chore: move some components to custom ui crate (#10)

Reviewed-on: https://git.reya.su/reya/signed/pulls/10

crates/signed_ui/src/util.rs

@@ -0,0 +1,38 @@
+/// `[head chars]...[tail chars]` middle truncation; the value is left alone
+/// when it is too short for the ellipsis to save space.
+pub fn middle_truncate(value: &str, head: usize, tail: usize) -> String {
+    let len = value.chars().count();
+    if len <= head + tail + 3 {
+        return value.to_string();
+    }
+    let head: String = value.chars().take(head).collect();
+    let tail: String = value.chars().skip(len - tail).collect();
+    format!("{head}...{tail}")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn middle_truncates_long_values_only() {
+        assert_eq!(
+            middle_truncate(
+                "a008def15796fba9a0d6fab04e8fd57089285d9fd505da5a83fe8aad57a3564d",
+                10,
+                10,
+            ),
+            "a008def157...ad57a3564d"
+        );
+        assert_eq!(
+            middle_truncate(
+                "30617:a008def15796fba9a0d6fab04e8fd57089285d9fd505da5a83fe8aad57a3564d:ngit",
+                10,
+                10
+            ),
+            "30617:a008...3564d:ngit"
+        );
+        // Too short to save space with the ellipsis: left alone.
+        assert_eq!(middle_truncate("short", 10, 10), "short");
+    }
+}