import UIKit

final class CategoryListViewController: UITableViewController {
    private let store: WordStore

    init(store: WordStore) {
        self.store = store
        super.init(style: .plain)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) { fatalError() }

    override func viewDidLoad() {
        super.viewDidLoad()
        title = "背单词"
        tableView.register(CategoryCardCell.self, forCellReuseIdentifier: "cell")
        tableView.separatorStyle = .none
        tableView.backgroundColor = .systemBackground
        tableView.contentInset.top = 8
        if let error = store.loadError {
            showError(error)
        }
    }

    private func showError(_ message: String) {
        let label = UILabel()
        label.text = "词库加载失败\n\(message)"
        label.numberOfLines = 0
        label.textAlignment = .center
        label.textColor = .secondaryLabel
        let background = UIView()
        background.addSubview(label)
        label.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            label.centerXAnchor.constraint(equalTo: background.centerXAnchor),
            label.centerYAnchor.constraint(equalTo: background.centerYAnchor),
            label.leadingAnchor.constraint(greaterThanOrEqualTo: background.leadingAnchor, constant: 24)
        ])
        tableView.backgroundView = background
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        store.categories.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath) as! CategoryCardCell
        cell.configure(with: store.categories[indexPath.row], color: Theme.Color.category(at: indexPath.row))
        return cell
    }

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        Haptics.selection()
        let category = store.categories[indexPath.row]
        if let subs = category.subcategories, !subs.isEmpty {
            let vc = SubcategoryListViewController(category: category, colorIndex: indexPath.row)
            navigationController?.pushViewController(vc, animated: true)
        } else {
            navigationController?.pushViewController(
                WordListViewController(category: category, colorIndex: indexPath.row), animated: true)
        }
    }
}