Regions - Object-Oriented Approach

import Darwin
struct Position { let x, y: Float }
typealias Distance = Float


// Start with a simple Battleship with a certain weapon reach

class Battleship
{
    let weaponRange: Distance = 5.0

    func shouldFireAtTarget(target: Position) -> Bool
    {
        return hypot(target.x, target.y) <= weaponRange
    }
}

let battleship = Battleship()
battleship.shouldFireAtTarget(Position(x: 2, y: 3))
battleship.shouldFireAtTarget(Position(x: 9, y: 15))



// - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Add ability to be shifted from the origin

class Battleship2
{
    let weaponReach: Distance = 5.0
    let ownPosition: Position

    init(ownPosition: Position)
    {
        self.ownPosition = ownPosition
    }

    func shouldFireAtTarget(target: Position) -> Bool
    {
        let dx = target.x - ownPosition.x
        let dy = target.y - ownPosition.y
        let targetDistance = hypot(dx, dy)

        return targetDistance <= weaponReach
    }
}

let battleship2 = Battleship2(ownPosition: Position(x: 10, y: 12))
battleship2.shouldFireAtTarget(Position(x: 2, y: 3))
battleship2.shouldFireAtTarget(Position(x: 9, y: 15))



// - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Don't fire too close to self

class Battleship3
{
    let weaponReach: Distance = 5.0
    let ownPosition: Position
    let safeDistance: Distance = 1.0

    init(ownPosition: Position)
    {
        self.ownPosition = ownPosition
    }

    func shouldFireAtTarget(target: Position) -> Bool
    {
        let dx = target.x - ownPosition.x
        let dy = target.y - ownPosition.y
        let targetDistance = hypot(dx, dy)

        return (targetDistance <= weaponReach
            && targetDistance > safeDistance)
    }
}

let battleship3 = Battleship3(ownPosition: Position(x: 10, y: 12))
battleship3.shouldFireAtTarget(Position(x: 9, y: 15))
battleship3.shouldFireAtTarget(Position(x: 10.5, y: 12))  // too close to us



// - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// Avoid friendly fire

class Battleship4
{
    let weaponReach: Distance = 5.0
    let ownPosition: Position
    let safeDistance: Distance = 1.0
    let friendlyPosition: Position

    init(ownPosition: Position, friendlyPosition: Position)
    {
        self.ownPosition = ownPosition
        self.friendlyPosition = friendlyPosition
    }

    func shouldFireAtTarget(target: Position) -> Bool
    {
        let dx = target.x - ownPosition.x
        let dy = target.y - ownPosition.y
        let targetDistance = hypot(dx, dy)

        let friendlyDx = friendlyPosition.x - target.x
        let friendlyDy = friendlyPosition.y - target.y
        let friendlyDistance = hypot(friendlyDx, friendlyDy)

        return (targetDistance <= weaponReach
            && targetDistance > safeDistance
            && friendlyDistance >= safeDistance)
    }
}

let battleship4 = Battleship4(ownPosition: Position(x: 10, y: 12), friendlyPosition: Position(x: 12, y: 9))
battleship4.shouldFireAtTarget(Position(x: 9, y: 15))
battleship4.shouldFireAtTarget(Position(x: 12.25, y: 9.25))  // too close to friendly