import UIKit

/// `ScrollViewKeyboardAvoiding` implementation.
public final class ScrollViewKeyboardAvoider: ScrollViewKeyboardAvoiding {
    /// Animates using provided duration and closure
    public typealias Animator = (TimeInterval, @escaping () -> Void) -> Void

    /// Create new avoider
    ///
    /// - Parameter animator: used to perform animations
    public init(animator: @escaping Animator) {
        self.animate = animator
    }

    // MARK: - ScrollViewKeyboardAvoiding

    public func handleKeyboardFrameChange(
        _ frame: CGRect,
        animationDuration: TimeInterval,
        for scrollView: UIScrollView
    ) {
        guard let superview = scrollView.superview else { return }
        let keyboardFrame = superview.convert(frame, from: nil)
        var insets = scrollView.contentInset
        let bottomCoverage = scrollView.frame.maxY - keyboardFrame.minY
        let safeAreaInsets: UIEdgeInsets
        if #available(iOS 11.0, *) {
            safeAreaInsets = scrollView.safeAreaInsets
        } else {
            safeAreaInsets = .zero
        }
        insets.bottom = max(0, bottomCoverage - safeAreaInsets.bottom)
        animate(animationDuration) {
            scrollView.contentInset = insets
            scrollView.scrollIndicatorInsets = insets
        }
    }

    // MARK: - Internals

    private let animate: Animator
}