//! XML escaping.

/// Escape text for an element's content.
pub fn text(value: &str) -> String {
    let mut out = String::with_capacity(value.len());
    for ch in value.chars() {
        match ch {
            '&' => out.push_str("&"),
            '<' => out.push_str("&lt;"),
            '>' => out.push_str("&gt;"),
            _ => out.push(ch),
        }
    }
    out
}

/// Escape text for an attribute value, which is always double-quoted here.
pub fn attr(value: &str) -> String {
    let mut out = String::with_capacity(value.len());
    for ch in value.chars() {
        match ch {
            '&' => out.push_str("&amp;"),
            '<' => out.push_str("&lt;"),
            '>' => out.push_str("&gt;"),
            '"' => out.push_str("&quot;"),
            _ => out.push(ch),
        }
    }
    out
}

/// Escape text for WML element content.
#[cfg(feature = "wml")]
///
/// WML reads `$` as the start of a variable reference, so a literal one has to be
/// doubled; otherwise a handset would substitute something or fail to parse.
pub fn wml(value: &str) -> String {
    text(value).replace('$', "$$")
}

/// Escape text for a WML attribute value.
#[cfg(feature = "wml")]
pub fn wml_attr(value: &str) -> String {
    attr(value).replace('$', "$$")
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn escapes_markup_characters() {
        assert_eq!(text("a & b < c > d"), "a &amp; b &lt; c &gt; d");
        // A quote is only significant inside an attribute, so content keeps it.
        assert_eq!(text("say \"hi\""), "say \"hi\"");
        assert_eq!(attr("say \"hi\" & bye"), "say &quot;hi&quot; &amp; bye");
    }

    #[test]
    #[cfg(feature = "wml")]
    fn wml_doubles_a_literal_dollar() {
        assert_eq!(wml("Permit fee: $5"), "Permit fee: $$5");
        assert_eq!(wml("a & $b"), "a &amp; $$b");
        assert_eq!(wml_attr("/x?a=1&b=$2"), "/x?a=1&amp;b=$$2");
        // The doubling runs after the markup escape, so an escaped entity is not
        // itself rewritten.
        assert_eq!(wml("<$>"), "&lt;$$&gt;");
    }

    #[test]
    fn leaves_ordinary_text_alone() {
        assert_eq!(text("plain text 123"), "plain text 123");
    }
}