#if 0
mkdir -p build
clang -o build/demo -g wayland_egl.c -lwayland-client -lwayland-egl -lEGL
exit 0
#endif

/*
** Reading From:
** (1) Wayland Docs   https://wayland.freedesktop.org/docs/html/
** (2) wayland/protocol.xml \
 **      https://chromium.googlesource.com/external/wayland/wayland/+/refs/heads/master/protocol/wayland.xml
** (3) EGL spec       https://registry.khronos.org/EGL/sdk/docs/man/
**
** (?) I cannot find any documentation for wl_egl_ except for headers
** and example usage code. :(
*/

/* [1] IMPORTANT NOTE
**
** (1) /ch04.html#sect-Protocol-Code-Generation
** " The interfaces, requests and events are defined in
 **   protocol/wayland.xml. This xml is used to generate the function
 **   prototypes that can be used by clients and compositors. "
**
** (1) /ch04.html#sect-Protocol-Basic-Principles
** " The Wayland protocol is an asynchronous object oriented protocol. 
**   All requests are method invocations on some object.
**   ...
**   The protocol is message-based. A message sent by a client to 
**   the server is called request. A message from the server to a 
**   client is called event. "
**
**~ 
**~ I have yet to see any place where it is *defined* how the xml
**~ is transformed into function prototypes. So I'm putting notes of
**~ my own inferences here.
**~
**~ From the client's perspective:
**~
**~ A request `R(...)` on an object interface `O` becomes the
 **~ function `O_R(O *obj, ...)`.
**~ ! Sometimes the arguments for `R(...)` include an argument that
**~ doesn't appear to have a documented type (at least in (1)).
**~ We can also refer to the xml (2) and see such arguments have
**~ the type "new_id". These seem to actually be a return value
**~ that does not appear in the generated signature as an id,
**~ but instead is translated into a typed return pointer.
**~ If the documentation does explicitly write the "new_id" type
**~ that also gets rewritten to a typed return.
**~
**~ An event `E(...)` on an object interface `O` will becomes a
**~ callback with the signature `(*)(void *data, O *obj, ...)`.
**~
**~ The collection of event callbacks on an object interface become
**~ `struct wl_O_listener` using the names `E` of the events as the
**~ field names.
**~
**~ A function for adding the listener to the object is also generated
**~ `wl_O_add_listener(O *obj, struct wl_O_listener *listener, void *data)`
**~
**~ Each object interface `O` becomes a `wl_O_interface` which (I think)
**~ is a global variable vtable representation of the interface.
**~
*/

#include <wayland-client.h>
#include <wayland-egl.h>
/*~ NOTE: wayland-egl.h *before* EGL/ */
#include <EGL/egl.h>
#include <EGL/eglext.h>
#include <GL/glcorearb.h>

#include <stdio.h>
#include <string.h>

// X(N:name,R:return,P:params)
#define GL_FUNCS_XLIST(X)\
X(glDrawBuffer, void, (GLenum buf)) \
X(glViewport, void, (GLint x, GLint y, GLsizei w, GLsizei h)) \
X(glClear, void, (GLbitfield mask)) \
X(glClearColor, void, (GLfloat r, GLfloat g, GLfloat b, GLfloat a))

#define X(N,R,P) R (*N)P = 0;
GL_FUNCS_XLIST(X)
#undef X

typedef struct Ctx{
  struct wl_display    *display;
  struct wl_registry   *registry;
  struct wl_compositor *compositor;
  struct wl_surface    *surface;
  struct wl_region     *region;
  struct wl_egl_window *egl_window;
  
  EGLDisplay egl_display;
  EGLContext egl_context;
  EGLSurface egl_surface;
} Ctx;

/* (1) Appendix A: wl_registry::global */
static void
wlevent_registry_global(void *data, struct wl_registry *registry, uint32_t name, const char *interface, uint32_t version){
  printf("wlevent_registry_global: interface=%s\n", interface);
  
  Ctx *ctx = (Ctx*)data;
  
  /* (1) Appendix A: wl_registry::bind
  ** " Binds a new, client-created object to the server "
  */
  if (strcmp(interface, "wl_compositor") == 0){
    ctx->compositor = (struct wl_compositor*)
      wl_registry_bind(registry, name, &wl_compositor_interface, 1);
  }
}

/* (1) Appendix A: wl_registry::global_remove */
static void
wlevent_registry_global_remove(void *data, struct wl_registry *registry, uint32_t name){}

const struct wl_registry_listener registry_listener = {
  wlevent_registry_global,
  wlevent_registry_global_remove,
};

int main(){
  Ctx ctx = {0};
  
