// Copyright (C) 2022 RozK
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

// Adapted from https://www.khronos.org/opengl/wiki/Tutorial:_OpenGL_3.0_Context_Creation_(GLX)

#include "render_context.hpp"
#include <cstdio>
#include <cstring>
#include <GLES3/gl32.h>
#include <X11/Xlib.h>

static Display * rk_display = nullptr;
static Colormap rk_colormap = 0;
static Window rk_window = 0;
static GLXContext rk_context = nullptr;
static bool rk_error_occured = false;

#define GLX_CONTEXT_MAJOR_VERSION_ARB 0x2091
#define GLX_CONTEXT_MINOR_VERSION_ARB 0x2092
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display *, GLXFBConfig, GLXContext, Bool, int const *);

PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC rk_DrawElementsInstancedBaseInstance = nullptr;
PFNGLMULTIDRAWELEMENTSINDIRECTPROC rk_MultiDrawElementsIndirect = nullptr;

static int const rk_visual_attribs[] = {
    GLX_X_RENDERABLE, True,
    GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
    GLX_RENDER_TYPE, GLX_RGBA_BIT,
    GLX_X_VISUAL_TYPE, GLX_TRUE_COLOR,
    GLX_RED_SIZE, 8,
    GLX_GREEN_SIZE, 8,
    GLX_BLUE_SIZE, 8,
    GLX_ALPHA_SIZE, 8,
    GLX_DEPTH_SIZE, 24,
    GLX_STENCIL_SIZE, 8,
    GLX_DOUBLEBUFFER, True,
    None
};

static int const rk_context_attribs[] = {
    GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
    GLX_CONTEXT_MINOR_VERSION_ARB, 2,
    GLX_CONTEXT_PROFILE_MASK_ARB, GLX_CONTEXT_ES_PROFILE_BIT_EXT,
    None
};

static void rk_printf(
    char const * messsage) {
    printf("[GLX] %s\n", messsage);
}

static bool rk_extension_supported(
    char const * extlist,
    char const * extension) {
    char const * where = strchr(extension, ' ');
    if (where || *extension == '\0') {
        return false;
    }
    for (char const * start = extlist;;) {
        where = strstr(start, extension);
        if (!where) {
            break;
        }
        char const * const terminator = where + strlen(extension);
        if ((where == start || *(where - 1) == ' ') && (*terminator == ' ' || *terminator == '\0')) {
            return true;
        }
        start = terminator;
    }
    return false;
}

static int rk_error_handler(
    Display * display,
    XErrorEvent * event) {
    rk_error_occured = true;
    return 0;
}

rk_window_t rk_create_context(
    char const * name,
    rk_uint width,
    rk_uint height) {
    rk_display = XOpenDisplay(nullptr);
    if (!rk_display) {
        rk_printf("Failed to open X display.");
        return nullptr;
    }

    int glx_major, glx_minor;
    if (!glXQueryVersion(rk_display, &glx_major, &glx_minor) || (glx_major == 1 && glx_minor < 3) || glx_major < 1) {
        rk_printf("Invalid GLX version.");
        rk_destroy_context();
        return nullptr;
    }

    int fbcount;
    GLXFBConfig * const fbc = glXChooseFBConfig(rk_display, DefaultScreen(rk_display), rk_visual_attribs, &fbcount);
    if (!fbc) {
        rk_printf("Failed to retrieve a framebuffer config.");
        rk_destroy_context();
        return nullptr;
    }

    int best_fbc = -1;
    int best_num_samp = -1;
    for (int i = 0; i < fbcount; ++i) {
        XVisualInfo * vi = glXGetVisualFromFBConfig(rk_display, fbc[i]);
        if (vi) {
            int srgb = 0;
            glXGetFBConfigAttrib(rk_display, fbc[i], GLX_FRAMEBUFFER_SRGB_CAPABLE_ARB, &srgb);
            if (srgb) {
                int samp_buf, samples;
                glXGetFBConfigAttrib(rk_display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);
                glXGetFBConfigAttrib(rk_display, fbc[i], GLX_SAMPLES, &samples);
                if (best_fbc < 0 || (samp_buf && samples > best_num_samp)) {
                    best_fbc = i;
                    best_num_samp = samples;
                }
            }
            XFree(vi);
        }
    }
    if (best_fbc == -1) {
        XFree(fbc);
        rk_printf("Failed to find sRGB framebuffer.");
        rk_destroy_context();
        return nullptr;
    }
    GLXFBConfig const bestFbc = fbc[best_fbc];
    XFree(fbc);

