/*	Copyright (C) 2011 by Eddy Luten

	Permission is hereby granted, free of charge, to any person obtaining a copy
	of this software and associated documentation files (the "Software"), to deal
	in the Software without restriction, including without limitation the rights
	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	copies of the Software, and to permit persons to whom the Software is
	furnished to do so, subject to the following conditions:

	The above copyright notice and this permission notice shall be included in
	all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	THE SOFTWARE.
*/

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <GL/glew.h>
#include <GL/freeglut.h>
#define WINDOW_TITLE_PREFIX "Chapter 3"

typedef struct
{
	float XYZW[4];
	float RGBA[4];
} Vertex;

int CurrentWidth = 600,
	CurrentHeight = 600,
	WindowHandle = 0;

unsigned FrameCount = 0;

GLuint
	VertexShaderId,
	FragmentShaderId,
	ProgramId,
	VaoId,
	BufferId,
	IndexBufferId;

const GLchar* VertexShader =
{
	"#version 400\n"\

	"layout(location=0) in vec4 in_Position;\n"\
	"layout(location=1) in vec4 in_Color;\n"\
	"out vec4 ex_Color;\n"\

	"void main(void)\n"\
	"{\n"\
	"	gl_Position = in_Position;\n"\
	"	ex_Color = in_Color;\n"\
	"}\n"
};

const GLchar* FragmentShader =
{
	"#version 400\n"\

	"in vec4 ex_Color;\n"\
	"out vec4 out_Color;\n"\

	"void main(void)\n"\
	"{\n"\
	"	out_Color = ex_Color;\n"\
	"}\n"
};

void Initialize(int, char*[]);
void InitWindow(int, char*[]);
void ResizeFunction(int, int);
void RenderFunction(void);
void TimerFunction(int);
void IdleFunction(void);
void Cleanup(void);
void CreateVBO(void);
void DestroyVBO(void);
void CreateShaders(void);
void DestroyShaders(void);

int main(int argc, char* argv[])
{
	Initialize(argc, argv);

	glutMainLoop();
	
	exit(EXIT_SUCCESS);
}

void Initialize(int argc, char* argv[])
{
	GLenum GlewInitResult;

	InitWindow(argc, argv);

	glewExperimental = GL_TRUE;
	GlewInitResult = glewInit();

	if (GLEW_OK != GlewInitResult) {
		fprintf(
			stderr,
			"ERROR: %s\n",
			glewGetErrorString(GlewInitResult)
		);
		exit(EXIT_FAILURE);
	}
	
	fprintf(
		stdout,
		"INFO: OpenGL Version: %s\n",
		glGetString(GL_VERSION)
	);

	CreateShaders();
	CreateVBO();

	glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
}

void InitWindow(int argc, char* argv[])
{
	glutInit(&argc, argv);
	
	glutInitContextVersion(4, 0);
	glutInitContextFlags(GLUT_FORWARD_COMPATIBLE);
	glutInitContextProfile(GLUT_CORE_PROFILE);

	glutSetOption(
		GLUT_ACTION_ON_WINDOW_CLOSE,
		GLUT_ACTION_GLUTMAINLOOP_RETURNS
	);
	
	glutInitWindowSize(CurrentWidth, CurrentHeight);

	glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);

	WindowHandle = glutCreateWindow(WINDOW_TITLE_PREFIX);

	if(WindowHandle < 1) {
		fprintf(
			stderr,
			"ERROR: Could not create a new rendering window.\n"
		);
		exit(EXIT_FAILURE);
	}
	
	glutReshapeFunc(ResizeFunction);
	glutDisplayFunc(RenderFunction);
	glutIdleFunc(IdleFunction);
	glutTimerFunc(0, TimerFunction, 0);
	glutCloseFunc(Cleanup);
}

void ResizeFunction(int Width, int Height)
{
	CurrentWidth = Width;
	CurrentHeight = Height;
	glViewport(0, 0, CurrentWidth, CurrentHeight);
}

void RenderFunction(void)
{
	++FrameCount;

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	
	glDrawElements(GL_TRIANGLES, 48, GL_UNSIGNED_BYTE, NULL);

	glutSwapBuffers();
	glutPostRedisplay();
}

void IdleFunction(void)
{
	glutPostRedisplay();
}

void TimerFunction(int Value)
{
	if (0 != Value) {
		char* TempString = (char*)
			malloc(512 + strlen(WINDOW_TITLE_PREFIX));

		sprintf(
			TempString,
			"%s: %d Frames Per Second @ %d x %d",
			WINDOW_TITLE_PREFIX,
			FrameCount * 4,
			CurrentWidth,
			CurrentHeight
		);

		glutSetWindowTitle(TempString);
		free(TempString);
	}
	
	FrameCount = 0;
	glutTimerFunc(250, TimerFunction, 1);
}

void Cleanup(void)
{
	DestroyShaders();
	DestroyVBO();
}

void CreateVBO(void)
{
	Vertex Vertices[] =
	{
		{ { 0.0f, 0.0f, 0.0f, 1.0f }, { 1.0f, 1.0f, 1.0f, 1.0f } }, // 0

