//g++ rgb_pbo2.cpp opengl/glad.c -o rgb_pbo2 -lglfw -ldl -lGL -I./include
#include <glad/glad.h>
#include <GLFW/glfw3.h>
#include <iostream>
#include <vector>
#include <cstring> // For memcpy
#include <string>

// Define window width and height for easy resolution control
const int WINDOW_WIDTH = 1920;
const int WINDOW_HEIGHT = 1080;

// Define the number of pre-created patches
const int NUM_PATCHES = 10000;

// Pre-created patches
struct RGBPatch {
    int x_offset;  // X position of the patch in the texture
    int y_offset;  // Y position of the patch in the texture
    int width;     // Width of the patch
    int height;    // Height of the patch
};

// Patches container
std::vector<RGBPatch> patches;

// Vertex Shader Source Code
const char* vertexShaderSource = R"(
#version 330 core
layout(location = 0) in vec2 aPos;
layout(location = 1) in vec2 aTex;

out vec2 TexCoord;

void main() {
    gl_Position = vec4(aPos, 0.0, 1.0);
    TexCoord = aTex;
}
)";

// Fragment Shader Source Code
const char* fragmentShaderSource = R"(
#version 330 core
in vec2 TexCoord;
out vec4 FragColor;

uniform sampler2D tex;

void main() {
    FragColor = texture(tex, TexCoord);
}
)";

// Utility function to compile a shader
GLuint compileShader(GLenum type, const char* source) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &source, nullptr);
    glCompileShader(shader);

    int success;
    char infoLog[512];
    glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
    if (!success) {
        glGetShaderInfoLog(shader, 512, nullptr, infoLog);
        std::cerr << "ERROR: Shader Compilation Failed\n" << infoLog << std::endl;
    }

    return shader;
}

// Utility function to create a shader program
GLuint createShaderProgram(const char* vertexSource, const char* fragmentSource) {
    GLuint vertexShader = compileShader(GL_VERTEX_SHADER, vertexSource);
    GLuint fragmentShader = compileShader(GL_FRAGMENT_SHADER, fragmentSource);

    GLuint program = glCreateProgram();
    glAttachShader(program, vertexShader);
    glAttachShader(program, fragmentShader);
    glLinkProgram(program);

    int success;
    char infoLog[512];
    glGetProgramiv(program, GL_LINK_STATUS, &success);
    if (!success) {
        glGetProgramInfoLog(program, 512, nullptr, infoLog);
        std::cerr << "ERROR: Shader Program Linking Failed\n" << infoLog << std::endl;
    }

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);

    return program;
}

// Pre-create 10,000 patches with random sizes and positions
void preCreatePatches(int textureWidth, int textureHeight) {
    for (int i = 0; i < NUM_PATCHES; ++i) {
        RGBPatch patch;
        patch.width = 1 + (i % 100);  // Width cycles between 1 and 100
        patch.height = 1 + ((i / 2) % 100);  // Height cycles between 1 and 100
        patch.x_offset = i % (textureWidth - patch.width);  // Offset cycles within bounds
        patch.y_offset = i % (textureHeight - patch.height);  // Offset cycles within bounds
        patches.push_back(patch);
    }
}

int main() {
    // Initialize GLFW
    if (!glfwInit()) {
        std::cerr << "Failed to initialize GLFW" << std::endl;
        return -1;
    }

    // Set OpenGL version to 3.3 Core
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    // Create a window
    GLFWwindow* window = glfwCreateWindow(WINDOW_WIDTH, WINDOW_HEIGHT, "OpenGL PBO RGB Patches", nullptr, nullptr);
    if (!window) {
        std::cerr << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);

    // Load OpenGL function pointers using GLAD
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        std::cerr << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    // Set up the viewport
    glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);

    // Compile and link the shader program
    GLuint shaderProgram = createShaderProgram(vertexShaderSource, fragmentShaderSource);

    // Define a fullscreen quad
    float quadVertices[] = {
        // Positions   // Texture Coords
        -1.0f, -1.0f,  0.0f, 0.0f,
         1.0f, -1.0f,  1.0f, 0.0f,
        -1.0f,  1.0f,  0.0f, 1.0f,
         1.0f,  1.0f,  1.0f, 1.0f
    };

