// Computed lengths: px → rem, and one fluid `clamp()` between two viewport widths. Functions only —
// nothing here emits CSS. The scale maps restate a constant; these compute a value from one.

@use 'sass:math';
@use 'sass:meta';
@use 'sass:string';

/// The one conversion both functions read, so `fluid(16px, 32px)` and `rem(16px)` cannot disagree
/// about what a px is — and so a refusal names the function the author actually called.
@function -to-rem($value, $root, $caller, $example) {
  @if meta.type-of($value) != 'number' or not (math.is-unitless($value) or math.unit($value) == 'px' or math.unit($value) == 'rem') {
    @error string.unquote('X_UI_INVALID_VALUE: #{$caller}() expected px, rem or a unitless px count — got `#{meta.inspect($value)}`. fix: pass a px length, e.g. #{$example}');
  }
  @if math.is-unitless($value) {
    @return math.div($value * 1px, $root) * 1rem;
  }
  @if math.unit($value) == 'rem' {
    @return $value;
  }
  @return math.div($value, $root) * 1rem;
}

/// px → rem against the root size. Lengths are rem so a layout holds at 200% text zoom; a unit
/// that cannot be converted is a build error rather than a size that is subtly off.
@function rem($value, $root: 16px) {
  @return -to-rem($value, $root, 'rem', 'rem(24px)');
}

/// One `clamp()` with a real slope and intercept: `$min` at a viewport `$from` wide, `$max` at
/// `$to`, linear between and held outside. Type and space then scale with the viewport instead of
/// stepping at a breakpoint. `$min` above `$max` is a size that shrinks, and is legal.
@function fluid($min, $max, $from: 20rem, $to: 80rem) {
  $min: -to-rem($min, 16px, 'fluid', 'fluid(16px, 32px)');
  $max: -to-rem($max, 16px, 'fluid', 'fluid(16px, 32px)');
  $from: -to-rem($from, 16px, 'fluid', 'fluid(16px, 32px)');
  $to: -to-rem($to, 16px, 'fluid', 'fluid(16px, 32px)');

  @if $from >= $to {
    @error string.unquote('X_UI_INVALID_VALUE: fluid() needs $from below $to — got `#{$from}` and `#{$to}`. fix: pass the narrower viewport first, e.g. fluid(1rem, 2rem, 20rem, 80rem)');
  }

  $slope: math.div($max - $min, $to - $from);
  $intercept: $min - $slope * $from;
  // `clamp(MIN, VAL, MAX)` with MIN above MAX answers MIN at every width, so the bounds are
  // ordered here rather than trusted to be.
  @return clamp(math.min($min, $max), $intercept + $slope * 100vw, math.max($min, $max));
}