		// Top
		{ { -0.2f, 0.8f, 0.0f, 1.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } }, // 1
		{ { 0.2f, 0.8f, 0.0f, 1.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }, // 2
		{ { 0.0f, 0.8f, 0.0f, 1.0f }, { 0.0f, 1.0f, 1.0f, 1.0f } }, //3
		{ { 0.0f, 1.0f, 0.0f, 1.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },	// 4

		// Bottom
		{ { -0.2f, -0.8f, 0.0f, 1.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }, // 5
		{ { 0.2f, -0.8f, 0.0f, 1.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } }, // 6
		{ { 0.0f, -0.8f, 0.0f, 1.0f }, { 0.0f, 1.0f, 1.0f, 1.0f } }, //7
		{ { 0.0f, -1.0f, 0.0f, 1.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },	// 8

		// Left
		{ { -0.8f, -0.2f, 0.0f, 1.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } }, // 9
		{ { -0.8f, 0.2f, 0.0f, 1.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }, // 10
		{ { -0.8f, 0.0f, 0.0f, 1.0f }, { 0.0f, 1.0f, 1.0f, 1.0f } }, //11
		{ { -1.0f, 0.0f, 0.0f, 1.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } },	// 12

		// Right
		{ { 0.8f, -0.2f, 0.0f, 1.0f }, { 0.0f, 0.0f, 1.0f, 1.0f } }, // 13
		{ { 0.8f, 0.2f, 0.0f, 1.0f }, { 0.0f, 1.0f, 0.0f, 1.0f } }, // 14
		{ { 0.8f, 0.0f, 0.0f, 1.0f }, { 0.0f, 1.0f, 1.0f, 1.0f } }, //15
		{ { 1.0f, 0.0f, 0.0f, 1.0f }, { 1.0f, 0.0f, 0.0f, 1.0f } }	// 16
	};

	GLubyte Indices[] = {
		// Top
		0, 1, 3,
		0, 3, 2,
		3, 1, 4,
		3, 4, 2,

		// Bottom
		0, 5, 7,
		0, 7, 6,
		7, 5, 8,
		7, 8, 6,

		// Left
		0, 9, 11,
		0, 11, 10,
		11, 9, 12,
		11, 12, 10,

		// Right
		0, 13, 15,
		0, 15, 14,
		15, 13, 16,
		15, 16, 14
	};

	GLenum ErrorCheckValue = glGetError();
	const size_t BufferSize = sizeof(Vertices);
	const size_t VertexSize = sizeof(Vertices[0]);
	const size_t RgbOffset = sizeof(Vertices[0].XYZW);
	
	glGenVertexArrays(1, &VaoId);
	glBindVertexArray(VaoId);
	
	glGenBuffers(1, &BufferId);
	glBindBuffer(GL_ARRAY_BUFFER, BufferId);
	glBufferData(GL_ARRAY_BUFFER, BufferSize, Vertices, GL_STATIC_DRAW);

	glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, VertexSize, 0);
	glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, VertexSize, (GLvoid*)RgbOffset);

	glEnableVertexAttribArray(0);
	glEnableVertexAttribArray(1);

	glGenBuffers(1, &IndexBufferId);
	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IndexBufferId);
	glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not create a VBO: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void DestroyVBO(void)
{
	GLenum ErrorCheckValue = glGetError();

	glDisableVertexAttribArray(1);
	glDisableVertexAttribArray(0);
	
	glBindBuffer(GL_ARRAY_BUFFER, 0);
	glDeleteBuffers(1, &BufferId);

	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
	glDeleteBuffers(1, &IndexBufferId);

	glBindVertexArray(0);
	glDeleteVertexArrays(1, &VaoId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not destroy the VBO: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void CreateShaders(void)
{
	GLenum ErrorCheckValue = glGetError();
	
	VertexShaderId = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(VertexShaderId, 1, &VertexShader, NULL);
	glCompileShader(VertexShaderId);

	FragmentShaderId = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(FragmentShaderId, 1, &FragmentShader, NULL);
	glCompileShader(FragmentShaderId);

	ProgramId = glCreateProgram();
		glAttachShader(ProgramId, VertexShaderId);
		glAttachShader(ProgramId, FragmentShaderId);
	glLinkProgram(ProgramId);
	glUseProgram(ProgramId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not create the shaders: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}

void DestroyShaders(void)
{
	GLenum ErrorCheckValue = glGetError();

	glUseProgram(0);

	glDetachShader(ProgramId, VertexShaderId);
	glDetachShader(ProgramId, FragmentShaderId);

	glDeleteShader(FragmentShaderId);
	glDeleteShader(VertexShaderId);

	glDeleteProgram(ProgramId);

	ErrorCheckValue = glGetError();
	if (ErrorCheckValue != GL_NO_ERROR)
	{
		fprintf(
			stderr,
			"ERROR: Could not destroy the shaders: %s \n",
			gluErrorString(ErrorCheckValue)
		);

		exit(-1);
	}
}