import SwiftUI

/// The button style for the controls of a ``RecordingView``.
///
/// The style renders the button's label, filled with the background color of the inverted color scheme, over a padded, circular red background, shrinks it
/// slightly while pressed, and dims it while disabled. Both the label and its padding scale relative to the current dynamic type size.
struct RecordingButtonStyle: ButtonStyle {

    // MARK: Properties

    /// The color scheme of the environment.
    @Environment(\.colorScheme) private var colorScheme

    /// Whether the button allows user interaction.
    @Environment(\.isEnabled) private var isEnabled
    
    /// The padding between the button's label and its background, scaled relative to the current dynamic type size.
    @ScaledMetric private var padding = Constant.Padding.button

    /// The width and height of the button's label, scaled relative to the current dynamic type size.
    @ScaledMetric private var size = Constant.Size.button

    // MARK: Methods

    /// Creates the styled body of the button.
    ///
    /// - Parameter configuration: The properties of the button being styled.
    func makeBody(
        configuration: Configuration
    ) -> some View {
        configuration.label
            .frame(
                width: size,
                height: size
            )
            .padding(padding)
            .scaledToFit()
            .foregroundStyle(.background)
            .environment(
                \.colorScheme,
                 colorSchemeInverted
            )
            .background(
                Circle()
                    .fill(.red)
            )
            .opacity(opacity)
            .scaleEffect(scaleEffect(configuration.isPressed))
            .animation(
                .easeOut(duration: Constant.Animation.duration),
                value: configuration.isPressed
            )
    }

}

// MARK: - Helpers

private extension RecordingButtonStyle {
    
    // MARK: Computed
    
    /// The color scheme opposite to the environment's, under which the label's background fill resolves to the inverted background color.
    var colorSchemeInverted: ColorScheme {
        colorScheme == .dark
            ? .light
            : .dark
    }

    /// The opacity of the button: dimmed while disabled, fully opaque otherwise.
    var opacity: Double {
        isEnabled
            ? Constant.Opacity.enabled
            : Constant.Opacity.disabled
    }
    
    // MARK: Methods
    
    /// Provides the scale of the button for a press state.
    ///
    /// - Parameter isPressed: Whether the button is currently pressed.
    /// - Returns: A slightly shrunken scale while pressed, the resting scale otherwise.
    func scaleEffect(
        _ isPressed: Bool
    ) -> CGFloat {
        isPressed
            ? Constant.Scale.pressed
            : Constant.Scale.idle
    }
    
}

// MARK: - Styles

extension ButtonStyle where Self == RecordingButtonStyle {

    /// The button style for the controls of a ``RecordingView``.
    static var recording: RecordingButtonStyle {
        .init()
    }

}

// MARK: - Constants

/// The constant values used across the button style.
private enum Constant {
    /// The animation constants.
    enum Animation {
        /// The duration of the press animation.
        static let duration: TimeInterval = 0.15
    }

    /// The opacity constants.
    enum Opacity {
        /// The opacity of a disabled button.
        static let disabled: Double = 0.4
        /// The opacity of an enabled button.
        static let enabled: Double = 1
    }
    
    /// The padding constants.
    enum Padding {
        /// The base padding between a button's label and its background, before dynamic type scaling.
        static let button: CGFloat = 8
    }

    /// The scale constants.
    enum Scale {
        /// The scale of a button at rest.
        static let idle: CGFloat = 1
        /// The scale of a button while pressed.
        static let pressed: CGFloat = 0.85
    }

    /// The size constants.
    enum Size {
        /// The base width and height of a button's label, before dynamic type scaling.
        static let button: CGFloat = 16
    }
}

// MARK: - Previews

#Preview(
    "Recording button style"
) {
    @Previewable @State var isDisabled: Bool = false
    
    Button {} label: {
        Image(.Icon.record)
            .resizable()
    }
    .buttonStyle(.recording)
    .disabled(isDisabled)
    .safeAreaInset(edge: .bottom) {
        Toggle(
            "Button disabled",
            isOn: $isDisabled
        )
        .fontWeight(.semibold)
        .dynamicTypeSize(.large)
        .padding()
        .tint(.red)
    }
}