@mixin _ (
	$key: NULL,
	$span: NULL,
	$context: NULL,
	$gutter: NULL,
	$shift: NULL
) {

	// Foundation check
	// -------------------------------------------------------------------------------
	// @param $key [Value] : checks if key is a foundation or container instance
	// -------------------------------------------------------------------------------
	// @output [Foundation] | container

	@if $key == "foundation" {

		// apply global border-box-sizing if true

		@if get-value(settings, border-box-sizing) == true {
			$foundation: "existant" !global;
		}
		
		// foundation is now globally existant
		
		@if $foundation == "existant" {
			@at-root *, *:before, *:after {
	  			-moz-box-sizing: border-box;
				-webkit-box-sizing: border-box;
				box-sizing: border-box;
				@content;
			}
		}

	} @else if $key == "clear" {

		@include clearfix;

	} @else if $key == "container"
		or exists($flint, $key) and $span != NULL
		or length($key) == 1 and exists($flint, $key) == false
		or length($span) > 1
		or length($key) > 1
		and type-of(nth($key, 1)) != "string"
		and type-of(nth($key, 2)) != "string"
	{

		// only apply display rule if the key is the default

		@if $key == get-value(settings, default) or $key == "container" {

			display: block;

		} @else if length($key) > 1 or type-of($key) != "string" {

			@for $i from 1 through length($flint__all--keys) {
				$calcKey: steal-key($i);

				@if $calcKey == get-value(settings, default) {
					display: block;
				}
			}
		}
		
		// apply individually if foundation is not set globally, but is set to true in config
		
		@if get-value(settings, border-box-sizing) == true and $foundation == "nonexistant" {
  			-moz-box-sizing: border-box;
			-webkit-box-sizing: border-box;
			box-sizing: border-box;

			// warn to either set a global foundation, or turn border-box-sizing off

			@if global-variable-exists(global-foundation-is-set) == false {
				@warn "Global foundation is #{$foundation}. To avoid repeated box-sizing incidents, set a global flint(foundation) rule, or turn border-box-sizing to false in your config file.";

				// declare global variable so only a single warning prints out

				$global-foundation-is-set: true !global;
			}
		}

		// check if max-width is set

		@if get-value(settings, max-width) == true {
			max-width: max(get-all-breakpoints()...);
		} @else if type-of(get-value(settings, max-width)) == number {
			max-width: get-value(settings, max-width);
		}

		// check if center container is set to true

		@if $key == "container" {
			float: none;

			@if get-value(settings, center-container) == true {
				margin-right: auto;
				margin-left: auto;
			} @else {
				margin-right: 0;
				margin-left: 0;
			}

		} @else {

			@if $key == get-value(settings, default) {

				float: unquote(get-value(settings, float-style));

			} @else if length($key) > 1 or type-of($key) != "string" {

				@for $i from 1 through length($flint__all--keys) {
					$calcKey: steal-key($i);

					@if $calcKey == get-value(settings, default) {
						float: unquote(get-value(settings, float-style));
					}
				}
			}
		}
	}

	// Recursive shorthand without context
	// -------------------------------------------------------------------------------
	// @param $span [Value] : span
	// -------------------------------------------------------------------------------
	// @output [Styles...]

	@if is-number($key) and length($key) == 1 or $key == "container" {

		@if $key == "container" {

			@if get-value(settings, grid) == "fixed" {

				@for $i from 1 through length($flint__all--keys) {

					$calcKey: steal-key($i);
					$calcSpan: $key;
					$calcContext: $span;
					$calcGutter: $gutter;
					$calcShift: $shift;

					@if max(get-all-breakpoints()...) == get-value($calcKey, breakpoint) {
						@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
							width: calc-width($calcKey, $calcSpan);
							@content;
						}
					} @else if get-value(settings, default) == $calcKey {
						width: calc-width($calcKey, $calcSpan);
						@content;
					} @else {
						@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
							width: calc-width($calcKey, $calcSpan);
							@content;
						}
					}
				}
			}

		} @else {

			@if length($key) == 1 and $span == NULL {

				@for $i from 1 through length($flint__all--keys) {

					$calcKey: steal-key($i);
					$calcSpan: $key;
					$calcContext: $span;
					$calcGutter: $gutter;
					$calcShift: $shift;

					@if get-value(settings, default) == $calcKey {

						@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);

					} @else {

			  			@if is-highest-breakpoint($calcKey) == true {

							@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
								@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}

			  			} @else {

				  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
				  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}

				  		}
					}
				}

			// Recursive shorthand with identical context
			// -------------------------------------------------------------------------------
			// @param $span [Value] : span
			// @param $context [Value] : context of span
			// -------------------------------------------------------------------------------
			// @output [Styles...]

