import { useState, useEffect, useRef } from 'react'
import { useParams, Link } from 'react-router-dom'
import Navbar from '../components/Navbar'
import Footer from '../components/Footer'
import ProductCard from '../components/ProductCard'
import { API_BASE, getCategoryImage, type Category, type Product } from '../types'

export default function CategoryPage() {
  const { id } = useParams<{ id: string }>()

  const [categories, setCategories] = useState<Category[]>([])
  const [category, setCategory] = useState<Category | null>(null)
  const [products, setProducts] = useState<Product[]>([])
  
  // Local progressive rendering
  const [displayCount, setDisplayCount] = useState(24)
  const loaderRef = useRef<HTMLDivElement>(null)
  
  const [loading, setLoading] = useState(true)
  const [error, setError] = useState<string | null>(null)

  useEffect(() => {
    fetch(`${API_BASE}/categories`)
      .then((r) => r.json())
      .then(setCategories)
      .catch(console.error)
  }, [])

  // Reset state when category changes
  useEffect(() => {
    window.scrollTo({ top: 0, behavior: 'smooth' })
    setDisplayCount(24)
  }, [id])

  useEffect(() => {
    if (!id) return
    setLoading(true)
    setError(null)

    Promise.all([
      // Fetch up to 1000 items (essentially all) in one go
      fetch(`${API_BASE}/categories/${id}/products?limit=1000`),
      fetch(`${API_BASE}/categories`),
    ])
      .then(async ([catRes, allCatsRes]) => {
        if (!catRes.ok) throw new Error('Category not found')
        const catPaginated = await catRes.json()
        const allCats: Category[] = await allCatsRes.json()
        
        setCategory(catPaginated.category)
        setProducts(catPaginated.data || [])
        setCategories(allCats)
      })
      .catch((err) => setError(err.message))
      .finally(() => setLoading(false))
  }, [id])

  // Intersection Observer for infinite scroll
  useEffect(() => {
    const observer = new IntersectionObserver(
      (entries) => {
        if (entries[0].isIntersecting && products.length > displayCount) {
          setDisplayCount((prev) => Math.min(prev + 12, products.length))
        }
      },
      { threshold: 0.1, rootMargin: '200px' } // Pre-load slightly before seeing the loader
    )

    if (loaderRef.current) {
      observer.observe(loaderRef.current)
    }

    return () => observer.disconnect()
  }, [products.length, displayCount, loading])

  return (
    <div className="min-h-screen">
      <Navbar categories={categories} />

      {/* Hero Banner for category */}
      <div className="relative h-64 md:h-80 overflow-hidden">
        <img
          src={getCategoryImage(category?.name ?? '')}
          className="absolute inset-0 w-full h-full object-cover brightness-30 scale-105"
          alt={category?.name}
          onError={(e) => { (e.target as HTMLImageElement).style.display = 'none' }}
        />
        <div className="absolute inset-0 bg-night-900/40" />
        <div className="absolute inset-0 bg-gradient-to-t from-night-900/90 via-night-900/10 to-transparent" />
        <div className="absolute bottom-0 left-0 right-0 px-6 pb-10 pt-20">
          <div className="max-w-7xl mx-auto">
            {/* Breadcrumb */}
            <div className="flex items-center gap-2 text-xs text-spa-sage/80 uppercase tracking-widest mb-4 font-semibold">
              <Link to="/" className="hover:text-white transition-colors">Home</Link>
              <span>/</span>
              <Link to="/shop" className="hover:text-white transition-colors">Shop</Link>
              <span>/</span>
              <span className="text-white">{category?.name ?? '...'}</span>
            </div>
            <h1 className="text-4xl md:text-5xl font-bold text-white">
              {loading ? (
                <div className="h-10 w-48 bg-white/20 animate-pulse rounded-lg" />
              ) : (
                category?.name
              )}
            </h1>
            {!loading && category?._count && (
              <p className="text-spa-sage mt-2">
                {category._count.products} products available
              </p>
            )}
          </div>
        </div>
      </div>

      {/* Products Grid */}
      <div className="max-w-7xl mx-auto px-6 py-16 space-y-10">
        {/* Other Category Pills */}
        <div className="flex flex-wrap gap-3">
          {categories.map((cat) => (
            <Link
              key={cat.id}
              to={`/category/${cat.id}`}
              className={`px-4 py-1.5 rounded-full text-xs font-bold uppercase tracking-widest transition-all duration-300 border ${
                cat.id === category?.id
                  ? 'bg-spa-forest text-white border-spa-forest shadow-md'
                  : 'bg-white text-spa-stone border-spa-stone/20 hover:border-spa-forest hover:text-spa-forest shadow-sm'
              }`}
            >
              {cat.name}
            </Link>
          ))}
        </div>

        {error ? (
          <div className="text-center py-24 space-y-3">
            <p className="text-4xl">⚠️</p>
            <p className="text-spa-stone font-medium">{error}</p>
            <Link to="/shop" className="text-spa-forest font-bold text-sm hover:underline">
              Back to Shop
            </Link>
          </div>
        ) : loading ? (
          <div className="grid grid-cols-2 md:grid-cols-3 gap-4 md:gap-8">
            {Array.from({ length: 9 }).map((_, i) => (
              <div key={i} className="rounded-2xl bg-spa-stone/10 animate-pulse h-96" />
            ))}
          </div>
        ) : products.length === 0 ? (
          <div className="text-center py-24 text-spa-stone/60 space-y-3 font-medium">
            <p className="text-4xl">🌿</p>
            <p>No products in this category yet.</p>
          </div>
        ) : (
          <div>
            <div className="grid grid-cols-2 md:grid-cols-3 gap-4 md:gap-8">
              {products.slice(0, displayCount).map((p) => (
                 <ProductCard key={p.id} product={p} />
              ))}
            </div>

            {/* Invisible target for IntersectionObserver */}
            {displayCount < products.length && (
              <div ref={loaderRef} className="py-12 flex justify-center">
                <div className="w-8 h-8 rounded-full border-2 border-spa-forest border-t-transparent animate-spin" />
              </div>
            )}
          </div>
        )}
      </div>

      <Footer categories={categories} />
    </div>
  )
}