//
//  AppButton.swift
//  MullvadVPN
//
//  Created by pronebird on 23/05/2019.
//  Copyright © 2019 Mullvad VPN AB. All rights reserved.
//

import UIKit

enum ButtonImageAlignment {
    /// Align image at the left edge of the title label
    case left

    /// Align image at the right edge of the title label
    case right

    /// Align image at the leading edge of the title label
    case leading

    /// Align image at the trailing edge of the title label
    case trailing

    /// Align image at the leading edge of content area
    case leadingFixed

    /// Align image at the trailing edge of the content area
    case trailingFixed

    /// Align image at the left edge of the content area
    case leftFixed

    /// Align image at the right edge of the content area
    case rightFixed
}

private extension UIControl.State {
    var customButtonTitleColor: UIColor? {
        switch self {
        case .normal:
            return UIColor.AppButton.normalTitleColor
        case .disabled:
            return UIColor.AppButton.disabledTitleColor.withAlphaComponent(0.5)
        case .highlighted:
            return UIColor.AppButton.highlightedTitleColor
        default:
            return nil
        }
    }
}

/// A subclass that implements the button that visually look like URL links on the web
class LinkButton: CustomButton {
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }

    var titleString: String? {
        didSet {
            updateAttributedTitle(string: titleString)
        }
    }

    private func commonInit() {
        imageAlignment = .trailing
        contentHorizontalAlignment = .leading

        accessibilityTraits.insert(.link)
    }

    private func updateAttributedTitle(string: String?) {
        let states: [UIControl.State] = [.normal, .highlighted, .disabled]
        states.forEach { state in
            let attributedTitle = string.flatMap { makeAttributedTitle($0, for: state) }
            self.setAttributedTitle(attributedTitle, for: state)
        }
    }

    private func makeAttributedTitle(
        _ title: String,
        for state: UIControl.State
    ) -> NSAttributedString {
        var attributes: [NSAttributedString.Key: Any] = [
            .underlineStyle: NSUnderlineStyle.single.rawValue,
        ]

        if let titleColor = state.customButtonTitleColor {
            attributes[.foregroundColor] = titleColor
        }

        return NSAttributedString(string: title, attributes: attributes)
    }
}

/// A subclass that implements action buttons used across the app
class AppButton: CustomButton {
    /// Default content insets based on current trait collection.
    var defaultContentInsets: UIEdgeInsets {
        switch traitCollection.userInterfaceIdiom {
        case .phone:
            return UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
        case .pad:
            return UIEdgeInsets(top: 15, left: 15, bottom: 15, right: 15)
        default:
            return .zero
        }
    }

    enum Style: Int {
        /// Default blue appearance.
        case `default`

        /// Destructive appearance.
        case danger

        /// Positive appearance suitable for actions that provide security.
        case success

        /// Translucent destructive appearance.
        case translucentDanger

        /// Translucent neutral appearance.
        case translucentNeutral

        /// Translucent destructive appearance for the left-hand side of a two component split button.
        case translucentDangerSplitLeft

        /// Translucent destructive appearance for the right-hand side of a two component split button.
        case translucentDangerSplitRight

        /// Default blue rounded button suitable for presentation in table view using `.insetGrouped` style.
        case tableInsetGroupedDefault

        /// Positive appearance for presentation in table view using `.insetGrouped` style.
        case tableInsetGroupedSuccess

        /// Destructive style suitable for presentation in table view using `.insetGrouped` style.
        case tableInsetGroupedDanger

        /// Returns a background image for the button.
        var backgroundImage: UIImage {
            switch self {
            case .default:
                UIImage(resource: .defaultButton)
            case .danger:
                UIImage(resource: .dangerButton)
            case .success:
                UIImage(resource: .successButton)
            case .translucentDanger:
                UIImage(resource: .translucentDangerButton)
            case .translucentNeutral:
                UIImage(resource: .translucentNeutralButton)
            case .translucentDangerSplitLeft:
                UIImage(resource: .translucentDangerSplitLeftButton).imageFlippedForRightToLeftLayoutDirection()
            case .translucentDangerSplitRight:
                UIImage(resource: .translucentDangerSplitRightButton).imageFlippedForRightToLeftLayoutDirection()
            case .tableInsetGroupedDefault:
                DynamicAssets.shared.tableInsetGroupedDefaultBackground
            case .tableInsetGroupedSuccess:
                DynamicAssets.shared.tableInsetGroupedSuccessBackground
            case .tableInsetGroupedDanger:
                DynamicAssets.shared.tableInsetGroupedDangerBackground
            }
        }
    }

