owlen/crates/owlen-tui/src/highlight.rs

use once_cell::sync::Lazy;
use ratatui::style::{Color as TuiColor, Modifier, Style as TuiStyle};
use std::path::{Path, PathBuf};
use syntect::easy::HighlightLines;
use syntect::highlighting::{FontStyle, Style as SynStyle, Theme, ThemeSet};
use syntect::parsing::{SyntaxReference, SyntaxSet};

static SYNTAX_SET: Lazy<SyntaxSet> = Lazy::new(SyntaxSet::load_defaults_newlines);
static THEME_SET: Lazy<ThemeSet> = Lazy::new(ThemeSet::load_defaults);
static THEME: Lazy<Theme> = Lazy::new(|| {
    THEME_SET
        .themes
        .get("base16-ocean.dark")
        .cloned()
        .or_else(|| THEME_SET.themes.values().next().cloned())
        .unwrap_or_default()
});

fn select_syntax(path_hint: Option<&Path>) -> &'static SyntaxReference {
    if let Some(path) = path_hint
        && let Ok(Some(syntax)) = SYNTAX_SET.find_syntax_for_file(path)
    {
        return syntax;
    }
    if let Some(path) = path_hint
        && let Some(ext) = path.extension().and_then(|ext| ext.to_str())
        && let Some(syntax) = SYNTAX_SET.find_syntax_by_extension(ext)
    {
        return syntax;
    }
    if let Some(path) = path_hint
        && let Some(name) = path.file_name().and_then(|name| name.to_str())
        && let Some(syntax) = SYNTAX_SET.find_syntax_by_token(name)
    {
        return syntax;
    }

    SYNTAX_SET.find_syntax_plain_text()
}

fn select_syntax_for_language(language: Option<&str>) -> &'static SyntaxReference {
    let token = language
        .map(|lang| lang.trim().to_ascii_lowercase())
        .filter(|lang| !lang.is_empty());

    if let Some(token) = token {
        let mut attempts: Vec<&str> = vec![token.as_str()];
        match token.as_str() {
            "c++" => attempts.extend(["cpp", "c"]),
            "c#" | "cs" => attempts.extend(["csharp", "cs"]),
            "shell" => attempts.extend(["bash", "sh"]),
            "typescript" | "ts" => attempts.extend(["typescript", "ts", "tsx"]),
            "javascript" | "js" => attempts.extend(["javascript", "js", "jsx"]),
            "py" => attempts.push("python"),
            "rs" => attempts.push("rust"),
            "yml" => attempts.push("yaml"),
            other => {
                if let Some(stripped) = other.strip_prefix('.') {
                    attempts.push(stripped);
                }
            }
        }

        for candidate in attempts {
            if let Some(syntax) = SYNTAX_SET.find_syntax_by_token(candidate) {
                return syntax;
            }
            if let Some(syntax) = SYNTAX_SET.find_syntax_by_extension(candidate) {
                return syntax;
            }
        }
    }

    SYNTAX_SET.find_syntax_plain_text()
}

fn path_hint_from_components(absolute: Option<&Path>, display: Option<&str>) -> Option<PathBuf> {
    if let Some(abs) = absolute {
        return Some(abs.to_path_buf());
    }
    display.map(PathBuf::from)
}

fn style_from_syntect(style: SynStyle) -> TuiStyle {
    let mut tui_style = TuiStyle::default().fg(TuiColor::Rgb(
        style.foreground.r,
        style.foreground.g,
        style.foreground.b,
    ));

    let mut modifiers = Modifier::empty();
    if style.font_style.contains(FontStyle::BOLD) {
        modifiers |= Modifier::BOLD;
    }
    if style.font_style.contains(FontStyle::ITALIC) {
        modifiers |= Modifier::ITALIC;
    }
    if style.font_style.contains(FontStyle::UNDERLINE) {
        modifiers |= Modifier::UNDERLINED;
    }

    if !modifiers.is_empty() {
        tui_style = tui_style.add_modifier(modifiers);
    }

    tui_style
}

pub fn build_highlighter(
    absolute: Option<&Path>,
    display: Option<&str>,
) -> HighlightLines<'static> {
    let hint_path = path_hint_from_components(absolute, display);
    let syntax = select_syntax(hint_path.as_deref());
    HighlightLines::new(syntax, &THEME)
}

pub fn highlight_line(
    highlighter: &mut HighlightLines<'static>,
    line: &str,
) -> Vec<(TuiStyle, String)> {
    let mut segments = Vec::new();
    match highlighter.highlight_line(line, &SYNTAX_SET) {
        Ok(result) => {
            for (style, piece) in result {
                let tui_style = style_from_syntect(style);
                segments.push((tui_style, piece.to_string()));
            }
        }
        Err(_) => {
            segments.push((TuiStyle::default(), line.to_string()));
        }
    }

    if segments.is_empty() {
        segments.push((TuiStyle::default(), String::new()));
    }

    segments
}

pub fn build_highlighter_for_language(language: Option<&str>) -> HighlightLines<'static> {
    let syntax = select_syntax_for_language(language);
    HighlightLines::new(syntax, &THEME)
}

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

    #[test]
    fn rust_highlighting_produces_colored_segment() {
        let mut highlighter = build_highlighter_for_language(Some("rust"));
        let segments = highlight_line(&mut highlighter, "fn main() {}");
        assert!(
            segments
                .iter()
                .any(|(style, text)| style.fg.is_some() && !text.trim().is_empty()),
            "Expected at least one colored segment"
        );
    }
}