//
//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
//

import UIKit
import PromiseKit

private protocol OnboardingCodeViewTextFieldDelegate {
    func textFieldDidDeletePrevious()
}

// MARK: -

// Editing a code should feel seamless, as even though
// the UITextField only lets you edit a single digit at
// a time.  For deletes to work properly, we need to
// detect delete events that would affect the _previous_
// digit.
private class OnboardingCodeViewTextField: UITextField {

    fileprivate var codeDelegate: OnboardingCodeViewTextFieldDelegate?

    override func deleteBackward() {
        var isDeletePrevious = false
        if let selectedTextRange = selectedTextRange {
            let cursorPosition = offset(from: beginningOfDocument, to: selectedTextRange.start)
            if cursorPosition == 0 {
                isDeletePrevious = true
            }
        }

        super.deleteBackward()

        if isDeletePrevious {
            codeDelegate?.textFieldDidDeletePrevious()
        }
    }

}

// MARK: -

protocol OnboardingCodeViewDelegate {
    func codeViewDidChange()
}

// MARK: -

// The OnboardingCodeView is a special "verification code"
// editor that should feel like editing a single piece
// of text (ala UITextField) even though the individual
// digits of the code are visually separated.
//
// We use a separate UILabel for each digit, and move
// around a single UITextfield to let the user edit the
// last/next digit.
private class OnboardingCodeView: UIView {

    var delegate: OnboardingCodeViewDelegate?

    public init() {
        super.init(frame: .zero)

        createSubviews()

        updateViewState()
    }

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

    private let digitCount = 6
    private var digitLabels = [UILabel]()

    // We use a single text field to edit the "current" digit.
    // The "current" digit is usually the "last"
    fileprivate let textfield = OnboardingCodeViewTextField()
    private var currentDigitIndex = 0
    private var textfieldConstraints = [NSLayoutConstraint]()

    // The current complete text - the "model" for this view.
    private var digitText = ""

    var isComplete: Bool {
        return digitText.count == digitCount
    }
    var verificationCode: String {
        return digitText
    }

    private func createSubviews() {
        textfield.textAlignment = .left
        textfield.delegate = self
        textfield.keyboardType = .numberPad
        textfield.textColor = Theme.primaryColor
        textfield.font = UIFont.ows_dynamicTypeLargeTitle1Clamped
        textfield.codeDelegate = self

        var digitViews = [UIView]()
        (0..<digitCount).forEach { (_) in
            let (digitView, digitLabel) = makeCellView(text: "", hasStroke: true)

            digitLabels.append(digitLabel)
            digitViews.append(digitView)
        }

        let (hyphenView, _) = makeCellView(text: "-", hasStroke: false)

        digitViews.insert(hyphenView, at: 3)

        let stackView = UIStackView(arrangedSubviews: digitViews)
        stackView.axis = .horizontal
        stackView.alignment = .center
        stackView.spacing = 8
        addSubview(stackView)
        stackView.autoPinHeightToSuperview()
        stackView.autoHCenterInSuperview()

        self.addSubview(textfield)
    }

    private func makeCellView(text: String, hasStroke: Bool) -> (UIView, UILabel) {
        let digitView = UIView()

        let digitLabel = UILabel()
        digitLabel.text = text
        digitLabel.font = UIFont.ows_dynamicTypeLargeTitle1Clamped
        digitLabel.textColor = Theme.primaryColor
        digitLabel.textAlignment = .center
        digitView.addSubview(digitLabel)
        digitLabel.autoCenterInSuperview()

        if hasStroke {
            let strokeView = UIView.container()
            strokeView.backgroundColor = Theme.primaryColor
            digitView.addSubview(strokeView)
            strokeView.autoPinWidthToSuperview()
            strokeView.autoPinEdge(toSuperviewEdge: .bottom)
            strokeView.autoSetDimension(.height, toSize: 1)
        }

        let vMargin: CGFloat = 4
        let cellHeight: CGFloat = digitLabel.font.lineHeight + vMargin * 2
        let cellWidth: CGFloat = cellHeight * 2 / 3
        digitView.autoSetDimensions(to: CGSize(width: cellWidth, height: cellHeight))

        return (digitView, digitLabel)
    }

    private func digit(at index: Int) -> String {
        guard index < digitText.count else {
            return ""
        }
        return digitText.substring(from: index).trim(after: 1)
    }

