//
//  WelcomeViewController.swift
//  Mastodon
//
//  Created by BradGao on 2021/2/20.
//

import UIKit
import Combine
import MastodonAsset
import MastodonCore
import MastodonLocalization

final class WelcomeViewController: UIViewController, NeedsDependency {
    
    private enum Constants {
        static let topAnchorInset: CGFloat = 20
    }
    
    weak var context: AppContext! { willSet { precondition(!isViewLoaded) } }
    weak var coordinator: SceneCoordinator! { willSet { precondition(!isViewLoaded) } }
    
    var disposeBag = Set<AnyCancellable>()
    var observations = Set<NSKeyValueObservation>()
    private(set) lazy var viewModel = WelcomeViewModel(context: context)
    
    let welcomeIllustrationView = WelcomeIllustrationView()
    
    private(set) lazy var dismissBarButtonItem = UIBarButtonItem(barButtonSystemItem: .close, target: self, action: #selector(WelcomeViewController.dismissBarButtonItemDidPressed(_:)))
    
    let buttonContainer = UIStackView()
    
    private(set) lazy var signUpButton: PrimaryActionButton = {
        let button = PrimaryActionButton()
        button.adjustsBackgroundImageWhenUserInterfaceStyleChanges = false
        button.contentEdgeInsets = WelcomeViewController.actionButtonPadding
        button.titleLabel?.adjustsFontForContentSizeCategory = true
        button.titleLabel?.font = UIFontMetrics(forTextStyle: .headline).scaledFont(for: .systemFont(ofSize: 17, weight: .semibold))
        button.setTitle(L10n.Common.Controls.Actions.signUp, for: .normal)
        let backgroundImageColor: UIColor = .white
        let backgroundImageHighlightedColor: UIColor = UIColor(white: 0.8, alpha: 1.0)
        button.setBackgroundImage(.placeholder(color: backgroundImageColor), for: .normal)
        button.setBackgroundImage(.placeholder(color: backgroundImageHighlightedColor), for: .highlighted)
        button.setTitleColor(.black, for: .normal)
        return button
    }()
    let signUpButtonShadowView = UIView()
    
    private(set) lazy var signInButton: UIButton = {
        let button = UIButton()
        button.contentEdgeInsets = WelcomeViewController.actionButtonPadding
        button.titleLabel?.adjustsFontForContentSizeCategory = true
        button.titleLabel?.font = UIFontMetrics(forTextStyle: .headline).scaledFont(for: .systemFont(ofSize: 17, weight: .semibold))
        button.setTitle(L10n.Scene.Welcome.logIn, for: .normal)
        let titleColor: UIColor = UIColor.white.withAlphaComponent(0.9)
        button.setTitleColor(titleColor, for: .normal)
        button.setTitleColor(titleColor.withAlphaComponent(0.3), for: .highlighted)
        return button
    }()
    
    private(set) lazy var pageViewController: UIPageViewController = {
        let pageController = UIPageViewController(transitionStyle: .scroll, navigationOrientation: .horizontal)
        pageController.setViewControllers([WelcomeContentViewController(page: .whatIsMastodon)], direction: .forward, animated: false)
        return pageController
    }()
    var currentPage: WelcomeContentPage = .whatIsMastodon
    var currentPageOffset = 0
}

extension WelcomeViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        definesPresentationContext = true
        preferredContentSize = CGSize(width: 547, height: 678)
        
        navigationController?.navigationBar.prefersLargeTitles = true
        view.overrideUserInterfaceStyle = .light
        
        setupOnboardingAppearance()
        
        view.addSubview(welcomeIllustrationView)
        welcomeIllustrationView.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            welcomeIllustrationView.topAnchor.constraint(equalTo: view.topAnchor),
            welcomeIllustrationView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: welcomeIllustrationView.trailingAnchor),
            view.bottomAnchor.constraint(equalTo: welcomeIllustrationView.bottomAnchor)
        ])
        
        buttonContainer.axis = .vertical
        buttonContainer.spacing = 12
        buttonContainer.isLayoutMarginsRelativeArrangement = true
        
        buttonContainer.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(buttonContainer)
        NSLayoutConstraint.activate([
            buttonContainer.leadingAnchor.constraint(equalTo: view.readableContentGuide.leadingAnchor),
            buttonContainer.trailingAnchor.constraint(equalTo: view.readableContentGuide.trailingAnchor),
            view.layoutMarginsGuide.bottomAnchor.constraint(equalTo: buttonContainer.bottomAnchor),
        ])
        
