/**
 * To develop a simple stopwatch that measures time intervals between
 * button presses.
 *
 * On pressing the START pseudo-button (GP15),
 * the stopwatch will begin,
 * and the elapsed time will be displayed every second on
 * the Serial Monitor (or equivalent).
 *
 * Releasing the START pseudo-button will stop the timer and
 * reset the elapsed time to zero.
 *
 * The START pseudo-button must incorporate a debouncing algorithm.
 *
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"

#define PSEUDO_BTN 15
#define DELAY_US 1000000

unsigned long long time = 0;
struct repeating_timer timer;

bool repeating_timer_callback(struct repeating_timer *t) {
    // Print elapsed time every second
    printf("Elapsed Time: %llus\n",
           (time_us_64() - time) / 1000000);
    return true;
}


void gpio_callback(uint gpio, uint32_t events) {
    // Start timer on button press
    if (gpio == PSEUDO_BTN && events == GPIO_IRQ_EDGE_FALL)
    {
        time = time_us_64();
        printf("Timer Started at %llu\n", time);

        add_repeating_timer_us(
                DELAY_US,
                repeating_timer_callback,
                NULL,
                &timer
                );
    }
    // Stop timer on button release
    else if (gpio == PSEUDO_BTN && events == GPIO_IRQ_EDGE_RISE)
    {
        printf("Timer Stopped at %llu\n", time_us_64());
        cancel_repeating_timer(&timer);

        // Print elapsed time and reset
        printf("Final Elapsed Time: %llus\n",
               (time_us_64() - time) / 1000000);

        time = 0;
    }
}

static void btn_init()
{
    gpio_init(PSEUDO_BTN);
    gpio_set_dir(PSEUDO_BTN, GPIO_IN);
    gpio_set_pulls(PSEUDO_BTN, true, false);

    gpio_set_irq_enabled_with_callback(
            PSEUDO_BTN,
            GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL,
            true,
            &gpio_callback
    );
}

int main()
{
    stdio_init_all();
    btn_init();

    while (true) {
        tight_loop_contents();
    }

}