web-capture 0.3.3

CLI and microservice to render web pages as HTML, Markdown, or PNG
Documentation 
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//! LaTeX formula extraction module (R1).
//!
//! Extracts LaTeX formulas from HTML content, handling multiple sources:
//! - Habr: `img.formula` elements with `source` attribute
//! - `KaTeX`: `.katex` elements with `annotation[encoding="application/x-tex"]`
//! - `MathJax`: `mjx-container` elements with `data-tex`/`data-latex` attributes
//!
//! Based on reference implementation from:
//! <https://github.com/link-foundation/meta-theory/blob/main/scripts/download-article.mjs>

use scraper::{ElementRef, Selector};

/// Check if an element is a formula image (Habr-specific).
///
/// Habr renders formulas as SVG/PNG images with class `formula`.
#[must_use]
pub fn is_formula_image(element: &ElementRef) -> bool {
    let value = element.value();
    if value.name() != "img" {
        return false;
    }
    let classes = value.attr("class").unwrap_or("");
    classes.contains("formula") || value.attr("source").is_some()
}

/// Check if an element is a math element (`KaTeX`, `MathJax`, or generic math class).
#[must_use]
pub fn is_math_element(element: &ElementRef) -> bool {
    let value = element.value();
    let tag = value.name();
    let classes = value.attr("class").unwrap_or("");
    classes.contains("katex")
        || classes.contains("math")
        || classes.contains("MathJax")
        || tag == "mjx-container"
}

/// Extract LaTeX source from a formula image element (Habr-specific).
///
/// Habr renders formulas as SVG/PNG images with class `formula`.
/// The original LaTeX source is in the `source` attribute.
#[must_use]
pub fn extract_habr_formula(element: &ElementRef) -> Option<String> {
    let value = element.value();
    if let Some(source) = value.attr("source") {
        let trimmed = source.trim();
        if !trimmed.is_empty() {
            return Some(trimmed.to_string());
        }
    }
    if let Some(alt) = value.attr("alt") {
        let trimmed = alt.trim();
        if !trimmed.is_empty() {
            return Some(trimmed.to_string());
        }
    }
    None
}

/// Extract LaTeX from `KaTeX` elements.
///
/// `KaTeX` stores the TeX source in `annotation[encoding="application/x-tex"]`.
#[must_use]
pub fn extract_katex_formula(element: &ElementRef) -> Option<String> {
    // Look for annotation element
    if let Ok(sel) = Selector::parse(r#"annotation[encoding="application/x-tex"]"#) {
        if let Some(annotation) = element.select(&sel).next() {
            let text: String = annotation.text().collect();
            let trimmed = text.trim();
            if !trimmed.is_empty() {
                return Some(trimmed.to_string());
            }
        }
    }
    // Fallback to data-tex or data-latex attributes
    let value = element.value();
    if let Some(tex) = value.attr("data-tex").or_else(|| value.attr("data-latex")) {
        let trimmed = tex.trim();
        if !trimmed.is_empty() {
            return Some(trimmed.to_string());
        }
    }
    None
}

/// Extract LaTeX from `MathJax` elements.
///
/// `MathJax` stores TeX in `data-tex` attribute or annotation elements.
#[must_use]
pub fn extract_mathjax_formula(element: &ElementRef) -> Option<String> {
    let value = element.value();
    // First try data-tex/data-latex attributes
    if let Some(tex) = value.attr("data-tex").or_else(|| value.attr("data-latex")) {
        let trimmed = tex.trim();
        if !trimmed.is_empty() {
            return Some(trimmed.to_string());
        }
    }
    // Fallback to annotation element
    if let Ok(sel) = Selector::parse(r#"annotation[encoding="application/x-tex"]"#) {
        if let Some(annotation) = element.select(&sel).next() {
            let text: String = annotation.text().collect();
            let trimmed = text.trim();
            if !trimmed.is_empty() {
                return Some(trimmed.to_string());
            }
        }
    }
    None
}

/// Extract formula from any supported element type.
#[must_use]
pub fn extract_formula(element: &ElementRef) -> Option<String> {
    if is_formula_image(element) {
        return extract_habr_formula(element);
    }
    let tag = element.value().name();
    if tag == "mjx-container" {
        return extract_mathjax_formula(element);
    }
    if is_math_element(element) {
        return extract_katex_formula(element);
    }
    None
}