/// Syntax Utilities for Extending Susy
/// ===================================
/// There are many steps involved
/// when translating between the Susy syntax layer,
/// and the Su core math.
/// That entire process can be condensed with these two functions.
/// For anyone that wants to access the full power of Susy,
/// and build their own plugins, functions, or mixins –
/// this is the primary API for compiling user input,
/// and accessing the core math.
///
/// This is the same technique we use internally,
/// to keep our API layer simple and light-weight.
/// Every function accepts two arguments,
/// a "shorthand" description of the span or context,
/// and an optional settings-map to override global defaults.
///
/// - Use `susy-compile()` to parse, merge, and normalize
///   all the user settings into a single map.
/// - Then use `su-call()` to call one of the core math functions,
///   with whatever data is needed for that function.
///
/// @group plugin-utils
/// @see susy-compile
/// @see su-call
///
/// @example scss - Susy API `gutter` function
///   @function susy-gutter(
///     $context: susy-get('columns'),
///     $config: ()
///   ) {
///     // compile and normalize all user arguments and global settings
///     $context: susy-compile($context, $config, 'context-only');
///     // call `su-gutter` with the appropriate data
///     @return su-call('su-gutter', $context);
///   }
///
/// @example scss - Sample `span` mixin for floated grids
///   @mixin span(
///     $span,
///     $config: ()
///   ) {
///     $context: susy-compile($span, $config);
///     width: su-call('su-span', $context);
///
///     $end: map-get($context, 'span') + map-get($context, 'location') - 1;
///     $is-last: ($end == map-get($context, 'columns'));
///
///     @if $is-last {
///       float: right;
///     } @else {
///       float: left;
///       margin-right: su-call('su-gutter', $context);
///     }
///   }



// Compile
// -------
/// Susy's syntax layer has various moving parts,
/// with syntax-parsing for the grid/span shorthand,
/// and normalization for each of the resulting values.
/// The compile function rolls this all together
/// in a single call –
/// for quick access from our internal API functions,
/// or any additional functions and mixins you add to your project.
/// Pass user input and configuration maps to the compiler,
/// and it will hand back a map of values ready for Su.
/// Combine this with the `su-call` function
/// to quickly parse, normalize, and process grid calculations.
///
/// @group plugin-utils
/// @see su-call
///
/// @param {list | map} $short [null] -
///   Shorthand expression to define the width of the span,
///   optionally containing:
///   - a count, length, or column-list span;
///   - `at $n`, `first`, or `last` location on asymmetrical grids;
///   - `narrow`, `wide`, or `wider` for optionally spreading
///     across adjacent gutters;
///   - `of $n <spread>` for available grid columns
///     and spread of the container
///     (span counts like `of 6` are only valid
///     in the context of symmetrical grids);
///   - and `set-gutters $n` to override global gutter settings
/// @param {map} $config [null] -
///   Optional map of Susy grid configuration settings
/// @param {bool} $context-only [false] -
///   Allow the parser to ignore span and span-spread values,
///   only parsing context and container-spread
///
/// @return {map} -
///   Parsed and normalized map of settings,
///   based on global and local configuration,
///   alongwith shorthad adjustments.
///
/// @example scss -
///   $user-input: 3 wide of susy-repeat(6, 120px) set-gutters 10px;
///   $grid-data: susy-compile($user-input, $susy);
///
///   @each $key, $value in $grid-data {
///     /* #{$key}: #{$value}, */
///   }
@function susy-compile(
  $short: null,
  $config: null,
  $context-only: false
) {
  // Get and normalize config
  $config: if($config, susy-settings($config), susy-settings());
  $normal-config: susy-normalize($config);

  // Parse and normalize shorthand
  $normal-short: ();

  @if $short {
    @if (type-of($short) != 'map') and (length($short) > 0) {
      $short: susy-parse($short, $context-only);
    }

    $normal-short: susy-normalize($short, $normal-config);
  }

  // Merge and return
  @return map-merge($normal-config, $normal-short);
}



// Call
// ----
/// The Susy parsing and normalization process
/// results in a map of configuration settings,
/// much like the global `$susy` settings map.
/// In order to pass that information along to Su math functions,
/// the proper values have to be picked out,
/// and converted to arguments.
///
/// The `su-call` function streamlines that process,
/// weeding out the unnecessary data,
/// and passing the rest along to Su in the proper format.
/// Combine this with `susy-compile` to quickly parse,
/// normalize, and process grid calculations.
///
/// @group plugin-utils
///
/// @require su-span
/// @require su-gutter
/// @require su-slice
/// @see susy-compile
///
/// @param {'su-span' | 'su-gutter' | 'su-slice'} $name -
///   Name of the Su math function to call.
/// @param {map} $config -
///   Parsed and normalized map of Susy configuration settings
///   to use for math-function arguments.
///
/// @return {*} -
///   Results of the function being called.
///
/// @example scss -
///   $user-input: 3 wide of susy-repeat(6, 120px) set-gutters 10px;
///   $grid-data: susy-compile($user-input, $susy);
///
///   .su-span {
///     width: su-call('su-span', $grid-data);
///   }
@function su-call(
  $name,
  $config
) {
  $grid-function-args: (
    'su-span': ('span', 'columns', 'gutters', 'spread', 'container-spread', 'location'),
    'su-gutter': ('columns', 'gutters', 'container-spread'),
    'su-slice': ('span', 'columns', 'location'),
  );

  $args: map-get($grid-function-args, $name);

  @if not $args {
    $options: 'Try one of these: #{map-keys($grid-function-args)}';
    @return _susy-error(
      '#{$name} is not a public Su function. #{$options}',
      'su-call');
  }

  $call: if(function-exists('get-function'), get-function($name), $name);
  $output: ();

  @each $arg in $args {
    $value: map-get($config, $arg);
    $output: if($value, map-merge($output, ($arg: $value)), $output);
  }

  @return call($call, $output...);
}