#include <GLES2/gl2.h>
#include <GLES2/gl2ext.h>
#include <EGL/egl.h>
#include <SDL2/SDL.h>
#include <SDL2/SDL_syswm.h>

GLuint load_gl_shader_from_sources(
	GLenum shader_unit,
	char const * const * const sources,
	GLint const * const lengths )
{
	GLuint shader = 0;
	GLint shader_status = GL_FALSE;
	char *shader_infolog = NULL;
	do {
		size_t n_sources = 0;
		while( sources[n_sources] ){ ++n_sources; }

		shader = glCreateShader(shader_unit);
		if( !shader ){ break; }
		glShaderSource(shader, n_sources, sources, lengths);
		glCompileShader(shader);

		glGetShaderiv(shader, GL_COMPILE_STATUS, &shader_status);
		if( !shader_status ){
			GLint log_length, returned_length;
			glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &log_length);

			shader_infolog = malloc(log_length);
			if( shader_infolog ){
				memset(shader_infolog, 0, log_length);
				glGetShaderInfoLog(
					shader,
					log_length,
					&returned_length,
					shader_infolog );
				char const * shader_unit_str = NULL;
				switch(shader_unit) {
				case GL_VERTEX_SHADER:   shader_unit_str = "vertex";   break;
				case GL_FRAGMENT_SHADER: shader_unit_str = "fragment"; break;
				}
				fprintf(stderr,
					"%s shader compilation failed;\n%*s",
					shader_unit_str,
					returned_length, shader_infolog );
			}
		}
	} while(0);


	if( !shader_status ){ glDeleteShader(shader); shader = 0; }
	if( shader_infolog ){ free(shader_infolog); }

	return shader;
}

GLuint load_gl_program_from_sources(
	char const * const * const sources_vs,
	GLint const * const lengths_vs,
	char const * const * const sources_fs,
	GLint const * const lengths_fs )
{
	GLint linkStatus = GL_FALSE;
	GLuint program = 0, vert_shader = 0, frag_shader = 0;
	char const *msg = NULL;
	do {
		program = glCreateProgram();
		if( !program ){ fprintf(stderr, "glCreateProgram(): %d", glGetError()); break; }

		if( sources_vs ){
			vert_shader = load_gl_shader_from_sources(GL_VERTEX_SHADER, sources_vs, lengths_vs);
			if( !vert_shader ){ break; }
			glAttachShader(program, vert_shader);
		}
		if( sources_fs ){
			frag_shader = load_gl_shader_from_sources(GL_FRAGMENT_SHADER, sources_fs, lengths_fs);
			if( !frag_shader ){ break; }
			glAttachShader(program, frag_shader);
		}

		glLinkProgram(program);
		glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);
		if( !linkStatus ){
			GLint log_length, returned_length;
			glGetProgramiv(program, GL_INFO_LOG_LENGTH, &log_length);

			char *program_infolog = malloc(log_length);
			if( program_infolog ){
				glGetProgramInfoLog(program, log_length, &returned_length, program_infolog);
				fprintf(stderr,
					"shader program linking failed;\n%*s",
					returned_length, program_infolog );
				free(program_infolog);
			}
		}
	} while(0);

	/* shaders are retained inside the GL context until their last holder,
	 * i.e. the shader program that was just linked is deleted. */
	if( vert_shader ){ glDeleteShader(vert_shader); }
	if( frag_shader ){ glDeleteShader(frag_shader); }

	if( !linkStatus ){ glDeleteProgram(program); program = 0; }

	return program;
}

extern char const _binary_pixels_raw_start;
extern char const _binary_pixels_raw_end;
#define _binary_pixels_raw ((void const*const)&_binary_pixels_raw_start)
#define _binary_pixels_raw_size (size_t)(&_binary_pixels_raw_end - &_binary_pixels_raw_start)
#define _binary_pixels_raw_width 1280
#define _binary_pixels_raw_height 960

extern char const _binary_debayer_vs_glsl_end;
extern char const _binary_debayer_vs_glsl_start;
#define _binary_debayer_vs_glsl ((void const*const)&_binary_debayer_vs_glsl_start)
#define _binary_debayer_vs_glsl_size (size_t)(&_binary_debayer_vs_glsl_end - &_binary_debayer_vs_glsl_start)

extern char const _binary_debayer_fs_glsl_end;
extern char const _binary_debayer_fs_glsl_start;
#define _binary_debayer_fs_glsl ((void const*const)&_binary_debayer_fs_glsl_start)
#define _binary_debayer_fs_glsl_size (size_t)(&_binary_debayer_fs_glsl_end - &_binary_debayer_fs_glsl_start)

static GLenum draw_debayer_RGB(GLuint texture)
{
#if 1
/* For the moment, just perform 1st degree unity mapping */
GLfloat const coef_r[16] = {
	1., 0., 0., 0.,
	0., 0., 0., 0.,
	0., 0., 0., 0.,
	0., 0., 0., 0. };
GLfloat const *const coef_g = coef_r;
GLfloat const *const coef_b = coef_r;