			} @else if length($key) == 1 and length($span) == 1 {

				@for $i from 1 through length($flint__all--keys) {

					$calcKey: steal-key($i);
					$calcSpan: $key;
					$calcContext: $span;
					$calcGutter: $gutter;
					$calcShift: $shift;

					@if get-value(settings, default) == $calcKey {

						@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);

					} @else {

			  			@if is-highest-breakpoint($calcKey) == true {

							@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
								@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}

			  			} @else {

				  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
				  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}

				  		}
					}
				}

			// Recursive shorthand with differing context
			// -------------------------------------------------------------------------------
			// @param $span [Value] : span
			// @param $context [Values...] : context of span for each breakpoint
			// -------------------------------------------------------------------------------
			// @output [Styles...]

			} @else if length($key) == 1 and length($span) > 1 {

				@for $i from 1 through length($flint__all--keys) {

					$calcKey: steal-key($i);
					$calcSpan: $key;
					$calcContext: $span;
					$calcGutter: $gutter;
					$calcShift: $shift;

					@if get-value(settings, default) == $calcKey {

						@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);

					} @else {

						@if is-highest-breakpoint($calcKey) == true {

							@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
								@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}

			  			} @else {

				  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
				  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
				  			}
				  			
				  		}
					}
				}
			}
		}
	}

	// Variable shorthand
	// -------------------------------------------------------------------------------
	// @param $span [Values...] : span for each breakpoint
	// -------------------------------------------------------------------------------
	// @output [Styles...]

	@if length($key) > 1
		and $span == NULL
		and is-not-string(nth($key, 1))
		and is-not-string(nth($key, 2))
	{
		@for $i from 1 through length($flint__all--keys) {

			$calcKey: steal-key($i);
			$calcSpan: $key;
			$calcContext: $context;
			$calcGutter: $gutter;
			$calcShift: $shift;

			@if get-value(settings, default) == $calcKey {

				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);

			} @else {

				@if is-highest-breakpoint($calcKey) == true {

					@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
						@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
		  			}

	  			} @else {

		  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
		  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
		  			}
		  			
		  		}
			}
		}

	// Variable shorthand with context
	// -------------------------------------------------------------------------------
	// @param $span [Values...] : span for each breakpoint 
	// @param $context [Values...] : context for each breakpoint
	// -------------------------------------------------------------------------------
	// @output [Styles...]

	} @else if length($key) > 1
		and length($span) >= 1
		and is-not-string(nth($key, 1))
		and is-not-string(nth($key, 2))
	{
		@for $i from 1 through length($flint__all--keys) {

			$calcKey: steal-key($i);
			$calcSpan: $key;
			$calcContext: $span;
			$calcGutter: $gutter;
			$calcShift: $shift;

			@if get-value(settings, default) == $calcKey {

				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);

			} @else {

				@if is-highest-breakpoint($calcKey) == true {

					@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) {
						@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
		  			}

	  			} @else {

		  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, $i) ) and ( max-width: calc-breakpoint(to, $calcKey, $i) ) {
		  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift, $i);
		  			}
		  			
		  		}
			}
		}

	// Call by key
	// -------------------------------------------------------------------------------
	// @param $key [Breakpoint] : breakpoint key 
	// @param $span [Value] : span
	// -------------------------------------------------------------------------------
	// @output [Styles...]

	} @else if exists($flint, $key) and $span != NULL and $context == NULL { 

		$calcKey: $key;
		$calcSpan: $span;
		$calcContext: $context;
		$calcGutter: $gutter;
		$calcShift: $shift;

		@if get-value(settings, default) == $calcKey {

			@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);

		} @else {

			@if is-highest-breakpoint($calcKey) == true {

				@media only screen and ( min-width: calc-breakpoint(from, $calcKey, get-index($calcKey)) ) {
					@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);
	  			}

  			} @else {

	  			@media only screen and ( min-width: calc-breakpoint(from, $calcKey, get-index($calcKey)) ) and ( max-width: calc-breakpoint(to, $calcKey, get-index($calcKey)) ) {
	  				@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);
	  			}
	  			
	  		}
		}

	// Call by key with context
	// -------------------------------------------------------------------------------
	// @param $key [Breakpoint] : breakpoint key 
	// @param $span [Value] : span
	// @param $context [Value] : context of span
	// -------------------------------------------------------------------------------
	// @output [Styles...]

