Scrolling

Cargo.toml

@@ -8,3 +8,4 @@ edition = "2018"
 
 [dependencies]
 termion = "1"
+unicode-segmentation = "1.7.1"

src/document.rs

@@ -28,4 +28,8 @@ impl Document {
     pub fn is_empty(&self) -> bool {
         self.rows.is_empty()
     }
+
+    pub fn len(&self) -> usize {
+        self.rows.len()
+    }
 }

src/editor.rs

@@ -16,6 +16,7 @@ pub struct Editor {
     should_quit: bool,
     terminal: Terminal,
     cursor_position: Position,
+    offset: Position,
     document: Document,
 }
 
@@ -48,6 +49,7 @@ impl Editor {
             terminal: Terminal::default().expect("Failed to initialize terminal"),
             document,
             cursor_position: Position::default(),
+            offset: Position::default(),
         }
     }
 
@@ -59,7 +61,10 @@ impl Editor {
             println!("Goodbye.\r");
         } else {
             self.draw_rows();
-            Terminal::cursor_position(&self.cursor_position);
+            Terminal::cursor_position(&Position {
+                x: self.cursor_position.x.saturating_sub(self.offset.x),
+                y: self.cursor_position.y.saturating_sub(self.offset.y),
+            });
         }
         Terminal::cursor_show();
         Terminal::flush()
@@ -79,14 +84,41 @@ impl Editor {
             | Key::Home => self.move_cursor(pressed_key),
             _ => (),
         }
+
+        self.scroll();
+
         Ok(())
     }
 
+    fn scroll(&mut self) {
+        let Position { x, y } = self.cursor_position;
+        let width = self.terminal.size().width as usize;
+        let height = self.terminal.size().height as usize;
+
+        let mut offset = &mut self.offset;
+
+        if y < offset.y {
+            offset.y = y;
+        } else if y >= offset.y.saturating_add(height) {
+            offset.y = y.saturating_sub(height).saturating_add(1);
+        }
+
+        if x < offset.x {
+            offset.x = x;
+        } else if x >= offset.x.saturating_add(width) {
+            offset.x = x.saturating_sub(width).saturating_add(1);
+        }
+    }
+
     fn move_cursor(&mut self, key: Key) {
+        let terminal_height = self.terminal.size().height as usize;
         let Position { mut y, mut x } = self.cursor_position;
-        let size = self.terminal.size();
-        let height = size.height.saturating_sub(1) as usize;
-        let width = size.width.saturating_sub(1) as usize;
+        let height = self.document.len();
+        let mut width = if let Some(row) = self.document.row(y) {
+            row.len()
+        } else {
+            0
+        };
 
         match key {
             Key::Up => y = y.saturating_sub(1),
@@ -95,19 +127,55 @@ impl Editor {
                     y = y.saturating_add(1);
                 }
             },
-            Key::Left => x = x.saturating_sub(1),
-            Key::Right => {
-                if x < width {
-                    x = x.saturating_add(1);
+            Key::Left => {
+                if x > 0 {
+                    x -= 1;
+                } else if y > 0 {
+                    y -= 1;
+                    if let Some(row) = self.document.row(y) {
+                        x = row.len()
+                    } else {
+                        x = 0
+                    }
+                }
+            },
+            Key::Right => {
+                if x < width {
+                    x += 1;
+                } else if y < height {
+                    y += 1;
+                    x = 0;
+                }
+            },
+            Key::PageUp => {
+                y  = if y > terminal_height {
+                    y - terminal_height
+                } else {
+                    0
+                }
+            },
+            Key::PageDown => {
+                y = if y.saturating_add(terminal_height) < height {
+                    y + terminal_height as usize
+                } else {
+                    height
                 }
             },
-            Key::PageUp => y = 0,
-            Key::PageDown => y = height,
             Key::Home => x = 0,
             Key::End => x = width,
             _ => (),
         }
 
+        width = if let Some(row) = self.document.row(y) {
+            row.len()
+        } else {
+            0
+        };
+
+        if x > width {
+            x = width;
+        }
+
         self.cursor_position = Position { x, y }
     }
 
@@ -123,8 +191,9 @@ impl Editor {
     }
 
     pub fn draw_row(&self, row: &Row) {
-        let start = 0;
-        let end = self.terminal.size().width as usize;
+        let width = self.terminal.size().width as usize;
+        let start = self.offset.x;
+        let end = self.offset.x + width;
         let row = row.render(start, end);
         println!("{}\r", row);
     }
@@ -132,10 +201,10 @@ impl Editor {
     fn draw_rows(&self) {
         let height = self.terminal.size().height;
 
-        for terminal_row in 0..height - 1 {
+        for terminal_row in 0..height {
             Terminal::clear_current_line();
 
-            if let Some(row) = self.document.row(terminal_row as usize) {
+            if let Some(row) = self.document.row(terminal_row as usize + self.offset.y) {
                 self.draw_row(row);
             } else if self.document.is_empty() && terminal_row == height / 3 {
                 self.draw_welcome_message();

src/row.rs

@@ -1,14 +1,20 @@
 use std::cmp;
+use unicode_segmentation::UnicodeSegmentation;
 
 pub struct Row {
     string: String,
+    len: usize,
 }
 
 impl From<&str> for Row {
     fn from(slice: &str) -> Self {
-        Self {
+        let mut row = Self {
             string: String::from(slice),
-        }
+            len: 0,
+        };
+        row.update_len();
+        row
+
     }
 }
 
@@ -16,6 +22,33 @@ impl Row {
     pub fn render(&self, start: usize, end: usize) -> String {
         let end = cmp::min(end, self.string.len());
         let start = cmp::min(start, end);
-        self.string.get(start..end).unwrap_or_default().to_string()
+
+        let mut result = String::new();
+
+        for grapheme in self.string[..]
+            .graphemes(true)
+            .skip(start)
+            .take(end - start)
+        {
+            if grapheme == "\t" {
+                result.push_str("    ");
+            } else {
+                result.push_str(grapheme);
+            }
+        }
+
+        result
+    }
+
+    pub fn len(&self) -> usize {
+        self.len
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.len == 0
+    }
+
+    fn update_len(&mut self) {
+        self.len = self.string[..].graphemes(true).count();
     }
 }

src/terminal.rs

@@ -20,7 +20,7 @@ impl Terminal {
         Ok(Self {
             size: Size {
                 width: size.0,
-                height: size.1,
+                height: size.1.saturating_sub(2),
             },
             _stdout: stdout().into_raw_mode()?,
         })