import Foundation
#if USE_SIMD
import simd
#endif


#if USE_SIMD
public typealias Vector2 = SIMD2
#else

public struct Vector2<T: FloatingPoint>: Equatable
{
	public typealias Scalar = T

	public var x, y: T

	public init() { self.x = 0; self.y = 0 }
	public init(_ x: T, _ y: T) { self.x = x; self.y = y }
}

public extension Vector2
{
	// constants
	@inline(__always) static var zero: Self { Self(0, 0) }
	@inline(__always) static var one: Self { Self(1, 1) }

	subscript(index: Int) -> T
	{
		get
		{
			switch index
			{
			case 0: x
			case 1: y
			default: fatalError()
			}
		}
	}

	// relational
	@inline(__always) static func == (lhs: Self, rhs: Self) -> Bool { lhs.x == rhs.x && lhs.y == rhs.y }
	@inline(__always) static func != (lhs: Self, rhs: Self) -> Bool { rhs.x != rhs.x || lhs.y != rhs.y }

	// arithmetic
	@inline(__always) static func + (lhs: Self, rhs: Self) -> Self { Self(lhs.x + rhs.x, lhs.y + rhs.y) }
	@inline(__always) static func - (lhs: Self, rhs: Self) -> Self { Self(lhs.x - rhs.x, lhs.y - rhs.y) }
	@inline(__always) static func * (lhs: Self, rhs: Self) -> Self { Self(lhs.x * rhs.x, lhs.y * rhs.y) }
	@inline(__always) static func / (lhs: Self, rhs: Self) -> Self { Self(lhs.x / rhs.x, lhs.y / rhs.y) }

	// scalar arithmetic
	@inline(__always) static func * (lhs: Self, rhs: T) -> Self { Self(lhs.x * rhs, lhs.y * rhs) }
	@inline(__always) static func / (lhs: Self, rhs: T) -> Self { Self(lhs.x / rhs, lhs.y / rhs) }
	@inline(__always) static func * (lhs: T, rhs: Self) -> Self { Self(lhs * rhs.x, lhs * rhs.y) }
	@inline(__always) static func / (lhs: T, rhs: Self) -> Self { Self(lhs / rhs.x, lhs / rhs.y) }

	// compound arithmetic
	@inline(__always) static func += (lhs: inout Self, rhs: Self) { lhs.x += rhs.x; lhs.y += rhs.y }
	@inline(__always) static func -= (lhs: inout Self, rhs: Self) { lhs.x -= rhs.x; lhs.y -= rhs.y }
	@inline(__always) static func *= (lhs: inout Self, rhs: Self) { lhs.x *= rhs.x; lhs.y *= rhs.y }
	@inline(__always) static func /= (lhs: inout Self, rhs: Self) { lhs.x /= rhs.x; lhs.y /= rhs.y }

	// compound scalar arithmetic
	@inline(__always) static func *= (lhs: inout Self, rhs: T) { lhs.x *= rhs; lhs.y *= rhs }
	@inline(__always) static func /= (lhs: inout Self, rhs: T) { lhs.x /= rhs; lhs.y /= rhs }

	// unary
	@inline(__always) static prefix func + (vec: Self) -> Self { vec }
	@inline(__always) static prefix func - (vec: Self) -> Self { Self(-vec.x, -vec.y) }
}

#endif

public extension Vector2 where Scalar: FloatingPoint
{
	@inline(__always) var len2: Scalar { x * x + y * y }
	@inline(__always) var len: Scalar { len2.squareRoot() }
	@inline(__always) var normalised: Self { let invLen = 1 / len; return self * invLen }

	@inline(__always) mutating func normalise() { let invLen = 1 / len; self *= invLen }

	@inline(__always) func dot(_ b: Self) -> Scalar { x * b.x + y * b.y }
	@inline(__always) func reflect(_ n: Self) -> Self { self - (n * 2 * self.dot(n)) }
	@inline(__always) func project(_ n: Self) -> Self { n * self.dot(n) }

	@inline(__always) func cross(_ b: Self) -> Scalar { x * b.y - y * b.x }

	@inline(__always) func lerp(_ b: Self, _ x: Scalar) -> Self
	{
		let invX = 1 - x
		return Self(self.x * invX + b.x * x, self.y * invX + b.y * x)
	}

	@inline(__always) func distance(_ b: Self) -> Scalar { return (b - self).len }
}


public typealias Vec2f = Vector2<Float>
public typealias Vec2d = Vector2<Double>
