src/components/Nav.tsx

'use client'

import Image from 'next/image'
import { useEffect, useState, useCallback } from 'react'

const NAV_SECTIONS = ['criteria', 'leaderboard', 'about', 'insights'] as const
const NAV_LABELS: Record<string, string> = {
  criteria: 'Overview',
  leaderboard: 'Results',
  about: 'Methodology',
  insights: 'Insights',
}

export default function Nav({ modelCount, lastUpdated }: { modelCount: number; lastUpdated: string }) {
  const [scrolled, setScrolled] = useState(false)
  const [showTitle, setShowTitle] = useState(false)
  const [activeSection, setActiveSection] = useState<string | null>(null)
  const [menuOpen, setMenuOpen] = useState(false)

  useEffect(() => {
    const update = () => {
      setScrolled(window.scrollY > 20)

      const heroTitle = document.getElementById('hero-title')
      if (heroTitle) {
        const rect = heroTitle.getBoundingClientRect()
        setShowTitle(rect.bottom < 0)
      }

      const scrollMid = window.scrollY + window.innerHeight * 0.35
      let current: string | null = null
      for (const id of NAV_SECTIONS) {
        const el = document.getElementById(id)
        if (el && el.offsetTop <= scrollMid) current = id
      }
      setActiveSection(current)
    }

    update()
    window.addEventListener('scroll', update, { passive: true })
    return () => window.removeEventListener('scroll', update)
  }, [])

  const closeMenu = useCallback(() => setMenuOpen(false), [])

  return (
    <>
      <nav
        className="nav-bar"
        style={{ boxShadow: scrolled ? '0 1px 8px rgba(0,0,0,0.08)' : 'none' }}
      >
        <div className="nav-logo">
          <Image
            src="/govtech-logo.jpg"
            alt="GovTech Singapore"
            height={26}
            width={104}
            style={{ objectFit: 'contain', objectPosition: 'left center', width: 'auto', height: 26 }}
            priority
          />
          <span
            className="nav-logo-sep"
            style={{
              opacity: showTitle ? 1 : 0,
              transition: 'opacity 0.35s cubic-bezier(0.16, 1, 0.3, 1)',
            }}
          />
          <span
            className="nav-logo-bench"
            style={{
              opacity: showTitle ? 1 : 0,
              transform: showTitle ? 'translateY(0)' : 'translateY(4px)',
              transition: 'opacity 0.35s cubic-bezier(0.16, 1, 0.3, 1), transform 0.35s cubic-bezier(0.16, 1, 0.3, 1)',
            }}
          >
            Responsible AI Bench
          </span>
        </div>

        <ul className="nav-links">
          {NAV_SECTIONS.map(id => (
            <li key={id}>
              <a href={`#${id}`} className={activeSection === id ? 'nav-active' : ''}>
                {NAV_LABELS[id]}
              </a>
            </li>
          ))}
        </ul>

        <button
          className="nav-hamburger"
          onClick={() => setMenuOpen(v => !v)}
          aria-label="Toggle navigation menu"
          aria-expanded={menuOpen}
        >
          <svg width="22" height="22" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round">
            {menuOpen ? (
              <>
                <line x1="6" y1="6" x2="18" y2="18" />
                <line x1="6" y1="18" x2="18" y2="6" />
              </>
            ) : (
              <>
                <line x1="4" y1="7" x2="20" y2="7" />
                <line x1="4" y1="12" x2="20" y2="12" />
                <line x1="4" y1="17" x2="20" y2="17" />
              </>
            )}
          </svg>
        </button>
      </nav>

      <div className={`nav-mobile-menu ${menuOpen ? 'open' : ''}`}>
        {NAV_SECTIONS.map(id => (
          <a
            key={id}
            href={`#${id}`}
            className={activeSection === id ? 'nav-active' : ''}
            onClick={closeMenu}
          >
            {NAV_LABELS[id]}
          </a>
        ))}
      </div>
    </>
  )
}