/**
 * Lab 3
 * 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          // GPIO 15 is the pseudo-button
#define DELAY_US    1000000     // 1-second delay for repeating timer
#define DEBOUNCE_MS 200         // Debounce delay

unsigned long long time = 0;    // Elapsed time
struct repeating_timer timer;   // Repeating timer

/**
 * Callback function for repeating timer
 * This function will print the elapsed time every second as required by the
 * lab specification.
 * @param t    The timer that triggered the callback
 * @return     True to keep the timer running, false to stop it
 */
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;
}

/**
 * Interrupt callback function for pseudo-button (pull-up)
 * This function will start the timer on button press (falling edge)
 * and stop the timer on button release. (rising edge)
 * @param gpio      The GPIO pin that triggered the interrupt
 * @param events    The type of interrupt that triggered the callback
 */
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;
        }
    }
}

/**
 * Initialize the pseudo-button (pull-up)
 * The pseudo-button is connected to GPIO 15 and is configured as an input
 * with a pull-up resistor.
 * The interrupt is configured to trigger on both rising and falling edges.
 */
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();
        // Debounce
        sleep_ms(DEBOUNCE_MS);
    }

}