String replace function

SassMeister-input-HTML.html

<div></div>

SassMeister-input.sass

// ----
// Sass (v3.3.0.rc.2)
// Compass (v1.0.0.alpha.17)
// ----

@function str-replace($string, $old, $new: "", $case-sensitive: true)
    @if type-of($string) != string or type-of($old) != string or type-of($new) != string
        @warn "One of the 3 arguments is not a string."
        @return $string
        
    @if str-index($new, $old) != 0
        @warn "The string to be replaced is contained in the new string. Infinite recursion avoided."
        @return $string
        
    $index: if(not $case-sensitive, str-index(to-lower-case($string), to-lower-case($old)), str-index($string, $old))
  
    @if $index > 0 and $new != $old
        $new-string: quote(str-slice($string, 1, $index - 1))
        @for $i from $index through str-length($string)
            @if $i < $index or $i >= $index + str-length($old)
                $new-string: $new-string + str-slice($string, $i, $i)
        @return quote(str-replace(str-insert($new-string, $new, $index), $old, $new, $case-sensitive))
    
    @return $string

        
=svg($filename)
    background-image: url($filename)

    +no-svg
        background-image: url(str-replace($filename, ".svg", ".png"))

=no-svg()
    .no-svg &
        @content
    
div
    +svg("http://placehold.it/200x100.svg")
    width: 200px
    height: 100px

SassMeister-output.css

div {
  background-image: url("http://placehold.it/200x100.svg");
  width: 200px;
  height: 100px;
}
.no-svg div {
  background-image: url("http://placehold.it/200x100.png");
}

SassMeister-rendered.html

<div></div>