chore: convert NIP-21 references to njump link

crates/chat/src/message.rs

@@ -8,6 +8,9 @@ use state::FileAttachment;
 
 pub(crate) const KIND_FILE_MESSAGE: Kind = Kind::Custom(15);
 
+const SCHEME_WITH_COLON: &str = "nostr:";
+const NEVENT_PREFIX: &str = "nevent1";
+
 /// Rendered message.
 #[derive(Debug, Clone)]
 pub struct Message {
@@ -148,7 +151,33 @@ impl Message {
             return format!("[File] {}", file.display_name()).into();
         }
 
-        self.content.clone().into()
+        // Media-only messages carry their URLs outside `.content`
+        if self.content.is_empty() && !self.media.is_empty() {
+            return self
+                .media
+                .iter()
+                .map(|url| url.to_string())
+                .collect::<Vec<_>>()
+                .join(" ")
+                .into();
+        }
+
+        let references = nevent_refs(&self.content);
+        if references.is_empty() {
+            return self.content.clone().into();
+        }
+
+        let mut preview = String::with_capacity(self.content.len());
+        let mut last = 0;
+
+        for reference in references {
+            preview.push_str(&self.content[last..reference.range.start]);
+            preview.push_str(&reference.label);
+            last = reference.range.end;
+        }
+        preview.push_str(&self.content[last..]);
+
+        preview.into()
     }
 
     /// Image URL of a `:shortcode:` reaction, if the shortcode is declared
@@ -219,6 +248,61 @@ fn extract_mentions(content: &str) -> Vec<Mention> {
         .collect()
 }
 
+/// A `nevent` reference found in a content string.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct NeventRef {
+    /// Range of the reference, including the optional `nostr:` scheme
+    pub range: Range<usize>,
+    /// Compact display label, like `https://njump.me/nevent1...d9sp`
+    pub label: String,
+}
+
+/// Extracts valid `nevent1...` and `nostr:nevent1...` references from content.
+pub fn nevent_refs(content: &str) -> Vec<NeventRef> {
+    let mut references = Vec::new();
+
+    for (match_start, _) in content.match_indices(NEVENT_PREFIX) {
+        // Only lowercase references are matched, matching NIP-19 encodings in practice
+        let start = if content[..match_start].ends_with(SCHEME_WITH_COLON) {
+            match_start - SCHEME_WITH_COLON.len()
+        } else {
+            match_start
+        };
+
+        // Skip matches glued to word characters, like the `nevent1` in `xnevent1...`
+        if content[..start].ends_with(char::is_alphanumeric) {
+            continue;
+        }
+
+        let end = match_start
+            + content[match_start..]
+                .bytes()
+                .take_while(u8::is_ascii_alphanumeric)
+                .count();
+
+        // The bech32 token excludes the optional `nostr:` scheme
+        let bech32 = &content[match_start..end];
+        if Nip19Event::from_bech32(bech32).is_err() {
+            continue;
+        }
+
+        references.push(NeventRef {
+            range: start..end,
+            label: nevent_label(bech32),
+        });
+    }
+
+    references
+}
+
+/// Compact display of a nevent link, like `https://njump.me/nevent1...d9sp`.
+fn nevent_label(bech32: &str) -> String {
+    match bech32.len() {
+        0..=4 => format!("https://njump.me/{bech32}"),
+        _ => format!("https://njump.me/nevent1...{}", &bech32[bech32.len() - 4..]),
+    }
+}
+
 /// Extracts all reply (ids) from the event tags.
 fn extract_reply_ids(inner: &Tags) -> Vec<EventId> {
     let mut replies_to = vec![];
@@ -283,4 +367,32 @@ mod tests {
         assert_eq!(Message::reaction_image("😂", &emojis), None);
         assert_eq!(Message::reaction_image(":unknown:", &emojis), None);
     }
+
+    fn valid_nevent() -> String {
+        Nip19Event::new(EventId::from_byte_array([7; 32]))
+            .to_bech32()
+            .expect("valid nevent")
+    }
+
+    #[test]
+    fn image_only_messages_preview_their_url() {
+        let url = "https://example.com/picture.png";
+        let message = Message::from(&rumor(Kind::PrivateDirectMessage, url, Tags::new()));
+
+        assert!(message.content.is_empty());
+        assert_eq!(message.preview().to_string(), url);
+    }
+
+    #[test]
+    fn preview_compacts_nevent_references() {
+        let nevent = valid_nevent();
+        let message = Message::from(&rumor(
+            Kind::PrivateDirectMessage,
+            &format!("see nostr:{nevent}"),
+            Tags::new(),
+        ));
+
+        let label = format!("https://njump.me/nevent1...{}", &nevent[nevent.len() - 4..]);
+        assert_eq!(message.preview().to_string(), format!("see {label}"));
+    }
 }