import UIKit

public class DotIndicator: UIView {
    
    // 当前页
    public var index = 0
    
    // 总页数
    public var count = 0 {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }
    
    // 默认颜色
    public var color = UIColor(red: 210 / 255, green: 210 / 255, blue: 210 / 255, alpha: 1)
    
    // 当前页颜色
    public var activeColor = UIColor.white
    
    // 默认半径
    public var radius = 3.0 {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }
    
    // 当前页半径
    public var activeRadius = 3.5 {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }
    
    // 圆点的间距
    public var gap = 4.0 {
        didSet {
            invalidateIntrinsicContentSize()
        }
    }
    
    private var contentWidth: Double {
        let interval = Double(count - 1)
        return 2 * radius * interval + 2 * activeRadius + gap * interval
    }
    
    private var contentHeight: Double {
        return 2 * max(radius, activeRadius)
    }
    
    public override var intrinsicContentSize: CGSize {
        return CGSize(width: contentWidth, height: contentHeight)
    }
    
    public override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
    }
    
    public required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        backgroundColor = .clear
    }

    public override func draw(_ rect: CGRect) {

        guard let context = UIGraphicsGetCurrentContext() else {
            return
        }
        
        if count <= 0 {
            return
        }
        
        let centerY = Double(bounds.midY)
        
        var startX = (Double(frame.width) - contentWidth) / 2
        var dotIndex = 0
        
        var dotRadius: Double
        var dotColor: UIColor
        
        while dotIndex < count {
            
            if dotIndex == index {
                dotRadius = activeRadius
                dotColor = activeColor
            }
            else {
                dotRadius = radius
                dotColor = color
            }
            
            context.setFillColor(dotColor.cgColor)
            context.addEllipse(in: CGRect(x: startX, y: centerY - dotRadius, width: 2 * dotRadius, height: 2 * dotRadius))
            context.drawPath(using: .fill)
            
            startX += 2 * dotRadius + gap
            
            dotIndex += 1
            
        }
        
    }
}