add basic cursor actions

src/app/cursor.rs

@@ -0,0 +1,51 @@
+use chrono::{Duration, Local, NaiveDate};
+use cursive::direction::Absolute;
+
+#[derive(Debug, Copy, Clone)]
+pub struct Cursor(pub NaiveDate);
+
+impl std::default::Default for Cursor {
+    fn default() -> Self {
+        Cursor::new()
+    }
+}
+
+impl Cursor {
+    pub fn new() -> Self {
+        Cursor {
+            0: Local::now().naive_local().date(),
+        }
+    }
+    pub fn do_move(&mut self, d: Absolute) {
+        let today = Local::now().naive_local().date();
+        let cursor = self.0;
+        match d {
+            Absolute::Right => {
+                // forward by 1 day
+                let next = cursor.succ_opt().unwrap_or(cursor);
+                if next <= today {
+                    self.0 = next;
+                }
+            }
+            Absolute::Left => {
+                // backward by 1 day
+                // assumes an infinite past
+                self.0 = cursor.pred_opt().unwrap_or(cursor);
+            }
+            Absolute::Down => {
+                // forward by 1 week
+                let next = cursor.checked_add_signed(Duration::weeks(1)).unwrap();
+                if next <= today {
+                    self.0 = next;
+                }
+            }
+            Absolute::Up => {
+                // backward by 1 week
+                // assumes an infinite past
+                let next = cursor.checked_sub_signed(Duration::weeks(1)).unwrap();
+                self.0 = next;
+            }
+            Absolute::None => {}
+        }
+    }
+}