    // Ensure that all labels are displaying the correct
    // digit (if any) and that the UITextField has replaced
    // the "current" digit.
    private func updateViewState() {
        currentDigitIndex = min(digitCount - 1,
                                digitText.count)

        (0..<digitCount).forEach { (index) in
            let digitLabel = digitLabels[index]
            digitLabel.text = digit(at: index)
            digitLabel.isHidden = index == currentDigitIndex
        }

        NSLayoutConstraint.deactivate(textfieldConstraints)
        textfieldConstraints.removeAll()

        let digitLabelToReplace = digitLabels[currentDigitIndex]
        textfield.text = digit(at: currentDigitIndex)
        textfieldConstraints.append(textfield.autoAlignAxis(.horizontal, toSameAxisOf: digitLabelToReplace))
        textfieldConstraints.append(textfield.autoAlignAxis(.vertical, toSameAxisOf: digitLabelToReplace))

        // Move cursor to end of text.
        let newPosition = textfield.endOfDocument
        textfield.selectedTextRange = textfield.textRange(from: newPosition, to: newPosition)
    }

    public override func becomeFirstResponder() -> Bool {
        return textfield.becomeFirstResponder()
    }
}

// MARK: -

extension OnboardingCodeView: UITextFieldDelegate {
    public func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString newString: String) -> Bool {
        var oldText = ""
        if let textFieldText = textField.text {
            oldText = textFieldText
        }
        let left = oldText.substring(to: range.location)
        let right = oldText.substring(from: range.location + range.length)
        let unfiltered = left + newString + right
        let characterSet = CharacterSet(charactersIn: "0123456789")
        let filtered = unfiltered.components(separatedBy: characterSet.inverted).joined()
        let filteredAndTrimmed = filtered.trim(after: 1)
        textField.text = filteredAndTrimmed

        digitText = digitText.trim(after: currentDigitIndex) + filteredAndTrimmed

        updateViewState()

        self.delegate?.codeViewDidChange()

        // Inform our caller that we took care of performing the change.
        return false
    }

    public func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        self.delegate?.codeViewDidChange()

        return false
    }
}

// MARK: -

extension OnboardingCodeView: OnboardingCodeViewTextFieldDelegate {
    public func textFieldDidDeletePrevious() {
        guard digitText.count > 0 else {
            return
        }
        digitText = digitText.substring(to: currentDigitIndex - 1)

        updateViewState()
    }
}

// MARK: -

@objc
public class OnboardingVerificationViewController: OnboardingBaseViewController {

    private enum CodeState {
        case pending
        case possiblyNotDelivered
        case resent
    }

    // MARK: -

    private var codeState = CodeState.pending

    private var titleLabel: UILabel?
    private let phoneNumberTextField = UITextField()
    private let onboardingCodeView = OnboardingCodeView()
    private var codeStateLink: OWSFlatButton?

    override public func loadView() {
        super.loadView()

        view.backgroundColor = Theme.backgroundColor
        view.layoutMargins = .zero

        let titleLabel = self.titleLabel(text: "")
        self.titleLabel = titleLabel

        let backLink = self.linkButton(title: NSLocalizedString("ONBOARDING_VERIFICATION_BACK_LINK",
                                                                comment: "Label for the link that lets users change their phone number."),
                                       selector: #selector(backLinkTapped))

        onboardingCodeView.delegate = self

        let codeStateLink = self.linkButton(title: "",
                                             selector: #selector(resendCodeLinkTapped))
        codeStateLink.enableMultilineLabel()
        self.codeStateLink = codeStateLink

