#include <opencv2/opencv.hpp>
#include <iostream>
// ============================================================================
struct mouse_state
{
    mouse_state()
        : position(-1, -1)
        , left_button_held(false)
        , left_button_clicked(false)
    {}

    void new_iteration()
    {
        left_button_clicked = false;
    }

    cv::Point2i position; // Last position where the LMB was down
    bool left_button_held; // Is the LMB down right now?
    bool left_button_clicked; // Was the LMB down in the last iteration?
};
// ============================================================================
void mouse_callback(int event, int x, int y, int flag, void* param)
{
    mouse_state* state(static_cast<mouse_state*>(param));

    if (event == cv::EVENT_LBUTTONDOWN) {
        std::cout << "LMB down @ (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = true;
    } else if (event == cv::EVENT_LBUTTONUP) {
        std::cout << "LMB up @(" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
        state->left_button_held = false;
        state->left_button_clicked = true;
    } else if ((flag == cv::EVENT_FLAG_LBUTTON) && (event == cv::EVENT_MOUSEMOVE)) {
        std::cout << "LMB held, mouse moved to (" << x << "," << y << ")\n";
        state->position = cv::Point2i(x, y);
    }
}
// ----------------------------------------------------------------------------
int main(int argc, char** argv)
{
    cv::String const WINDOW_NAME("Original Feed");
    cv::namedWindow(WINDOW_NAME, CV_WINDOW_AUTOSIZE);

    mouse_state ms;
    cv::setMouseCallback(WINDOW_NAME, mouse_callback, &ms);

    int const FRAME_WIDTH(720);
    int const FRAME_HEIGHT(540);

    cv::VideoCapture cap(0);
    if (!cap.isOpened()) {
        std::cerr << "Unable to open camera, exiting...\n";
        return -1;
    }

    cap.set(CV_CAP_PROP_FRAME_WIDTH, FRAME_WIDTH);
    cap.set(CV_CAP_PROP_FRAME_HEIGHT, FRAME_HEIGHT);

    for (;;) {
        // We can have `image` here, since `cap.read` always gives us
        // a reference to its internal buffer
        cv::Mat image;
        if (!cap.read(image)) {
            std::cerr << "Failed to read image, exiting...\n";
            break; // Failed to read image, nothing else to do
        }

        if (ms.left_button_clicked || ms.left_button_held) {
            cv::circle(image, ms.position, 3, cv::Scalar(0, 0, 255));
            cv::circle(image, ms.position, 10, cv::Scalar(0, 0, 255), 2);
        }

        ms.new_iteration();

        cv::imshow(WINDOW_NAME, image);
        if (cv::waitKey(30) == 27) {
            std::cout << "Esc pressed, exiting...\n";
            break;
        }
    }
    return 0;
}
// ============================================================================