/* Utility functions for generating correct `@font-face` code
   ========================================================================== */

/**
 * Function to return a list of values associated with a list of keys
 *
 * Examples
 *   $map: (a: 1, b: 2, c: 3)
 *   map-selected-values($map, (a, c))
 *     => (1, 3)
 * Returns list
 */

@function map-select-values($map, $selection, $separator) {
  $values: ();
  @each $key in $selection {
    $values: append($values, map-get($map, $key), $separator);
  }
  @return $values;
}


/**
 * Internal: This builds the list of font formats based on what browsers and font
 * types we're supporting.  These are defined by the global variables
 * $support-ie8 and $use-opentype.
 * The default is to support ie8 but not to use opentype.
 *
 * Supporting ie8 enables additional formats.  Using opentype makes more font
 * styles available but for a larger download.
 */

@function choose-browser-formats() {
  $chosen-formats: ();

  @if $use-opentype {
    $chosen-formats: join($chosen-formats, opentype-woff opentype-woff2 opentype);
  } @else {
    $chosen-formats: join($chosen-formats, truetype-woff truetype-woff2 truetype);
  }

  @return $chosen-formats;
}


/**
 * This chooses the font sources based on font type and browser support, which
 * is set by global variables.
 *
 * Examples
 * Given the following SASS:
 *    @font-face {
 *       src: supported-font-sources((
 *          embedded-opentype: url('font.eot') format('embedded-opentype'),
 *          truetype-woff2:    url('font.ttf.woff2') format('woff2'),
 *          opentype-woff2:    url('font.otf.woff2') format('woff2'),
 *          truetype-woff:     url('font.ttf.woff') format('woff'),
 *          opentype-woff:     url('font.otf.woff') format('woff')
 *    }
 *
 * if $enable-ie8: true and $use-opentype: true the following CSS is generated:
 *    font-face {
 *      src: url('font.eot') format('embedded-opentype'),
 *       opentype-woff2:    url('font.otf.woff2') format('woff2'),
 *       opentype-woff:     url('font.otf.woff') format('woff')
 *    }
 * Returns a list suitable for the src attribute of @font-face
 */

@function supported-font-sources($sources) {
  $chosen-formats: choose-browser-formats();
  @return map-select-values($sources, $chosen-formats, comma);
}