"""Headless GPU-accelerated OpenGL context creation on Google Colaboratory.

Typical usage:

    # Optional PyOpenGL configuratiopn can be done here.
    # import OpenGL
    # OpenGL.ERROR_CHECKING = True

    # 'glcontext' must be imported before any OpenGL.* API.
    from lucid.misc.gl.glcontext import create_opengl_context

    # Now it's safe to import OpenGL and EGL functions
    import OpenGL.GL as gl

    # create_opengl_context() creates a GL context that is attached to an
    # offscreen surface of the specified size. Note that rendering to buffers
    # of other sizes and formats is still possible with OpenGL Framebuffers.
    #
    # Users are expected to directly use the EGL API in case more advanced
    # context management is required.
    width, height = 640, 480
    create_opengl_context((width, height))

    # OpenGL context is available here.

"""

from __future__ import print_function

# pylint: disable=unused-import,g-import-not-at-top,g-statement-before-imports

import os

os.environ['PYOPENGL_PLATFORM'] = 'egl'

try:
  import OpenGL
except:
  print('This module depends on PyOpenGL.')
  print('Please run "\033[1m!pip install -q pyopengl\033[0m" '
        'prior importing this module.')
  raise

import ctypes
from ctypes import pointer
from ctypes import util
from ctypes.util import find_library

# OpenGL loading workaround.
#
# * PyOpenGL tries to load libGL, but we need libOpenGL, see [1,2].
#   This could have been solved by a symlink libGL->libOpenGL, but:
#
# * Python 2.7 can't find libGL and linEGL due to a bug (see [3])
#   in ctypes.util, that was only wixed in Python 3.6.
#
# So, the only solution I've found is to monkeypatch ctypes.util
# [1] https://devblogs.nvidia.com/egl-eye-opengl-visualization-without-x-server/
# [2] https://devblogs.nvidia.com/linking-opengl-server-side-rendering/
# [3] https://bugs.python.org/issue9998
_find_library_old = ctypes.util.find_library
try:

  def _find_library_new(name):
    return {
        'GL': 'libOpenGL.so',
        'EGL': 'libEGL.so',
    }.get(name, _find_library_old(name))
  ctypes.util.find_library = _find_library_new
  import OpenGL.GL as gl
  import OpenGL.EGL as egl
except:
  print('Unable to load OpenGL libraries. '
        'Make sure you use GPU-enabled backend.')
  print('Press "Runtime->Change runtime type" and set '
        '"Hardware accelerator" to GPU.')
  raise
finally:
  ctypes.util.find_library = _find_library_old


class Context:
    def __init__(self):
        pass

    def create_opengl_context(self, surface_size=(640, 480)):
        """Create offscreen OpenGL context and make it current.

        Users are expected to directly use EGL API in case more advanced
        context management is required.

        Args:
        surface_size: (width, height), size of the offscreen rendering surface.
        """
        egl_display = egl.eglGetDisplay(egl.EGL_DEFAULT_DISPLAY)

        major, minor = egl.EGLint(), egl.EGLint()
        egl.eglInitialize(egl_display, pointer(major), pointer(minor))

        config_attribs = [
          egl.EGL_SURFACE_TYPE, egl.EGL_PBUFFER_BIT, egl.EGL_BLUE_SIZE, 8,
          egl.EGL_GREEN_SIZE, 8, egl.EGL_RED_SIZE, 8, egl.EGL_DEPTH_SIZE, 24,
          egl.EGL_RENDERABLE_TYPE, egl.EGL_OPENGL_BIT, egl.EGL_NONE
        ]
        # if need MSAA https://www.khronos.org/opengl/wiki/Multisampling
        config_attribs = (egl.EGLint * len(config_attribs))(*config_attribs)

        num_configs = egl.EGLint()
        egl_cfg = egl.EGLConfig()
        egl.eglChooseConfig(egl_display, config_attribs, pointer(egl_cfg), 1,
                          pointer(num_configs))

        width, height = surface_size
        pbuffer_attribs = [
          egl.EGL_WIDTH,
          width,
          egl.EGL_HEIGHT,
          height,
          egl.EGL_NONE,
        ]
        pbuffer_attribs = (egl.EGLint * len(pbuffer_attribs))(*pbuffer_attribs)
        egl_surf = egl.eglCreatePbufferSurface(egl_display, egl_cfg, pbuffer_attribs)

        egl.eglBindAPI(egl.EGL_OPENGL_API)

        egl_context = egl.eglCreateContext(egl_display, egl_cfg, egl.EGL_NO_CONTEXT,
                                         None)
        egl.eglMakeCurrent(egl_display, egl_surf, egl_surf, egl_context)
        self.display = egl_display

    def destroy(self):
        egl.eglTerminate(self.display)
