element);
    });

    return () => observer.disconnect();
  }, [sections]);

  // Scroll progress tracking
  useEffect(() => {
    const handleScroll = () => {
      const winScroll = document.documentElement.scrollTop;
      const height = document.documentElement.scrollHeight - document.documentElement.clientHeight;
      const scrolled = (winScroll / height) * 100;
      setReadProgress(scrolled);
    };

    window.addEventListener('scroll', handleScroll);
    return () => window.removeEventListener('scroll', handleScroll);
  }, []);

  return (
    <div className="min-h-screen">
      {/* Reading Progress Bar */}
      <div className="fixed top-0 left-0 right-0 h-1 bg-gray-200 dark:bg-gray-800 z-50">
        <div 
          className="h-full bg-gradient-to-r from-brand-500 via-purple-500 to-pink-500 transition-all duration-150"
          style={{ width: `${readProgress}%` }}
        />
      </div>

      {/* Sidebar Navigation */}
      {sections.length > 0 && (
        <Sidebar 
          sections={sections} 
          activeSection={activeSection}
          onSectionClick={setActiveSection}
        />
      )}

      {/* Main Content */}
      <div className="lg:ml-72 xl:mr-8">
        <div ref={contentRef} className="max-w-3xl mx-auto px-6 py-8">
          
          {/* Loading State - Paper Analysis */}
          {loadingStage === 'analyzing' && (
            <div className="flex flex-col items-center justify-center min-h-[60vh] animate-in fade-in duration-500">
              <div className="relative">
                <div className="w-24 h-24 rounded-full bg-gradient-to-r from-brand-500 to-purple-600 animate-pulse flex items-center justify-center">
                  <Sparkles size={40} className="text-white animate-bounce" />
                </div>
                <div className="absolute inset-0 rounded-full bg-gradient-to-r from-brand-500 to-purple-600 animate-ping opacity-20" />
              </div>
              <h2 className="mt-8 text-2xl font-display font-bold text-gray-900 dark:text-white">
                Analyzing Paper Structure
              </h2>
              <p className="mt-3 text-gray-500 dark:text-gray-400 text-center max-w-md">
                Understanding the paper's key contributions, methodology, and findings to create the optimal narrative structure...
              </p>
            </div>
          )}

          {/* Generation Progress Banner */}
          {loadingStage === 'generating' && (
            <div className="mb-8 p-4 rounded-2xl bg-gradient-to-r from-brand-50 to-purple-50 dark:from-brand-900/20 dark:to-purple-900/20 border border-brand-200 dark:border-brand-800 animate-in slide-in-from-top duration-500">
              <div className="flex items-center gap-4">
                <div className="flex-shrink-0">
                  <div className="w-10 h-10 rounded-full bg-brand-500 flex items-center justify-center">
                    <Loader2 size={20} className="text-white animate-spin" />
                  </div>
                </div>
                <div className="flex-1 min-w-0">
                  <div className="flex items-center justify-between mb-2">
                    <span className="text-sm font-semibold text-brand-700 dark:text-brand-300">
                      Generating sections...
                    </span>
                    <span className="text-sm text-brand-600 dark:text-brand-400">
                      {completedCount} / {sections.length}
                    </span>
                  </div>
                  <div className="h-2 bg-brand-100 dark:bg-brand-900/30 rounded-full overflow-hidden">
                    <div 
                      className="h-full bg-gradient-to-r from-brand-500 to-purple-500 rounded-full transition-all duration-500"
                      style={{ width: `${(completedCount / sections.length) * 100}%` }}
                    />
                  </div>
                  {currentSection >= 0 && sections[currentSection] && (
                    <p className="mt-2 text-xs text-gray-600 dark:text-gray-400 truncate">
                      Currently writing: <span className="font-medium">{sections[currentSection].title}</span>
                    </p>
                  )}
                </div>
              </div>
            </div>
          )}

          {/* Article Header */}
          {(sections.length > 0 || paperStructure) && (
            <header className="mb-16 animate-in fade-in slide-in-from-bottom-8 duration-700">
              {/* Paper Badge */}
              <div className="flex items-center gap-2 mb-6">
                <span className="inline-flex items-center gap-2 px-3 py-1.5 rounded-full bg-brand-50 dark:bg-brand-900/20 text-brand-700 dark:text-brand-300 text-xs font-semibold uppercase tracking-wider">
                  <FileText size={12} />
                  Research Summary
                </span>
                {loadingStage === 'generating' && (
                  <span className="inline-flex items-center gap-2 px-3 py-1.5 rounded-full bg-amber-50 dark:bg-amber-900/20 text-amber-700 dark:text-amber-300 text-xs font-semibold">
                    <Loader2 size={12} className="animate-spin" />
                    Generating...
                  </span>
                )}
              </div>

