/**
 * 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_US 100          // 100us debounce delay

u_int64_t time = 0;             // Elapsed time
u_int prev_state = 0;           // Previous state of pseudo-button
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 elapsed_time_callback (struct repeating_timer *t) {
    time++;
    // Print elapsed time every second
    printf("Elapsed Time: %llus\n", time);
    return true;
}

/**
 * Debounce callback function to check if the current state
 * is equal to the previous state.
 * @param id         The alarm ID
 * @param new_event  The previous state of the pseudo-button
 * @return           True if the current state is equal to the previous state
 */
int64_t debounce_callback(alarm_id_t id, void *new_event) {
    printf("Debounce Callback\n");
    return (prev_state == *(uint32_t *)new_event);
}

/**
 * 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) {
    // Debounce algorithm
    prev_state = prev_state == 0 ? events : prev_state;

    // Create an alarm that will trigger after 10ms
    add_alarm_in_us(
            DEBOUNCE_US,
            debounce_callback,
            &events,
            false
            );

    // Start timer on button press
    if (gpio == PSEUDO_BTN && events == GPIO_IRQ_EDGE_FALL)
    {
        printf("\n====================================\n");
        printf("Timer Started\n");
        printf("====================================\n");

        add_repeating_timer_us(
                DELAY_US,
                elapsed_time_callback,
                NULL,
                &timer
        );
    }
    // Stop timer on button release
    if (gpio == PSEUDO_BTN && events == GPIO_IRQ_EDGE_RISE)
    {
        cancel_repeating_timer(&timer);

        // Print elapsed time and reset
        printf("\n====================================\n");
        printf("Timer Stopped\n");
        printf("====================================\n");
        printf("Final Elapsed Time: %llus\n", time);
        printf("====================================\n");

        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();
    }

}