From ab464b107da156097d3e55a2cadc7f21179b9018 Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Thu, 24 Sep 2015 14:24:45 +0200
Subject: [PATCH] Add a basic writer type to print single bytes

It prints always to the last line and shifts lines up on newline or line wrap. To easily shift lines up, we make the ColorCode and ScreenChar types Copy.
---
 src/lib.rs        |  2 +-
 src/vga_buffer.rs | 52 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/src/lib.rs b/src/lib.rs
index 29afba64..8cbf9724 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,7 +13,7 @@
 // limitations under the License.
 
 #![feature(no_std, lang_items)]
-#![feature(const_fn)]
+#![feature(const_fn, unique)]
 #![no_std]
 
 extern crate rlibc;
diff --git a/src/vga_buffer.rs b/src/vga_buffer.rs
index efc42ed7..46c5f73a 100644
--- a/src/vga_buffer.rs
+++ b/src/vga_buffer.rs
@@ -1,3 +1,5 @@
+use core::ptr::Unique;
+
 const BUFFER_HEIGHT: usize = 25;
 const BUFFER_WIDTH: usize = 80;
 
@@ -21,6 +23,55 @@ pub enum Color {
     White      = 15,
 }
 
+pub struct Writer {
+    column_position: usize,
+    color_code: ColorCode,
+    buffer: Unique<Buffer>,
+}
+
+impl Writer {
+    pub fn write_byte(&mut self, byte: u8) {
+        match byte {
+            b'\n' => self.new_line(),
+            byte => {
+                if self.column_position >= BUFFER_WIDTH {
+                    self.new_line();
+                }
+                let row = BUFFER_HEIGHT - 1;
+                let col = self.column_position;
+
+                self.buffer().chars[row][col] = ScreenChar {
+                    ascii_character: byte,
+                    color_code: self.color_code,
+                };
+                self.column_position += 1;
+            }
+        }
+    }
+
+    fn buffer(&mut self) -> &mut Buffer {
+        unsafe{self.buffer.get_mut()}
+    }
+
+    fn new_line(&mut self) {
+        for row in 0..(BUFFER_HEIGHT-1) {
+            let buffer = self.buffer();
+            buffer.chars[row] = buffer.chars[row + 1]
+        }
+        self.clear_row(BUFFER_HEIGHT-1);
+        self.column_position = 0;
+    }
+
+    fn clear_row(&mut self, row: usize) {
+        let blank = ScreenChar {
+            ascii_character: ' ' as u8,
+            color_code: self.color_code,
+        };
+        self.buffer().chars[row] = [blank; BUFFER_WIDTH];
+    }
+}
+
+#[derive(Clone, Copy)]
 struct ColorCode(u8);
 
 impl ColorCode {
@@ -29,6 +80,7 @@ impl ColorCode {
     }
 }
 
+#[derive(Clone, Copy)]
 struct ScreenChar {
     ascii_character: u8,
     color_code: ColorCode,