        let topSpacer = UIView.vStretchingSpacer()
        let bottomSpacer = UIView.vStretchingSpacer()

        let stackView = UIStackView(arrangedSubviews: [
            titleLabel,
            UIView.spacer(withHeight: 21),
            backLink,
            topSpacer,
            onboardingCodeView,
            bottomSpacer,
            codeStateLink
            ])
        stackView.axis = .vertical
        stackView.alignment = .fill
        stackView.layoutMargins = UIEdgeInsets(top: 32, left: 32, bottom: 32, right: 32)
        stackView.isLayoutMarginsRelativeArrangement = true
        view.addSubview(stackView)
        stackView.autoPinWidthToSuperview()
        stackView.autoPin(toTopLayoutGuideOf: self, withInset: 0)
        autoPinView(toBottomOfViewControllerOrKeyboard: stackView, avoidNotch: true)

        // Ensure whitespace is balanced, so inputs are vertically centered.
        topSpacer.autoMatch(.height, to: .height, of: bottomSpacer)

        startCodeCountdown()

        updateCodeState()
    }

     // MARK: - Code State

    private let countdownDuration: TimeInterval = 60
    private var codeCountdownTimer: Timer?
    private var codeCountdownStart: NSDate?

    deinit {
        if let codeCountdownTimer = codeCountdownTimer {
            codeCountdownTimer.invalidate()
        }
    }

    private func startCodeCountdown() {
        codeCountdownStart = NSDate()
        codeCountdownTimer = Timer.weakScheduledTimer(withTimeInterval: 1, target: self, selector: #selector(codeCountdownTimerFired), userInfo: nil, repeats: true)
    }

    @objc
    public func codeCountdownTimerFired() {
        guard let codeCountdownStart = codeCountdownStart else {
            owsFailDebug("Missing codeCountdownStart.")
            return
        }
        guard let codeCountdownTimer = codeCountdownTimer else {
            owsFailDebug("Missing codeCountdownTimer.")
            return
        }

        let countdownInterval = abs(codeCountdownStart.timeIntervalSinceNow)

        guard countdownInterval < countdownDuration else {
            // Countdown complete.
            codeCountdownTimer.invalidate()
            self.codeCountdownTimer = nil

            if codeState != .pending {
                owsFailDebug("Unexpected codeState: \(codeState)")
            }
            codeState = .possiblyNotDelivered
            updateCodeState()
            return
        }

        // Update the "code state" UI to reflect the countdown.
        updateCodeState()
    }

    private func updateCodeState() {
        AssertIsOnMainThread()

        guard let codeCountdownStart = codeCountdownStart else {
            owsFailDebug("Missing codeCountdownStart.")
            return
        }
        guard let titleLabel = titleLabel else {
            owsFailDebug("Missing titleLabel.")
            return
        }
        guard let codeStateLink = codeStateLink else {
            owsFailDebug("Missing codeStateLink.")
            return
        }

        var e164PhoneNumber = ""
        if let phoneNumber = onboardingController.phoneNumber {
            e164PhoneNumber = phoneNumber.e164
        }
        let formattedPhoneNumber = PhoneNumber.bestEffortLocalizedPhoneNumber(withE164: e164PhoneNumber)

        // Update titleLabel
        switch codeState {
        case .pending, .possiblyNotDelivered:
            titleLabel.text = String(format: NSLocalizedString("ONBOARDING_VERIFICATION_TITLE_DEFAULT_FORMAT",
                                                               comment: "Format for the title of the 'onboarding verification' view. Embeds {{the user's phone number}}."),
                                     formattedPhoneNumber)
        case .resent:
            titleLabel.text = String(format: NSLocalizedString("ONBOARDING_VERIFICATION_TITLE_RESENT_FORMAT",
                                                               comment: "Format for the title of the 'onboarding verification' view after the verification code has been resent. Embeds {{the user's phone number}}."),
                                     formattedPhoneNumber)
        }

