// set list of values matching breakpoints (index) for a given parameter.
// $values: list of values to set
// $param: parameter to assign values to
// $negate: if value should be negated (* -1)
// $from: start from this breakpoint (inclusive)
// $to: stop after this breakpoint
// $exclude: list of breakpoints to exclude
@mixin responsify($values: (1em), $param: 'font-size', $negate: false, $from: null, $to: null, $exclude: ()) {

	// get the index for the from and to breakpoints
	$fromIndex: index(($breakpoints), ($from breakpoint($from)));
	$toIndex: index(($breakpoints), ($to breakpoint($to)));

	// set default index, if no index is returned
	$fromIndex: 0 !default;
	$toIndex: length($breakpoints) !default;

	// only set initial value if:
	// - from index is below or equal to 1 (0 means no from breakpoint)
	// - first breakpoint is not in the list of excluded breakpoints
	@if ($fromIndex <= 1 and not index($exclude, index-to-key(1, $breakpoints))) {
		@if ($negate) {
			#{$param}: -1 * first($values);
		}
		@else {
			#{$param}: first($values);
		}
	}

	// loop through the list of breakpoints
	@each $breakpoint, $size in $breakpoints {
    $index: index(($breakpoints), ($breakpoint $size));

		// only set value if:
		// - the index is not higher than the length of values
		// - the index is not below the from index
		// - the index is not above the to index
		// - the index is not in the list of excluded breakpoints
		@if (length($values) >= $index and $index >= $fromIndex and $index <= $toIndex and not index($exclude, $breakpoint)) {
    	@include media('>=#{$breakpoint}') {
				@if ($negate) {
					#{$param}: -1 * nth($values, $index);
        }
        @else {
					#{$param}: nth($values, $index);
				}
			}
		}
	}
}