// Copyright 2014 The go-gl/mathgl Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// <<.Comment>>
// Edit <<.TemplateName>> and run "go generate" to make changes.

package mgl32

import (
	"math"
)

type Vec2 [2]float32
type Vec3 [3]float32
type Vec4 [4]float32

// Vec3 constructs a 3-dimensional vector by appending the given coordinates.
func (v Vec2) Vec3(z float32) Vec3 {
	return Vec3{v[0], v[1], z}
}

// Vec4 constructs a 4-dimensional vector by appending the given coordinates.
func (v Vec2) Vec4(z, w float32) Vec4 {
	return Vec4{v[0], v[1], z, w}
}

// Vec4 constructs a 4-dimensional vector by appending the given coordinates.
func (v Vec3) Vec4(w float32) Vec4 {
	return Vec4{v[0], v[1], v[2], w}
}

// Vec2 constructs a 2-dimensional vector by discarding coordinates.
func (v Vec3) Vec2() Vec2 {
	return Vec2{v[0], v[1]}
}

// Vec2 constructs a 2-dimensional vector by discarding coordinates.
func (v Vec4) Vec2() Vec2 {
	return Vec2{v[0], v[1]}
}

// Vec3 constructs a 3-dimensional vector by discarding coordinates.
func (v Vec4) Vec3() Vec3 {
	return Vec3{v[0], v[1], v[2]}
}

// Elem extracts the elements of the vector for direct value assignment.
func (v Vec2) Elem() (x, y float32) {
	return v[0], v[1]
}

// Elem extracts the elements of the vector for direct value assignment.
func (v Vec3) Elem() (x, y, z float32) {
	return v[0], v[1], v[2]
}

// Elem extracts the elements of the vector for direct value assignment.
func (v Vec4) Elem() (x, y, z, w float32) {
	return v[0], v[1], v[2], v[3]
}

// Cross is the vector cross product. This operation is only defined on 3D
// vectors. It is equivalent to Vec3{v1[1]*v2[2]-v1[2]*v2[1],
// v1[2]*v2[0]-v1[0]*v2[2], v1[0]*v2[1] - v1[1]*v2[0]}. Another interpretation
// is that it's the vector whose magnitude is |v1||v2|sin(theta) where theta is
// the angle between v1 and v2.
//
// The cross product is most often used for finding surface normals. The cross
// product of vectors will generate a vector that is perpendicular to the plane
// they form.
//
// Technically, a generalized cross product exists as an "(N-1)ary" operation
// (that is, the 4D cross product requires 3 4D vectors). But the binary 3D (and
// 7D) cross product is the most important. It can be considered the area of a
// parallelogram with sides v1 and v2.
//
// Like the dot product, the cross product is roughly a measure of
// directionality. Two normalized perpendicular vectors will return a vector
// with a magnitude of 1.0 or -1.0 and two parallel vectors will return a vector
// with magnitude 0.0. The cross product is "anticommutative" meaning
// v1.Cross(v2) = -v2.Cross(v1), this property can be useful to know when
// finding normals, as taking the wrong cross product can lead to the opposite
// normal of the one you want.
func (v1 Vec3) Cross(v2 Vec3) Vec3 {
	return Vec3{v1[1]*v2[2] - v1[2]*v2[1], v1[2]*v2[0] - v1[0]*v2[2], v1[0]*v2[1] - v1[1]*v2[0]}
}

// Quat reinterprets this vector as a quaternion, with the individual elements
// staying the same.
func (v Vec4) Quat() Quat {
	return Quat{v[3], Vec3{v[0], v[1], v[2]}}
}


<</* Common functions for all vectors */>>
<<range $m := enum 2 3 4>>
<<$type := typename $m 1>>

// Add performs element-wise addition between two vectors. It is equivalent to iterating
// over every element of v1 and adding the corresponding element of v2 to it.
func (v1 <<$type>>) Add(v2 <<$type>>) <<$type>> {
	return <<$type>>{<<range $i := iter 0 $m>> v1[<<$i>>] + v2[<<$i>>], <<end>>}
}

// Sub performs element-wise subtraction between two vectors. It is equivalent to iterating
// over every element of v1 and subtracting the corresponding element of v2 from it.
func (v1 <<$type>>) Sub(v2 <<$type>>) <<$type>> {
	return <<$type>>{<<range $i := iter 0 $m>> v1[<<$i>>] - v2[<<$i>>], <<end>>}
}

// Mul performs a scalar multiplication between the vector and some constant value
// c. This is equivalent to iterating over every vector element and multiplying by c.
func (v1 <<$type>>) Mul(c float32) <<$type>> {
	return <<$type>>{<<range $i := iter 0 $m>> v1[<<$i>>] * c, <<end>>}
}