    /// Button style.
    var style: Style {
        didSet {
            updateButtonBackground()
        }
    }

    /// Prevents updating `contentEdgeInsets` on changes to trait collection.
    var overrideContentEdgeInsets = false

    override var contentEdgeInsets: UIEdgeInsets {
        didSet {
            // Reset inner directional insets when contentEdgeInsets are set directly.
            innerDirectionalContentEdgeInsets = nil
        }
    }

    /// Directional content edge insets that are automatically translated into `contentEdgeInsets` immeditely upon updating the property and on trait collection
    /// changes.
    var directionalContentEdgeInsets: NSDirectionalEdgeInsets {
        get {
            innerDirectionalContentEdgeInsets ?? contentEdgeInsets.toDirectionalInsets
        }
        set {
            innerDirectionalContentEdgeInsets = newValue
            updateContentEdgeInsetsFromDirectional()
        }
    }

    private var innerDirectionalContentEdgeInsets: NSDirectionalEdgeInsets?

    init(style: Style) {
        self.style = style
        super.init(frame: .zero)
        commonInit()
    }

    override init(frame: CGRect) {
        style = .default
        super.init(frame: frame)
        commonInit()
    }

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

    private func commonInit() {
        super.contentEdgeInsets = defaultContentInsets
        imageAlignment = .trailingFixed

        titleLabel?.font = UIFont.systemFont(ofSize: 18, weight: .semibold)

        let states: [UIControl.State] = [.normal, .highlighted, .disabled]
        states.forEach { state in
            if let titleColor = state.customButtonTitleColor {
                setTitleColor(titleColor, for: state)
            }
        }

        // Avoid setting the background image if it's already set via Interface Builder
        if backgroundImage(for: .normal) == nil {
            updateButtonBackground()
        }
    }

    /// Set background image based on current style.
    private func updateButtonBackground() {
        setBackgroundImage(style.backgroundImage, for: .normal)
    }

    /// Update content edge insets from directional edge insets if set.
    private func updateContentEdgeInsetsFromDirectional() {
        guard let directionalEdgeInsets = innerDirectionalContentEdgeInsets else { return }
        super.contentEdgeInsets = directionalEdgeInsets.toEdgeInsets(effectiveUserInterfaceLayoutDirection)
    }

    override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
        super.traitCollectionDidChange(previousTraitCollection)

        if traitCollection.userInterfaceIdiom != previousTraitCollection?.userInterfaceIdiom {
            if overrideContentEdgeInsets {
                updateContentEdgeInsetsFromDirectional()
            } else {
                contentEdgeInsets = defaultContentInsets
            }
        }
    }
}

/// A custom `UIButton` subclass that implements additional layouts for the image
class CustomButton: UIButton {
    var imageAlignment: ButtonImageAlignment = .leading {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }

    var inlineImageSpacing: CGFloat = 4 {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }

    override var intrinsicContentSize: CGSize {
        var intrinsicSize = super.intrinsicContentSize

        // Add spacing between the image and title label in intrinsic size calculation
        if let imageSize = currentImage?.size, imageSize.width > 0 {
            intrinsicSize.width += inlineImageSpacing
        }

        return intrinsicSize
    }

    var effectiveImageAlignment: ButtonImageAlignment {
        switch (imageAlignment, effectiveUserInterfaceLayoutDirection) {
        case (.left, _),
             (.leading, .leftToRight),
             (.trailing, .rightToLeft):
            return .left

        case (.right, _),
             (.trailing, .leftToRight),
             (.leading, .rightToLeft):
            return .right

        case (.leftFixed, _),
             (.leadingFixed, .leftToRight),
             (.trailingFixed, .rightToLeft):
            return .leftFixed

        case (.rightFixed, _),
             (.trailingFixed, .leftToRight),
             (.leadingFixed, .rightToLeft):
            return .rightFixed

