ctrl+u clears to the beginning of the line

src/line.rs

@@ -1,3 +1,5 @@
+use crate::log::*;
+
 pub struct Line {
     /// the current contents of the line
     chars: Vec<char>,
@@ -17,11 +19,13 @@ impl Line {
     pub fn clear(&mut self) {
         self.cursor = 0;
         self.chars.clear();
+        self.show_debug();
     }
 
     pub fn pop(&mut self) -> String {
         let s: String = self.chars.iter().collect();
         self.clear();
+        self.show_debug();
         s
     }
 
@@ -32,6 +36,7 @@ impl Line {
     pub fn back(&mut self) -> bool {
         if self.cursor > 0 {
             self.cursor -= 1;
+            self.show_debug();
             true
         } else {
             false
@@ -39,18 +44,34 @@ impl Line {
     }
 
     pub fn backspace(&mut self) -> bool {
+        if self.chars.len() > 0 {
             if self.cursor > 0 {
                 self.cursor -= 1;
+            }
             self.chars.remove(self.cursor);
+            self.show_debug();
             true
         } else {
             false
         }
     }
 
+    /// removes the elements left of the cursor, returning the count of removed elements
+    pub fn clear_left(&mut self) -> usize {
+        if self.cursor > 0 {
+            let n = self.chars.drain(..self.cursor).count();
+            self.cursor = 0;
+            self.show_debug();
+            n
+        } else {
+            0
+        }
+    }
+
     pub fn forward(&mut self) -> bool {
         if self.cursor < self.chars.len() {
             self.cursor += 1;
+            self.show_debug();
             true
         } else {
             false
@@ -60,6 +81,7 @@ impl Line {
     pub fn insert(&mut self, c: char) {
         self.chars.insert(self.cursor, c);
         self.cursor += 1;
+        self.show_debug();
     }
 
     pub fn tail(&self) -> String {
@@ -71,4 +93,8 @@ impl Line {
         let chars = &self.chars[start..];
         chars.iter().collect()
     }
+
+    fn show_debug(&self) {
+        debug!("  {: <4} {: >5} {}", self.cursor, self.chars.len(), self.show());
+    }
 }

src/main.rs

@@ -318,12 +318,14 @@ fn main() -> Result<()> {
 
                 if event.code == key::BACKSPACE {
                     if line.backspace() {
-                        let text = format!("\x1b[2D");
                         unsafe {
-                            Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
+                            // move cursor back two spaces
+                            Error::check(Console::WriteConsoleA(stdout, "\x1b[2D".as_bytes(), None, None))?;
                         }
                         let tail = format!("{} ", line.tail());
+                        let n = tail.chars().count();
                         unsafe {
+                            // write the rest of the line plus a space to erase the last character
                             Error::check(Console::WriteConsoleA(
                                 stdout,
                                 tail.as_bytes(),
@@ -331,14 +333,26 @@ fn main() -> Result<()> {
                                 None,
                             ))?;
                         }
-                        let text = format!("\x1b[1D");
+
+                        // after writing out the tail, rewind by the number of characters in
+                        // the tail
+                        if n > 1 {
+                            let text = format!("\x1b[{}D", n-1);
+                            unsafe {
+                                Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
+                            }
+                        } else {
+                            // honestly I can't remember how I figured this out
+                            let text = format!(" \x1b[1D");
                             unsafe {
                                 Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
                             }
                         }
+                    }
                     continue;
                 }
 
+                // CTRL-D to exit
                 if event.ctrl && event.code == key::D {
                     info!("» exit");
                     unsafe {
@@ -347,6 +361,7 @@ fn main() -> Result<()> {
                     return Ok(());
                 }
 
+                // CTRL-J to draw a cool little dot
                 if event.ctrl && event.code == key::J {
                     debug!("⎈ j: dot");
                     unsafe {
@@ -357,6 +372,7 @@ fn main() -> Result<()> {
                     continue;
                 }
 
+                // CTRL-L to clear the screen
                 if event.ctrl && event.code == key::L {
                     info!("» clear");
                     let text = "\x1b[2J\x1b[0;0H";
@@ -370,6 +386,31 @@ fn main() -> Result<()> {
                     continue;
                 }
 
+                // CTRL-U to erase to the beginning of the line
+                if event.ctrl && event.code == key::U {
+                    info!("» clear-left");
+                    let n = line.clear_left();
+                    if n > 0 {
+                        // move left by the number of elements removed
+                        let text = format!("\x1b[{}D", n);
+                        unsafe {
+                            Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
+                        }
+                        // draw the elements remaining, followed by a space for each removed
+                        // element
+                        let kept = line.show();
+                        let text = format!("{}{:width$}", kept, "", width = n);
+                        unsafe {
+                            Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
+                        }
+                        let text = format!("\x1b[{}D", n + kept.chars().count());
+                        unsafe {
+                            Error::check(Console::WriteConsoleA(stdout, text.as_bytes(), None, None))?;
+                        }
+                    }
+                    continue;
+                }
+
                 // TODO: something better here, this is crappy. I should be checking characters
                 // based on their unicode categories, not this garbo
                 if !event.char.is_control() {