  /* (1) Appendix B: wl_display_connect
  ** " Connect to a Wayland display. "
  */
  ctx.display = wl_display_connect(0);
  if (ctx.display == 0){
    printf("wl_display_connect failed\n");
  }
  
  /* (1) Appendix A: wl_display::get_registry
  ** " creates a registry object that allows the client to list 
  **   and bind the global objects available from the compositor "
  */
  if (ctx.display != 0){
    ctx.registry = wl_display_get_registry(ctx.display);
    if (ctx.registry == 0){
      printf("wl_display_get_registry failed\n");
    }
  }
  
  if (ctx.registry != 0){
    /* [1] */
    wl_registry_add_listener(ctx.registry, &registry_listener, &ctx);
    
    /* (1) Appendix B: wl_display::dispatch
    ** " Dispatch events on the default event queue.
    **   ... this function blocks until there are events to be read ... "
    */
    wl_display_dispatch(ctx.display);
    
    /* (1) Appendix B: wl_display_roundtrip
    ** " Block until all pending request are processed by the server "
    */
    wl_display_roundtrip(ctx.display);
    
    if (ctx.compositor == 0){
      printf("failed to get wl_compositor\n");
    }
  }
  
  int opengl_load_success = 0;
  if (ctx.display != 0 && ctx.compositor != 0){
    /* (3) eglGetDisplay
    ** " obtains the EGL display connection for the native display "
    */
    ctx.egl_display = eglGetDisplay(ctx.display);
    if (ctx.egl_display == 0){
      printf("eglGetDisplay failed\n");
    }
    
    /* (3) eglInitialize
    ** " initializes* the EGL display connection obtained with eglGetDisplay "
    */
    int egl_init_success = 0;
    EGLint major = 0, minor = 0;
    if (ctx.egl_display != 0){
      egl_init_success = eglInitialize(ctx.egl_display, &major, &minor);
      if (!egl_init_success){
        printf("eglInitialize failed\n");
      }
    }
    
    // print version
    if (egl_init_success){
      printf("EGL version %d.%d\n", major, minor);
      if (major < 1 || (major == 1 && minor < 5)){
        printf("version 1.5 or higher\n");
        egl_init_success = 0;
      }
    }
    
    /* (3) eglBindAPI 
    ** " defines the current rendering API for EGL in the thread it is
    **   called from "
    */
    EGLBoolean bind_api_success = 0;
    if (egl_init_success){
      bind_api_success = eglBindAPI(EGL_OPENGL_API);
    }
    
    /*~ NOTE:
    **~ Create OpenGL context & link OpenGL procedures
    */
    
    /* (3) eglCreateContext
    ** " creates an EGL rendering context for the current rendering API
    **   (as set with eglBindAPI) and returns a handle to the context "
    */
    if (bind_api_success){
      EGLint attr[] = {
        EGL_CONTEXT_MAJOR_VERSION, 3,
        EGL_CONTEXT_MINOR_VERSION, 3,
        EGL_CONTEXT_OPENGL_PROFILE_MASK, EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT,
        EGL_NONE,
      };
      ctx.egl_context = eglCreateContext(ctx.egl_display, EGL_NO_CONFIG_KHR, EGL_NO_CONTEXT, attr);
      if (ctx.egl_context == EGL_NO_CONTEXT){
        printf("eglCreateContext failed\n");
      }
    }
    
    /* (3) eglMakeCurrent
    ** " binds context to the current rendering thread "
    */
    EGLBoolean make_current_success = 0;
    if (ctx.egl_context != 0){
      make_current_success = eglMakeCurrent(ctx.egl_display, EGL_NO_SURFACE, EGL_NO_SURFACE, ctx.egl_context);
      if (!make_current_success){
        printf("eglMakeCurrent failed\n");
      }
    }
    
    /* (3) eglGetProcAddress
    ** " returns the address of the client API or EGL function "
    */
    if (make_current_success){
      opengl_load_success = 1;
#define X(N,R,P) N = (R(*)P)(eglGetProcAddress(#N)); if (N == 0) opengl_load_success = 0;
      GL_FUNCS_XLIST(X)
#undef X
      if (!opengl_load_success){
        printf("GL procedure loading failed\n");
      }
    }
  }
  
  if (opengl_load_success){
    /* (1) Appendix A: wl_compositor::create_surface
    ** " create new surface "
    */
    ctx.surface = wl_compositor_create_surface(ctx.compositor);
    if (ctx.surface == 0){
      printf("wl_compositor_create_surface failed\n");
    }
    
