feat: add support for custom emojis (NIP-30) (#63)

Reviewed-on: #63

crates/chat_ui/src/text.rs

@@ -1,17 +1,18 @@
 use chat::Mention;
 use gpui::{App, Entity};
+use nostr_sdk::prelude::Url;
 use person::PersonRegistry;
 use ui::markdown::InlineReplacement;
 pub use ui::markdown::RenderedText;
 
-/// Render message `content`, replacing mentions with their display names.
 pub fn rendered_text(
     content: &str,
     mentions: &[Mention],
+    emojis: &[(String, Url)],
     persons: &Entity<PersonRegistry>,
     cx: &App,
 ) -> RenderedText {
-    let replacements = mentions
+    let mut replacements = mentions
         .iter()
         .map(|mention| {
             InlineReplacement::new(
@@ -21,5 +22,62 @@ pub fn rendered_text(
         })
         .collect::<Vec<_>>();
 
+    replacements.extend(emoji_replacements(content, emojis));
+    replacements.sort_by_key(|replacement| replacement.range.start);
+
     RenderedText::new(content, &replacements)
 }
+
+fn emoji_replacements(content: &str, emojis: &[(String, Url)]) -> Vec<InlineReplacement> {
+    let mut replacements = Vec::new();
+
+    for (shortcode, url) in emojis {
+        let pattern = format!(":{shortcode}:");
+        for (start, _) in content.match_indices(&pattern) {
+            let range = start..start + pattern.len();
+
+            // Skip matches glued to word characters, like the `30` in `12:30:45`
+            if content[..start].ends_with(char::is_alphanumeric)
+                || content[range.end..].starts_with(char::is_alphanumeric)
+            {
+                continue;
+            }
+
+            replacements.push(InlineReplacement::image(
+                range,
+                shortcode.clone(),
+                url.to_string(),
+            ));
+        }
+    }
+
+    replacements
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn emoji(shortcode: &str, url: &str) -> (String, Url) {
+        (String::from(shortcode), Url::parse(url).expect("valid url"))
+    }
+
+    #[test]
+    fn declared_shortcodes_become_image_replacements() {
+        let emojis = vec![emoji("soapbox", "https://example.com/soapbox.png")];
+
+        let replacements = emoji_replacements("hi :soapbox: and :other:", &emojis);
+
+        assert_eq!(replacements.len(), 1);
+        assert_eq!(replacements[0].range, 3..12);
+    }
+
+    #[test]
+    fn matches_glued_to_word_characters_are_skipped() {
+        let emojis = vec![emoji("30", "https://example.com/30.png")];
+
+        assert!(emoji_replacements("at 12:30:45 exactly", &emojis).is_empty());
+        assert!(emoji_replacements("x:30: and :30:y", &emojis).is_empty());
+        assert_eq!(emoji_replacements("(:30:)", &emojis).len(), 1);
+    }
+}