/* Those coefficients seem to be way off. Need to investigate further. */
#elif  0
GLfloat const coef_r[16] = {
	 4.41898209e-01, -1.08617799e-01, -5.05377382e+00,  9.52185120e+00,
	 2.05420594e+02, -6.17439055e+02, -2.71301881e+03,  1.26291235e+04,
	 4.06578493e+03, -9.34105168e+04,  1.33991823e+05,  1.27240329e+05,
	-5.67983982e+05,  6.77352564e+05, -3.70453281e+05,  7.96913561e+04 };

GLfloat const coef_g[16] = {
	 1.75630153e-01,  1.77970251e-01,  3.93921859e+00, -3.83900750e+01,
	-8.50868580e+01,  1.39497351e+03, -1.50332837e+03, -1.85003596e+04,
	 6.53562460e+04, -1.00909757e+04, -3.92586418e+05,  1.06909568e+06,
	-1.42125035e+06,  1.07029531e+06, -4.38315295e+05,  7.62246706e+04 };

GLfloat const coef_b[16] = {
	 2.44126153e-01,  1.71659546e-01,  5.35993954e-01, -8.10729044e+00,
	-7.11102399e+00,  1.24421866e+02,  1.22255723e-02, -8.74245656e+02,
	 4.72294698e+02,  2.99248407e+03, -2.85191269e+03, -4.54081854e+03,
	 6.46045466e+03,  1.41007972e+03, -5.12551110e+03,  1.94825904e+03 };
#else
GLfloat const coef_r[16] = {
	 2.43242336e+00,  1.29527225e+01, -1.67053874e+02, -1.03264624e+03,
	 3.89533658e+04, -3.79431617e+05,  2.04443576e+06, -7.12156509e+06,
	 1.71198465e+07, -2.92874193e+07,  3.60398126e+07, -3.17297224e+07,
	 1.95237028e+07, -7.98040387e+06,  1.94790465e+06, -2.14928147e+05 };

GLfloat const coef_g[16] = {
	 5.24353947e+00,  2.96584994e+01, -1.73865606e+02, -1.93045987e+03,
	 1.85513793e+04, -4.48754651e+04, -1.32006487e+05,  1.24471739e+06,
	-4.25234811e+06,  8.83297659e+06, -1.23501912e+07,  1.19377860e+07,
	-7.90632536e+06,  3.43589308e+06, -8.84463954e+05,  1.02356618e+05 };

GLfloat const coef_b[16] = {
	 4.04493164e+00, -1.46245348e+01,  1.71095269e+02,  2.06498987e+03,
	-4.93803069e+04,  3.95481675e+05, -1.82105431e+06,  5.53531911e+06,
	-1.17786850e+07,  1.80202854e+07, -1.99760831e+07,  1.59213215e+07,
	-8.89476364e+06,  3.30494584e+06, -7.32930586e+05,  7.33188936e+04 };
#endif

	static GLuint prog = 0, a_position, u_sampler, u_coef_r, u_coef_g, u_coef_b;
	if( !prog ){
		char const *src_vs[] = { _binary_debayer_vs_glsl, NULL };
		GLint const  sz_vs[] = { _binary_debayer_vs_glsl_size, 0 };
		char const *src_fs[] = { _binary_debayer_fs_glsl, NULL };
		GLint const  sz_fs[] = { _binary_debayer_fs_glsl_size, 0 };
		prog = load_gl_program_from_sources(src_vs, sz_vs, src_fs, sz_fs);
		if( !prog ){ _Exit(1); return GL_INVALID_VALUE; }
		a_position = glGetAttribLocation(prog,  "a_position");
		u_sampler  = glGetUniformLocation(prog, "u_sampler");
		u_coef_r   = glGetUniformLocation(prog, "u_coef_r");
		u_coef_g   = glGetUniformLocation(prog, "u_coef_g");
		u_coef_b   = glGetUniformLocation(prog, "u_coef_b");
	}

	static GLuint vbo_xy = 0;
	if( !vbo_xy ){
		// a triangle that fully covers the rectangle
		// ((0,0),(1,1)) in counter clock vertex order.
		GLfloat const data[] = {
			0.0, 0.0,
			2.0, 0.0,
			0.0, 2.0
		};
		glGenBuffers(1, &vbo_xy);
		if( !vbo_xy ){ return glGetError(); }
		glBindBuffer(GL_ARRAY_BUFFER, vbo_xy);
		glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);
		glBindBuffer(GL_ARRAY_BUFFER, 0);
	}

