SwiftMixins.swift

import Foundation

protocol Mixin {
    var storage: [String : Any] { get set }
}

protocol CanMoveMixin : Mixin {
    var position: CGPoint { get set }
    var speed: CGVector { get set }
    mutating func move(forTimeSlice timeSlice: CGFloat)
}

extension CanMoveMixin {
    
    var position: CGPoint {
        get {
            return storage["position"] as? CGPoint ?? CGPoint.zero
        }
        set {
            storage["position"] = newValue
        }
    }
    
    var speed: CGVector {
        get {
            return storage["speed"] as? CGVector ?? CGVector.zero
        }
        set {
            storage["speed"] = newValue
        }
    }
    
    mutating func move(forTimeSlice timeSlice: CGFloat) {
        position = CGPoint(x: position.x + timeSlice * speed.dx,
                           y: position.y + timeSlice * speed.dy)
    }
    
}

protocol HealthMixin : Mixin {
    var health: CGFloat { get set }
    mutating func absorb(damage: CGFloat)
}

extension HealthMixin {
    
    var health: CGFloat {
        get {
            return storage["health"] as? CGFloat ?? 0
        }
        set {
            storage["health"] = newValue
        }
    }
    
    mutating func absorb(damage: CGFloat) {
        health -= damage
    }
    
}

struct Player: CanMoveMixin, HealthMixin {
    var storage: [String : Any]
}

struct Enemy: CanMoveMixin {
    var storage: [String : Any]
}