// Sass Utilities
// ==============
// - Susy Error Output Override [variable]
// - Susy Error [function]



// Susy Error Output Override
// --------------------------
/// Turn off error output for testing
/// @group x-utility
/// @access private
$_susy-error-output-override: false !default;



// Susy Error
// ----------
/// Optionally return error messages without failing,
/// as a way to test error cases
///
/// @group x-utility
/// @access private
///
/// @param {string} $message -
///   A useful error message, explaining the problem
/// @param {string} $source -
///   The original source of the error for debugging
/// @param {bool} $override [$_susy-error-output-override] -
///   Optionally return the error rather than failing
/// @return {string} -
///   Combined error with source and message
/// @throws When `$override == true`
@function _susy-error(
  $message,
  $source,
  $override: $_susy-error-output-override
) {
  @if $override {
    @return 'ERROR [#{$source}] #{$message}';
  }

  @error '[#{$source}] #{$message}';
}


// Su Is Comparable
// ----------------
/// Check that the units in a grid are comparable
///
/// @group _validation
/// @access private
///
/// @param {numbers} $lengths… -
///   Arglist of all the number values to compare
///   (columns, gutters, span, etc)
///
/// @return {'fluid' | 'static' | false} -
///   The type of span (fluid or static) when units match,
///   or `false` for mismatched units
@function _su-is-comparable(
  $lengths...
) {
  $first: nth($lengths, 1);

  @if (length($lengths) == 1) {
    @return if(unitless($first), 'fluid', 'static');
  }

  @for $i from 2 through length($lengths) {
    $comp: nth($lengths, $i);

    $fail: not comparable($first, $comp);
    $fail: $fail or (unitless($first) and not unitless($comp));
    $fail: $fail or (unitless($comp) and not unitless($first));

    @if $fail {
      @return false;
    }
  }

  @return if(unitless($first), 'fluid', 'static');
}


// Su Map Add Units
// ----------------
/// The calc features use a map of units and values
/// to compile the proper algorythm.
/// This function adds a new value to any comparable existing unit/value,
/// or adds a new unit/value pair to the map
///
/// @group x-utility
/// @access private
///
/// @param {map} $map -
///   A map of unit/value pairs, e.g. ('px': 120px)
/// @param {length} $value -
///   A new length to be added to the map
/// @return {map} -
///   The updated map, with new value added
///
/// @example scss -
///   $map: (0px: 120px);
///   $map: _su-map-add-units($map, 1in); // add a comparable unit
///   $map: _su-map-add-units($map, 3vw); // add a new unit
///
///   @each $units, $value in $map {
///     /* #{$units}: #{$value} */
///   }
@function _su-map-add-units(
  $map,
  $value
) {
  $unit: $value * 0;
  $has: map-get($map, $unit) or 0;

  @if ($has == 0) {
    @each $try, $could in $map {
      $match: comparable($try, $value);
      $unit: if($match, $try, $unit);
      $has: if($match, $could, $has);
    }
  }

  @return map-merge($map, ($unit: $has + $value));
}


// Susy Flatten
// ------------
/// Flatten a multidimensional list
///
/// @group x-utility
/// @access private
///
/// @param {list} $list -
///   The list to be flattened
/// @return {list} -
///   The flattened list
///
/// @example scss -
///   $list: 120px (30em 30em) 120px;
///   /* #{_susy-flatten($list)} */
@function _susy-flatten(
  $list
) {
  $flat: ();

  // Don't iterate over maps
  @if (type-of($list) == 'map') {
    @return $list;
  }

  // Iterate over lists (or single items)
  @each $item in $list {
    @if (type-of($item) == 'list') {
      $item: _susy-flatten($item);
      $flat: join($flat, $item);
    } @else {
      $flat: append($flat, $item);
    }
  }

  // Return flattened list
  @return $flat;
}