              {/* Title */}
              <h1 className="text-4xl md:text-5xl lg:text-6xl font-display font-bold text-gray-900 dark:text-white leading-[1.1] mb-8">
                {(paperStructure?.paperTitle || paperTitle).replace('.pdf', '')}
              </h1>

              {/* Abstract Preview */}
              {paperStructure?.paperAbstract && (
                <p className="text-xl text-gray-600 dark:text-gray-300 leading-relaxed mb-8 italic border-l-4 border-brand-500 pl-4">
                  {paperStructure.paperAbstract}
                </p>
              )}

              {/* Meta Info */}
              <div className="flex flex-wrap items-center gap-6 text-sm text-gray-500 dark:text-gray-400">
                <div className="flex items-center gap-2">
                  <Clock size={16} />
                  <span>{readingTime} min read</span>
                </div>
                <div className="flex items-center gap-2">
                  <BookOpen size={16} />
                  <span>{sections.length} sections</span>
                </div>
                {completedCount === sections.length && sections.length > 0 && (
                  <div className="flex items-center gap-2 text-green-600 dark:text-green-400">
                    <CheckCircle2 size={16} />
                    <span>Complete</span>
                  </div>
                )}
                <div className="flex items-center gap-1 ml-auto">
                  <button 
                    onClick={onShare}
                    className="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-800 transition-colors"
                    title="Share"
                  >
                    <Share2 size={18} />
                  </button>
                  <button 
                    onClick={onExport}
                    className="p-2 rounded-lg hover:bg-gray-100 dark:hover:bg-gray-800 transition-colors"
                    title="Export"
                  >
                    <Download size={18} />
                  </button>
                </div>
              </div>

              {/* Decorative Line */}
              <div className="mt-10 flex items-center gap-4">
                <div className="flex-1 h-px bg-gradient-to-r from-brand-500 via-purple-500 to-transparent" />
                <div className="w-2 h-2 rounded-full bg-brand-500 animate-pulse" />
              </div>
            </header>
          )}

          {/* Key Contribution Highlight */}
          {paperStructure?.mainContribution && (
            <div className="mb-16 p-8 rounded-2xl bg-gradient-to-br from-brand-50 to-purple-50 dark:from-brand-900/20 dark:to-purple-900/20 border border-brand-200 dark:border-brand-800 shadow-xl shadow-brand-200/20 dark:shadow-none animate-in fade-in slide-in-from-bottom-4 duration-700">
              <div className="flex items-center gap-2 text-xs font-bold uppercase tracking-widest text-brand-600 dark:text-brand-400 mb-4">
                <Sparkles size={14} />
                Key Contribution
              </div>
              <p className="text-xl md:text-2xl leading-relaxed text-gray-800 dark:text-gray-200 font-medium">
                {paperStructure.mainContribution}
              </p>
            </div>
          )}

          {/* Sections */}
          <div className="space-y-4">
            {sections.map((section, index) => (
              <div key={section.id}>
                {section.isLoading ? (
                  <SectionLoadingPlaceholder 
                    title={section.title} 
                    index={index}
                    isCurrentlyGenerating={index === currentSection}
                  />
                ) : section.error ? (
                  <SectionErrorState title={section.title} error={section.error} index={index} />
                ) : (
                  <BlogSectionComponent 
                    section={section}
                    theme={theme}
                    index={index}
                  />
                )}
              </div>
            ))}
          </div>

          {/* Footer */}
          <footer className="mt-20 pt-10 border-t border-gray-200 dark:border-gray-800">
            <div className="text-center">
              <p className="text-sm text-gray-500 dark:text-gray-400 mb-4">
                Generated with PaperStack • Powered by Gemini AI
              </p>
              <div className="flex justify-center gap-4">
                <button 
                  onClick={() => window.scrollTo({ top: 0, behavior: 'smooth' })}
                  className="px-6 py-3 rounded-xl bg-gray-100 dark:bg-gray-800 hover:bg-gray-200 dark:hover:bg-gray-700 text-sm font-semibold transition-colors"
                >
                  Back to Top ↑
                </button>
              </div>
            </div>
          </footer>
        </div>
      </div>
    </div>
  );
};

export default BlogView;