separate logic to move cursor

src/cursor.rs

@@ -0,0 +1,56 @@
+#[derive(Clone, Copy, Debug)]
+pub enum CursorMove {
+    Forward,
+    Back,
+    Up,
+    Down,
+    Head,
+    End,
+}
+
+impl CursorMove {
+    pub fn next_cursor(
+        &self,
+        (row, col): (usize, usize),
+        lines: &[String],
+    ) -> Option<(usize, usize)> {
+        match self {
+            CursorMove::Forward if col + 1 >= lines[row].chars().count() => {
+                if row + 1 < lines.len() {
+                    Some((row + 1, 0))
+                } else {
+                    None
+                }
+            }
+            CursorMove::Forward => Some((row, col + 1)),
+            CursorMove::Back if col == 0 => {
+                if row > 0 {
+                    Some((row - 1, lines[row - 1].chars().count() - 1))
+                } else {
+                    None
+                }
+            }
+            CursorMove::Back => Some((row, col - 1)),
+            CursorMove::Up if row == 0 => None,
+            CursorMove::Up => {
+                let mut col = col;
+                let end = lines[row - 1].chars().count();
+                if end <= col {
+                    col = end - 1;
+                }
+                Some((row - 1, col))
+            }
+            CursorMove::Down if row + 1 >= lines.len() => None,
+            CursorMove::Down => {
+                let mut col = col;
+                let end = lines[row + 1].chars().count();
+                if end <= col {
+                    col = end - 1;
+                }
+                Some((row + 1, col))
+            }
+            CursorMove::Head => Some((row, 0)),
+            CursorMove::End => Some((row, lines[row].chars().count() - 1)),
+        }
+    }
+}

src/lib.rs

@@ -1,7 +1,9 @@
+mod cursor;
 mod edit;
 mod history;
 mod input;
 mod textarea;
 
+pub use cursor::CursorMove;
 pub use input::{Input, Key};
 pub use textarea::TextArea;

src/textarea.rs

@@ -1,3 +1,4 @@
+use crate::cursor::CursorMove;
 use crate::edit::{Edit, EditKind};
 use crate::history::EditHistory;
 use crate::input::{Input, Key};
@@ -34,12 +35,12 @@ impl<'a> TextArea<'a> {
             match input.key {
                 Key::Char('h') => self.delete_char(),
                 Key::Char('m') => self.insert_newline(),
-                Key::Char('p') => self.cursor_up(),
-                Key::Char('f') => self.cursor_forward(),
-                Key::Char('n') => self.cursor_down(),
-                Key::Char('b') => self.cursor_back(),
-                Key::Char('a') => self.cursor_start(),
-                Key::Char('e') => self.cursor_end(),
+                Key::Char('p') => self.move_cursor(CursorMove::Up),
+                Key::Char('f') => self.move_cursor(CursorMove::Forward),
+                Key::Char('n') => self.move_cursor(CursorMove::Down),
+                Key::Char('b') => self.move_cursor(CursorMove::Back),
+                Key::Char('a') => self.move_cursor(CursorMove::Head),
+                Key::Char('e') => self.move_cursor(CursorMove::End),
                 Key::Char('u') => self.undo(),
                 Key::Char('r') => self.redo(),
                 _ => {}
@@ -50,12 +51,12 @@ impl<'a> TextArea<'a> {
                 Key::Backspace => self.delete_char(),
                 Key::Tab => self.insert_tab(),
                 Key::Enter => self.insert_newline(),
-                Key::Up => self.cursor_up(),
-                Key::Right => self.cursor_forward(),
-                Key::Down => self.cursor_down(),
-                Key::Left => self.cursor_back(),
-                Key::Home => self.cursor_start(),
-                Key::End => self.cursor_end(),
+                Key::Up => self.move_cursor(CursorMove::Up),
+                Key::Right => self.move_cursor(CursorMove::Forward),
+                Key::Down => self.move_cursor(CursorMove::Down),
+                Key::Left => self.move_cursor(CursorMove::Back),
+                Key::Home => self.move_cursor(CursorMove::Head),
+                Key::End => self.move_cursor(CursorMove::End),
                 _ => {}
             }
         }
@@ -165,60 +166,12 @@ impl<'a> TextArea<'a> {
         }
     }
 
-    pub fn cursor_forward(&mut self) {
-        let (r, c) = self.cursor;
-        if c + 1 >= self.lines[r].chars().count() {
-            if r + 1 < self.lines.len() {
-                self.cursor = (r + 1, 0);
-            }
-        } else {
-            self.cursor.1 += 1;
+    pub fn move_cursor(&mut self, m: CursorMove) {
+        if let Some(cursor) = m.next_cursor(self.cursor, &self.lines) {
+            self.cursor = cursor;
         }
     }
 
-    pub fn cursor_back(&mut self) {
-        let (r, c) = self.cursor;
-        if c == 0 {
-            if r > 0 {
-                self.cursor = (r - 1, self.lines[r - 1].chars().count() - 1);
-            }
-        } else {
-            self.cursor.1 -= 1;
-        }
-    }
-
-    pub fn cursor_down(&mut self) {
-        let (r, c) = self.cursor;
-        if r + 1 >= self.lines.len() {
-            return;
-        }
-        self.cursor.0 += 1;
-        let len = self.lines[r + 1].chars().count();
-        if len <= c {
-            self.cursor.1 = len - 1;
-        }
-    }
-
-    pub fn cursor_up(&mut self) {
-        let (r, c) = self.cursor;
-        if r == 0 {
-            return;
-        }
-        self.cursor.0 -= 1;
-        let len = self.lines[r - 1].chars().count();
-        if len <= c {
-            self.cursor.1 = len - 1;
-        }
-    }
-
-    pub fn cursor_start(&mut self) {
-        self.cursor.1 = 0;
-    }
-
-    pub fn cursor_end(&mut self) {
-        self.cursor.1 = self.lines[self.cursor.0].chars().count() - 1;
-    }
-
     pub fn undo(&mut self) {
         if let Some(cursor) = self.history.undo(&mut self.lines) {
             self.cursor = cursor;