parse-hyperlinks 0.9.3

//! This module implements parsers to extract all
//! hyperlinks from a text input.
#![allow(dead_code)]

pub mod markdown;
pub mod restructured_text;

use crate::parser::markdown::md_link;
use crate::parser::markdown::md_link_ref;
use crate::parser::restructured_text::rst_link;
use crate::parser::restructured_text::rst_link_ref;
use nom::branch::alt;
use nom::bytes::complete::take_till;
use nom::character::complete::anychar;
use nom::combinator::*;

/// Consumes the input until it finds a Markdown or RestructuredText hyperlink.  Returns
/// `Ok(remaining_input, (link_name, link_destination, link_title)`.  The parser finds stand alone links
/// and link references.  ReStructuredText's anonymous links are not supported.
/// ```
/// use parse_hyperlinks::parser::take_hyperlink;
/// let i = "[a]: b 'c'\n.. _d: e\n--[f](g 'h')--`i <j>`_--";
///
/// let (i, r) = take_hyperlink(i).unwrap();
/// assert_eq!(r, ("a".to_string(),"b".to_string(),"c".to_string()));
/// let (i, r) = take_hyperlink(i).unwrap();
/// assert_eq!(r, ("d".to_string(),"e".to_string(),"".to_string()));
/// let (i, r) = take_hyperlink(i).unwrap();
/// assert_eq!(r, ("f".to_string(),"g".to_string(),"h".to_string()));
/// let (i, r) = take_hyperlink(i).unwrap();
/// assert_eq!(r, ("i".to_string(),"j".to_string(),"".to_string()));
/// ```
/// The parser might silently consume some additional bytes after the actual finding: This happens,
/// when directly after a finding a `md_link_ref` or `rst_link_ref` appears. These must be ignored,
/// as they are only allowed at the beginning of a line. The skip has to happen at this moment, as
/// the next parser does not know if the first byte it gets, is it at the beginning of a line or
/// not.
pub fn take_hyperlink(mut i: &str) -> nom::IResult<&str, (String, String, String)> {
    let mut input_start = true;
    let res = loop {
        // This might not consume bytes and never fails.
        i = if input_start {
            take_till(|c|
            // Here we should check for `md_link_ref` and `rst_link_ref`
            c == '\n' || c == ' ' || c == '.'
            // these are candidates for `md_link`and `rst_link`
            || c == '`' || c == '[')(i)?
            .0
        } else {
            take_till(|c|
            // Here we should check for `md_link_ref` and `rst_link_ref`
            c == '\n'
            // these are candidates for `md_link`and `rst_link`
            || c == '`' || c == '[')(i)?
            .0
        };

        let mut line_start = false;
        // Are we on a new line character?
        if peek(anychar)(i)?.1 == '\n' {
            line_start = true;
            // Consume the `\n`.
            // Advance one character.
            let (j, _) = anychar(i)?;
            i = j;
        };

        // Start searching for links.

        // Are we at the beginning of a line?
        if line_start || input_start {
            if let Ok(r) = alt((
                map(md_link_ref, |(ln, lta, lti)| {
                    (ln.to_string(), lta.to_string(), lti.to_string())
                }),
                map(rst_link_ref, |(ln, lt)| (ln, lt, "".to_string())),
            ))(i)
            {
                break r;
            };
        };
        input_start = false;

        // Regular links can start everywhere.
        if let Ok(r) = alt((
            map(rst_link, |(ln, lt)| (ln, lt, "".to_string())),
            map(md_link, |(ln, lta, lti)| {
                (ln.to_string(), lta.to_string(), lti.to_string())
            }),
        ))(i)
        {
            break r;
        };

        // This makes sure that we advance.
        let (j, _) = anychar(i)?;
        i = j;
    };

    // Before we return `res`, we need to check again for `md_link_ref` and
    // `rst_link_ref` and consume them silently, without returning their result.
    // These are only allowed at the beginning of a line and we know here, that
    // we are definately not. The next parser can not tell, because it does not
    // know if it was called for the first time ore not. This way, we make sure
    // that `md_link_ref` and `rst_link_ref` are mistakenly recognized in the
    // middle of a line.
    // We do this check only once, because we know, if one of the parser
    // succeeds, it will consume the whole line.
    if let Ok((i, _)) = alt((
        map(rst_link_ref, |(ln, lt)| (ln, lt, "".to_string())),
        map(md_link_ref, |(ln, lta, lti)| {
            (ln.to_string(), lta.to_string(), lti.to_string())
        }),
    ))(res.0)
    {
        Ok((i, res.1))
    } else {
        Ok(res)
    }
}

/// Searches for hyperlinks in the input text and returns the first
/// finding as tuple:
/// `Some((link_name, link_destination, link_title))`
/// The function recognizes hyperlinks in Markdown or RestructuredText
/// format. ReStructuredText's anonymous links are not supported.
/// ```
/// use parse_hyperlinks::parser::first_hyperlink;
/// let i = "abc\n   [u]: v \"w\"abc";
///
/// let r = first_hyperlink(i);
/// assert_eq!(r, Some(("u".to_string(), "v".to_string(), "w".to_string())));
/// ```
pub fn first_hyperlink(i: &str) -> Option<(String, String, String)> {
    if let Ok((_, result)) = take_hyperlink(i) {
        Some(result)
    } else {
        None
    }
}

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

    #[test]
    fn test_take_hyperlink() {
        let expected = nom::Err::Error(nom::error::Error::new("", nom::error::ErrorKind::Eof));
        let err = take_hyperlink("").unwrap_err();
        assert_eq!(err, expected);

        let i = r#"[md link name]: md_link_destination "md link title"
abc [md link name](md_link_destination "md link title")abc
   [md link name]: md_link_destination "md link title"[nomd]: no[nomd]: no
abc`rst link name <rst_link_destination>`_abc
abc`rst link name <rst_link_destination>`_ .. _norst: no .. _norst: no
.. _rst link name: rst_link_destination
  .. _rst link name: rst_link_d
     estination
"#;

        let expected = (
            "md link name".to_string(),
            "md_link_destination".to_string(),
            "md link title".to_string(),
        );
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);

        let expected = (
            "rst link name".to_string(),
            "rst_link_destination".to_string(),
            "".to_string(),
        );
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
        let (i, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
        let (_, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);

        let i = " .. _`My: home page`: http://getreu.net\nabc";
        let expected = (
            "My: home page".to_string(),
            "http://getreu.net".to_string(),
            "".to_string(),
        );
        let (_, res) = take_hyperlink(i).unwrap();
        assert_eq!(res, expected);
    }

    #[test]
    fn test_first_hyperlink() {
        let i = "abc\n   [md link name]: md_link_destination \"md link title\"abc";

        let expected = (
            "md link name".to_string(),
            "md_link_destination".to_string(),
            "md link title".to_string(),
        );
        let res = first_hyperlink(i).unwrap();
        assert_eq!(res, expected);

        let err = first_hyperlink("no link here");
        assert_eq!(err, None);

        let err = first_hyperlink("");
        assert_eq!(err, None);
    }
}