// gcc -o test.exe -mwindows -mconsole test.c glad.c -lopengl32 -lglfw3

#include <stdio.h>
#include <glad\glad.h>
#include <GLFW\glfw3.h>

float step = 0.1f;
float scale = 1.04f;

#define PAN_X_DEFAULT -0.1f
#define PAN_Y_DEFAULT -0.35f
#define ZOOM_K_DEFAULT 180.0f

GLFWmonitor* test_monitor = NULL;
GLFWwindow*  test_window  = NULL;

int test_width = 1024;
int test_height = 780;

BOOL test_fullscreen = FALSE;

GLfloat pan_x = PAN_X_DEFAULT;
GLfloat pan_y = PAN_Y_DEFAULT;
GLfloat zoom_k = ZOOM_K_DEFAULT;

int test_verbose = 2;

GLvoid reset(GLvoid)
{
    pan_x = PAN_X_DEFAULT;
    pan_y = PAN_Y_DEFAULT;
    zoom_k = ZOOM_K_DEFAULT;
}

GLvoid zoom(double factor)
{
    zoom_k *= factor;

    if (zoom_k < 0.01f) zoom_k = 0.01f;
    if (zoom_k > 1000000.0f) zoom_k = 1000000.0f;
}

GLvoid pan(double dx, double dy)
{
    pan_x += dx / zoom_k;
    pan_y += dy / zoom_k;
}

GLvoid zoom_at(double x, double y, double factor)
{
    pan(-x, -y);
    zoom(factor);
    pan(x, y);
}

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

void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    if (action != GLFW_PRESS)
        return;

    switch (key)
    {
        case GLFW_KEY_ESCAPE:
            glfwSetWindowShouldClose(window, GLFW_TRUE);
            break;

        case GLFW_KEY_HOME:
            if (test_verbose >= 2) printf("reset to original view\n");
            reset();
            break;

        case GLFW_KEY_UP:
            if (test_verbose >= 2) printf("move up\n");
            pan(0, -step);
            break;

        case GLFW_KEY_DOWN:
            if (test_verbose >= 2) printf("move down\n");
            pan(0,  step);
            break;

        case GLFW_KEY_RIGHT:
            if (test_verbose >= 2) printf("move right\n");
            pan(-step, 0);
            break;

        case GLFW_KEY_LEFT:
            if (test_verbose >= 2) printf("move left\n");
            pan( step, 0);
            break;

        case GLFW_KEY_PAGE_UP:
            if (test_verbose >= 2) printf("zoom in\n");
            zoom_at(test_width/2, test_height/2, scale);
            break;

        case GLFW_KEY_PAGE_DOWN:
            if (test_verbose >= 2) printf("zoom out\n");
            zoom_at(test_width/2, test_height/2, 1.0/scale);
            break;
    }
}

GLvoid draw_map(GLvoid)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glScalef(zoom_k, zoom_k, 1);
    glTranslatef(pan_x, pan_y, 0);

    glLineWidth(2.0f);
    glColor3f(1.0, 1.0, 1.0);   // white
    glBegin(GL_LINE_STRIP);
        glVertex2f(0.1, 0.1);
        glVertex2f(0.2, 0.1);
        glVertex2f(0.1, 0.2);
        glVertex2f(0.2, 0.2);
        glVertex2f(100.3, 10.1);
        glVertex2f(100.4, 10.1);
        glVertex2f(100.3, 10.2);
        glVertex2f(100.4, 10.2);
        glVertex2f(1100.3, 110.1);
        glVertex2f(1100.4, 110.1);
        glVertex2f(1100.3, 110.2);
        glVertex2f(1100.4, 110.2);
    glEnd();
}

GLvoid DrawGLScene(GLvoid)
{
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    draw_map();
}

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

    glfwSetErrorCallback(error_callback);

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

    glfwWindowHint(GLFW_DECORATED, GLFW_TRUE);

    test_monitor = glfwGetPrimaryMonitor();

    test_window = glfwCreateWindow(test_width, test_height, "Test Program", NULL, NULL);
    if (!test_window)
    {
        fprintf( stderr, "Failed to create GLFW window\n" );
        glfwTerminate();
        exit( EXIT_FAILURE );
    }

    glfwSetWindowSizeLimits(test_window, 640, 480, GLFW_DONT_CARE, GLFW_DONT_CARE);

    glfwSetKeyCallback(test_window, key_callback);
    glfwMakeContextCurrent(test_window);
    gladLoadGLLoader((GLADloadproc) glfwGetProcAddress);
    glfwSwapInterval(1);

    glfwGetFramebufferSize(test_window, &test_width, &test_height);
    glViewport(0, 0, test_width, test_height);

    while ( !glfwWindowShouldClose(test_window))
    {

        DrawGLScene();

        glfwSwapBuffers(test_window);
        glfwPollEvents();
    }

    glfwTerminate();
    exit(EXIT_SUCCESS);
}