(require :cl-opengl)
(require :sdl2)

(defvar vertices nil)
(defvar elements nil)

(setf vertices (make-array 9 :fill-pointer 0))
(setf elements (make-array 9 :fill-pointer 0))

(defvar *vertex-shader* "
#version 330 core
layout (location = 0) in vec3 aPos;

void main() {
    gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
}
")

(defvar *fragment-shader* "
#version 330 core
out vec4 FragColor;

void main() {
    FragColor = vec4(0.95f, 0.98f, 0.65f, 1.0f);
}
")

(defun split-str-1 (string &optional (separator " ") (r nil))
  (let ((n (position separator string
                 :from-end t
                 :test #'(lambda (x y)
                           (find y x :test #'string=)))))
(if n
    (split-str-1 (subseq string 0 n) separator (cons (subseq string (1+ n)) r))
    (cons string r))))

(defun split-str (string &optional (separator " "))
  (split-str-1 string separator))

(defun parse-float (number)
  (with-input-from-string (in number)
  (read in)))

(defun load-obj (file-name)
   (let ((file (open file-name)))
     (with-open-stream (source file)
       (loop for line = (read-line source nil nil)
          while line do
            (let* ((split-line (split-str line " "))
                   (header (car split-line))
                   (rest (cdr split-line)))
              (cond ((string= header "v") (dolist (vertex rest) (vector-push (parse-float vertex) vertices)))
                  ((string= header "f") (dolist (face rest) (let ((element      (parse-integer (car (split-str face "/")))))
                                                              (vector-push (- element 1) elements))))))))))

(defun main ()
  (load-obj "tortoise.obj")
  (sdl2:with-init (:everything)
(sdl2:gl-set-attr :context-profile-mask 0)
(sdl2:gl-set-attr :context-major-version 3)
(sdl2:gl-set-attr :context-minor-version 3)

(sdl2:with-window (win :flags `(:shown :opengl))
  (sdl2:with-gl-context (gl-context win)
  (sdl2:gl-make-current win gl-context)
  (gl:viewport 0 0 800 600)
  (gl:clear-color 0.957 0.376 0.286 1.0)

  (let ((glarray (gl:alloc-gl-array :float (length vertices)))
        (glarray-2 (gl:alloc-gl-array :unsigned-short (length elements))))
    (dotimes (i (length elements))
      (setf (gl:glaref glarray-2 i) (aref elements i)))
    (dotimes (i (length vertices))
      (setf (gl:glaref glarray i) (aref vertices i)))

    (let ((vbo (gl:gen-buffer))
          (vao (gl:gen-vertex-array))
          (ebo (gl:gen-buffer)))
      (gl:bind-vertex-array vao)
      (gl:bind-buffer :array-buffer vbo)
      (gl:buffer-data :array-buffer :static-draw glarray)
      (gl:free-gl-array glarray)
      (gl:bind-buffer :element-array-buffer ebo)
      (gl:buffer-data :element-array-buffer :static-draw glarray-2)
      (gl:vertex-attrib-pointer 0 4 :float nil 0 0)
      (gl:enable-vertex-attrib-array 0)

      (let ((vertex-shader (gl:create-shader :vertex-shader))
            (fragment-shader (gl:create-shader :fragment-shader)))
        (gl:shader-source vertex-shader *vertex-shader*)
        (gl:shader-source fragment-shader *fragment-shader*)
        (gl:compile-shader vertex-shader)
        (gl:compile-shader fragment-shader)
        (print (gl:get-shader-info-log vertex-shader))
        (print (gl:get-shader-info-log fragment-shader))

        (let ((program (gl:create-program)))
          (gl:attach-shader program vertex-shader)
          (gl:attach-shader program fragment-shader)
          (gl:link-program program)
          (gl:delete-shader vertex-shader)
          (gl:delete-shader fragment-shader)
          (gl:use-program program)))

      (sdl2:with-event-loop (:method :poll)
        (:idle ()
               (gl:clear :color-buffer)
               (gl:bind-vertex-array vao)
               (gl:draw-elements :triangles glarray-2)
               (gl:flush)
               (sdl2:gl-swap-window win))
        (:quit () t))))))))