/**
 * 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 TIMER_US    1000000     // 1-second delay for repeating timer
#define DEBOUNCE_US 100         // 100us debounce time

struct repeating_timer timer;   // Repeating timer
u_int64_t time = 0;             // Elapsed time

typedef enum btn_state {        // Button state
    PRESSED = 0,
    RELEASED = 1
} btn_state_t;

struct btn_status {             // Button status
    uint btn_pressed;
    uint btn_released;
} btn_status = {0, 0};

/**
 * 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;
}

/**
 * Get the state of the pseudo-button (pull-up)
 * This function will implement a debounce algorithm to
 * get the state of the pseudo-button. (With added complexity)
 * @return The state of the pseudo-button
 */
btn_state_t get_btn_state () {
    u_int64_t start_time = time_us_64();
    while (time_us_64() - start_time < DEBOUNCE_US)
    {
        if (gpio_get(PSEUDO_BTN))
        {
            btn_status.btn_released += 1;
        }
        else
        {
            btn_status.btn_pressed += 1;
        }
    }

    btn_state_t state = (btn_status.btn_pressed > btn_status.btn_released) ?
                           PRESSED : RELEASED;

    btn_status.btn_pressed = 0;
    btn_status.btn_released = 0;

    return state;
}

/**
 * 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) {
    btn_state_t btn_state = get_btn_state();

    if (events == GPIO_IRQ_EDGE_FALL && btn_state == PRESSED)
    {
        printf("\n====================================\n");
        printf("Timer Started\n");
        printf("====================================\n");

        add_repeating_timer_us(
                TIMER_US,
                elapsed_time_callback,
                NULL,
                &timer
        );

    }

    if (events == GPIO_IRQ_EDGE_RISE && btn_state == RELEASED)
    {
        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();
    }

}