strip_markdown 0.2.0

#![warn(clippy::all, clippy::pedantic)]
#![allow(clippy::match_same_arms)]

#[macro_use]
extern crate log;

use pulldown_cmark::Event::{
    Code, End, FootnoteReference, HardBreak, Html, Rule, SoftBreak, Start, TaskListMarker, Text,
};
use pulldown_cmark::{Options, Parser, Tag};

#[must_use]
pub fn strip_markdown(markdown: &str) -> String {
    // GFM tables and tasks lists are not enabled.
    let mut options = Options::empty();
    options.insert(Options::ENABLE_STRIKETHROUGH);

    let parser = Parser::new_ext(&markdown, options);
    let mut buffer = String::new();

    // For each event we push into the buffer to produce the 'stripped' version.
    for event in parser {
        debug!("{:?}", event);
        match event {
            // The start and end events don't contain the text inside the tag. That's handled by the `Event::Text` arm.
            Start(tag) => start_tag(&tag, &mut buffer),
            End(tag) => end_tag(&tag, &mut buffer),
            Text(text) => {
                debug!("Pushing {}", &text);
                buffer.push_str(&text);
            }
            Code(code) => buffer.push_str(&code),
            Html(_) => (),
            FootnoteReference(_) => (),
            TaskListMarker(_) => (),
            SoftBreak | HardBreak => fresh_line(&mut buffer),
            Rule => fresh_line(&mut buffer),
        }
    }
    buffer
}

fn start_tag(tag: &Tag, buffer: &mut String) {
    match tag {
        Tag::CodeBlock(_info) => fresh_hard_break(buffer),
        Tag::List(_number) => fresh_line(buffer),
        Tag::Link(_link_type, _dest, title) | Tag::Image(_link_type, _dest, title) => {
            if !title.is_empty() {
                buffer.push_str(&title);
            }
        }
        Tag::Paragraph => (),
        Tag::Heading(_) => (),
        Tag::Table(_alignments) => (),
        Tag::TableHead => (),
        Tag::TableRow => (),
        Tag::TableCell => (),
        Tag::BlockQuote => (),
        Tag::Item => (),
        Tag::Emphasis => (),
        Tag::Strong => (),
        Tag::FootnoteDefinition(_) => (),
        Tag::Strikethrough => (),
    }
}

fn end_tag(tag: &Tag, buffer: &mut String) {
    match tag {
        Tag::Paragraph => (),
        Tag::Table(_) => {
            fresh_line(buffer);
        }
        Tag::TableHead => {
            fresh_line(buffer);
        }
        Tag::TableRow => {
            fresh_line(buffer);
        }
        Tag::Heading(_) => fresh_line(buffer),
        Tag::Emphasis => (),
        Tag::TableCell => (),
        Tag::Strong => (),
        Tag::Link(_, _, _) => (),
        Tag::BlockQuote => fresh_line(buffer),
        Tag::CodeBlock(_) => fresh_line(buffer),
        Tag::List(_) => (),
        Tag::Item => fresh_line(buffer),
        Tag::Image(_, _, _) => (), // shouldn't happen, handled in start
        Tag::FootnoteDefinition(_) => (),
        Tag::Strikethrough => (),
    }
}

fn fresh_line(buffer: &mut String) {
    debug!("Pushing \\n");
    buffer.push('\n');
}

fn fresh_hard_break(buffer: &mut String) {
    debug!("Pushing \\n\\n");
    buffer.push_str("\n\n");
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn basic_inline_strong() {
        let markdown = r#"**Hello**"#;
        let expected = "Hello";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn basic_inline_emphasis() {
        let markdown = r#"_Hello_"#;
        let expected = "Hello";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn basic_header() {
        let markdown = r#"# Header"#;
        let expected = "Header\n";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn alt_header() {
        let markdown = r#"
Header
======
"#;
        let expected = "Header\n";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn strong_emphasis() {
        let markdown = r#"**asterisks and _underscores_**"#;
        let expected = "asterisks and underscores";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn strikethrough() {
        let markdown = r#"~~strikethrough~~"#;
        let expected = "strikethrough";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn mixed_list() {
        let markdown = r#"
1. First ordered list item
2. Another item
1. Actual numbers don't matter, just that it's a number
  1. Ordered sub-list
4. And another item.
"#;

        let expected = r#"
First ordered list item
Another item
Actual numbers don't matter, just that it's a number
Ordered sub-list
And another item.
"#;
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn basic_list() {
        let markdown = r#"
* alpha
* beta
"#;
        let expected = r#"
alpha
beta
"#;
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn list_with_header() {
        let markdown = r#"# Title
* alpha
* beta
"#;
        let expected = r#"Title

alpha
beta
"#;
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn basic_link() {
        let markdown = "[I'm an inline-style link](https://www.google.com)";
        let expected = "I'm an inline-style link";
        assert_eq!(strip_markdown(markdown), expected)
    }

    #[ignore]
    #[test]
    fn link_with_itself() {
        let markdown = "[https://www.google.com]";
        let expected = "https://www.google.com";
        assert_eq!(strip_markdown(markdown), expected)
    }

    #[test]
    fn basic_image() {
        let markdown = "![alt text](https://github.com/adam-p/markdown-here/raw/master/src/common/images/icon48.png)";
        let expected = "alt text";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn inline_code() {
        let markdown = "`inline code`";
        let expected = "inline code";
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn code_block() {
        let markdown = r#"
```javascript
var s = "JavaScript syntax highlighting";
alert(s);
```"#;
        let expected = r#"

var s = "JavaScript syntax highlighting";
alert(s);

"#;
        assert_eq!(strip_markdown(markdown), expected);
    }

    #[test]
    fn block_quote() {
        let markdown = r#"> Blockquotes are very handy in email to emulate reply text.
> This line is part of the same quote."#;
        let expected = "Blockquotes are very handy in email to emulate reply text.
This line is part of the same quote.\n";
        assert_eq!(strip_markdown(markdown), expected);
    }
}