local module = {}
local gl = honey.gl
setmetatable(module, {__index=_G})
setfenv(1, module)


local function insertVertex(vertices, attrib, vertex)
	local pos = 3*vertex.v_idx
	for i=1,3 do
		table.insert(vertices, attrib.vertices[pos+i])
	end

	local normal = 3*vertex.vn_idx
	for i=1,3 do
		table.insert(vertices, attrib.normals[normal+i])
	end

	local tex = 3*vertex.vt_idx
	for i=1,2 do
		table.insert(vertices, attrib.texcoords[tex+i])
	end
end


function loadShape(shape, attrib)
	local vertices = {}
	local indices = {}

	local start = shape.face_offset
	local finish = start + shape.length
	for i=start,finish-1 do
		assert(attrib.face_num_verts[i+1] == 3, "non-triangular face!")
		for j=0,2 do
			local vertex = attrib.faces[(3*i) + j + 1]
			insertVertex(vertices, attrib, vertex)
			table.insert(indices, #indices)
		end
	end

	return vertices, indices
end


function loadFile(filename)
	local flags = honey.tinyobj.FLAG_TRIANGULATE
	local attrib, shapes, materials = honey.tinyobj.parse_obj(filename, flags)
	
	local meshes = {}
	for _, shape in ipairs(shapes) do
		local vertices, indices = loadShape(shape, attrib)
		table.insert(meshes, Mesh(vertices, indices))
	end
	return meshes
end


cache = {}
function loadCached(filename, index)
	if not cache[filename] then
		cache[filename] = loadFile(filename)
	end
	return cache[filename][index]
end


Mesh = {}
Mesh.__index = Mesh


function Mesh.new(_, vertices, indices)
	local self = {}
	setmetatable(self, Mesh)

	self.vertexArray = gl.GenVertexArrays()
	self.vertexBuffer = gl.GenBuffers()
	self.elementBuffer = gl.GenBuffers()
	self.vertexCount = #indices

	gl.BindVertexArray(self.vertexArray)
	gl.BindBuffer(gl.ARRAY_BUFFER, self.vertexBuffer)
	gl.BufferData(gl.ARRAY_BUFFER, gl.FLOAT, vertices, gl.STATIC_DRAW)

	gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, self.elementBuffer)
	gl.BufferData(gl.ELEMENT_ARRAY_BUFFER, gl.UNSIGNED_INT, indices, gl.STATIC_DRAW)

	gl.VertexAttribPointer(0, 3, false, 8, 0)
	gl.EnableVertexAttribArray(0)
	gl.VertexAttribPointer(1, 3, false, 8, 3)
	gl.EnableVertexAttribArray(1)
	gl.VertexAttribPointer(2, 2, false, 8, 6)
	gl.EnableVertexAttribArray(2)

	return self
end
setmetatable(Mesh, {__call=Mesh.new})


function Mesh.drawElements(self)
	gl.BindVertexArray(self.vertexArray)
	gl.DrawElements(gl.TRIANGLES, self.vertexCount, gl.UNSIGNED_INT, 0)
end


--===== builtin meshes =====--

function createBuiltins()
	cache["builtin.quad"] = {Mesh(
		{ 0, 0, 0,   0, 1, 0,   0, 0,
		  1, 0, 0,   0, 1, 0,   1, 0,
		  0, 1, 0,   0, 1, 0,   0, 1,
		  1, 1, 0,   0, 1, 0,   1, 1 },
		{ 0, 1, 3, 0, 3, 2 }
	)}
end


return module