	static GLuint tex;
	if( !tex ){
		glGenTextures(1, &tex);
		if( !tex ){ return glGetError(); }
		glBindTexture(GL_TEXTURE_2D, tex);
		if( !(_binary_pixels_raw_width % 4) ){
			glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
		} else
		if( !(_binary_pixels_raw_width % 2) ){
			glPixelStorei(GL_UNPACK_ALIGNMENT, 2);
		} else {
			glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
		}
		/* when loading the pixels into the texture, each two consecutive
		 * primitive pixels are coalesced into a single 2-channel texel.
		 * Furthermore, since primitives order are distinct between
		 * even and odd rows, a texture half the primitive height is created
		 * but at the primitive picture width. Hence we will end up a
		 * texture that contains two pictures side by side, even rows
		 * on the left and odd rows on the right. Since the subpictures
		 * have uniform primitives arrangement each, we can use built-in
		 * mipmap generation to downsample the picture for mipmapping
		 * without impeding the de-Bayering process. */
		glTexImage2D(
			/* target = */ GL_TEXTURE_2D,
			/* level  = */ 0, 
			/* The 2 component image format of OpenGL-ES 2
			 * is GL_LUMINANCE_ALPHA; on later versions you'd
			 * use GL_RG; internalformat = */ GL_LUMINANCE_ALPHA,
			/* width  = */ _binary_pixels_raw_width,
			/* height = */ _binary_pixels_raw_height/2,
			/* border = */ 0,
			/* format = */ GL_LUMINANCE_ALPHA,
			/* type   = */ GL_UNSIGNED_BYTE,
			/* data   = */ _binary_pixels_raw );
		glGenerateMipmap(GL_TEXTURE_2D);
		glBindTexture(GL_TEXTURE_2D, 0);
	}

	glUseProgram(prog);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, tex);
	glUniform1i(u_sampler, 0);
	glUniformMatrix4fv(u_coef_r, 1, GL_FALSE, coef_r);
	glUniformMatrix4fv(u_coef_g, 1, GL_FALSE, coef_g);
	glUniformMatrix4fv(u_coef_b, 1, GL_FALSE, coef_b);
	glBindBuffer(GL_ARRAY_BUFFER, vbo_xy);
	glEnableVertexAttribArray(a_position);
	glVertexAttribPointer(a_position, 2, GL_FLOAT, GL_FALSE, 0, NULL);
	glDrawArrays(GL_TRIANGLES, 0, 3);
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glBindTexture(GL_TEXTURE_2D, 0);
	glUseProgram(0);

	return glGetError();
}

int main()
{
	int screenwidth  = _binary_pixels_raw_width;
	int screenheight = _binary_pixels_raw_height;

	EGLint numConfigs, majorVersion, minorVersion;
	SDL_Window *window = SDL_CreateWindow(
		"GLESv2 / fragment shader de-Bayer", 0, 0,
		screenwidth, screenheight, SDL_WINDOW_OPENGL);

	EGLConfig config = {0};
	EGLint const egl_config_attr[] = {
		EGL_BUFFER_SIZE, 24,
		EGL_DEPTH_SIZE,  24,
		EGL_STENCIL_SIZE, 8,
		EGL_SURFACE_TYPE, EGL_WINDOW_BIT,
		EGL_NONE
	};
	EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
	eglInitialize(display, &majorVersion, &minorVersion);
	eglChooseConfig(display, egl_config_attr, &config, 1, &numConfigs);

	SDL_SysWMinfo sysInfo;
	SDL_VERSION(&sysInfo.version);
	SDL_GetWindowWMInfo(window, &sysInfo);

	EGLint const egl_context_attr[] = {
		EGL_CONTEXT_MAJOR_VERSION, 2,
		EGL_NONE
	};
	EGLContext context = eglCreateContext(display, config, EGL_NO_CONTEXT, egl_context_attr);
	EGLSurface surface = eglCreateWindowSurface(display, config, (EGLNativeWindowType)sysInfo.info.x11.window, 0); // X11?
	eglMakeCurrent(display, surface, surface, context);
	eglSwapInterval(display, 1);

	for( SDL_Event event = {0}
	   ; SDL_QUIT != event.type
	   ; SDL_PollEvent(&event)
	){
		glViewport(0, 0, screenwidth, screenheight);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		draw_debayer_RGB(0);
		eglSwapBuffers(display, surface);
	}

	eglDestroySurface(display, surface);
	eglDestroyContext(display, context);
	eglTerminate(display);
	SDL_DestroyWindow(window);
	return 0;
}