//
//  SelectLocationViewController.swift
//  MullvadVPN
//
//  Created by pronebird on 02/05/2019.
//  Copyright © 2019 Mullvad VPN AB. All rights reserved.
//

import MullvadLogging
import MullvadTypes
import RelayCache
import UIKit

final class SelectLocationViewController: UIViewController, UITableViewDelegate {
    private var tableView: UITableView?

    private let tableHeaderFooterView = SelectLocationHeaderView()
    private var tableHeaderFooterViewTopConstraints: [NSLayoutConstraint] = []
    private var tableHeaderFooterViewBottomConstraints: [NSLayoutConstraint] = []

    private var dataSource: LocationDataSource?
    private var setCachedRelaysOnViewDidLoad: CachedRelays?
    private var setRelayLocationOnViewDidLoad: RelayLocation?
    private var setScrollPositionOnViewDidLoad: UITableView.ScrollPosition = .none
    private var isViewAppeared = false

    private var showHeaderViewAtTheBottom = false {
        didSet {
            setTableHeaderFooterConstraints()
        }
    }

    override var preferredStatusBarStyle: UIStatusBarStyle {
        return .lightContent
    }

    var didSelectRelay: ((SelectLocationViewController, RelayLocation) -> Void)?
    var didFinish: ((SelectLocationViewController) -> Void)?

    var scrollToSelectedRelayOnViewWillAppear = true

    init() {
        super.init(nibName: nil, bundle: nil)
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // MARK: - View lifecycle

    override func viewDidLoad() {
        super.viewDidLoad()

        navigationItem.largeTitleDisplayMode = .never
        navigationItem.title = NSLocalizedString(
            "NAVIGATION_TITLE",
            tableName: "SelectLocation",
            value: "Select Location",
            comment: ""
        )
        navigationItem.rightBarButtonItem = UIBarButtonItem(
            barButtonSystemItem: .done,
            target: self,
            action: #selector(handleDone)
        )

        let tableView = UITableView(frame: view.bounds, style: .plain)
        tableView.translatesAutoresizingMaskIntoConstraints = false
        tableView.backgroundColor = .clear
        tableView.separatorColor = .secondaryColor
        tableView.separatorInset = .zero
        tableView.estimatedRowHeight = 53
        tableView.indicatorStyle = .white

        self.tableView = tableView
        dataSource = LocationDataSource(tableView: tableView)
        tableView.dataSource = dataSource

        dataSource?.didSelectRelayLocation = { [weak self] location in
            guard let self = self else { return }

            self.didSelectRelay?(self, location)
        }

        view.accessibilityElements = [tableHeaderFooterView, tableView]
        view.backgroundColor = .secondaryColor
        view.addSubview(tableView)

        tableHeaderFooterView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(tableHeaderFooterView)

        tableHeaderFooterViewTopConstraints = [
            tableHeaderFooterView.topAnchor.constraint(equalTo: view.topAnchor),
            tableView.topAnchor.constraint(equalTo: tableHeaderFooterView.bottomAnchor),
            tableView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ]
        tableHeaderFooterViewBottomConstraints = [
            tableHeaderFooterView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            tableView.topAnchor.constraint(equalTo: view.topAnchor),
            tableView.bottomAnchor.constraint(equalTo: tableHeaderFooterView.topAnchor),
        ]

        NSLayoutConstraint.activate([
            tableHeaderFooterView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            tableHeaderFooterView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            tableView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            tableView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        ])
        setTableHeaderFooterConstraints()

        if let setCachedRelaysOnViewDidLoad = setCachedRelaysOnViewDidLoad {
            dataSource?.setRelays(setCachedRelaysOnViewDidLoad.relays)
        }

        if let setRelayLocationOnViewDidLoad = setRelayLocationOnViewDidLoad {
            dataSource?.setSelectedRelayLocation(
                setRelayLocationOnViewDidLoad,
                animated: false
            )
        }
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)

        // Show header view at the bottom when controller is presented inline and show header view
        // at the top of the view when controller is presented modally.
        showHeaderViewAtTheBottom = presentingViewController == nil

        if let indexPath = dataSource?.indexPathForSelectedRelay(),
           scrollToSelectedRelayOnViewWillAppear, !isViewAppeared
        {
            tableView?.scrollToRow(at: indexPath, at: .middle, animated: false)
        }
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        isViewAppeared = true

        tableView?.flashScrollIndicators()
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)

        isViewAppeared = false
    }

    override func viewWillTransition(
        to size: CGSize,
        with coordinator: UIViewControllerTransitionCoordinator
    ) {
        super.viewWillTransition(to: size, with: coordinator)

        coordinator.animate(alongsideTransition: nil) { context in
            guard let indexPath = self.dataSource?.indexPathForSelectedRelay() else { return }

            self.tableView?.scrollToRow(at: indexPath, at: .middle, animated: false)
        }
    }

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        updateTableHeaderTopLayoutMargin()
    }

    // MARK: - Public

    func setCachedRelays(_ cachedRelays: CachedRelays) {
        guard isViewLoaded else {
            setCachedRelaysOnViewDidLoad = cachedRelays
            return
        }
        dataSource?.setRelays(cachedRelays.relays)
    }

    func setSelectedRelayLocation(
        _ relayLocation: RelayLocation?,
        animated: Bool,
        scrollPosition: UITableView.ScrollPosition
    ) {
        guard isViewLoaded else {
            setRelayLocationOnViewDidLoad = relayLocation
            setScrollPositionOnViewDidLoad = scrollPosition
            return
        }

        dataSource?.setSelectedRelayLocation(
            relayLocation,
            animated: animated
        )
    }

    // MARK: - Private

    private func updateTableHeaderTopLayoutMargin() {
        // When contained within the navigation controller, we want the distance between
        // the navigation title and the table header label to be exactly 24pt.
        if let navigationBar = navigationController?.navigationBar, !showHeaderViewAtTheBottom {
            tableHeaderFooterView.topLayoutMarginAdjustmentForNavigationBarTitle = navigationBar
                .titleLabelBottomInset
        } else {
            tableHeaderFooterView.topLayoutMarginAdjustmentForNavigationBarTitle = 0
        }
    }

    private func setTableHeaderFooterConstraints() {
        if showHeaderViewAtTheBottom {
            NSLayoutConstraint.deactivate(
                tableHeaderFooterViewTopConstraints
            )
            NSLayoutConstraint.activate(tableHeaderFooterViewBottomConstraints)
        } else {
            NSLayoutConstraint.deactivate(
                tableHeaderFooterViewBottomConstraints
            )
            NSLayoutConstraint.activate(tableHeaderFooterViewTopConstraints)
        }
        view.layoutIfNeeded()
    }

    @objc private func handleDone() {
        didFinish?(self)
    }
}