//
//  BackgroundCircles.swift
//  PrivadoVPN
//
//  Created by Lizaveta Malinouskaya on 6/18/21.
//  Copyright © 2021 Privado LLC. All rights reserved.
//

import UIKit

public class BackgroundCircles: UIView {

    enum Constants {
        enum Geometry {
            static let viewHeight: CGFloat = 1250
        }
        enum Image {
            static let logo = "create.logo.dark"
        }
    }

    private var numberOfCircles: Int = 0
    private var multiplier: CGFloat = 0 {
        didSet {
            if multiplier <= 0 {
                multiplier = 1.20
            } else if multiplier < 1 {
                multiplier = abs(1 / multiplier)
            }
            setOffset()
        }
    }
    private var circlesAlpha: CGFloat = 0.04

    private var parent: UIView?
    private var circles: [UIView] = []
    private var circleRadiuses: [CGFloat] = []
    private var offset: CGFloat = 104
    
    init(numberOfCircles: Int = 5, multiplier: CGFloat = 1.2, alpha: CGFloat = 0.05) {
        super.init(frame: .zero)
        self.frame = CGRect(x: 0, y: 0, width: Constants.Geometry.viewHeight, height: Constants.Geometry.viewHeight)
        self.numberOfCircles = numberOfCircles
        self.multiplier = multiplier
        self.circlesAlpha = alpha
        configureUI()
    }

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

    private func configureUI() {
        
        setOffset()
        initializeRadiuses()

        for radius in circleRadiuses {
            circles.append(initializeGradientCircle(with: self, radius: radius, alpha: circlesAlpha))
        }

        self.layer.cornerRadius = self.bounds.height / 2

        for (circle, radius) in zip(circles, circleRadiuses) {
            NSLayoutConstraint.activate([
                circle.centerXAnchor.constraint(equalTo: self.centerXAnchor),
                circle.centerYAnchor.constraint(equalTo: self.centerYAnchor),
                circle.widthAnchor.constraint(equalToConstant: 2 * radius),
                circle.heightAnchor.constraint(equalToConstant: 2 * radius)
            ])
        }
        let image = self.initializeLogoImage(with: self)
        NSLayoutConstraint.activate([
            image.centerXAnchor.constraint(equalTo: self.centerXAnchor),
            image.centerYAnchor.constraint(equalTo: self.centerYAnchor)
        ])
    }

    private func initializeRadiuses() {
        var radius = self.bounds.height/2
        for _ in 0..<self.numberOfCircles {
            circleRadiuses.append(radius)
            radius = calculateNewRadius(of: radius, with: self.offset)
        }
    }

    private func initializeLogoImage(with container: UIView) -> UIImageView {

        let image = UIImage(imageLiteralResourceName: Constants.Image.logo)
        let view = UIImageView(image: image)
        view.translatesAutoresizingMaskIntoConstraints = false
        view.contentMode = .scaleAspectFit
        container.addSubview(view)
        return view
    }

    private func calculateNewRadius(of circleRadius: CGFloat, with offset: CGFloat) -> CGFloat {
        if circleRadius > offset {
            return (circleRadius - offset)
        } else {
            return 0
        }
    }
    
    private func setOffset() {
        offset = Constants.Geometry.viewHeight / 2 * (multiplier - 1) / multiplier
    }

    private func initializeGradientCircle(with container: UIView, radius: CGFloat, alpha: CGFloat) -> UIView {
        let gradientView = GradientView()
        gradientView.translatesAutoresizingMaskIntoConstraints = false
        gradientView.cornerRadius = radius
        gradientView.horizontalMode = false
        gradientView.stops = [
            .init(color: Colors.AnimationBackgrounds.loadingCircleTop.color, location: 0),
            .init(color: Colors.AnimationBackgrounds.loadingCircleBottom.color, location: 1)
        ]
        gradientView.backgroundColor = .red
        gradientView.alpha = alpha
        container.addSubview(gradientView)
        return gradientView
    }
}