	} @else if exists($flint, $key) and $span != NULL and $context != NULL {
	  
		$calcKey: $key;
		$calcSpan: $span;
		$calcContext: $context;
		$calcGutter: $gutter;
		$calcShift: $shift;

		@if get-value(settings, default) == $calcKey {

			@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);

		} @else {

			@if is-highest-breakpoint($calcKey) == true {

				@media only screen and ( min-width: calc-breakpoint(from, $calcKey, get-index($calcKey)) ) {
					@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);
				}

			} @else {

				@media only screen and ( min-width: calc-breakpoint(from, $calcKey, get-index($calcKey)) ) and ( max-width: calc-breakpoint(to, $calcKey, get-index($calcKey)) ) {
					@include calcFlint ($calcKey, $calcSpan, $calcContext, $calcGutter, $calcShift);
				}
				
			}
		}

	// Wrap @content in media queries
	// -------------------------------------------------------------------------------
	// @param $key [Values...] : defines how o make up media query 
	// @param ["from $x to $y"] | ["greater than $x"] | ["less than $x"] | ["for $x $y $z"]
	// -------------------------------------------------------------------------------
	// @output [Media Query]

	} @else if exists($flint, $key) and $span == NULL and $context == NULL or length($key) > 1 {

		// only key-x breakpoint

		@if length($key) == 1 {
			
			@if is-highest-breakpoint($key) == true {
				@media only screen and ( min-width: calc-breakpoint(from, $key, get-index($key)) ) {
					@content;
				}
			} @else {
				@media only screen and ( min-width: calc-breakpoint(from, $key, get-index($key)) ) and ( max-width: calc-breakpoint(to, $key, get-index($key)) ) {
					@content;
				}
			}

			// from key breakpoint to infinity

		} @else if length($key) > 1 and nth($key, 1) == "from" and nth($key, 3) == "to" and nth($key, 4) == "infinity" {
			@media only screen and ( min-width: calc-breakpoint(from, nth($key, 2), get-index(nth($key, 2))) ) {
				@content;
			}

			// from key-x breakpoint to key-y breakpoint

		} @else if length($key) > 1 and nth($key, 1) == "from" and nth($key, 3) == "to" {
			@media only screen and ( min-width: calc-breakpoint(from, nth($key, 2), get-index(nth($key, 2))) ) and ( max-width: calc-breakpoint(to, nth($key, 4), get-index(nth($key, 4))) ) {
				@content;
			}

			// greater than key-x breakpoint

		} @else if length($key) > 1 and nth($key, 1) == "greater" and nth($key, 2) == "than" {
			@if get-value(settings, grid) == "fluid" {
				@media only screen and ( min-width: (calc-breakpoint(to, nth($key, 3), get-index(nth($key, 3))) + 1) ) {
					@content;
				}
			} @else if get-value(settings, grid) == "fixed" {
				@media only screen and ( min-width: (calc-breakpoint(to, nth($key, 3), get-index(nth($key, 3)))) ) {
					@content;
				}
			}

			// (y)px greater than key-x breakpoint

		} @else if length($key) > 1 and nth($key, 2) == "greater" and nth($key, 3) == "than" {
			@media only screen and ( min-width: (calc-breakpoint(to, nth($key, 4), get-index(nth($key, 4))) + nth($key, 1)) ) {
				@content;
			}

			// less than key-x breakpoint

		} @else if length($key) > 1 and nth($key, 1) == "less" and nth($key, 2) == "than" {
			@if get-value(settings, grid) == "fluid" {
				@media only screen and ( max-width: (calc-breakpoint(to, nth($key, 3), get-index(nth($key, 3))) - 1) ) {
					@content;
				}
			} @else if get-value(settings, grid) == "fixed" {
				@media only screen and ( max-width: (calc-breakpoint(to, nth($key, 3), get-index(nth($key, 3)))) ) {
					@content;
				}
			}

			// (y)px less than key-x breakpoint

		} @else if length($key) > 1 and nth($key, 2) == "less" and nth($key, 3) == "than" {
			@media only screen and ( max-width: (calc-breakpoint(to, nth($key, 4), get-index(nth($key, 4))) - nth($key, 1)) ) {
				@content;
			}

			// for key-x key-y key-z

		} @else if length($key) > 1 and nth($key, 1) == "for" {
			@for $i from 1 through length($key) {
				@if exists($flint, nth($key, $i)) {
					@if is-highest-breakpoint(nth($key, $i)) == true {
						@media only screen and ( min-width: calc-breakpoint(from, nth($key, $i), get-index(nth($key, $i))) ) {
							@content;
						}
					} @else {
						@media only screen and ( min-width: calc-breakpoint(from, nth($key, $i), get-index(nth($key, $i))) ) and ( max-width: calc-breakpoint(to, nth($key, $i), get-index(nth($key, $i))) ) {
							@content;
						}
					}
				}
			}
		}
	}
}