sysfs gpio edge detector

#include "sysfs-gpio.h"  // https://github.com/mvduin/sysfs-gpio
#include <stdio.h>

int main()
{
    struct Gpio gpio = GPIO_INITIALIZER;
    gpio_open_input( &gpio, "/sys/class/gpio/gpio60", GPIO_EDGE_BOTH, GPIO_RDONLY );

    bool const invert = gpio_is_active_low( &gpio );

    bool level = gpio_read( &gpio ) ^ invert;

    printf( "%c ", level ? 'H' : 'L' );  // print initial level

    for(;;) {
        fflush( stdout );

        gpio_wait_event( &gpio, -1 );

        bool prev_level = level;
        level = gpio_read( &gpio ) ^ invert;

        printf( "%c ", prev_level ? 'F' : 'R' );

        // if an edge was detected but level didn't change then we must have had a second edge
        if( level == prev_level )
            printf( "%c ", prev_level ? 'R' : 'F' );
    }
}