    /* (1) Appendix A: wl_compositor::create_region
    ** " create new region "
    */
    ctx.region = wl_compositor_create_region(ctx.compositor);
    if (ctx.region == 0){
      printf("wl_compositor_create_region failed\n");
    }
    
    if (ctx.surface != 0 && ctx.region != 0){
      /* (1) Appendix A: wl_region::add
      ** " add rectangle to region "
      */
      wl_region_add(ctx.region, 0, 0, 640, 480);
      
      /* (1) Appendix A: wl_region::set_opaque_region
      ** " The opaque region is an optimization hint for the compositor
       **   that lets it optimize out redrawing of content behind opaque
       **   regions. "
      */
      wl_surface_set_opaque_region(ctx.surface, ctx.region);
      
      /* (?) */
      ctx.egl_window =  wl_egl_window_create(ctx.surface, 640, 480);
      if (ctx.egl_window == EGL_NO_SURFACE){
        printf("wl_egl_window_create failed\n");
      }
    }
  }
  
  if (ctx.egl_window != EGL_NO_SURFACE){
    /* (3) eglChooseConfig
    ** " returns in configs a list of all EGL frame buffer configurations
    **   that match the attributes specified in attrib_list "
    */
    EGLConfig configs[64];
    EGLint config_cap = sizeof(configs)/sizeof(*configs);
    EGLint config_count = 0;
    {
      EGLint attributes[] = {
        EGL_SURFACE_TYPE,      EGL_WINDOW_BIT,
        EGL_CONFORMANT,        EGL_OPENGL_BIT,
        EGL_RENDERABLE_TYPE,   EGL_OPENGL_BIT,
        EGL_COLOR_BUFFER_TYPE, EGL_RGB_BUFFER,
        EGL_RED_SIZE,      8,
        EGL_GREEN_SIZE,    8,
        EGL_BLUE_SIZE,     8,
        EGL_DEPTH_SIZE,   24,
        EGL_STENCIL_SIZE,  8,
        EGL_NONE,
      };
      if (!eglChooseConfig(ctx.egl_display, attributes, configs, config_cap, &config_count)){
        printf("eglChooseConfig failed\n");
        config_count = 0;
      }
    }
    
    /* (3) eglCreateWindowSurface
    ** " creates an on-screen EGL window surface and returns a handle to it "
    */
    {
      EGLint attributes[] = {
        EGL_RENDER_BUFFER, EGL_BACK_BUFFER,
        EGL_NONE,
      };
      for (EGLint i = 0; i < config_count; i += 1){
        ctx.egl_surface = eglCreateWindowSurface(ctx.egl_display, configs[i], ctx.egl_window, attributes);
        if (ctx.egl_surface != EGL_NO_SURFACE){
          break;
        }
      }
      if (ctx.egl_surface == EGL_NO_SURFACE){
        printf("eglCreateWindowSurface failed\n");
      }
    }
  }
  
  /* (3) eglMakeCurrent */
  EGLBoolean make_current_success2 = 0;
  if (ctx.egl_surface != EGL_NO_SURFACE){
    make_current_success2 = eglMakeCurrent(ctx.egl_display, ctx.egl_surface, ctx.egl_surface, ctx.egl_context);
  }
  
  /* (3) eglSwapInterval 
  ** " Specifies the minimum number of video frames that are displayed before
  **   a buffer swap will occur "
  */
  EGLBoolean swap_interval_success = 0;
  if (make_current_success2){
    swap_interval_success = eglSwapInterval(ctx.egl_display, 1);
  }
  
  /*~ NOTE: Main loop */
  int exit_loop = 0;
  for (;!exit_loop;){
    /* (1) Appendix B: wl_display_dispatch_pending
    ** " This function dispatches events on the main event queue.
    **   ... it doesn't block."
    */
    wl_display_dispatch_pending(ctx.display);
    
    /*~ NOTE: render */
    {
      glDrawBuffer(GL_BACK);
      glViewport(0, 0, 640, 480);
      glClearColor(0.40f, 0.90f, 0.15f, 1.f);
      glClear(GL_COLOR_BUFFER_BIT);
    }
    
    /* (2) eglSwapBuffers
    ** " back-buffered window surface, then the color buffer is copied 
    **   (posted) to the native window associated with that surface "
    */
    EGLBoolean swap_success = eglSwapBuffers(ctx.egl_display, ctx.egl_surface);
    if (!swap_success){
      printf("eglSwapBuffers failed\n");
    }
  }
  
  /* (1) #Client-classwl__display_1a9150a7e3213a58b469a6966e60a9f108
  ** " Close the connection to display "
  */
  if (ctx.display != 0){
    wl_display_disconnect(ctx.display);
  }
  
  return(0);
}