////
// Mixins

/**
 * Pseudo random generator between [0,1]
 */
@function next_random($x) {
    $a: 11;  // a - 1 should be divisible by m's prime factors
    $c: 17;  // c and m should be co-prime
    $m: 25;
    @return ($a * $x + $c) % $m;
}


////
// Vars

// number of unique reveal blocks
$reveal-seqences: 18;

// duration of the reveal animation
$reveal-duration: 1.5s;

// animation delay
$reveal-base-delay: 0.05s;


////
// Styles

.revealing {
    span {
        opacity: 0;
        transition: opacity ease $reveal-duration;
    }

    &.reveal {
        span {
            opacity: 1;
        }
        @for $i from 1 through $reveal-seqences {
            $rand: next_random($i);
            span:nth-child(#{$reveal-seqences}n+#{$rand}) {
                transition-delay: $i * $reveal-base-delay;
            }
        }
    }

    &.reset {
    	span {
    		transition: none;
    	}
    }
}

.unrevealing {
    span {
        opacity: 1;
        transition: opacity ease $reveal-duration;
    }

    &.reveal {
        span {
            opacity: 0;
        }
        @for $i from 1 through $reveal-seqences {
            $rand: next_random($i);
            span:nth-child(#{$reveal-seqences}n+#{$rand}) {
                transition-delay: $i * $reveal-base-delay;
            }
        }
    }

    &.reset {
        span {
            transition: none;
        }
    }
}