[backends] Improve termion backend

* Add AlternateScreenBackend
* Add a way to create a TermionBackend with a custom config
* Improve return values of several methods

src/backend/termion.rs

@@ -20,11 +20,13 @@ where
 pub type RawBackend = TermionBackend<termion::raw::RawTerminal<io::Stdout>>;
 pub type MouseBackend =
     TermionBackend<termion::input::MouseTerminal<termion::raw::RawTerminal<io::Stdout>>>;
+pub type AlternateScreenBackend =
+    TermionBackend<termion::screen::AlternateScreen<termion::raw::RawTerminal<io::Stdout>>>;
 
 impl RawBackend {
     pub fn new() -> Result<RawBackend, io::Error> {
         let raw = io::stdout().into_raw_mode()?;
-        Ok(TermionBackend { stdout: raw })
+        Ok(TermionBackend::with_stdout(raw))
     }
 }
 
@@ -32,7 +34,37 @@ impl MouseBackend {
     pub fn new() -> Result<MouseBackend, io::Error> {
         let raw = io::stdout().into_raw_mode()?;
         let mouse = termion::input::MouseTerminal::from(raw);
-        Ok(TermionBackend { stdout: mouse })
+        Ok(TermionBackend::with_stdout(mouse))
+    }
+}
+
+impl AlternateScreenBackend {
+    pub fn new() -> Result<AlternateScreenBackend, io::Error> {
+        let raw = io::stdout().into_raw_mode()?;
+        let screen = termion::screen::AlternateScreen::from(raw);
+        Ok(TermionBackend::with_stdout(screen))
+    }
+}
+
+impl<W> TermionBackend<W>
+where
+    W: Write,
+{
+    pub fn with_stdout(stdout: W) -> TermionBackend<W> {
+        TermionBackend { stdout }
+    }
+}
+
+impl<W> Write for TermionBackend<W>
+where
+    W: Write,
+{
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.stdout.write(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.stdout.flush()
     }
 }
 
@@ -41,28 +73,25 @@ where
     W: Write,
 {
     /// Clears the entire screen and move the cursor to the top left of the screen
-    fn clear(&mut self) -> Result<(), io::Error> {
+    fn clear(&mut self) -> io::Result<()> {
         write!(self.stdout, "{}", termion::clear::All)?;
         write!(self.stdout, "{}", termion::cursor::Goto(1, 1))?;
-        self.stdout.flush()?;
-        Ok(())
+        self.stdout.flush()
     }
 
     /// Hides cursor
-    fn hide_cursor(&mut self) -> Result<(), io::Error> {
+    fn hide_cursor(&mut self) -> io::Result<()> {
         write!(self.stdout, "{}", termion::cursor::Hide)?;
-        self.stdout.flush()?;
-        Ok(())
+        self.stdout.flush()
     }
 
     /// Shows cursor
-    fn show_cursor(&mut self) -> Result<(), io::Error> {
+    fn show_cursor(&mut self) -> io::Result<()> {
         write!(self.stdout, "{}", termion::cursor::Show)?;
-        self.stdout.flush()?;
-        Ok(())
+        self.stdout.flush()
     }
 
-    fn draw<'a, I>(&mut self, content: I) -> Result<(), io::Error>
+    fn draw<'a, I>(&mut self, content: I) -> io::Result<()>
     where
         I: Iterator<Item = (u16, u16, &'a Cell)>,
     {
@@ -108,8 +137,7 @@ where
             Color::Reset.termion_fg(),
             Color::Reset.termion_bg(),
             Modifier::Reset.termion_modifier()
-        )?;
-        Ok(())
+        )
     }
 
     /// Return the size of the terminal
@@ -123,9 +151,8 @@ where
         })
     }
 
-    fn flush(&mut self) -> Result<(), io::Error> {
-        try!(self.stdout.flush());
-        Ok(())
+    fn flush(&mut self) -> io::Result<()> {
+        self.stdout.flush()
     }
 }