        default:
            fatalError()
        }
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }

    private func commonInit() {
        // Align the text color with the tint color which is applied to the image view
        if let imageTintColor = UIControl.State.normal.customButtonTitleColor {
            tintColor = imageTintColor
        }
    }

    private func computeLayout(forContentRect contentRect: CGRect) -> (CGRect, CGRect) {
        var imageRect = super.imageRect(forContentRect: contentRect)
        var titleRect = super.titleRect(forContentRect: contentRect)

        switch (effectiveContentHorizontalAlignment, effectiveImageAlignment) {
        case (.left, .left):
            imageRect.origin.x = contentRect.minX
            titleRect.origin.x = imageRect.width > 0
                ? imageRect.maxX + inlineImageSpacing
                : contentRect.minX

        case (.left, .right):
            titleRect.origin.x = contentRect.minX
            imageRect.origin.x = titleRect.maxX + inlineImageSpacing

        case (.left, .leftFixed):
            imageRect.origin.x = contentRect.minX
            titleRect.origin.x = imageRect.width > 0
                ? imageRect.maxX + inlineImageSpacing
                : contentRect.minX

        case (.left, .rightFixed):
            imageRect.origin.x = contentRect.maxX - imageRect.width
            titleRect.origin.x = contentRect.minX

        case (.center, .leftFixed):
            imageRect.origin.x = contentRect.minX
            titleRect.origin.x = contentRect.midX - titleRect.width * 0.5

        case (.center, .rightFixed):
            imageRect.origin.x = contentRect.maxX - imageRect.width
            titleRect.origin.x = contentRect.midX - titleRect.width * 0.5

        case (.center, .left):
            titleRect.origin.x = contentRect.midX - titleRect.width * 0.5
            imageRect.origin.x = titleRect.minX - inlineImageSpacing - imageRect.width

        case (.center, .right):
            titleRect.origin.x = contentRect.midX - titleRect.width * 0.5
            imageRect.origin.x = titleRect.maxX + inlineImageSpacing

        case (.right, .left):
            titleRect.origin.x = contentRect.maxX - titleRect.width
            imageRect.origin.x = titleRect.minX - imageRect.width - inlineImageSpacing

        case (.right, .leftFixed):
            imageRect.origin.x = contentRect.minX
            titleRect.origin.x = contentRect.maxX - titleRect.width

        case (.right, .rightFixed):
            imageRect.origin.x = contentRect.maxX - imageRect.width
            titleRect.origin.x = imageRect.width > 0
                ? imageRect.minX - inlineImageSpacing - titleRect.width
                : contentRect.maxX - titleRect.width

        default:
            fatalError()
        }

        return (titleRect, imageRect)
    }

    override func imageRect(forContentRect contentRect: CGRect) -> CGRect {
        computeLayout(forContentRect: contentRect).1
    }

    override func titleRect(forContentRect contentRect: CGRect) -> CGRect {
        computeLayout(forContentRect: contentRect).0
    }
}

private extension AppButton {
    class DynamicAssets {
        static let shared = DynamicAssets()

        private init() {}

        /// Default cell corner radius in inset grouped table view
        private let tableViewCellCornerRadius: CGFloat = 10

        lazy var tableInsetGroupedDefaultBackground: UIImage = {
            roundedRectImage(fillColor: .primaryColor)
        }()

        lazy var tableInsetGroupedSuccessBackground: UIImage = {
            roundedRectImage(fillColor: .successColor)
        }()

        lazy var tableInsetGroupedDangerBackground: UIImage = {
            roundedRectImage(fillColor: .dangerColor)
        }()

        private func roundedRectImage(fillColor: UIColor) -> UIImage {
            let cornerRadius = tableViewCellCornerRadius
            let bounds = CGRect(x: 0, y: 0, width: 44, height: 44)
            let image = UIGraphicsImageRenderer(bounds: bounds).image { _ in
                fillColor.setFill()
                UIBezierPath(roundedRect: bounds, cornerRadius: cornerRadius).fill()
            }
            let caps = UIEdgeInsets(top: cornerRadius, left: cornerRadius, bottom: cornerRadius, right: cornerRadius)
            return image.resizableImage(withCapInsets: caps)
        }
    }
}