// 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 "../display.hpp"
#include "display_glx.hpp"
#include <cstdio>
#include <cstring>

static bool rk_error_occured = false;

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

rk_DrawElementsInstancedBaseInstanceFunc rk_DrawElementsInstancedBaseInstance = nullptr;
rk_MultiDrawElementsIndirectFunc 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_glx_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_display_t rk_create_display(
    rk_char const * name,
    rk_uint width,
    rk_uint height) {
    if (!name || !width || !height) {
        return nullptr;
    };
    rk_display_glx * const display = new rk_display_glx;
    display->display = XOpenDisplay(nullptr);
    display->window = 0;
    display->colormap = 0;
    display->context = nullptr;
    if (!display->display) {
        rk_glx_printf("Failed to open X display.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    }

    int glx_major, glx_minor;
    if (!glXQueryVersion(display->display, &glx_major, &glx_minor) ||
            (glx_major == 1 && glx_minor < 3) || glx_major < 1) {
        rk_glx_printf("Invalid GLX version.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    }
    char const * const glx_exts = glXQueryExtensionsString(display->display, DefaultScreen(display->display));

    int fbcount;
    GLXFBConfig * const fbc = glXChooseFBConfig(
        display->display, DefaultScreen(display->display), rk_visual_attribs, &fbcount);
    if (!fbc) {
        rk_glx_printf("Failed to retrieve framebuffer configs.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    }
    printf("[GLX] Found %d framebuffer configs.\n", fbcount);

    int best_fbc = -1;
    int best_num_samp = -1;
    for (int i = 0; i < fbcount; ++i) {
        XVisualInfo * const vi = glXGetVisualFromFBConfig(display->display, fbc[i]);
        if (vi) {
            int samp_buf, samples;
            glXGetFBConfigAttrib(display->display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf);
            glXGetFBConfigAttrib(display->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_glx_printf("Failed to find a suitable framebuffer config.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    }
    GLXFBConfig const bestFbc = fbc[best_fbc];
    XFree(fbc);
    printf("[GLX] Select framebuffer config with %d samples.\n", best_num_samp);

    XVisualInfo * const vi = glXGetVisualFromFBConfig(display->display, bestFbc);
    display->colormap = XCreateColormap(
        display->display, RootWindow(display->display, vi->screen), vi->visual, AllocNone);
    XSetWindowAttributes swa;
    swa.colormap = display->colormap;
//    swa.background_pixmap = None;
//    swa.border_pixel = 0;
    swa.event_mask = RK_EVENTS_MASK;
    display->window = XCreateWindow(display->display, RootWindow(display->display, vi->screen),
        0, 0, width, height, 0, vi->depth, InputOutput, vi->visual,
        /*CWBorderPixel |*/ CWColormap | CWEventMask, &swa);
    XFree(vi);
    if (!display->window) {
        rk_glx_printf("Failed to create window.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    }
    XStoreName(display->display, display->window, name);
    XMapWindow(display->display, display->window);

    rk_CreateContextAttribsFunc const glXCreateContextAttribs =
        reinterpret_cast<rk_CreateContextAttribsFunc>(
            glXGetProcAddressARB(reinterpret_cast<GLubyte const *>("glXCreateContextAttribsARB")));

    if (!rk_extension_supported(glx_exts, "GLX_ARB_create_context") || !glXCreateContextAttribs) {
        rk_glx_printf("glXCreateContextAttribsARB extension not found.");
        rk_destroy_display(reinterpret_cast<rk_display_t>(display));
        return nullptr;
    } else {
        rk_error_occured = false;
        int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&rk_error_handler);
        display->context = glXCreateContextAttribs(display->display, bestFbc, 0, True, rk_context_attribs);
        XSync(display->display, False);
        XSetErrorHandler(oldHandler);
        if (rk_error_occured || !display->context) {
            rk_glx_printf("Failed to create context.");
            rk_destroy_display(reinterpret_cast<rk_display_t>(display));
            return nullptr;
        }
    }

    if (!glXIsDirect(display->display, display->context)) {
        rk_glx_printf("Warning: Rendering context is indirect.");
    }
    glXMakeCurrent(display->display, display->window, display->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<rk_DrawElementsInstancedBaseInstanceFunc>(
                glXGetProcAddressARB(reinterpret_cast<GLubyte const *>("DrawElementsInstancedBaseInstance")));
        if (rk_DrawElementsInstancedBaseInstance) {
            rk_glx_printf("Using extension GL_EXT_base_instance::DrawElementsInstancedBaseInstance.");
            if (rk_extension_supported(gl_exts, "GL_EXT_multi_draw_indirect")) {
                rk_MultiDrawElementsIndirect =
                    reinterpret_cast<rk_MultiDrawElementsIndirectFunc>(
                        glXGetProcAddressARB(reinterpret_cast<GLubyte const *>("MultiDrawElementsIndirectEXT")));
                if (rk_MultiDrawElementsIndirect) {
                    rk_glx_printf("Using extension GL_EXT_multi_draw_indirect::MultiDrawElementsIndirectEXT.");
                }
            }
        }
    }

    return reinterpret_cast<rk_display_t>(display);
}

void rk_destroy_display(
    rk_display_t _display) {
    rk_display_glx * const display = reinterpret_cast<rk_display_glx *>(_display);
    if (display) {
        if (display->display) {
            glXMakeCurrent(display->display, 0, nullptr);
            if (display->context) {
                glXDestroyContext(display->display, display->context);
            }
            if (display->window) {
                XDestroyWindow(display->display, display->window);
            }
            if (display->colormap) {
                XFreeColormap(display->display, display->colormap);
            }
            XCloseDisplay(display->display);
        }
        delete display;
    }
}

void rk_swap_buffers(
    rk_display_t _display) {
    rk_display_glx const * const display = reinterpret_cast<rk_display_glx const *>(_display);
    if (display && display->display && display->window) {
        glXSwapBuffers(display->display, display->window);
    }
}