Allow scrolling up and down.

1 files changed, 21 insertions, 11 deletions

diff --git a/src/main.rs b/src/main.rs
index c9e8928..4c93cb7 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,6 +10,7 @@ use term::Key;
 
 struct State {
     buf: Rope,
+    row_start: usize,
     cursor_row: usize,
     cursor_col: usize,
     line_offset: usize,
@@ -46,11 +47,11 @@ impl State {
         return Ok(pos);
     }
 
-    fn repaint_full(&mut self) -> Result<(), Box<dyn Error>> {
+    fn repaint_all(&mut self) -> Result<(), Box<dyn Error>> {
         let size = term::size()?;
 
         write!(stdout(), "\x1b[H\x1b[J")?;
-        for i in 0..usize::from(size.ws_row) {
+        for i in self.row_start..self.row_start+usize::from(size.ws_row) {
             if i > 0 {
                 write!(stdout(), "\r\n")?;
             }
@@ -71,7 +72,7 @@ impl State {
         let term_size = term::size()?;
 
         write!(stdout(), "\x1b[{}H\x1b[K", self.cursor_row+1)?;
-        let mut line = self.buf.line(self.cursor_row);
+        let mut line = self.buf.line(self.row_start+self.cursor_row);
         let max_len = line.char(usize::from(term_size.ws_col-1));
         let mut truncated = false;
         if max_len < line.len() {
@@ -122,12 +123,13 @@ fn edit(file: &OsStr) -> Result<(), Box<dyn Error>> {
     let size = term::size()?;
     let mut state = State{
         buf: r,
+        row_start: 0,
         cursor_row: 0,
         cursor_col: 0,
         line_offset: 0,
         line_cols: 0,
     };
-    let _ = state.repaint_full();
+    let _ = state.repaint_all();
     let _ = write!(stdout(), "\x1b[H");
     let _ = stdout().flush();
 
@@ -141,20 +143,28 @@ fn edit(file: &OsStr) -> Result<(), Box<dyn Error>> {
                 let _ = state.buf.save(Path::new(file));
             }
             Key::Up => {
-                if state.cursor_row == 0 {
+                if state.cursor_row == 0 && state.row_start == 0 {
                     continue;
                 }
-                state.cursor_row -= 1;
-
+                if state.cursor_row == 0 {
+                    state.row_start -= 1;
+                    let _ = state.repaint_all();
+                } else {
+                    state.cursor_row -= 1;
+                }
                 let _ = state.repaint_line_full();
                 let _ = stdout().flush();
             }
             Key::Down => {
-                if state.cursor_row == usize::from(size.ws_row - 1) || state.cursor_row == state.buf.lines() {
+                if state.row_start+state.cursor_row == state.buf.lines() {
                     continue;
                 }
-                state.cursor_row += 1;
-
+                if state.cursor_row == usize::from(size.ws_row - 1) {
+                    state.row_start += 1;
+                    let _ = state.repaint_all();
+                } else {
+                    state.cursor_row += 1;
+                }
                 let _ = state.repaint_line_full();
                 let _ = stdout().flush();
             }
@@ -183,7 +193,7 @@ fn edit(file: &OsStr) -> Result<(), Box<dyn Error>> {
             }
             Key::Char(c) => {
                 state.cursor_col = std::cmp::min(state.cursor_col, state.line_cols);
-                state.buf = state.buf.insert(state.buf.line_idx(state.cursor_row)+state.line_offset, c);
+                state.buf = state.buf.insert(state.buf.line_idx(state.row_start+state.cursor_row)+state.line_offset, c);
                 state.cursor_col += 1;
                 let _ = state.repaint_line_full();
                 let _ = stdout().flush();