[Add] basic split

iota-core/src/terms/focus.rs

@@ -0,0 +1,25 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Focus {
+    Eula,
+    Tos,
+    Pp,
+    Cancel,
+    Continue,
+    ContinueAll,
+}
+
+impl Focus {
+    pub fn next(&mut self, order: &[Focus]) {
+        if let Some(pos) = order.iter().position(|&f| f == *self) {
+            let next_pos = (pos + 1) % order.len();
+            *self = order[next_pos];
+        }
+    }
+
+    pub fn prev(&mut self, order: &[Focus]) {
+        if let Some(pos) = order.iter().position(|&f| f == *self) {
+            let prev_pos = if pos == 0 { order.len() - 1 } else { pos - 1 };
+            *self = order[prev_pos];
+        }
+    }
+}