From cbded6a95af970ce5159ea4850ce6388328c51c2 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sun, 25 Jun 2023 09:49:18 -0700
Subject: [PATCH 1/2] terminal: horizontalTabBack function

---
 src/terminal/Terminal.zig | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/src/terminal/Terminal.zig b/src/terminal/Terminal.zig
index 0f0fef511..bcc909714 100644
--- a/src/terminal/Terminal.zig
+++ b/src/terminal/Terminal.zig
@@ -1218,6 +1218,21 @@ pub fn horizontalTab(self: *Terminal) !void {
     }
 }
 
+// Same as horizontalTab but moves to the previous tabstop instead of the next.
+pub fn horizontalTabBack(self: *Terminal) !void {
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    while (true) {
+        // If we're already at the edge of the screen, then we're done.
+        if (self.screen.cursor.x == 0) return;
+
+        // Move the cursor left
+        self.screen.cursor.x -= 1;
+        if (self.tabstops.get(self.screen.cursor.x)) return;
+    }
+}
+
 /// Clear tab stops.
 /// TODO: test
 pub fn tabClear(self: *Terminal, cmd: csi.TabClear) void {
@@ -1798,6 +1813,29 @@ test "Terminal: horizontal tabs" {
     try testing.expectEqual(@as(usize, 19), t.screen.cursor.x);
 }
 
+test "Terminal: horizontal tabs back" {
+    const alloc = testing.allocator;
+    var t = try init(alloc, 20, 5);
+    defer t.deinit(alloc);
+
+    // Edge of screen
+    t.screen.cursor.x = 19;
+
+    // HT
+    try t.horizontalTabBack();
+    try testing.expectEqual(@as(usize, 15), t.screen.cursor.x);
+
+    // HT
+    try t.horizontalTabBack();
+    try testing.expectEqual(@as(usize, 7), t.screen.cursor.x);
+
+    // HT
+    try t.horizontalTabBack();
+    try testing.expectEqual(@as(usize, 0), t.screen.cursor.x);
+    try t.horizontalTabBack();
+    try testing.expectEqual(@as(usize, 0), t.screen.cursor.x);
+}
+
 test "Terminal: setCursorPosition" {
     var t = try init(testing.allocator, 80, 80);
     defer t.deinit(testing.allocator);

From 03fd649b5e21d0299146db47470972a5130e7da6 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Sun, 25 Jun 2023 09:53:58 -0700
Subject: [PATCH 2/2] terminal: CHT/CBT

---
 src/terminal/stream.zig | 26 +++++++++++++++++++++++++-
 src/termio/Exec.zig     | 16 ++++++++++++++--
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/terminal/stream.zig b/src/terminal/stream.zig
index e78b3f457..3b6b9b06b 100644
--- a/src/terminal/stream.zig
+++ b/src/terminal/stream.zig
@@ -92,7 +92,7 @@ pub fn Stream(comptime Handler: type) type {
                     log.warn("unimplemented execute: {x}", .{c}),
 
                 .HT => if (@hasDecl(T, "horizontalTab"))
-                    try self.handler.horizontalTab()
+                    try self.handler.horizontalTab(1)
                 else
                     log.warn("unimplemented execute: {x}", .{c}),
 
@@ -205,6 +205,18 @@ pub fn Stream(comptime Handler: type) type {
                     else => log.warn("invalid CUP command: {}", .{action}),
                 } else log.warn("unimplemented CSI callback: {}", .{action}),
 
+                // CHT - Cursor Horizontal Tabulation
+                'I' => if (@hasDecl(T, "horizontalTab")) try self.handler.horizontalTab(
+                    switch (action.params.len) {
+                        0 => 1,
+                        1 => action.params[0],
+                        else => {
+                            log.warn("invalid horizontal tab command: {}", .{action});
+                            return;
+                        },
+                    },
+                ) else log.warn("unimplemented CSI callback: {}", .{action}),
+
                 // Erase Display
                 // TODO: test
                 'J' => if (@hasDecl(T, "eraseDisplay")) try self.handler.eraseDisplay(
@@ -316,6 +328,18 @@ pub fn Stream(comptime Handler: type) type {
                     },
                 ) else log.warn("unimplemented CSI callback: {}", .{action}),
 
+                // CHT - Cursor Horizontal Tabulation Back
+                'Z' => if (@hasDecl(T, "horizontalTabBack")) try self.handler.horizontalTabBack(
+                    switch (action.params.len) {
+                        0 => 1,
+                        1 => action.params[0],
+                        else => {
+                            log.warn("invalid horizontal tab back command: {}", .{action});
+                            return;
+                        },
+                    },
+                ) else log.warn("unimplemented CSI callback: {}", .{action}),
+
                 // Repeat Previous Char (REP)
                 'b' => if (@hasDecl(T, "printRepeat")) try self.handler.printRepeat(
                     switch (action.params.len) {
diff --git a/src/termio/Exec.zig b/src/termio/Exec.zig
index 1345d8f0d..75491dc6f 100644
--- a/src/termio/Exec.zig
+++ b/src/termio/Exec.zig
@@ -959,8 +959,20 @@ const StreamHandler = struct {
         self.terminal.backspace();
     }
 
-    pub fn horizontalTab(self: *StreamHandler) !void {
-        try self.terminal.horizontalTab();
+    pub fn horizontalTab(self: *StreamHandler, count: u16) !void {
+        for (0..count) |_| {
+            const x = self.terminal.screen.cursor.x;
+            try self.terminal.horizontalTab();
+            if (x == self.terminal.screen.cursor.x) break;
+        }
+    }
+
+    pub fn horizontalTabBack(self: *StreamHandler, count: u16) !void {
+        for (0..count) |_| {
+            const x = self.terminal.screen.cursor.x;
+            try self.terminal.horizontalTabBack();
+            if (x == self.terminal.screen.cursor.x) break;
+        }
     }
 
     pub fn linefeed(self: *StreamHandler) !void {