// Turn a string into a tidy URL slug.
pub fn make_url_safe(text: &str) -> String {
    text.to_ascii_lowercase().chars().filter_map(|c|
        if c.is_alphanumeric() || "-_~.+/#".contains(c) { Some(c) }
        else if c == ' ' { Some('-') }
        else { None } )
    .collect()
}

// Prevent link hrefs from breaking out of quotations.
pub fn url_encode(text: &str) -> String {
    let mut output = String::new();
    for c in text.chars() {
        match c {
            '"' => output.push_str("%22"),
            '\'' => output.push_str("%27"),
            _ => output.push(c),
        }
    }
    return output;
}

/// Replace each HTML-reserved character with an HTML-escaped character.
pub fn sanitize_text(text: &str, fancy: bool) -> String {
    let mut output = String::new();
    let chars: Vec<char> = text.chars().collect();
    for (i, c) in chars.iter().enumerate() {
        let prev = match i > 0 {
            true => chars[i - 1],
            false => ' ',
        };
        let next = match i + 1 < chars.len() {
            true => chars[i + 1],
            false => ' ',
        };
        let is_whitespace = |c: char| c.is_whitespace() || "()[].,".contains(c);

        match c {
            '&' => {
                // The HTML syntax for unicode characters is &#0000
                if let Some('#') = chars.get(i+1) { output.push(*c) }
                else { output.push_str("&amp;") }
            },
            '<' => output.push_str("&lt;"),
            '>' => output.push_str("&gt;"),
            '"' => match fancy {
                true => match is_whitespace(prev) {
                    true  => output.push('“'),
                    false => output.push('”'),
                }
                false => output.push_str("&#34;"),
            },
            '\'' => match fancy {
                true => match is_whitespace(prev) {
                    true  => output.push('‘'),
                    false => output.push('’'),
                }
                false => output.push_str("&#39;"),
            },
            '-' if fancy => match prev.is_whitespace() && next.is_whitespace() {
                true => match i > 0 {
                    true => output.push('—'),  // em-dash, for mid-sentence
                    false => output.push('–'),  // en-dash, for start of line
                }
                false => output.push('-'),      // regular dash, for mid-word
            }
            _ => output.push(*c),
        }
    }
    return output;
}