import Messages
import UIKit

final class StickerBrowserViewController: MSStickerBrowserViewController {
	private struct Pack {
		let savedPack: SavedPack
		let thumbnail: UIImage?
		let stickers: [MSSticker]
	}

	private var packs: [Pack] = []
	private var selectedPackIndex: Int? // nil = all packs
	private var displayedStickers: [MSSticker] = []

	private var tabCollectionView: UICollectionView!

	private let tabSize: CGFloat = 36
	private let tabSpacing: CGFloat = 6
	private let tabInset: CGFloat = 8

	// MARK: - Lifecycle

	init() {
		super.init(stickerSize: .small)
	}

	@available(*, unavailable)
	required init?(coder: NSCoder) {
		fatalError("init(coder:) is not supported")
	}

	override func viewDidLoad() {
		super.viewDidLoad()
		setupTabBar()
	}

	// MARK: - Data

	func reloadStickers() {
		packs = StickerStore.shared.savedPacks
			.sorted { $0.title.localizedCaseInsensitiveCompare($1.title) == .orderedAscending }
			.compactMap { pack in
				let urls = StickerStore.shared.stickerFileURLs(forPack: pack.name)
				let stickers = urls.compactMap { url in
					try? MSSticker(contentsOfFileURL: url, localizedDescription: pack.title)
				}
				guard !stickers.isEmpty else { return nil }
				let thumbnail = StickerStore.shared.thumbnail(forPack: pack.name)
				return Pack(savedPack: pack, thumbnail: thumbnail, stickers: stickers)
			}

		if let index = selectedPackIndex, index >= packs.count {
			selectedPackIndex = nil
		}

		updateDisplayedStickers()
		tabCollectionView?.reloadData()
	}

	private func updateDisplayedStickers() {
		if let index = selectedPackIndex {
			displayedStickers = packs[index].stickers
		} else {
			displayedStickers = packs.flatMap(\.stickers)
		}
		stickerBrowserView.reloadData()
	}

	// MARK: - Tab bar

	private func setupTabBar() {
		let tabBarHeight = tabSize + tabInset * 2

		let layout = UICollectionViewFlowLayout()
		layout.scrollDirection = .horizontal
		layout.minimumInteritemSpacing = tabSpacing
		layout.minimumLineSpacing = tabSpacing
		layout.sectionInset = UIEdgeInsets(top: 0, left: tabInset, bottom: 0, right: tabInset)
		layout.itemSize = CGSize(width: tabSize, height: tabSize)

		tabCollectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
		tabCollectionView.translatesAutoresizingMaskIntoConstraints = false
		tabCollectionView.backgroundColor = .secondarySystemBackground
		tabCollectionView.showsHorizontalScrollIndicator = false
		tabCollectionView.dataSource = self
		tabCollectionView.delegate = self
		tabCollectionView.register(TabCell.self, forCellWithReuseIdentifier: TabCell.reuseID)

		let separator = UIView()
		separator.translatesAutoresizingMaskIntoConstraints = false
		separator.backgroundColor = .separator

		view.addSubview(tabCollectionView)
		view.addSubview(separator)

		NSLayoutConstraint.activate([
			tabCollectionView.topAnchor.constraint(equalTo: view.topAnchor),
			tabCollectionView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
			tabCollectionView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
			tabCollectionView.heightAnchor.constraint(equalToConstant: tabBarHeight),

			separator.topAnchor.constraint(equalTo: tabCollectionView.bottomAnchor),
			separator.leadingAnchor.constraint(equalTo: view.leadingAnchor),
			separator.trailingAnchor.constraint(equalTo: view.trailingAnchor),
			separator.heightAnchor.constraint(equalToConstant: 1.0 / UIScreen.main.scale),
		])

		additionalSafeAreaInsets = UIEdgeInsets(top: tabBarHeight, left: 0, bottom: 0, right: 0)
	}

	private func selectPack(at index: Int?) {
		guard selectedPackIndex != index else { return }
		selectedPackIndex = index
		updateDisplayedStickers()
		tabCollectionView.reloadData()
	}

	// MARK: - MSStickerBrowserViewDataSource

	override func numberOfStickers(in stickerBrowserView: MSStickerBrowserView) -> Int {
		displayedStickers.count
	}

	override func stickerBrowserView(_ stickerBrowserView: MSStickerBrowserView, stickerAt index: Int) -> MSSticker {
		displayedStickers[index]
	}
}

// MARK: - UICollectionViewDataSource

extension StickerBrowserViewController: UICollectionViewDataSource {
	func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
		packs.count + 1 // +1 for "All" tab
	}

	func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
		let cell = collectionView.dequeueReusableCell(withReuseIdentifier: TabCell.reuseID, for: indexPath) as! TabCell
		if indexPath.item == 0 {
			let isSelected = selectedPackIndex == nil
			cell.configureAsAll(isSelected: isSelected)
		} else {
			let pack = packs[indexPath.item - 1]
			let isSelected = selectedPackIndex == indexPath.item - 1
			cell.configure(image: pack.thumbnail, isSelected: isSelected)
		}
		return cell
	}
}

// MARK: - UICollectionViewDelegate

extension StickerBrowserViewController: UICollectionViewDelegate {
	func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
		if indexPath.item == 0 {
			selectPack(at: nil)
		} else {
			selectPack(at: indexPath.item - 1)
		}
	}
}

// MARK: - TabCell

private final class TabCell: UICollectionViewCell {
	static let reuseID = "TabCell"

	private let imageView = UIImageView()
	private let label = UILabel()

	override init(frame: CGRect) {
		super.init(frame: frame)
		contentView.layer.cornerRadius = 8
		contentView.clipsToBounds = true

		imageView.contentMode = .scaleAspectFit
		imageView.translatesAutoresizingMaskIntoConstraints = false
		contentView.addSubview(imageView)

		label.font = .systemFont(ofSize: 11, weight: .medium)
		label.textAlignment = .center
		label.translatesAutoresizingMaskIntoConstraints = false
		label.isHidden = true
		contentView.addSubview(label)

		let inset: CGFloat = 4
		NSLayoutConstraint.activate([
			imageView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: inset),
			imageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -inset),
			imageView.leadingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: inset),
			imageView.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -inset),

			label.centerXAnchor.constraint(equalTo: contentView.centerXAnchor),
			label.centerYAnchor.constraint(equalTo: contentView.centerYAnchor),
		])
	}

	@available(*, unavailable)
	required init?(coder: NSCoder) {
		fatalError("init(coder:) is not supported")
	}

	func configure(image: UIImage?, isSelected: Bool) {
		imageView.image = image
		imageView.isHidden = false
		label.isHidden = true
		contentView.backgroundColor = isSelected ? .systemGray5 : .clear
		imageView.alpha = isSelected ? 1.0 : 0.5
	}

	func configureAsAll(isSelected: Bool) {
		imageView.isHidden = true
		label.isHidden = false
		label.text = "All"
		label.textColor = isSelected ? .label : .secondaryLabel
		contentView.backgroundColor = isSelected ? .systemGray5 : .clear
	}

	override func prepareForReuse() {
		super.prepareForReuse()
		imageView.image = nil
		imageView.isHidden = false
		label.isHidden = true
	}
}