//
//  ViewController.swift
//  Test
//
//  Created by Gunter Kwon on 9/27/24.
//

import UIKit

class ViewController: UIViewController {

	@IBOutlet weak var collectionView: UICollectionView!

	struct Section: Hashable {
		let id: String
		var title: String
	}

	struct Item: Hashable {
		let id: String
		let title: String
	}

	var dataSource: UICollectionViewDiffableDataSource!

	var sections: [Section] = [
		Section(
			id: "1",
			title: "Fruits"
		),
		Section(
			id: "2",
			title: "Vegetables"
		)
	]

	var itemsInSection: [Section: [Item]] = [:]

	var sectionLayoutsCache: [UUID: NSCollectionLayoutSection] = [:]

	override func viewDidLoad() {
		super.viewDidLoad()
		configureCollectionView()
		configureDataSource()
		initializeData()
		applySnapshot(animatingDifferences: false)
	}

	func configureCollectionView() {
		collectionView.collectionViewLayout = createLayout()

		collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "MyCell")

		collectionView.register(
			UICollectionReusableView.self,
			forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
			withReuseIdentifier: "HeaderView"
		)
	}

	func createLayout() -> UICollectionViewLayout {
		let layout = UICollectionViewCompositionalLayout { [weak self] (sectionIndex, environment) -> NSCollectionLayoutSection? in
			guard let self = self else { return nil }
			let section = self.sections[sectionIndex]
			let sectionID = section.id
			
			debugPrint("gunter \(#function) \(sectionID)")

			let sectionLayout: NSCollectionLayoutSection = {
				let itemSize = NSCollectionLayoutSize(
					widthDimension: .fractionalWidth(1.0),
					heightDimension: .absolute(50)
				)
				let item = NSCollectionLayoutItem(layoutSize: itemSize)
				let groupSize = NSCollectionLayoutSize(
					widthDimension: .fractionalWidth(1.0),
					heightDimension: .absolute(50)
				)
				let group = NSCollectionLayoutGroup.horizontal(
					layoutSize: groupSize,
					subitems: [item]
				)

				let sectionLayout = NSCollectionLayoutSection(group: group)
				let headerSize = NSCollectionLayoutSize(
					widthDimension: .fractionalWidth(1.0),
					heightDimension: .estimated(44)
				)
				let sectionHeader = NSCollectionLayoutBoundarySupplementaryItem(
					layoutSize: headerSize,
					elementKind: UICollectionView.elementKindSectionHeader,
					alignment: .top
				)
				sectionLayout.boundarySupplementaryItems = [sectionHeader]

				return sectionLayout
			}()

			return sectionLayout
		}
		return layout
	}

	func configureDataSource() {
		dataSource = UICollectionViewDiffableDataSource(
			collectionView: collectionView,
			cellProvider: { (collectionView, indexPath, item) -> UICollectionViewCell? in
				let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MyCell", for: indexPath)
				cell.contentView.backgroundColor = .systemGray5
				cell.layer.cornerRadius = 8
				let tag = 100
				if let label = cell.contentView.viewWithTag(tag) as? UILabel {
					label.text = item.title
				} else {
					let label = UILabel(frame: cell.contentView.bounds)
					label.tag = tag
					label.text = item.title
					label.textAlignment = .center
					cell.contentView.addSubview(label)
				}

				return cell
			}
		)

		dataSource.supplementaryViewProvider = { (collectionView, kind, indexPath) in
			guard kind == UICollectionView.elementKindSectionHeader else { return nil }
			let headerView = collectionView.dequeueReusableSupplementaryView(
				ofKind: kind,
				withReuseIdentifier: "HeaderView",
				for: indexPath
			)

			let tag = 200
			if let label = headerView.viewWithTag(tag) as? UILabel {
				let section = self.sections[indexPath.section]
				label.text = section.title
			} else {
				let label = UILabel(frame: headerView.bounds)
				label.tag = tag
				label.textAlignment = .left
				label.font = UIFont.boldSystemFont(ofSize: 20)
				let section = self.sections[indexPath.section]
				label.text = section.title
				headerView.addSubview(label)
			}

			return headerView
		}
	}

	func initializeData() {
		// 각 섹션에 아이템 초기화
		let fruits = [
			Item(id: "1",title: "Apple"),
			Item(id: "2", title: "Banana"),
			Item(id: "3", title: "Cherry")
		]

		let vegetables = [
			Item(id: "4", title: "Carrot"),
			Item(id: "5", title: "Lettuce"),
			Item(id: "6", title: "Tomato")
		]

		itemsInSection[sections[0]] = fruits
		itemsInSection[sections[1]] = vegetables
	}

	func applySnapshot(animatingDifferences: Bool = true) {
		var snapshot = NSDiffableDataSourceSnapshot()
		snapshot.appendSections(sections)
		for section in sections {
			let items = itemsInSection[section] ?? []
			snapshot.appendItems(items, toSection: section)
		}
		dataSource.apply(snapshot, animatingDifferences: animatingDifferences)
	}

	@IBAction func addSection(_ sender: Any) {
		let newSection = Section(id: UUID().uuidString, title: "Section \(sections.count + 1)")
		sections.append(newSection)
		itemsInSection[newSection] = []

		applySnapshot()
	}

	@IBAction func removeSection(_ sender: Any) {
		guard !sections.isEmpty else { return }
		let removedSection = sections.removeLast()
		itemsInSection[removedSection] = nil

		applySnapshot()
	}

	@IBAction func addItem(_ sender: Any) {
		guard !sections.isEmpty else { return }
		let randomSection = sections.randomElement()!
		let newItem = Item(id: UUID().uuidString, title: "New Item \(Int.random(in: 1...100))")
		itemsInSection[randomSection]?.append(newItem)
		applySnapshot()
	}

	@IBAction func removeItem(_ sender: Any) {
		guard !sections.isEmpty else { return }
		let randomSection = sections.randomElement()!
		guard var items = itemsInSection[randomSection], !items.isEmpty else { return }
		items.removeLast()
		itemsInSection[randomSection] = items
		applySnapshot()
	}
}