// Create a modular font scale. 
// Returns a nested list of font-size and line-height values.

@function ss-make-font-scale(
	$base-size, 
	$base-line-height,
	$max-size,
	$max-line-height,
	$numb-smaller-sizes: 1,
	$numb-larger-sizes: 4,
	$rounding: false 
) {

	// If line-height params are unitless values, 
	// covert to unit values.
	$base-line-height: if(unitless($base-line-height), $base-size * $base-line-height, $base-line-height);
	$max-line-height: if(unitless($max-line-height), $max-size * $max-line-height, $max-line-height);

	// Create font-size and line-height scales
	$font-size-scale: ss-make-scale($base-size, $max-size, $numb-smaller-sizes, $numb-larger-sizes, $rounding);
	$line-height-scale: ss-make-scale($base-line-height, $max-line-height, $numb-smaller-sizes, $numb-larger-sizes, $rounding);
    
	$font-scale: ();
	
	// Pair each size with the correponding font-size 
	// and line-height, then add the size to the scale.
	@for $i from -$numb-smaller-sizes to $numb-larger-sizes + 1 {
		
		// Calculate array position in order to lookup sizes in lists.
		$arr-position: $i + $numb-smaller-sizes + 1;

		// Key for size
		$name-of-size: $i;

		// Values for size
		$values: (
			font-size: nth($font-size-scale, $arr-position),
			line-height: nth($line-height-scale, $arr-position)
		);

		// Merge into $font-scale. 
		$font-scale: map-merge($font-scale, ($name-of-size: $values));
	}
 
	@return $font-scale;
}