        signUpButton.translatesAutoresizingMaskIntoConstraints = false
        buttonContainer.addArrangedSubview(signUpButton)
        NSLayoutConstraint.activate([
            signUpButton.heightAnchor.constraint(greaterThanOrEqualToConstant: WelcomeViewController.actionButtonHeight).priority(.required - 1),
        ])
        signInButton.translatesAutoresizingMaskIntoConstraints = false
        buttonContainer.addArrangedSubview(signInButton)
        NSLayoutConstraint.activate([
            signInButton.heightAnchor.constraint(greaterThanOrEqualToConstant: WelcomeViewController.actionButtonHeight).priority(.required - 1),
        ])
        
        signUpButtonShadowView.translatesAutoresizingMaskIntoConstraints = false
        buttonContainer.addSubview(signUpButtonShadowView)
        buttonContainer.sendSubviewToBack(signUpButtonShadowView)
        signUpButtonShadowView.pinTo(to: signUpButton)
        
        signUpButton.addTarget(self, action: #selector(signUpButtonDidClicked(_:)), for: .touchUpInside)
        signInButton.addTarget(self, action: #selector(signInButtonDidClicked(_:)), for: .touchUpInside)
        
        pageViewController.delegate = self
        pageViewController.dataSource = self
        addChild(pageViewController)
        pageViewController.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(pageViewController.view)
        pageViewController.didMove(toParent: self)
        
        let scrollviews = pageViewController.view.subviews.filter { type(of: $0).isSubclass(of: UIScrollView.self) }.compactMap { $0 as? UIScrollView }
        
        for scrollView in scrollviews {
            scrollView.delegate = self
        }
        
        NSLayoutConstraint.activate([
            pageViewController.view.topAnchor.constraint(equalTo: view.topAnchor, constant: computedTopAnchorInset),
            pageViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: pageViewController.view.trailingAnchor),
            buttonContainer.topAnchor.constraint(equalTo: pageViewController.view.bottomAnchor, constant: 16),
        ])
        
        viewModel.$needsShowDismissEntry
            .receive(on: DispatchQueue.main)
            .sink { [weak self] needsShowDismissEntry in
                guard let self = self else { return }
                self.navigationItem.leftBarButtonItem = needsShowDismissEntry ? self.dismissBarButtonItem : nil
            }
            .store(in: &disposeBag)
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        
        setupButtonShadowView()
    }
    
    override func viewSafeAreaInsetsDidChange() {
        super.viewSafeAreaInsetsDidChange()
        
        var overlap: CGFloat = 5
        // shift illustration down for non-notch phone
        if view.safeAreaInsets.bottom == 0 {
            overlap += 56
        }
    }
    
    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)
        
        view.layoutIfNeeded()
        
        setupIllustrationLayout()
        setupButtonShadowView()
    }
    
    private var computedTopAnchorInset: CGFloat {
        (navigationController?.navigationBar.bounds.height ?? UINavigationBar().bounds.height) + Constants.topAnchorInset
    }
}

extension WelcomeViewController {
    
    private func setupButtonShadowView() {
        signUpButtonShadowView.layer.setupShadow(
            color: .black,
            alpha: 0.25,
            x: 0,
            y: 1,
            blur: 2,
            spread: 0,
            roundedRect: signUpButtonShadowView.bounds,
            byRoundingCorners: .allCorners,
            cornerRadii: CGSize(width: 10, height: 10)
        )
    }
    
    private func updateButtonContainerLayoutMargins(traitCollection: UITraitCollection) {
        switch traitCollection.userInterfaceIdiom {
        case .phone:
            buttonContainer.layoutMargins = UIEdgeInsets(
                top: 0,
                left: WelcomeViewController.actionButtonMargin,
                bottom: WelcomeViewController.viewBottomPaddingHeight,
                right: WelcomeViewController.actionButtonMargin
            )
        default:
            let margin = traitCollection.horizontalSizeClass == .regular ? WelcomeViewController.actionButtonMarginExtend : WelcomeViewController.actionButtonMargin
            buttonContainer.layoutMargins = UIEdgeInsets(
                top: 0,
                left: margin,
                bottom: WelcomeViewController.viewBottomPaddingHeightExtend,
                right: margin
            )
        }
    }
    
    private func setupIllustrationLayout() {
        welcomeIllustrationView.setup()
    }
}

extension WelcomeViewController {
    @objc
    private func signUpButtonDidClicked(_ sender: UIButton) {
        _ = coordinator.present(scene: .mastodonPickServer(viewMode: MastodonPickServerViewModel(context: context)), from: self, transition: .show)
    }
    
