update front and back lines in next_line

Author: aaron-ang

src/uu/more/src/more.rs

@@ -460,7 +460,7 @@ struct Pager<'a> {
     line_count: usize,
     silent: bool,
     squeeze: bool,
-    line_squeezed: usize,
+    lines_squeezed: usize,
 }
 
 impl<'a> Pager<'a> {
@@ -501,7 +501,7 @@ impl<'a> Pager<'a> {
             line_count,
             silent: options.silent,
             squeeze: options.squeeze,
-            line_squeezed: 0,
+            lines_squeezed: 0,
         }
     }
 
@@ -557,7 +557,7 @@ impl<'a> Pager<'a> {
     fn page_up(&mut self) {
         self.upper_mark = self
             .upper_mark
-            .saturating_sub(self.content_rows.saturating_add(self.line_squeezed));
+            .saturating_sub(self.content_rows.saturating_add(self.lines_squeezed));
 
         if self.squeeze {
             let mut line = String::new();
@@ -578,32 +578,64 @@ impl<'a> Pager<'a> {
     }
 
     fn next_line(&mut self) {
+        // Don't proceed if we're already at the last line
         if self.upper_mark >= self.line_count.saturating_sub(1) {
             return;
         }
 
+        // Remove the line that's no longer visible at the top
+        self.lines.pop_front();
+
+        // Move the viewing window down by one line
         self.upper_mark = self.upper_mark.saturating_add(1);
-        self.lines.clear();
+
+        let next_line_position = self.upper_mark + self.lines.len();
+        self.seek_to_line(next_line_position).unwrap();
+
+        self.lines_squeezed = 0;
+
+        // Read new lines until we've filled the view
+        let mut line = String::new();
+        while self.lines.len() < self.content_rows {
+            line.clear();
+            if self.reader.read_line(&mut line).unwrap() == 0 {
+                break; // EOF
+            }
+
+            if self.should_squeeze_line(&line) {
+                self.lines_squeezed += 1;
+            } else {
+                self.lines.push_back(std::mem::take(&mut line));
+            }
+        }
     }
 
     fn prev_line(&mut self) {
+        // Don't proceed if we're already at the first line
         if self.upper_mark == 0 {
             return;
         }
 
+        // Remove the line that's no longer visible at the bottom
+        self.lines.pop_back();
+
+        // Move the viewing window up by one line
         self.upper_mark = self.upper_mark.saturating_sub(1);
+
         self.seek_to_line(self.upper_mark).unwrap();
 
-        let mut line = String::new();
-        self.reader.read_line(&mut line).unwrap();
+        self.lines_squeezed = 0;
 
-        if !self.should_squeeze_line(&line) {
-            if self.lines.len() >= self.content_rows {
-                self.lines.pop_back();
+        // Read new lines until we've filled the view
+        let mut line = String::new();
+        while self.lines.len() < self.content_rows {
+            line.clear();
+            self.reader.read_line(&mut line).unwrap();
+            if self.should_squeeze_line(&line) {
+                self.lines_squeezed += 1;
+            } else {
+                self.lines.push_front(std::mem::take(&mut line));
             }
-            self.lines.push_front(line);
-        } else {
-            self.line_squeezed += 1;
         }
     }
 
@@ -666,21 +698,19 @@ impl<'a> Pager<'a> {
     }
 
     fn load_visible_lines(&mut self) -> UResult<()> {
-        let lines_needed = self.content_rows - self.lines.len();
+        self.lines_squeezed = 0;
 
         self.seek_to_line(self.upper_mark + self.lines.len())?;
 
-        self.line_squeezed = 0;
-
         let mut line = String::new();
-        while self.lines.len() < lines_needed {
+        while self.lines.len() < self.content_rows {
             line.clear();
             if self.reader.read_line(&mut line)? == 0 {
                 break; // EOF
             }
 
             if self.should_squeeze_line(&line) {
-                self.line_squeezed += 1;
+                self.lines_squeezed += 1;
             } else {
                 self.lines.push_back(std::mem::take(&mut line));
             }