// default configration for typeline
$typeline_config: (
        points: (0 1.2, 50 1.6, 200 1.8),
        breakpoints: 1200px 760px 560px,
        rules: (
                'body': 16px,
                'h0': 80px,
                'h1': 50px,
                'h2': 54px,
                'h3': 36px,
                'h4': 24px
        )
) !default;

$typeline_points: 		map-get($typeline_config, points) 		!default;
$typeline_breakpoints: 	map-get($typeline_config, breakpoints) 	!default;
$typeline_rules: 		map-get($typeline_config, rules) 		!default;

$A: nth($typeline_points, 1);
$B: nth($typeline_points, 2);
$C: nth($typeline_points, 3);

@function strip-unit($number) {
    @if type-of($number) == 'number' and not unitless($number) {
        @return $number / ($number * 0 + 1);
    }
    @return $number;
}

@function pow($base, $exponent) {
    // reset value
    $value: $base;
    // positive intergers get multiplied
    @if $exponent > 1 {
        @for $i from 2 through $exponent {
            $value: $value * $base;
        }
    }
    // negitive intergers get divided. A number divided by itself is 1
    @if $exponent < 1 {
        @for $i from 0 through -$exponent {
            $value: $value / $base;
        }
    }
    // return the last value written
    @return $value;
}

// returns Y value for a given font-size for the first breakpont
// according to the given variable values
@function getY($fontSize) {
    $fontSize: strip-unit($fontSize);
    @if $fontSize < nth($B, 1) {
        // if given fontSize is smaller then B.x
        // use an exponential function to determine Y value [ ie. y = ab^(x^3) ]
        $a: nth($A, 2);
        $b: (nth($B, 2) - nth($A, 2)) / pow(nth($B, 1), 3);
        @return $a + $b * pow($fontSize, 3);
    } @else {
        // otherwise use a basic linear equation solving method
        @return nth($B, 2) + (nth($C, 2) - nth($B, 2)) * ($fontSize - nth($B, 1)) / (nth($C, 1) - nth($B, 1));
    }
}

// used to get the actual font-size for a given breakpoint
@function getFontSize($fontSize, $breakpoint: false) {

    $index: index($typeline_breakpoints, $breakpoint);
    @if $index == null {
        @return $fontSize;
    }

    // we need to find values that are equally spread across the interval [1, getY($fontSize)] for each breakpoint we have
    $y: getY($fontSize);
    $ratio: ($y - 1) * $index / length($typeline_breakpoints) + 1;
    @return round($fontSize / $ratio);
}

//dd
@each $selector, $value in $typeline_rules {
    #{$selector} {
        font-size: $value;
    }
}

@each $breakpoint in $typeline_breakpoints {
    @media only screen and (max-width: $breakpoint) {
        @each $selector, $value in $typeline_rules {
            #{$selector} {
                font-size: getFontSize($value, $breakpoint);
            }
        }
    }
}