    // Create VAO and VBO for the quad
    GLuint VAO, VBO;
    glGenVertexArrays(1, &VAO);
    glGenBuffers(1, &VBO);

    glBindVertexArray(VAO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), quadVertices, GL_STATIC_DRAW);

    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)0);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(2 * sizeof(float)));
    glEnableVertexAttribArray(1);

    // Create a texture
    GLuint texture;
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);

    // Set texture parameters
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

    // Allocate storage for the texture
    int textureWidth = WINDOW_WIDTH;
    int textureHeight = WINDOW_HEIGHT;
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, textureWidth, textureHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, nullptr);

    // Create PBO
    GLuint pbo;
    glGenBuffers(1, &pbo);
    glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
    glBufferData(GL_PIXEL_UNPACK_BUFFER, textureWidth * textureHeight * 3, nullptr, GL_STREAM_DRAW);

    // Unbind the PBO
    glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);

    // Pre-create patches
    preCreatePatches(textureWidth, textureHeight);

    // Desired frame time for 60 FPS
    const double frameTime = 1.0 / 60.0;

    // FPS calculation variables
    double lastTime = glfwGetTime();
    int frameCount = 0;

    // Initialize color counter
    unsigned char colorValue = 0;

    // Main render loop
    while (!glfwWindowShouldClose(window)) {
        // Start frame time
        double frameStartTime = glfwGetTime();

        // Update the single color for this frame
        // colorValue = (colorValue + 3) % 256;
        colorValue = 120;

        // Bind the PBO for updating
        glBindBuffer(GL_PIXEL_UNPACK_BUFFER, pbo);
        unsigned char* pboMemory = (unsigned char*)glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_WRITE_ONLY);

        for (const auto& patch : patches) {
            memset(pboMemory + (patch.y_offset * textureWidth + patch.x_offset) * 3, colorValue, patch.width * patch.height * 3);
        }
        glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);

        // Bind the texture and update it using the PBO
        glBindTexture(GL_TEXTURE_2D, texture);

            // Perform GPU-GPU copies using glTexSubImage2D
        int currentOffset = 0;
        for (const auto& patch : patches) {
            currentOffset = (patch.y_offset * textureWidth + patch.x_offset) * 3;
            glTexSubImage2D(GL_TEXTURE_2D, 0, patch.x_offset, patch.y_offset, patch.width, patch.height, GL_RGB, GL_UNSIGNED_BYTE, (void*)currentOffset);
        }

        // glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, textureWidth, textureHeight, GL_RGB, GL_UNSIGNED_BYTE, nullptr);

        // Clear the screen
        glClear(GL_COLOR_BUFFER_BIT);

        // Bind the shader program and texture
        glUseProgram(shaderProgram);
        glBindTexture(GL_TEXTURE_2D, texture);

        // Render the quad
        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

        // Unbind the PBO
        glBindBuffer(GL_PIXEL_UNPACK_BUFFER, 0);

        // Swap buffers and poll events
        glfwSwapBuffers(window);
        glfwPollEvents();

        // Increment frame count
        frameCount++;

        // Calculate FPS every second and update the window title
        double currentTime = glfwGetTime();
        if (currentTime - lastTime >= 1.0) {
            std::string title = "OpenGL PBO RGB Patches - FPS: " + std::to_string(frameCount);
            glfwSetWindowTitle(window, title.c_str());
            frameCount = 0;
            lastTime = currentTime;
        }

        // Cap the frame rate to 60 FPS
        // double frameEndTime = glfwGetTime();
        // double elapsedTime = frameEndTime - frameStartTime;
        // if (elapsedTime < frameTime) {
        //     glfwWaitEventsTimeout(frameTime - elapsedTime);
        // }
    }

    // Clean up
    glDeleteBuffers(1, &pbo);
    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);
    glDeleteTextures(1, &texture);
    glDeleteProgram(shaderProgram);

    glfwTerminate();
    return 0;
}