    XVisualInfo * const vi = glXGetVisualFromFBConfig(rk_display, bestFbc);
    rk_colormap = XCreateColormap(rk_display, RootWindow(rk_display, vi->screen), vi->visual, AllocNone);
    XSetWindowAttributes swa;
    swa.colormap = rk_colormap;
    swa.background_pixmap = None;
    swa.border_pixel = 0;
    swa.event_mask = StructureNotifyMask;
    rk_window = XCreateWindow(rk_display, RootWindow(rk_display, vi->screen),
                                0, 0, width, height, 0, vi->depth, InputOutput, vi->visual,
                                CWBorderPixel | CWColormap | CWEventMask, &swa);
    if (!rk_window) {
        rk_printf("Failed to create window.");
        rk_destroy_context();
        return nullptr;
    }
    XFree(vi);
    XStoreName(rk_display, rk_window, name);
    XMapWindow(rk_display, rk_window);

    char const * const glx_exts = glXQueryExtensionsString(rk_display, DefaultScreen(rk_display));
    glXCreateContextAttribsARBProc const glXCreateContextAttribsARB =
        reinterpret_cast<glXCreateContextAttribsARBProc>(
            glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("glXCreateContextAttribsARB")));

    rk_error_occured = false;
    int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&rk_error_handler);
    if (!rk_extension_supported(glx_exts, "GLX_ARB_create_context") || !glXCreateContextAttribsARB) {
        rk_printf("glXCreateContextAttribsARB() extension not found.");
        rk_destroy_context();
        return nullptr;
    } else {
        rk_context = glXCreateContextAttribsARB(rk_display, bestFbc, 0, True, rk_context_attribs);
        XSync(rk_display, False);
        if (rk_error_occured || !rk_context) {
            rk_printf("Failed to create context.");
            rk_destroy_context();
            return nullptr;
        }
    }
    XSetErrorHandler(oldHandler);

    if (!glXIsDirect(rk_display, rk_context)) {
        rk_printf("Warning: Rendering context is indirect.");
    }
    glXMakeCurrent(rk_display, rk_window, rk_context);

    char const * const gl_exts = reinterpret_cast<char const *>(glGetString(GL_EXTENSIONS));
    if (rk_extension_supported(gl_exts, "GL_EXT_base_instance")) {
        rk_DrawElementsInstancedBaseInstance =
            reinterpret_cast<PFNGLDRAWELEMENTSINSTANCEDBASEINSTANCEPROC>(
                glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("DrawElementsInstancedBaseInstance")));
        if (rk_DrawElementsInstancedBaseInstance) {
            rk_printf("Using extension GL_EXT_base_instance::DrawElementsInstancedBaseInstance.");
            if (rk_extension_supported(gl_exts, "GL_EXT_multi_draw_indirect")) {
                rk_MultiDrawElementsIndirect =
                    reinterpret_cast<PFNGLMULTIDRAWELEMENTSINDIRECTPROC>(
                        glXGetProcAddressARB(reinterpret_cast<const GLubyte *>("MultiDrawElementsIndirectEXT")));
                if (rk_MultiDrawElementsIndirect) {
                    rk_printf("Using extension GL_EXT_multi_draw_indirect::MultiDrawElementsIndirectEXT.");
                }
            }
        }
    }

    return reinterpret_cast<rk_window_t>(rk_window);
}

void rk_swap_buffers() {
    if (rk_display && rk_window) {
        glXSwapBuffers(rk_display, rk_window);
    }
}

void rk_destroy_context() {
    if (rk_display) {
        glXMakeCurrent(rk_display, 0, nullptr);
        if (rk_context) {
            glXDestroyContext(rk_display, rk_context);
            rk_context = nullptr;
        }
        if (rk_window) {
            XDestroyWindow(rk_display, rk_window);
            rk_window = 0;
        }
        if (rk_colormap) {
            XFreeColormap(rk_display, rk_colormap);
            rk_colormap = 0;
        }
        XCloseDisplay(rk_display);
        rk_display = nullptr;
    }
}