1 files changed, 59 insertions, 27 deletions

diff --git a/src/content_window.rs b/src/content_window.rs
index 6c0ac1c..a734387 100644
--- a/src/content_window.rs
+++ b/src/content_window.rs
@@ -1,6 +1,5 @@
 use std::cmp::{max, min};
 
-pub const RESERVED_ROWS: usize = 3;
 /// Holds the information about the displayed window of lines.
 /// When there's too much lines to display in one screen, we can scroll
 /// and this struct is responsible for that.
@@ -8,37 +7,59 @@ pub const RESERVED_ROWS: usize = 3;
 /// methods.
 #[derive(Debug, Clone)]
 pub struct ContentWindow {
-    /// The index of the first displayed file.
+    /// The index of the first displayed element.
     pub top: usize,
-    /// The index of the last displayed file.
+    /// The index of the last displayed element + 1.
     pub bottom: usize,
-    /// The number of displayble file in the current folder.
+    /// The number of displayble elements.
     pub len: usize,
     /// The height of the terminal.
     pub height: usize,
 }
 
 impl ContentWindow {
+    /// The padding around the last displayed filename
+    const WINDOW_PADDING: usize = 4;
+    /// The space of the top element
+    pub const WINDOW_MARGIN_TOP: usize = 2;
+    /// How many rows are reserved for the header ?
+    pub const HEADER_ROWS: usize = 3;
+    /// How many rows are reserved for the footer ?
+    const FOOTER_ROWS: usize = 1;
+    /// Footer and bottom padding
+    const BOTTOM_ROWS: usize = 2;
+
+    /// How many rows could be displayed with given height ?
+    /// It's not the number of rows displayed since the content may
+    /// not be long enough to fill the window.
+    fn nb_displayed_rows(height: usize) -> usize {
+        height - Self::HEADER_ROWS - Self::FOOTER_ROWS
+    }
+
+    /// Default value for the bottom index.
+    /// minimum of terminal height minus reserved rows and the length of the content.
+    fn default_bottom(len: usize, height: usize) -> usize {
+        min(height - Self::BOTTOM_ROWS, len)
+    }
+
     /// Returns a new `ContentWindow` instance with values depending of
-    /// number of files and height of the terminal screen.
-    pub fn new(len: usize, height: usize) -> Self {
+    /// number of displayable elements and height of the terminal screen.
+    pub fn new(len: usize, terminal_height: usize) -> Self {
+        let height = Self::nb_displayed_rows(terminal_height);
+        let top = 0;
+        let bottom = Self::default_bottom(len, height);
         ContentWindow {
-            top: 0,
-            bottom: min(len, height - RESERVED_ROWS),
+            top,
+            bottom,
             len,
-            height: height - RESERVED_ROWS,
+            height,
         }
     }
 
-    /// The padding around the last displayed filename
-    const WINDOW_PADDING: usize = 4;
-    /// The space of the top element
-    pub const WINDOW_MARGIN_TOP: usize = 2;
-    /// How many rows are reserved at bottom
-
     /// Set the height of file window.
-    pub fn set_height(&mut self, height: usize) {
-        self.height = height - RESERVED_ROWS;
+    pub fn set_height(&mut self, terminal_height: usize) {
+        self.height = Self::nb_displayed_rows(terminal_height);
+        self.bottom = Self::default_bottom(self.len, self.height);
     }
 
     /// Move the window one line up if possible.
@@ -61,23 +82,34 @@ impl ContentWindow {
             self.top += 1;
             self.bottom += 1;
         }
-
         self.scroll_to(index)
     }
 
-    /// Reset the window to the first files of the current directory.
-    pub fn reset(&mut self, len: usize) {
-        self.len = len;
-        self.top = 0;
-        self.bottom = min(len, self.height);
-    }
-
     /// Scroll the window to this index if possible.
     /// Does nothing if the index can't be reached.
     pub fn scroll_to(&mut self, index: usize) {
-        if index < self.top || index > self.bottom {
+        if self.len < self.height {
+            return;
+        }
+        if self.is_index_outside_window(index) {
             self.top = max(index, Self::WINDOW_PADDING) - Self::WINDOW_PADDING;
-            self.bottom = self.top + min(self.len, self.height - 3);
+            self.bottom = (self.top + Self::default_bottom(self.height, self.len))
+                .checked_sub(Self::BOTTOM_ROWS)
+                .unwrap_or(2);
         }
     }
+
+    /// Reset the window to the first item of the content.
+    pub fn reset(&mut self, len: usize) {
+        self.len = len;
+        self.top = 0;
+        self.bottom = Self::default_bottom(self.len, self.height);
+    }
+
+    /// True iff the index is outside the displayed window or
+    /// too close from the border.
+    /// User shouldn't be able to reach the last elements
+    fn is_index_outside_window(&self, index: usize) -> bool {
+        index < self.top || index >= self.bottom
+    }
 }