feat: Add support for links by replacing inner value (#62)

Links are displayed by appending a space and then the link
destination in parenthesis. The link is styled blue and underlined.

tui-markdown/src/lib.rs

@@ -95,6 +95,9 @@ struct TextWriter<'a, I> {
     /// Current list index as a stack of indices.
     list_indices: Vec<Option<u64>>,
 
+    /// A link which will be appended to the current line when the link tag is closed.
+    link: Option<CowStr<'a>>,
+
     needs_newline: bool,
 }
 
@@ -118,6 +121,7 @@ where
             needs_newline: false,
             #[cfg(feature = "highlight-code")]
             code_highlighter: None,
+            link: None,
         }
     }
 
@@ -164,7 +168,7 @@ where
             Tag::Emphasis => self.push_inline_style(Style::new().italic()),
             Tag::Strong => self.push_inline_style(Style::new().bold()),
             Tag::Strikethrough => self.push_inline_style(Style::new().crossed_out()),
-            Tag::Link { .. } => warn!("Link not yet supported"),
+            Tag::Link { dest_url, .. } => self.push_link(dest_url),
             Tag::Image { .. } => warn!("Image not yet supported"),
             Tag::MetadataBlock(_) => warn!("Metadata block not yet supported"),
             Tag::DefinitionList => warn!("Definition list not yet supported"),
@@ -190,7 +194,7 @@ where
             TagEnd::Emphasis => self.pop_inline_style(),
             TagEnd::Strong => self.pop_inline_style(),
             TagEnd::Strikethrough => self.pop_inline_style(),
-            TagEnd::Link => {}
+            TagEnd::Link => self.pop_link(),
             TagEnd::Image => {}
             TagEnd::MetadataBlock(_) => {}
             TagEnd::DefinitionList => {}
@@ -413,6 +417,22 @@ where
             self.push_line(Line::from(vec![span]));
         }
     }
+
+    /// Store the link to be appended to the link text
+    #[instrument(level = "trace", skip(self))]
+    fn push_link(&mut self, dest_url: CowStr<'a>) {
+        self.link = Some(dest_url);
+    }
+
+    /// Append the link to the current line
+    #[instrument(level = "trace", skip(self))]
+    fn pop_link(&mut self) {
+        if let Some(link) = self.link.take() {
+            self.push_span(" (".into());
+            self.push_span(Span::styled(link, styles::LINK));
+            self.push_span(")".into());
+        }
+    }
 }
 
 mod styles {
@@ -438,6 +458,9 @@ mod styles {
         .add_modifier(Modifier::ITALIC);
     pub const BLOCKQUOTE: Style = Style::new().fg(Color::Green);
     pub const CODE: Style = Style::new().fg(Color::White).bg(Color::Black);
+    pub const LINK: Style = Style::new()
+        .fg(Color::Blue)
+        .add_modifier(Modifier::UNDERLINED);
 }
 
 #[cfg(test)]
@@ -763,4 +786,17 @@ mod tests {
             ]))
         );
     }
+
+    #[rstest]
+    fn link(with_tracing: DefaultGuard) {
+        assert_eq!(
+            from_str("[Link](https://example.com)"),
+            Text::from(Line::from_iter([
+                Span::from("Link"),
+                Span::from(" ("),
+                Span::from("https://example.com").blue().underlined(),
+                Span::from(")")
+            ]))
+        );
+    }
 }