//
//  ToastCenter.swift
//  suixinkan
//
//  Created by Codex on 2026/6/18.
//

import UIKit

@MainActor
/// 全局 Toast 状态中心，负责保存和清除当前提示文案。
final class ToastCenter {
    var onChange: (() -> Void)?
    private(set) var message: String? { didSet { onChange?() } }

    private let autoDismissNanoseconds: UInt64
    private var dismissTask: Task<Void, Never>?
    private var displayToken: UInt64 = 0
    private weak var overlayView: ToastOverlayView?

    /// 创建 Toast 状态中心，默认 2.2 秒后自动隐藏。
    init(autoDismissNanoseconds: UInt64 = 2_200_000_000) {
        self.autoDismissNanoseconds = autoDismissNanoseconds
    }

    /// 显示一条全局 Toast 文案。
    func show(_ message: String) {
        displayToken &+= 1
        self.message = message
        scheduleAutoDismiss(token: displayToken)
    }

    /// 清除当前 Toast 文案。
    func dismiss() {
        displayToken &+= 1
        dismissTask?.cancel()
        dismissTask = nil
        message = nil
    }

    /// 将全局 Toast 展示层挂载到指定窗口，通常只在应用根部调用一次。
    func attachToWindow(_ window: UIWindow) {
        if let overlayView, overlayView.superview === window {
            return
        }

        let overlay = ToastOverlayView(center: self)
        overlay.frame = window.bounds
        overlay.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        window.addSubview(overlay)
        overlayView = overlay
    }

    /// 为当前 Toast 安排自动隐藏任务，并避免旧任务误清除新 Toast。
    private func scheduleAutoDismiss(token: UInt64) {
        dismissTask?.cancel()
        let delay = autoDismissNanoseconds
        dismissTask = Task { [weak self] in
            do {
                try await Task.sleep(nanoseconds: delay)
            } catch {
                return
            }
            await MainActor.run {
                guard let self, self.displayToken == token else { return }
                self.message = nil
                self.dismissTask = nil
            }
        }
    }

    #if DEBUG
    /// 测试专用快照，业务代码不应读取 Toast 展示状态。
    var snapshotForTests: ToastSnapshot {
        ToastSnapshot(message: message)
    }
    #endif
}

#if DEBUG
/// 全局 Toast 测试快照，用于验证文案和自动隐藏行为。
struct ToastSnapshot: Equatable {
    let message: String?
}
#endif

/// 全局 Toast 展示层，负责把 Toast 展示到窗口顶部。
final class ToastOverlayView: UIView {
    private weak var toastCenter: ToastCenter?
    private let bannerView = UIView()
    private let messageLabel = UILabel()

    /// 使用 Toast 状态中心初始化展示层。
    init(center: ToastCenter) {
        self.toastCenter = center
        super.init(frame: .zero)
        isUserInteractionEnabled = false
        configureViews()
        center.onChange = { [weak self] in
            self?.refreshPresentation(animated: true)
        }
        refreshPresentation(animated: false)
    }

    required init?(coder: NSCoder) {
        nil
    }

    private func configureViews() {
        bannerView.backgroundColor = AppDesign.primary
        bannerView.isHidden = true
        bannerView.alpha = 0

        messageLabel.font = .systemFont(ofSize: 14, weight: .medium)
        messageLabel.textColor = .white
        messageLabel.textAlignment = .center
        messageLabel.numberOfLines = 2

        bannerView.addSubview(messageLabel)
        addSubview(bannerView)

        bannerView.translatesAutoresizingMaskIntoConstraints = false
        messageLabel.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            bannerView.leadingAnchor.constraint(equalTo: leadingAnchor),
            bannerView.trailingAnchor.constraint(equalTo: trailingAnchor),
            bannerView.topAnchor.constraint(equalTo: topAnchor),

            messageLabel.leadingAnchor.constraint(equalTo: bannerView.leadingAnchor, constant: AppMetrics.Spacing.pageHorizontal),
            messageLabel.trailingAnchor.constraint(equalTo: bannerView.trailingAnchor, constant: -AppMetrics.Spacing.pageHorizontal),
            messageLabel.topAnchor.constraint(equalTo: bannerView.safeAreaLayoutGuide.topAnchor, constant: AppMetrics.Spacing.small),
            messageLabel.bottomAnchor.constraint(equalTo: bannerView.bottomAnchor, constant: -AppMetrics.Spacing.small)
        ])
    }

    private func refreshPresentation(animated: Bool) {
        guard let message = toastCenter?.message, !message.isEmpty else {
            hideBanner(animated: animated)
            return
        }

        messageLabel.text = message
        showBanner(animated: animated)
    }

    private func showBanner(animated: Bool) {
        guard bannerView.isHidden || bannerView.alpha < 1 else { return }

        bannerView.isHidden = false
        guard animated else {
            bannerView.alpha = 1
            bannerView.transform = .identity
            return
        }

        bannerView.alpha = 0
        bannerView.transform = CGAffineTransform(translationX: 0, y: -12)
        UIView.animate(withDuration: 0.18, delay: 0, options: [.curveEaseInOut]) {
            self.bannerView.alpha = 1
            self.bannerView.transform = .identity
        }
    }

    private func hideBanner(animated: Bool) {
        guard !bannerView.isHidden else { return }

        guard animated else {
            bannerView.isHidden = true
            bannerView.alpha = 0
            return
        }

        UIView.animate(withDuration: 0.18, delay: 0, options: [.curveEaseInOut], animations: {
            self.bannerView.alpha = 0
            self.bannerView.transform = CGAffineTransform(translationX: 0, y: -12)
        }, completion: { _ in
            self.bannerView.isHidden = true
            self.bannerView.transform = .identity
        })
    }
}