Coordinates.swift

//
//  Coordinates.swift
//  Scrapyard
//
//  Created by Maciej Konieczny aka narf
//  https://vis.social/@narf/111654813643291716
//

import Foundation


// the protocol is not required
// but I'm using it for documentation purposes and as a "namespace"
protocol CoordinateSystemType {}

enum YDown: CoordinateSystemType {}
enum YUp: CoordinateSystemType {}
enum YUpRetina2x: CoordinateSystemType {}


/// This is shader’s `float2` with a phantom type
/// used by the compiler to make sure I won’t mix coordinate systems again.
///
/// The downside of this approach is that, since the original `float2` is hidden
/// inside, I have to implement proxies for all the operators (and protocols?)
/// that I find missing.
struct Point2D<CoordinateSystem: CoordinateSystemType> {
    private let value: SIMD2<Float>

    var x: Float { value.x }
    var y: Float { value.y }

    init(_ x: Float, _ y: Float) {
        self.init(value: .init(x, y))
    }

    init(x: Float, y: Float) {
        self.init(value: .init(x, y))
    }

    fileprivate init(value: SIMD2<Float>) {
        self.value = value
    }

    static var zero: Self { .init(value: .zero) }

    // TODO: could this be done with a macro?
    static func == (a: Self, b: Self) -> Bool { a.value == b.value }
    static func != (a: Self, b: Self) -> Bool { a.value != b.value }
    static func + (a: Self, b: Self) -> Self { .init(value: a.value + b.value) }
    static func - (a: Self, b: Self) -> Self { .init(value: a.value - b.value) }
    static func * (a: Self, b: Self) -> Self { .init(value: a.value * b.value) }
    static func / (a: Self, b: Self) -> Self { .init(value: a.value / b.value) }
}


extension Point2D: CustomDebugStringConvertible {
    var debugDescription: String {
        .init(format: "(%.2f, %.2f)", x, y)
    }
}


let p1 = Point2D<YUp>(1, 2)
let p2 = Point2D<YUp>(2, 3)
let p3 = p1 + p2  // (3, 5)

let p4 = Point2D<YDown>(3, 1920)
let p5 = p3 + p4  // compile time error: Cannot convert value of type 'Point2D<YDown>' to expected argument type 'Point2D<YUp>'