refactored display for decoupling

src/directory.rs

@@ -92,7 +92,7 @@ impl Directory {
         }
         Ok(())
     }
-    
+
     fn delete(&self) -> Result<(), Error> {
         if self.selected().is_file {
             remove_file(self.path())
@@ -109,11 +109,11 @@ impl Directory {
         let idx = self.selection();
         &mut self.dirs[idx]
     }
-    
+
     pub const fn selection(&self) -> usize {
         self.selection as usize
     }
-    
+
     pub fn update_navigation(&mut self, key: KeyCode) -> Result<Message, Error> {
         match key {
             KeyCode::Char(c) => {
@@ -191,6 +191,42 @@ impl Directory {
         Ok(Message::Nothing)
     }
 
+    fn display_lines(&self) -> impl Iterator<Item = String> + '_ {
+        let iter = self.dirs.iter().enumerate();
+
+        iter.scan(
+            Vec::new(),
+            |indent_parts, (i, current)| {
+                let is_last_at_this_depth = is_last_at_this_depth(&self.dirs[i+1..], current.depth);
+                let (new_part, continue_part) = if is_last_at_this_depth {
+                    (TreePart::Last, TreePart::Blank)
+                } else {
+                    (TreePart::First, TreePart::Wait)
+                };
+
+                if i == 0 { return Some(current.name.to_owned() + "/") }
+                
+                if current.depth as usize > indent_parts.len() {
+                    indent_parts.push(continue_part);
+                } else {
+                    indent_parts[current.depth as usize-1] = continue_part;
+                }
+
+                let result = indent_parts[0 .. current.depth as usize - 1]
+                    .iter()
+                    .fold(String::new(), |result, t| result + t.display())
+                    + new_part.display()
+                    + &current.name
+                    + if current.is_file {
+                        "\n"
+                    } else {
+                        "/\n"
+                    };
+
+                Some(result)
+            }
+        )
+    }
 }
 
 impl Pane for Directory {
@@ -221,57 +257,7 @@ impl Pane for Directory {
     }
 
     fn display(&self, output: OutputSink, area: Rect) {
-        let mut iter = self.dirs.iter().enumerate();
-        let Some((_, init)) = iter.by_ref()
-            .next()
-            else { return };
-
-        let mut indent_parts = Vec::new();
-        let mut result = init.name.clone() + "/\n";
-
-        for (i, current) in iter {            
-            // first, determine if there is another item at this depth.
-            // that decides what art we use
-            let is_last_at_this_depth = is_last_at_this_depth(&self.dirs[i+1..], current.depth);
-            let (new_part, continue_part) = if is_last_at_this_depth {
-                (TreePart::Last, TreePart::Blank)
-            } else {
-                (TreePart::First, TreePart::Wait)
-            };
-
-            // setting indent_parts is important.
-            // indent_parts[i] is the indent for depth i,
-            // and it needs to be set to what we decided the `continue_part`
-            // needs to be.
-            // The if branch is for when we exceed the current depth and must
-            // add a new indent part. the else branch is when we already
-            // defined a branch at this point, and we do need to update it
-            // every time
-            // TODO: figure out why
-            if current.depth as usize > indent_parts.len() {
-                indent_parts.push(continue_part);
-            } else {
-                indent_parts[current.depth as usize-1] = continue_part;
-            }
-
-            // I have inlined this to avoid making extra strings
-            // because I believe it is less efficient
-            indent_parts[0 .. current.depth as usize - 1]
-                .iter()
-                .copied()
-                .map(TreePart::display)
-                .for_each(|s| result += s);
-
-            result.push_str(new_part.display());
-            result.push_str(&current.name);
-            if !current.is_file {
-                result.push('/');
-            }
-            result.push('\n');
-        }
-
-        let rows = result
-            .lines()
+        let rows = self.display_lines()
             .enumerate()
             .map(|(i, s)| {
                 let row = ListItem::new(s);