feat: adopt the native OS theme (#66)

Reviewed-on: reya/coop#66

crates/common/src/parser.rs

@@ -4,6 +4,62 @@ use nostr::prelude::*;
 
 const BECH32_SEPARATOR: u8 = b'1';
 const SCHEME_WITH_COLON: &str = "nostr:";
+const NEVENT_PREFIX: &str = "nevent1";
+
+/// 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..]),
+    }
+}
 
 /// Nostr parsed token with its range in the original text
 #[derive(Debug, Clone, PartialEq, Eq)]