package geometry

import (
	"errors"

	"github.com/go-gl/gl/v4.6-core/gl"
	"github.com/go-gl/mathgl/mgl32"
	"github.com/udhos/gwob"
)

// attributes:
// position 3 * float
// texture  2 * float
// normal   3 * float
// tangent  3 * float

type Geometry struct {
	vao  uint32
	vbo  uint32
	ebo  uint32
	size int32
}

func (g Geometry) Draw() {
	gl.BindVertexArray(g.vao)
	gl.BindBuffer(gl.ARRAY_BUFFER, g.vbo)
	gl.DrawElementsWithOffset(gl.TRIANGLES, g.size, gl.UNSIGNED_INT, 0)
}

func (g Geometry) Delete() {
	gl.DeleteVertexArrays(1, &g.vao)
	gl.DeleteBuffers(1, &g.ebo)
	gl.DeleteBuffers(1, &g.vbo)
}

func new(coords []float32, indicies []int) (Geometry, error) {
	var geometry Geometry

	unsignedIndicies := make([]uint32, len(indicies))
	for i, v := range indicies {
		unsignedIndicies[i] = uint32(v)
	}

	// vao
	gl.GenVertexArrays(1, &geometry.vao)
	gl.BindVertexArray(geometry.vao)

	// vbo
	gl.GenBuffers(1, &geometry.vbo)
	gl.BindBuffer(gl.ARRAY_BUFFER, geometry.vbo)
	gl.BufferData(gl.ARRAY_BUFFER, len(coords)*4, gl.Ptr(coords), gl.STATIC_DRAW)

	var i uint32 = 0

	// attributes
	// position
	gl.VertexAttribPointerWithOffset(i, 3, gl.FLOAT, false, 11*4, 0)
	gl.EnableVertexAttribArray(i)
	i++

	// texture
	gl.VertexAttribPointerWithOffset(i, 2, gl.FLOAT, false, 11*4, 3*4)
	gl.EnableVertexAttribArray(i)
	i++

	// normal
	gl.VertexAttribPointerWithOffset(2, 3, gl.FLOAT, false, 11*4, 5*4)
	gl.EnableVertexAttribArray(i)
	i++

	// tangent
	gl.VertexAttribPointerWithOffset(i, 3, gl.FLOAT, false, 11*4, 8*4)
	gl.EnableVertexAttribArray(i)
	i++

	// ebo
	gl.GenBuffers(1, &geometry.ebo)
	gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, geometry.ebo)
	gl.BufferData(gl.ELEMENT_ARRAY_BUFFER, len(unsignedIndicies)*4, gl.Ptr(unsignedIndicies), gl.STATIC_DRAW)
	geometry.size = int32(len(indicies))

	return geometry, nil
}

func LoadOBJ(path string) (geometry Geometry, err error) {
	o, err := gwob.NewObjFromFile(path, &gwob.ObjParserOptions{})
	if err != nil {
		return geometry, err
	}

	if !o.NormCoordFound {
		return geometry, errors.New("missing normals in OBJ")
	}

	if !o.TextCoordFound {
		return geometry, errors.New("missing texture UVs in OBJ")
	}

	// add tangent
	coords := make([]float32, 0, len(o.Coord)*11)
	tangents := make([][3]float32, len(o.Coord)/8)

	// iterate faces
	for i := 0; i < len(o.Indices); i += 3 {
		i0 := o.Indices[i+0]
		i1 := o.Indices[i+1]
		i2 := o.Indices[i+2]

		// positions
		v0 := o.Coord[i0*8 : i0*8+3]
		v1 := o.Coord[i1*8 : i1*8+3]
		v2 := o.Coord[i2*8 : i2*8+3]

		// UVs
		uv0 := o.Coord[i0*8+3 : i0*8+5]
		uv1 := o.Coord[i1*8+3 : i1*8+5]
		uv2 := o.Coord[i2*8+3 : i2*8+5]

		// edges
		edge1 := [3]float32{v1[0] - v0[0], v1[1] - v0[1], v1[2] - v0[2]}
		edge2 := [3]float32{v2[0] - v0[0], v2[1] - v0[1], v2[2] - v0[2]}

		// UV deltas
		delta1 := [2]float32{uv1[0] - uv0[0], uv1[1] - uv0[1]}
		delta2 := [2]float32{uv2[0] - uv0[0], uv2[1] - uv0[1]}

		// calculate tangents
		f := 1.0 / (delta1[0]*delta2[1] - delta2[0]*delta1[1])
		tangent := [3]float32{
			f * (delta2[1]*edge1[0] - delta1[1]*edge2[0]),
			f * (delta2[1]*edge1[1] - delta1[1]*edge2[1]),
			f * (delta2[1]*edge1[2] - delta1[1]*edge2[2]),
		}

		tangents[i0] = mgl32.Vec3(tangents[i0]).Add(tangent)
		tangents[i1] = mgl32.Vec3(tangents[i1]).Add(tangent)
		tangents[i2] = mgl32.Vec3(tangents[i2]).Add(tangent)
	}

	// build coords
	for i := 0; i < len(o.Coord)/8; i++ {
		pos := o.Coord[i*8 : i*8+3]
		uv := o.Coord[i*8+3 : i*8+5]
		norm := o.Coord[i*8+5 : i*8+8]
		tan := mgl32.Vec3(tangents[i]).Normalize()

		coords = append(coords, pos...)
		coords = append(coords, uv...)
		coords = append(coords, norm...)
		coords = append(coords, tan[0:3]...)
	}

	return new(coords, o.Indices)
}

func Screen() (Geometry, error) {
	return new(
		[]float32{
			// xyz, uv, nrm, tan
			-1, -1, 0, 0, 0, 0, 0, 0, 0, 0, 0,
			1, -1, 0, 1, 0, 0, 0, 0, 0, 0, 0,
			-1, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0,
			1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0,
		},
		[]int{
			0, 1, 2,
			1, 3, 2,
		})
}