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

import UIKit
import Logging

protocol SelectLocationViewControllerDelegate: AnyObject {
    func selectLocationViewController(_ controller: SelectLocationViewController, didSelectRelayLocation relayLocation: RelayLocation)
}

class SelectLocationViewController: UIViewController, UITableViewDelegate {

    static let cellReuseIdentifier = "Cell"

    private var tableView: UITableView?

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

    private let logger = Logger(label: "SelectLocationController")
    private var dataSource: LocationDataSource?
    private var setCachedRelaysOnViewDidLoad: RelayCache.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
    }

    weak var delegate: SelectLocationViewControllerDelegate?
    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", comment: "Navigation title")

        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

        tableView.register(SelectLocationCell.self, forCellReuseIdentifier: Self.cellReuseIdentifier)

        self.tableView = tableView

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

        tableHeaderFooterView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(tableHeaderFooterView)

        dataSource = LocationDataSource(
            tableView: tableView,
            cellProvider: { [weak self] (tableView, indexPath, item) -> UITableViewCell? in
                guard let self = self else { return nil }

                let cell = tableView.dequeueReusableCell(withIdentifier: Self.cellReuseIdentifier, for: indexPath)
                    as! SelectLocationCell

                cell.accessibilityIdentifier = item.location.stringRepresentation
                cell.isDisabled = !item.isActive
                cell.locationLabel.text = item.displayName
                cell.showsCollapseControl = item.isCollapsible
                cell.isExpanded = item.showsChildren
                cell.didCollapseHandler = { [weak self] (cell) in
                    self?.collapseCell(cell)
                }

                return cell
            })

        tableView.delegate = self
        tableView.dataSource = dataSource

        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 = self.setCachedRelaysOnViewDidLoad {
            dataSource?.setRelays(setCachedRelaysOnViewDidLoad.relays)
        }

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

    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 = self.presentingViewController == nil

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

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        updateTableHeaderTopLayoutMargin()
    }

    // MARK: - UITableViewDelegate

    func tableView(_ tableView: UITableView, shouldHighlightRowAt indexPath: IndexPath) -> Bool {
        return dataSource?.item(for: indexPath)?.isActive ?? false
    }

    func tableView(_ tableView: UITableView, indentationLevelForRowAt indexPath: IndexPath) -> Int {
        return dataSource?.item(for: indexPath)?.indentationLevel ?? 0
    }

    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
        if let item = dataSource?.item(for: indexPath), item.location == dataSource?.selectedRelayLocation {
            cell.setSelected(true, animated: false)
        }
    }

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        guard let item = dataSource?.item(for: indexPath) else { return }

        dataSource?.setSelectedRelayLocation(
            item.location,
            showHiddenParents: false,
            animated: false,
            scrollPosition: .none
        )

        self.delegate?.selectLocationViewController(self, didSelectRelayLocation: item.location)
    }

    // MARK: - Public

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

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

        self.dataSource?.setSelectedRelayLocation(
            relayLocation,
            showHiddenParents: true,
            animated: animated,
            scrollPosition: scrollPosition
        )
    }

    // MARK: - Collapsible cells

    private func collapseCell(_ cell: SelectLocationCell) {
        guard let cellIndexPath = tableView?.indexPath(for: cell),
              let dataSource = dataSource, let location = dataSource.relayLocation(for: cellIndexPath) else {
            return
        }

        dataSource.toggleChildren(location, animated: true)
    }

    // 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 as? CustomNavigationBar, !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()
    }
}