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    //! mdman markdown to man converter.

    use anyhow::{bail, Context, Error};
    use pulldown_cmark::{CowStr, Event, LinkType, Options, Parser, Tag};
    use std::collections::HashMap;
    use std::fs;
    use std::io::{self, BufRead};
    use std::ops::Range;
    use std::path::Path;
    use url::Url;

    mod format;
    mod hbs;
    mod util;

    use format::Formatter;

    /// Mapping of `(name, section)` of a man page to a URL.
    pub type ManMap = HashMap<(String, u8), String>;

    /// A man section.
    pub type Section = u8;

    /// The output formats supported by mdman.
    #[derive(Copy, Clone)]
    pub enum Format {
        Man,
        Md,
        Text,
    }

    impl Format {
        /// The filename extension for the format.
        pub fn extension(&self, section: Section) -> String {
            match self {
                Format::Man => section.to_string(),
                Format::Md => "md".to_string(),
                Format::Text => "txt".to_string(),
            }
        }
    }

    /// Converts the handlebars markdown file at the given path into the given
    /// format, returning the translated result.
    pub fn convert(
        file: &Path,
        format: Format,
        url: Option<Url>,
        man_map: ManMap,
    ) -> Result<String, Error> {
        let formatter: Box<dyn Formatter + Send + Sync> = match format {
            Format::Man => Box::new(format::man::ManFormatter::new(url)),
            Format::Md => Box::new(format::md::MdFormatter::new(man_map)),
            Format::Text => Box::new(format::text::TextFormatter::new(url)),
        };
        let expanded = hbs::expand(file, &*formatter)?;
        // pulldown-cmark can behave a little differently with Windows newlines,
        // just normalize it.
        let expanded = expanded.replace("\r\n", "\n");
        formatter.render(&expanded)
    }

    /// Pulldown-cmark iterator yielding an `(event, range)` tuple.
    type EventIter<'a> = Box<dyn Iterator<Item = (Event<'a>, Range<usize>)> + 'a>;

    /// Creates a new markdown parser with the given input.
    pub(crate) fn md_parser(input: &str, url: Option<Url>) -> EventIter<'_> {
        let mut options = Options::empty();
        options.insert(Options::ENABLE_TABLES);
        options.insert(Options::ENABLE_FOOTNOTES);
        options.insert(Options::ENABLE_STRIKETHROUGH);
        options.insert(Options::ENABLE_SMART_PUNCTUATION);
        let parser = Parser::new_ext(input, options);
        let parser = parser.into_offset_iter();
        // Translate all links to include the base url.
        let parser = parser.map(move |(event, range)| match event {
            Event::Start(Tag::Link(lt, dest_url, title)) if !matches!(lt, LinkType::Email) => (
                Event::Start(Tag::Link(lt, join_url(url.as_ref(), dest_url), title)),
                range,
            ),
            Event::End(Tag::Link(lt, dest_url, title)) if !matches!(lt, LinkType::Email) => (
                Event::End(Tag::Link(lt, join_url(url.as_ref(), dest_url), title)),
                range,
            ),
            _ => (event, range),
        });
        Box::new(parser)
    }

    fn join_url<'a>(base: Option<&Url>, dest: CowStr<'a>) -> CowStr<'a> {
        match base {
            Some(base_url) => {
                // Absolute URL or page-relative anchor doesn't need to be translated.
                if dest.contains(':') || dest.starts_with('#') {
                    dest
                } else {
                    let joined = base_url.join(&dest).unwrap_or_else(|e| {
                        panic!("failed to join URL `{}` to `{}`: {}", dest, base_url, e)
                    });
                    String::from(joined).into()
                }
            }
            None => dest,
        }
    }

    pub fn extract_section(file: &Path) -> Result<Section, Error> {
        let f = fs::File::open(file).with_context(|| format!("could not open `{}`", file.display()))?;
        let mut f = io::BufReader::new(f);
        let mut line = String::new();
        f.read_line(&mut line)?;
        if !line.starts_with("# ") {
            bail!("expected input file to start with # header");
        }
        let (_name, section) = util::parse_name_and_section(&line[2..].trim()).with_context(|| {
            format!(
                "expected input file to have header with the format `# command-name(1)`, found: `{}`",
                line
            )
        })?;
        Ok(section)
    }