// Dot returns the dot product of this vector with another. There are multiple ways
// to describe this value. One is the multiplication of their lengths and cos(theta) where
// theta is the angle between the vectors: v1.v2 = |v1||v2|cos(theta).
//
// The other (and what is actually done) is the sum of the element-wise multiplication of all
// elements. So for instance, two Vec3s would yield v1.x * v2.x + v1.y * v2.y + v1.z * v2.z.
//
// This means that the dot product of a vector and itself is the square of its Len (within
// the bounds of floating points error).
//
// The dot product is roughly a measure of how closely two vectors are to pointing in the same
// direction. If both vectors are normalized, the value will be -1 for opposite pointing,
// one for same pointing, and 0 for perpendicular vectors.
func (v1 <<$type>>) Dot(v2 <<$type>>) float32 {
	return <<range $i := iter 0 $m>><<sep "+" $i>> v1[<<$i>>]*v2[<<$i>>] <<end>>
}

// Len returns the vector's length. Note that this is NOT the dimension of
// the vector (len(v)), but the mathematical length. This is equivalent to the square
// root of the sum of the squares of all elements. E.G. for a Vec2 it's
// math.Hypot(v[0], v[1]).
func (v1 <<$type>>) Len() float32 {
	<<if eq $m 2 >>
	return float32(math.Hypot(float64(v1[0]), float64(v1[1])))
	<<else>>
	return float32(math.Sqrt(float64(<<repeat $m "v1[%d]*v1[%d]" "+">>)))
	<<end>>
}

// LenSqr returns the vector's square length. This is equivalent to the sum of the squares of all elements.
func (v1 <<$type>>) LenSqr() float32 {
	return <<repeat $m "v1[%d]*v1[%d]" "+">>
}

// Normalize normalizes the vector. Normalization is (1/|v|)*v,
// making this equivalent to v.Scale(1/v.Len()). If the len is 0.0,
// this function will return an infinite value for all elements due
// to how floating point division works in Go (n/0.0 = math.Inf(Sign(n))).
//
// Normalization makes a vector's Len become 1.0 (within the margin of floating point error),
// while maintaining its directionality.
//
// (Can be seen here: http://play.golang.org/p/Aaj7SnbqIp )
func (v1 <<$type>>) Normalize() <<$type>> {
	l := 1.0 / v1.Len()
	return <<$type>>{<<range $i := iter 0 $m>>v1[<<$i>>] * l,<<end>>}
}

// ApproxEqual takes in a vector and does an element-wise approximate float
// comparison as if FloatEqual had been used
func (v1 <<$type>>) ApproxEqual(v2 <<$type>>) bool {
	for i := range v1 {
		if !FloatEqual(v1[i], v2[i]) {
			return false
		}
	}
	return true
}

// ApproxEqualThreshold takes in a threshold for comparing two floats, and uses
// it to do an element-wise comparison of the vector to another.
func (v1 <<$type>>) ApproxEqualThreshold(v2 <<$type>>, threshold float32) bool {
	for i := range v1 {
		if !FloatEqualThreshold(v1[i], v2[i], threshold) {
			return false
		}
	}
	return true
}

// ApproxFuncEqual takes in a func that compares two floats, and uses it to do an element-wise
// comparison of the vector to another. This is intended to be used with FloatEqualFunc
func (v1 <<$type>>) ApproxFuncEqual(v2 <<$type>>, eq func(float32, float32) bool) bool {
	for i := range v1 {
		if !eq(v1[i], v2[i]) {
			return false
		}
	}
	return true
}

<<range $i := iter 0 $m>>
// <<elementname $i>> is an element access func, it is equivalent to v[n] where
// n is some valid index. The mappings are XYZW (X=0, Y=1 etc). Benchmarks
// show that this is more or less as fast as direct acces, probably due to
// inlining, so use v[0] or v.X() depending on personal preference.
func (v <<$type>>) <<elementname $i>>() float32 {
	return v[<<$i>>]
}
<<end>>

<<range $n := enum 2 3 4>>
// OuterProd<<$n>> does the vector outer product
// of two vectors. The outer product produces an
// <<$m>>x<<$n>> matrix. E.G. a Vec<<$m>> * Vec<<$n>> = <<typename $m $n>>.
//
// The outer product can be thought of as the "opposite"
// of the Dot product. The Dot product treats both vectors like matrices
// oriented such that the left one has N columns and the right has N rows.
// So Vec3.Vec3 = Mat1x3*Mat3x1 = Mat1 = Scalar.
//
// The outer product orients it so they're facing "outward": Vec2*Vec3
// = Mat2x1*Mat1x3 = Mat2x3.
func (v1 <<$type>>) OuterProd<<$n>>(v2 <<typename $n 1>>) <<typename $m $n>> {
	return <<typename $m $n>>{<<range $i := matiter $m $n>>v1[<<$i.M>>] * v2[<<$i.N>>], <<end>>}
}
<<end>>

<<end>> <</* range $m */>>