#include <glad/glad.h>
#include <GLFW/glfw3.h>

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>
#include <vector>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void key_callback(GLFWwindow* window, int key, int scancode, int action, int modifiers);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;
int useWireframe = 0;
int displayGrayscale = 0;

// camera - give pretty starting point
Camera camera(glm::vec3(67.0f, 627.5f, 169.9f),
              glm::vec3(0.0f, 1.0f, 0.0f),
              -128.1f, -42.4f);
float lastX = SCR_WIDTH / 2.0f;
float lastY = SCR_HEIGHT / 2.0f;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main()
{
    // glfw: initialize and configure
    // ------------------------------
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

    // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL: Terrain CPU", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
    glfwSetKeyCallback(window, key_callback);
    glfwSetCursorPosCallback(window, mouse_callback);
    glfwSetScrollCallback(window, scroll_callback);

    // tell GLFW to capture our mouse
    glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // configure global opengl state
    // -----------------------------
    glEnable(GL_DEPTH_TEST);

    // build and compile our shader program
    // ------------------------------------
    Shader heightMapShader("8.3.cpuheight.vs","8.3.cpuheight.fs");

    // load and create a texture
    // -------------------------
    // load image, create texture and generate mipmaps
    // The FileSystem::getPath(...) is part of the GitHub repository so we can find files on any IDE/platform; replace it with your own image path.
    stbi_set_flip_vertically_on_load(true);
    int width, height, nrChannels;
    unsigned char *data = stbi_load("heightmaps/iceland_heightmap.png", &width, &height, &nrChannels, 0);
    if (data)
    {
        std::cout << "Loaded heightmap of size " << height << " x " << width << std::endl;
    }
    else
    {
        std::cout << "Failed to load texture" << std::endl;
    }


    // set up vertex data (and buffer(s)) and configure vertex attributes
    // ------------------------------------------------------------------
    std::vector<float> vertices;
    float yScale = 64.0f / 256.0f, yShift = 16.0f;
    int rez = 1;
    unsigned bytePerPixel = nrChannels;
    for(int i = 0; i < height; i++)
    {
        for(int j = 0; j < width; j++)
        {
            unsigned char* pixelOffset = data + (j + width * i) * bytePerPixel;
            unsigned char y = pixelOffset[0];

            // vertex
            vertices.push_back( -height/2.0f + height*i/(float)height );   // vx
            vertices.push_back( (int) y * yScale - yShift);   // vy
            vertices.push_back( -width/2.0f + width*j/(float)width );   // vz
        }
    }
    std::cout << "Loaded " << vertices.size() / 3 << " vertices" << std::endl;
    stbi_image_free(data);

    std::vector<unsigned> indices;
    for(unsigned i = 0; i < height-1; i += rez)
    {
        for(unsigned j = 0; j < width; j += rez)
        {
            for(unsigned k = 0; k < 2; k++)
            {
                indices.push_back(j + width * (i + k*rez));
            }
        }
    }
    std::cout << "Loaded " << indices.size() << " indices" << std::endl;

    const int numStrips = (height-1)/rez;
    const int numTrisPerStrip = (width/rez)*2-2;
    std::cout << "Created lattice of " << numStrips << " strips with " << numTrisPerStrip << " triangles each" << std::endl;
    std::cout << "Created " << numStrips * numTrisPerStrip << " triangles total" << std::endl;

    // first, configure the cube's VAO (and terrainVBO + terrainIBO)
    unsigned int terrainVAO, terrainVBO, terrainIBO;
    glGenVertexArrays(1, &terrainVAO);
    glBindVertexArray(terrainVAO);

    glGenBuffers(1, &terrainVBO);
    glBindBuffer(GL_ARRAY_BUFFER, terrainVBO);
    glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(float), &vertices[0], GL_STATIC_DRAW);

    // position attribute
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);

    glGenBuffers(1, &terrainIBO);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, terrainIBO);
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned), &indices[0], GL_STATIC_DRAW);

    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // per-frame time logic
        // --------------------
        float currentFrame = glfwGetTime();
        deltaTime = currentFrame - lastFrame;
        lastFrame = currentFrame;

//        std::cout << deltaTime << "ms (" << 1.0f / deltaTime << " FPS)" << std::endl;

        // input
        // -----
        processInput(window);

        // render
        // ------
        glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        // be sure to activate shader when setting uniforms/drawing objects
        heightMapShader.use();

        // view/projection transformations
        glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100000.0f);
        glm::mat4 view = camera.GetViewMatrix();
        heightMapShader.setMat4("projection", projection);
        heightMapShader.setMat4("view", view);

        // world transformation
        glm::mat4 model = glm::mat4(1.0f);
        heightMapShader.setMat4("model", model);
        
        // render the cube
        glBindVertexArray(terrainVAO);
//        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
        for(unsigned strip = 0; strip < numStrips; strip++)
        {
            glDrawElements(GL_TRIANGLE_STRIP,   // primitive type
                           numTrisPerStrip+2,   // number of indices to render
                           GL_UNSIGNED_INT,     // index data type
                           (void*)(sizeof(unsigned) * (numTrisPerStrip+2) * strip)); // offset to starting index
        }

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    // optional: de-allocate all resources once they've outlived their purpose:
    // ------------------------------------------------------------------------
    glDeleteVertexArrays(1, &terrainVAO);
    glDeleteBuffers(1, &terrainVBO);
    glDeleteBuffers(1, &terrainIBO);

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);

    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        camera.ProcessKeyboard(FORWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        camera.ProcessKeyboard(BACKWARD, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        camera.ProcessKeyboard(LEFT, deltaTime);
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        camera.ProcessKeyboard(RIGHT, deltaTime);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}

// glfw: whenever a key event occurs, this callback is called
// ---------------------------------------------------------------------------------------------
void key_callback(GLFWwindow* window, int key, int scancode, int action, int modifiers)
{
    if(action == GLFW_PRESS)
    {
        switch(key)
        {
            case GLFW_KEY_SPACE:
                useWireframe = 1 - useWireframe;
                break;
            case GLFW_KEY_G:
                displayGrayscale = 1 - displayGrayscale;
                break;
            default:
                break;
        }
    }
}


// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
    if (firstMouse)
    {
        lastX = xpos;
        lastY = ypos;
        firstMouse = false;
    }

    float xoffset = xpos - lastX;
    float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

    lastX = xpos;
    lastY = ypos;

    camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
    camera.ProcessMouseScroll(yoffset);
}