//========================================================================
// Simple GLFW example
// Copyright (c) Camilla Berglund <elmindreda@elmindreda.org>
// Copyright (c) Emmanuel Gil Peyrot <emmanuel.peyrot@collabora.com>
//
// This software is provided 'as-is', without any express or implied
// warranty. In no event will the authors be held liable for any damages
// arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute it
// freely, subject to the following restrictions:
//
// 1. The origin of this software must not be misrepresented; you must not
//    claim that you wrote the original software. If you use this software
//    in a product, an acknowledgment in the product documentation would
//    be appreciated but is not required.
//
// 2. Altered source versions must be plainly marked as such, and must not
//    be misrepresented as being the original software.
//
// 3. This notice may not be removed or altered from any source
//    distribution.
//
//========================================================================
//! [code]

#include <epoxy/gl.h>
#include <GLFW/glfw3.h>

#include <stdlib.h>
#include <stdio.h>

static const struct
{
    float x, y;
    float r, g, b;
} vertices[3] =
{
    { -0.6f, -0.4f, 1.f, 0.f, 0.f },
    {  0.6f, -0.4f, 0.f, 1.f, 0.f },
    {   0.f,  0.6f, 0.f, 0.f, 1.f }
};

static const char* vertex_shader_text =
"#version 150\n"
"in vec3 vCol;\n"
"in vec2 vPos;\n"
"out vec3 color;\n"
"out float red;\n"
"void main()\n"
"{\n"
"    gl_Position = vec4(vPos, 0.0, 1.0);\n"
"    color = vCol;\n"
//"    red = 1.0;\n"
"}\n";

static const char* fragment_shader_text =
"#version 150\n"
"in vec3 color;\n"
"in float red;\n"
"void main()\n"
"{\n"
"    gl_FragColor = vec4(color, 1.0);\n"
"    gl_FragColor.r = red;\n"
"}\n";

static void error_callback(int error, const char* description)
{
    fprintf(stderr, "Error: %s\n", description);
}

static void debug_callback(GLenum source, GLenum type, GLuint id,
                           GLenum severity, GLsizei length,
                           const GLchar* message, const void* user_param)
{
    fprintf(stderr, "KHR_debug: %s\n", message);
}

static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
        glfwSetWindowShouldClose(window, 1);
}

int main(void)
{
    GLFWwindow* window;
    GLuint vertex_buffer, array_buffer, vertex_shader, fragment_shader, program;
    GLint mvp_location, vpos_location, vcol_location;

    glfwSetErrorCallback(error_callback);

    if (!glfwInit())
        exit(EXIT_FAILURE);

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);

    window = glfwCreateWindow(640, 480, "Simple example", NULL, NULL);
    if (!window)
    {
        glfwTerminate();
        exit(EXIT_FAILURE);
    }

    glfwSetKeyCallback(window, key_callback);

    glfwMakeContextCurrent(window);
    glfwSwapInterval(1);

    glEnable(GL_DEBUG_OUTPUT);
    glDebugMessageCallback(debug_callback, NULL);

    vertex_shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertex_shader, 1, &vertex_shader_text, NULL);
    glCompileShader(vertex_shader);

    fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragment_shader, 1, &fragment_shader_text, NULL);
    glCompileShader(fragment_shader);

    program = glCreateProgram();
    glAttachShader(program, vertex_shader);
    glAttachShader(program, fragment_shader);
    glLinkProgram(program);

    GLint temp;
    glGetProgramiv(program, GL_LINK_STATUS, &temp);
    if (!temp) {
        glGetProgramiv(program, GL_INFO_LOG_LENGTH, &temp);
        GLchar* buf = malloc(temp * sizeof(GLchar));
        glGetProgramInfoLog(program, temp, NULL, buf);
        fprintf(stderr, "Program link error: %s\n", buf);
    }

    mvp_location = glGetUniformLocation(program, "MVP");
    vpos_location = glGetAttribLocation(program, "vPos");
    vcol_location = glGetAttribLocation(program, "vCol");

    glGenVertexArrays(1, &array_buffer);
    glBindVertexArray(array_buffer);

    glGenBuffers(1, &vertex_buffer);
    glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    glEnableVertexAttribArray(vpos_location);
    glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
                          sizeof(float) * 5, (void*) 0);
    glEnableVertexAttribArray(vcol_location);
    glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
                          sizeof(float) * 5, (void*) (sizeof(float) * 2));

    int width, height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);
    glUseProgram(program);

    while (!glfwWindowShouldClose(window))
    {
        glClear(GL_COLOR_BUFFER_BIT);

        glDrawArrays(GL_TRIANGLES, 0, 3);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwDestroyWindow(window);

    glfwTerminate();
    exit(EXIT_SUCCESS);
}