//! Syntax highlighting with syntect, emitted as classed spans so the

//! stylesheet colours them in both themes (`templates/style.css`).

use std::sync::OnceLock;

use syntect::html::{ClassStyle, ClassedHTMLGenerator};

use syntect::parsing::SyntaxSet;

use syntect::util::LinesWithEndings;

fn syntaxes() -> &'static SyntaxSet {

    static SET: OnceLock<SyntaxSet> = OnceLock::new();

    SET.get_or_init(SyntaxSet::load_defaults_newlines)

}

/// The language name shown for a file, if syntect knows the extension.

pub fn language(path: &str) -> Option<&'static str> {

    let ext = path.rsplit('.').next().unwrap_or("");

    let name = path.rsplit('/').next().unwrap_or(path);

    let set = syntaxes();

    set.find_syntax_by_extension(ext)

        .or_else(|| set.find_syntax_by_extension(name))

        .or_else(|| match name {

            "Makefile" | "GNUmakefile" => set.find_syntax_by_name("Makefile"),

            "Dockerfile" => set.find_syntax_by_name("Dockerfile"),

            _ => None,

        })

        .map(|s| s.name.as_str())

}

/// Highlight `text`, returning one HTML fragment per line (no trailing

/// newline); plain escaped lines when the language is unknown.

pub fn lines(path: &str, text: &str) -> Vec<String> {

    let set = syntaxes();

    let ext = path.rsplit('.').next().unwrap_or("");

    let name = path.rsplit('/').next().unwrap_or(path);

    let syntax = set.find_syntax_by_extension(ext).or_else(|| set.find_syntax_by_extension(name)).or_else(|| match name {

        "Makefile" | "GNUmakefile" => set.find_syntax_by_name("Makefile"),

        _ => None,

    });

    let Some(syntax) = syntax else {

        return text.lines().map(super::escape).collect();

    };

    let mut generator = ClassedHTMLGenerator::new_with_class_style(syntax, set, ClassStyle::Spaced);

    let mut out = Vec::new();

    for line in LinesWithEndings::from(text) {

        if generator.parse_html_for_line_which_includes_newline(line).is_err() {

            return text.lines().map(super::escape).collect();

        }

    }

    let html = generator.finalize();

    // syntect emits the whole file with spans that may span lines; split

    // on newlines and keep spans balanced per line.

    let mut open: Vec<String> = Vec::new();

    let mut raw_lines: Vec<&str> = html.split('\n').collect();

    // syntect closes the outermost spans after the final newline; that

    // segment holds no text and every span is balanced per line below.

    if raw_lines.last().is_some_and(|l| l.replace("</span>", "").trim().is_empty()) {

        raw_lines.pop();

    }

    for raw in raw_lines {

        let mut line = String::new();

        for tag in &open {

            line.push_str(tag);

        }

        line.push_str(raw);

        // Track spans opened and closed on this line.

        let mut i = 0;

        while let Some(p) = raw[i..].find('<') {

            let start = i + p;

            let Some(end_rel) = raw[start..].find('>') else { break };

            let tag = &raw[start..start + end_rel + 1];

            if tag.starts_with("</") {

                open.pop();

            } else if tag.starts_with("<span") {

                open.push(tag.to_string());

            }

            i = start + end_rel + 1;

        }

        for _ in &open {

            line.push_str("</span>");

        }

        out.push(line);

    }

    out

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn highlights_rust_and_falls_back() {

        let l = lines("main.rs", "fn main() {\n    let x = 1;\n}\n");

        assert_eq!(l.len(), 3);

        assert!(l[0].contains("<span class=\"source rust\">"), "{}", l[0]);

        assert!(l[0].contains("storage type function"), "{}", l[0]);

        assert!(l[1].ends_with("</span>"), "spans are balanced per line: {}", l[1]);

        assert_eq!(lines("x.unknownext", "a<b\nc"), vec!["a&lt;b", "c"]);

        assert_eq!(language("a/b/lib.rs"), Some("Rust"));

        assert_eq!(language("Makefile"), Some("Makefile"));

        assert_eq!(language("blob.bin"), None);

    }

}