From 753a946fd5ec594e1b68fa714d27fb1d7961358c Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Mon, 18 Apr 2022 12:35:15 -0700
Subject: [PATCH] terminal: C0.BS

---
 src/terminal/Terminal.zig | 27 +++++++++++++++++++++++++--
 src/terminal/ansi.zig     |  2 ++
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/terminal/Terminal.zig b/src/terminal/Terminal.zig
index ef2cbcd51..3ed3ae695 100644
--- a/src/terminal/Terminal.zig
+++ b/src/terminal/Terminal.zig
@@ -115,11 +115,17 @@ fn print(self: *Terminal, alloc: Allocator, c: u8) !void {
 
 fn execute(self: *Terminal, c: u8) !void {
     switch (@intToEnum(ansi.C0, c)) {
+        .BS => self.backspace(),
         .LF => self.linefeed(),
         .CR => self.carriage_return(),
     }
 }
 
+/// Backspace moves the cursor back a column (but not less than 0).
+pub fn backspace(self: *Terminal) void {
+    self.cursor.x -|= 1;
+}
+
 /// Carriage return moves the cursor to the first column.
 pub fn carriage_return(self: *Terminal) void {
     self.cursor.x = 0;
@@ -151,7 +157,7 @@ test {
     _ = Parser;
 }
 
-test "Terminal: simple input" {
+test "Terminal: input with no control characters" {
     var t = init(80, 80);
     defer t.deinit(testing.allocator);
 
@@ -166,7 +172,7 @@ test "Terminal: simple input" {
     }
 }
 
-test "Terminal: multiline input" {
+test "Terminal: C0 control LF and CR" {
     var t = init(80, 80);
     defer t.deinit(testing.allocator);
 
@@ -180,3 +186,20 @@ test "Terminal: multiline input" {
         try testing.expectEqualStrings("hello\nworld", str);
     }
 }
+
+test "Terminal: C0 control BS" {
+    var t = init(80, 80);
+    defer t.deinit(testing.allocator);
+
+    // BS
+    try t.append(testing.allocator, "hello");
+    try t.appendChar(testing.allocator, @enumToInt(ansi.C0.BS));
+    try t.append(testing.allocator, "y");
+    try testing.expectEqual(@as(usize, 0), t.cursor.y);
+    try testing.expectEqual(@as(usize, 5), t.cursor.x);
+    {
+        var str = try t.plainString(testing.allocator);
+        defer testing.allocator.free(str);
+        try testing.expectEqualStrings("helly", str);
+    }
+}
diff --git a/src/terminal/ansi.zig b/src/terminal/ansi.zig
index 35735562b..a4310b82d 100644
--- a/src/terminal/ansi.zig
+++ b/src/terminal/ansi.zig
@@ -3,6 +3,8 @@
 /// This is not complete, control characters are only added to this
 /// as the terminal emulator handles them.
 pub const C0 = enum(u7) {
+    /// Backspace
+    BS = 0x08,
     /// Line feed
     LF = 0x0A,
     /// Carriage return