package hrend

// This is the linear algebra junk? Vectors, matrices, etc
import (
	"math"
)

type Vec3f struct {
	X, Y, Z float32
}

type Vec2i struct {
	X, Y int
}

type Vec2f struct {
	X, Y float32
}

// A ROW MAJOR matrix
type Mat44f [16]float32

func (m *Mat44f) Set(x int, y int, val float32) {
	m[x+y*4] = val
}
func (m *Mat44f) Get(x int, y int) float32 {
	return m[x+y*4]
}
func (m *Mat44f) ZeroFill() {
	for i := range m {
		m[i] = 0
	}
}
func (m *Mat44f) SetIdentity() {
	m.ZeroFill()
	for i := range 4 {
		m.Set(i, i, 1)
	}
}

// NOTE: we use "Set" instead of "Create" for all these so we reuse the matrix
// instead of creating a new one all the time (garbage collection)

// Compute the projection matrix, filling the given matrix. FOV is in degrees
func (m *Mat44f) SetProjection(fov float32, near float32, far float32) {
	// Projection matrix is (ROW MAJOR!)
	// S    0    0    0
	// 0    S    0    0
	// 0    0 -f/(f-n) -1
	// 0    0 -fn/(f-n) 0
	// where S (scale) is 1 / tan(fov / 2) (assuming fov is radians)
	// NOTE: -1 there is actually -1/c, where c is distance from viewer to
	// projection plane. We fix it at 1 for now but...
	m.ZeroFill()
	scale := float32(1 / math.Tan(float64(fov)*0.5*math.Pi/180))
	m.Set(0, 0, scale)
	m.Set(1, 1, scale)
	m.Set(2, 2, -far/(far-near))
	m.Set(3, 2, -1)
	m.Set(2, 3, -far*near/(far-near))
}

func (m *Mat44f) SetTranslation(x, y, z float32) {
	m.SetIdentity()
	m.Set(0, 3, x) // Let user decide how to offset x
	m.Set(1, 3, y) // Let user decide how to offset x
	m.Set(2, 3, z) // Get farther away from the face (user)
}

func (m *Mat44f) SetViewport(tl Vec3f, br Vec3f) { //width, height, depth int) {
	m.ZeroFill()
	m.Set(0, 0, (br.X-tl.X)/2)
	m.Set(1, 1, (tl.Y-br.Y)/2) // Inverted because screen funny
	m.Set(2, 2, (br.Z-tl.Z)/2)
	m.Set(3, 3, 1)
	m.Set(0, 3, (br.X+tl.X)/2)
	m.Set(1, 3, (br.Y+tl.Y)/2)
	m.Set(2, 3, (br.Z+tl.Z)/2)
}

func (m *Mat44f) SetViewportSimple(width, height, depth int) {
	var tl Vec3f // All zero
	br := Vec3f{
		X: float32(width),
		Y: float32(height),
		Z: float32(depth),
	}
	m.SetViewport(tl, br)
}

// Multiply the given point by our vector. Remember this is row-major order
func (m *Mat44f) MultiplyPoint3(p Vec3f) Vec3f {
	var out Vec3f
	// We hope very much that Go will optimize the function calls for us,
	// along with computing the constants.
	out.X = p.X*m.Get(0, 0) + p.Y*m.Get(0, 1) + p.Z*m.Get(0, 2) + m.Get(0, 3)
	out.Y = p.X*m.Get(1, 0) + p.Y*m.Get(1, 1) + p.Z*m.Get(1, 2) + m.Get(1, 3)
	out.Z = p.X*m.Get(2, 0) + p.Y*m.Get(2, 1) + p.Z*m.Get(2, 2) + m.Get(2, 3)
	w := p.X*m.Get(3, 0) + p.Y*m.Get(3, 1) + p.Z*m.Get(3, 2) + m.Get(3, 3)
	if w != 1 {
		out.X /= w
		out.Y /= w
		out.Z /= w
	}
	return out
}

// Multiply two 4x4 matrices together (not optimized)
func (m *Mat44f) Multiply(m2 *Mat44f) Mat44f {
	var result Mat44f
	// This is the x and y of our resulting matrix
	for y := 0; y < 4; y++ {
		for x := 0; x < 4; x++ {
			for i := 0; i < 4; i++ {
				result[x+y*4] += m[i+y*4] * m2[x+i*4]
			}
		}
	}
	return result
}

func (vi *Vec2i) ToF() Vec2f {
	return Vec2f{float32(vi.X), float32(vi.Y)}
}

func (vi *Vec3f) ToVec2i() Vec2i {
	return Vec2i{int(vi.X), int(vi.Y)}
}

func (v0 *Vec3f) Sub(v1 Vec3f) Vec3f {
	return Vec3f{
		X: v0.X - v1.X,
		Y: v0.Y - v1.Y,
		Z: v0.Z - v1.Z,
	}
}

func (v0 *Vec3f) CrossProduct(v1 Vec3f) Vec3f {
	return Vec3f{
		X: v0.Y*v1.Z - v0.Z*v1.Y,
		Y: v0.Z*v1.X - v0.X*v1.Z,
		Z: v0.X*v1.Y - v0.Y*v1.X,
	}
}

//func (v

func (v *Vec3f) Normalize() Vec3f {
	l := float32(math.Sqrt(float64(v.MultSimp(v))))
	return Vec3f{
		X: v.X / l,
		Y: v.Y / l,
		Z: v.Z / l,
	}
}

func (v0 *Vec3f) MultSimp(v1 *Vec3f) float32 {
	return v0.X*v1.X + v0.Y*v1.Y + v0.Z*v1.Z
}