    @objc
    private func signInButtonDidClicked(_ sender: UIButton) {
        _ = coordinator.present(scene: .mastodonLogin, from: self, transition: .show)
    }
    
    @objc
    private func dismissBarButtonItemDidPressed(_ sender: UIButton) {
        dismiss(animated: true, completion: nil)
    }
}

// MARK: - OnboardingViewControllerAppearance
extension WelcomeViewController: OnboardingViewControllerAppearance {
    func setupNavigationBarAppearance() {
        // always transparent
        let barAppearance = UINavigationBarAppearance()
        barAppearance.configureWithTransparentBackground()
        navigationItem.standardAppearance = barAppearance
        navigationItem.compactAppearance = barAppearance
        navigationItem.scrollEdgeAppearance = barAppearance
        navigationItem.compactScrollEdgeAppearance = barAppearance
    }
}

// MARK: - UIAdaptivePresentationControllerDelegate
extension WelcomeViewController: UIAdaptivePresentationControllerDelegate {
    
    func adaptivePresentationStyle(for controller: UIPresentationController, traitCollection: UITraitCollection) -> UIModalPresentationStyle {
        
        // update button layout
        updateButtonContainerLayoutMargins(traitCollection: traitCollection)
        
        let navigationController = navigationController as? OnboardingNavigationController
        
        switch traitCollection.userInterfaceIdiom {
        case .phone:
            navigationController?.gradientBorderView.isHidden = true
            // make underneath view controller alive to fix layout issue due to view life cycle
            return .fullScreen
        default:
            switch traitCollection.horizontalSizeClass {
            case .compact:
                navigationController?.gradientBorderView.isHidden = true
                return .fullScreen
            default:
                navigationController?.gradientBorderView.isHidden = false
                return .formSheet
            }
        }
    }
    
    func presentationController(_ controller: UIPresentationController, viewControllerForAdaptivePresentationStyle style: UIModalPresentationStyle) -> UIViewController? {
        return nil
    }
    
    func presentationControllerShouldDismiss(_ presentationController: UIPresentationController) -> Bool {
        return false
    }
}

//MARK: - UIPageViewControllerDelegate

extension WelcomeViewController: UIPageViewControllerDelegate {
    func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
        guard let currentViewController = pageViewController.viewControllers?.first as? WelcomeContentViewController else { return }
        
        currentPage = currentViewController.page
        
        if let pageIndex = WelcomeContentPage.allCases.firstIndex(of: currentPage) {
            let offset = Int(pageIndex) * Int(pageViewController.view.frame.width)
            currentPageOffset = offset
            welcomeIllustrationView.update(contentOffset: CGFloat(offset))
        }
    }
}

//MARK: - UIPageViewDataSource

extension WelcomeViewController: UIPageViewControllerDataSource {
    
    func presentationIndex(for pageViewController: UIPageViewController) -> Int {
        WelcomeContentPage.allCases.firstIndex(of: currentPage) ?? 0
    }
    
    func presentationCount(for pageViewController: UIPageViewController) -> Int {
        return WelcomeContentPage.allCases.count
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
        guard let viewController = viewController as? WelcomeContentViewController else { return nil }
        
        let currentPage = viewController.page
        
        switch currentPage {
        case .whatIsMastodon:
            return nil
        case .mastodonIsLikeThat:
            return WelcomeContentViewController(page: .whatIsMastodon)
        case .howDoIPickAServer:
            return WelcomeContentViewController(page: .mastodonIsLikeThat)
        }
    }
    
    func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
        guard let viewController = viewController as? WelcomeContentViewController else { return nil }
        
        let currentPage = viewController.page
        
        switch currentPage {
        case .whatIsMastodon:
            return WelcomeContentViewController(page: .mastodonIsLikeThat)
        case .mastodonIsLikeThat:
            return WelcomeContentViewController(page: .howDoIPickAServer)
        case .howDoIPickAServer:
            return nil
        }
    }
}

extension WelcomeViewController: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let weirdScrollViewJumpingCorrectionFactor = pageViewController.view.frame.width
        let contentOffset = CGFloat(currentPageOffset) + scrollView.contentOffset.x - weirdScrollViewJumpingCorrectionFactor
        
        welcomeIllustrationView.update(contentOffset: contentOffset)
    }
}