        // Update codeStateLink
        switch codeState {
        case .pending:
            let countdownInterval = abs(codeCountdownStart.timeIntervalSinceNow)
            let countdownRemaining = max(0, countdownDuration - countdownInterval)
            let formattedCountdown = OWSFormat.formatDurationSeconds(Int(round(countdownRemaining)))
            let text = String(format: NSLocalizedString("ONBOARDING_VERIFICATION_CODE_COUNTDOWN_FORMAT",
                                                        comment: "Format for the label of the 'pending code' label of the 'onboarding verification' view. Embeds {{the time until the code can be resent}}."),
                              formattedCountdown)
            codeStateLink.setTitle(title: text, font: .ows_dynamicTypeBodyClamped, titleColor: Theme.secondaryColor)
//            codeStateLink.setBackgroundColors(upColor: Theme.backgroundColor)
        case .possiblyNotDelivered:
            codeStateLink.setTitle(title: NSLocalizedString("ONBOARDING_VERIFICATION_ORIGINAL_CODE_MISSING_LINK",
                                                            comment: "Label for link that can be used when the original code did not arrive."),
                                   font: .ows_dynamicTypeBodyClamped,
                                   titleColor: .ows_materialBlue)
        case .resent:
            codeStateLink.setTitle(title: NSLocalizedString("ONBOARDING_VERIFICATION_RESENT_CODE_MISSING_LINK",
                                                            comment: "Label for link that can be used when the resent code did not arrive."),
                                   font: .ows_dynamicTypeBodyClamped,
                                   titleColor: .ows_materialBlue)
        }
    }

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

        _ = onboardingCodeView.becomeFirstResponder()
    }

    // MARK: - Events

    @objc func backLinkTapped() {
        Logger.info("")

        self.navigationController?.popViewController(animated: true)
    }

    @objc func ignoreEvent() {
        Logger.info("")
    }

    @objc func resendCodeLinkTapped() {
        Logger.info("")

        switch codeState {
        case .pending:
            // Ignore taps until the countdown expires.
            break
        case .possiblyNotDelivered, .resent:
            showResendActionSheet()
        }
    }

    private func showResendActionSheet() {
        Logger.info("")

        let actionSheet = UIAlertController(title: NSLocalizedString("ONBOARDING_VERIFICATION_RESEND_CODE_ALERT_TITLE",
                                                                     comment: "Title for the 'resend code' alert in the 'onboarding verification' view."),
                                            message: NSLocalizedString("ONBOARDING_VERIFICATION_RESEND_CODE_ALERT_MESSAGE",
                                                                       comment: "Message for the 'resend code' alert in the 'onboarding verification' view."),
                                            preferredStyle: .actionSheet)

        actionSheet.addAction(UIAlertAction(title: NSLocalizedString("ONBOARDING_VERIFICATION_RESEND_CODE_BY_SMS_BUTTON",
                                                                     comment: "Label for the 'resend code by SMS' button in the 'onboarding verification' view."),
                                            style: .default) { _ in
                                                self.onboardingController.tryToRegister(fromViewController: self, smsVerification: true)
        })
        actionSheet.addAction(UIAlertAction(title: NSLocalizedString("ONBOARDING_VERIFICATION_RESEND_CODE_BY_VOICE_BUTTON",
                                                                     comment: "Label for the 'resend code by voice' button in the 'onboarding verification' view."),
                                            style: .default) { _ in
                                                self.onboardingController.tryToRegister(fromViewController: self, smsVerification: false)
        })
        actionSheet.addAction(OWSAlerts.cancelAction)

        self.present(actionSheet, animated: true)
    }

    private func tryToVerify() {
        Logger.info("")

        guard onboardingCodeView.isComplete else {
            return
        }
        onboardingController.tryToVerify(fromViewController: self, verificationCode: onboardingCodeView.verificationCode, pin: nil)
    }
}

// MARK: -

extension OnboardingVerificationViewController: OnboardingCodeViewDelegate {
    public func codeViewDidChange() {
        AssertIsOnMainThread()

        tryToVerify()
    }
}