pub fn strip_html(input: &str) -> String {
    let mut result = String::with_capacity(input.len());
    let mut in_tag = false;
    let mut in_entity = false;
    let mut entity = String::new();

    for c in input.chars() {
        match c {
            '<' => in_tag = true,
            '>' if in_tag => in_tag = false,
            '&' if !in_tag => {
                in_entity = true;
                entity.clear();
            }
            ';' if in_entity => {
                in_entity = false;
                let decoded = match entity.as_str() {
                    "amp" => "&",
                    "lt" => "<",
                    "gt" => ">",
                    "quot" => "\"",
                    "nbsp" => " ",
                    _ => "",
                };
                result.push_str(decoded);
            }
            c if !in_tag && !in_entity => result.push(c),
            c if in_entity => entity.push(c),
            _ => {}
        }
    }
    result
}

#[derive(Debug, Clone)]
pub struct TocEntry {
    pub label: String,
    pub section: usize,
    pub children: Vec<TocEntry>,
}

#[derive(Debug, Clone)]
pub struct Section {
    pub title: String,
    pub content: String,
    pub pages: Vec<usize>,
}

#[derive(Debug, Clone)]
pub struct Book {
    pub title: String,
    pub author: String,
    pub cover: Option<Vec<u8>>,
    pub sections: Vec<Section>,
    pub toc: Vec<TocEntry>,
}

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

    #[test]
    fn test_strip_html_plain_text() {
        assert_eq!(strip_html("Hello World"), "Hello World");
    }

    #[test]
    fn test_strip_html_simple_tags() {
        assert_eq!(strip_html("<p>Hello</p>"), "Hello");
    }

    #[test]
    fn test_strip_html_nested_tags() {
        assert_eq!(
            strip_html("<div><p>Hello <b>World</b></p></div>"),
            "Hello World"
        );
    }

    #[test]
    fn test_strip_html_html_entities() {
        assert_eq!(strip_html("Hello &amp; World"), "Hello & World");
        assert_eq!(strip_html("Hello&nbsp;World"), "Hello World");
    }

    #[test]
    fn test_strip_html_empty() {
        assert_eq!(strip_html(""), "");
    }
}