Fix the ticket tui so it does not panic

The tui for ticket uses indexing in order to have quicker unchecked
access into data structures for the data needed that gets displayed in
the tui. However, you can't index empty data. We add a check for this in
places that expect data to exist so that nothing will cause a panic. We
also add fixes to handle the fact that you can't divide by zero in our
index modifying logic when pressing the left/right/up/down arrow keys.
With this the tui shouldn't panic anymore and can work in an empty
state.

Closes: 4c37e800-2e38-11ea-b6e0-32f54a3ad7cd 'Having no tickets causes
the TUI to crash'

2 files changed, 39 insertions, 25 deletions

diff --git a/.dev-suite/ticket/open/having-no-tickets-causes-the-tui-to-crash.toml b/.dev-suite/ticket/closed/having-no-tickets-causes-the-tui-to-crash.toml
index e4ffd42..960ee5d 100644
--- a/.dev-suite/ticket/open/having-no-tickets-causes-the-tui-to-crash.toml
+++ b/.dev-suite/ticket/closed/having-no-tickets-causes-the-tui-to-crash.toml
@@ -1,5 +1,5 @@
 title = 'Having no tickets causes the TUI to crash'
-status = 'Open'
+status = 'Closed'
 id = '4c37e800-2e38-11ea-b6e0-32f54a3ad7cd'
 assignees = [[
     '64c00ccc-761e-4484-86ac-904e461bb300',
diff --git a/ticket/src/tui.rs b/ticket/src/tui.rs
index df62106..e20c112 100644
--- a/ticket/src/tui.rs
+++ b/ticket/src/tui.rs
@@ -86,11 +86,13 @@ impl<'a> TabsState<'a> {
   }
 
   pub fn next(&mut self) {
-    self.index = (self.index + 1) % self.titles.len()
+    if !self.titles.is_empty() {
+      self.index = (self.index + 1) % self.titles.len()
+    }
   }
 
   pub fn previous(&mut self) {
-    if self.index > 0 {
+    if self.index > 0 && !self.titles.is_empty() {
       self.index = (self.index - 1) % self.titles.len()
     }
   }
@@ -123,11 +125,13 @@ impl TicketState {
   }
 
   pub fn next(&mut self) {
-    self.index = (self.index + 1) % self.len()
+    if self.len() > 0 {
+      self.index = (self.index + 1) % self.len()
+    }
   }
 
   pub fn previous(&mut self) {
-    if self.index > 0 {
+    if self.index > 0 && self.len() > 0 {
       self.index = (self.index - 1) % self.len()
     }
   }
@@ -331,28 +335,35 @@ fn handle_event(
       KeyCode::Up => app.tickets.previous(),
       KeyCode::Down => app.tickets.next(),
       KeyCode::Backspace => {
-        let _ = app.tickets.tickets.get_mut(status).unwrap()[app.tickets.index]
-          .1
-          .pop();
+        if app.tickets.len() > 0 {
+          let _ = app.tickets.tickets.get_mut(status).unwrap()
+            [app.tickets.index]
+            .1
+            .pop();
+        }
       }
       KeyCode::Char(c) => {
-        app.tickets.tickets.get_mut(status).unwrap()[app.tickets.index]
-          .1
-          .push(c);
+        if app.tickets.len() > 0 {
+          app.tickets.tickets.get_mut(status).unwrap()[app.tickets.index]
+            .1
+            .push(c);
+        }
       }
       KeyCode::Enter => {
-        let ticket =
-          &mut app.tickets.tickets.get_mut(status).unwrap()[app.tickets.index];
-        if !ticket.1.is_empty() {
-          let _ = ticket.0.comments.insert(
-            uuid_v1()?,
-            (
-              user_config.uuid,
-              Name(user_config.name.clone()),
-              Comment(ticket.1.clone()),
-            ),
-          );
-          ticket.1.clear();
+        if app.tickets.len() > 0 {
+          let ticket = &mut app.tickets.tickets.get_mut(status).unwrap()
+            [app.tickets.index];
+          if !ticket.1.is_empty() {
+            let _ = ticket.0.comments.insert(
+              uuid_v1()?,
+              (
+                user_config.uuid,
+                Name(user_config.name.clone()),
+                Comment(ticket.1.clone()),
+              ),
+            );
+            ticket.1.clear();
+          }
         }
       }
       _ => {}
@@ -450,9 +461,12 @@ impl<'a> App<'a> {
 
   #[inline]
   fn comment(&self, tab: &'a str, f: &mut Frame<impl Backend>, rect: Rect) {
-    let (_, s) = &self.tickets.tickets.get(tab).unwrap()[self.tickets.index];
+    let tickets = self.tickets.tickets.get(tab).unwrap();
     let mut text = String::from("> ");
-    text.push_str(&s);
+    if !tickets.is_empty() {
+      let (_, s) = &tickets[self.tickets.index];
+      text.push_str(&s);
+    }
 
     Paragraph::new([Text::raw(text)].iter())
       .block(Block::default().borders(Borders::ALL).title("Comment"))