"use client"

import { useState, useEffect } from "react"
import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card"
import { Button } from "@/components/ui/button"
import { Badge } from "@/components/ui/badge"
import { List, ChevronRight, Hash } from "lucide-react"

interface TOCItem {
  id: string
  title: string
  level: number
}

interface TableOfContentsProps {
  items: TOCItem[]
  className?: string
}

export default function TableOfContents({ items, className = "" }: TableOfContentsProps) {
  const [activeId, setActiveId] = useState<string>("")
  const [isVisible, setIsVisible] = useState(false)

  // Read initial hash from URL on mount
  useEffect(() => {
    const hash = window.location.hash.slice(1) // Remove the # symbol
    if (hash && items.some(item => item.id === hash)) {
      setActiveId(hash)
    }
  }, [items])

  // Listen for hash changes
  useEffect(() => {
    const handleHashChange = () => {
      const hash = window.location.hash.slice(1) // Remove the # symbol
      if (hash && items.some(item => item.id === hash)) {
        setActiveId(hash)
      }
    }

    window.addEventListener('hashchange', handleHashChange)
    return () => window.removeEventListener('hashchange', handleHashChange)
  }, [items])

  useEffect(() => {
    if (items.length === 0) return

    // Calculate header height dynamically
    const header = document.querySelector('header')
    const headerHeight = header ? header.offsetHeight + 20 : 100 // 20px buffer
    const rootMargin = `-${headerHeight}px 0% -35% 0%`

    const observer = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (entry.isIntersecting) {
            setActiveId(entry.target.id)
            // Update URL hash when scrolling to a section
            if (window.location.hash !== `#${entry.target.id}`) {
              window.history.replaceState(null, '', `#${entry.target.id}`)
            }
          }
        })
      },
      {
        rootMargin,
        threshold: 0.1,
      }
    )

    // Observe all TOC items
    items.forEach((item) => {
      const element = document.getElementById(item.id)
      if (element) {
        observer.observe(element)
      }
    })

    return () => {
      items.forEach((item) => {
        const element = document.getElementById(item.id)
        if (element) {
          observer.unobserve(element)
        }
      })
    }
  }, [items])

  useEffect(() => {
    // Show TOC if there are items
    setIsVisible(items.length > 0)
  }, [items])

  const scrollToSection = (id: string) => {
    const element = document.getElementById(id)
    if (element) {
      // Update URL hash immediately
      window.history.pushState(null, '', `#${id}`)
      setActiveId(id)
      
      // Get the actual header height dynamically
      const header = document.querySelector('header')
      const headerHeight = header ? header.offsetHeight + 20 : 100 // 20px buffer
      const elementPosition = element.offsetTop - headerHeight
      
      // Add a small delay to ensure smooth scrolling
      setTimeout(() => {
        window.scrollTo({
          top: Math.max(0, elementPosition), // Ensure we don't scroll to negative position
          behavior: "smooth"
        })
      }, 10)
    }
  }

  if (!isVisible) return null

  return (
    <aside className={`w-72 fixed right-0 top-16 h-[calc(100vh-4rem)] z-40 overflow-y-auto hidden xl:block ${className}`}>
      <div className="p-2">
        <Card className="bg-card/80 border-border/30 shadow-lg backdrop-blur-sm">
          <CardHeader className="pb-4 border-b border-border/20">
            <CardTitle className="text-base text-foreground flex items-center gap-3 font-semibold">
              <div className="p-2 rounded-lg bg-primary/10">
                <List className="h-4 w-4 text-primary" />
              </div>
              <div>
                <div>Table of Contents</div>
                <div className="text-xs text-muted-foreground font-normal mt-1">
                  {items.length} {items.length === 1 ? 'section' : 'sections'}
                </div>
              </div>
            </CardTitle>
          </CardHeader>
          <CardContent className="p-0">
            <nav className="space-y-1 p-4">
              {items.map((item, index) => {
                const isActive = activeId === item.id
                const indentClass = item.level > 1 ? `ml-${(item.level - 1) * 6}` : ""

                return (
                  <div key={item.id} className="group">
                    <Button
                      variant="ghost"
                      size="sm"
                      className={`w-full justify-start gap-3 text-sm transition-all duration-300 group-hover:translate-x-1 ${
                        isActive
                          ? "bg-primary text-primary-foreground hover:bg-primary/90 shadow-md"
                          : "hover:bg-primary/5 text-muted-foreground hover:text-foreground"
                      } ${indentClass} h-10 px-3`}
                      onClick={() => scrollToSection(item.id)}
                    >
                      <div className={`flex items-center gap-2 flex-1 min-w-0`}>
                        {isActive ? (
                          <div className="w-2 h-2 rounded-full bg-primary-foreground flex-shrink-0" />
                        ) : (
                          <Hash className="h-3 w-3 flex-shrink-0 text-muted-foreground group-hover:text-foreground transition-colors" />
                        )}
                        <span className="truncate font-medium">{item.title}</span>
                      </div>
                      {isActive && (
                        <ChevronRight className="h-3 w-3 flex-shrink-0 animate-pulse" />
                      )}
                    </Button>
                    {index < items.length - 1 && (
                      <div className="h-px bg-border/30 mx-3 my-1" />
                    )}
                  </div>
                )
              })}
            </nav>
          </CardContent>
        </Card>
      </div>
    </aside>
  )
}