From 0100b8b9b531e16442f6084f7ee2cb038b6602bc Mon Sep 17 00:00:00 2001
From: Ayman Bagabas <ayman.bagabas@gmail.com>
Date: Mon, 8 Apr 2024 12:26:57 +0300
Subject: [PATCH] feat(term): ansi: add passthrough sequences

Screen and Tmux passthrough
---
 exp/term/ansi/passthrough.go      | 63 +++++++++++++++++++++++++++++++
 exp/term/ansi/passthrough_test.go | 63 +++++++++++++++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 exp/term/ansi/passthrough.go
 create mode 100644 exp/term/ansi/passthrough_test.go

diff --git a/exp/term/ansi/passthrough.go b/exp/term/ansi/passthrough.go
new file mode 100644
index 00000000..14a74522
--- /dev/null
+++ b/exp/term/ansi/passthrough.go
@@ -0,0 +1,63 @@
+package ansi
+
+import (
+	"bytes"
+)
+
+// ScreenPassthrough wraps the given ANSI sequence in a DCS passthrough
+// sequence to be sent to the outer terminal. This is used to send raw escape
+// sequences to the outer terminal when running inside GNU Screen.
+//
+//	DCS <data> ST
+//
+// Note: Screen limits the length of string sequences to 768 bytes (since 2014).
+// Use zero to indicate no limit, otherwise, this will chunk the returned
+// string into limit sized chunks.
+//
+// See: https://www.gnu.org/software/screen/manual/screen.html#String-Escapes
+// See: https://git.savannah.gnu.org/cgit/screen.git/tree/src/screen.h?id=c184c6ec27683ff1a860c45be5cf520d896fd2ef#n44
+func ScreenPassthrough(seq string, limit int) string {
+	var b bytes.Buffer
+	b.WriteString("\x1bP")
+	if limit > 0 {
+		for i := 0; i < len(seq); i += limit {
+			end := i + limit
+			if end > len(seq) {
+				end = len(seq)
+			}
+			b.WriteString(seq[i:end])
+			if end < len(seq) {
+				b.WriteString("\x1b\\\x1bP")
+			}
+		}
+	} else {
+		b.WriteString(seq)
+	}
+	b.WriteString("\x1b\\")
+	return b.String()
+}
+
+// TmuxPassthrough wraps the given ANSI sequence in a special DCS passthrough
+// sequence to be sent to the outer terminal. This is used to send raw escape
+// sequences to the outer terminal when running inside Tmux.
+//
+//	DCS tmux ; <escaped-data> ST
+//
+// Where <escaped-data> is the given sequence in which all occurrences of ESC
+// (0x1b) are doubled i.e. replaced with ESC ESC (0x1b 0x1b).
+//
+// Note: this needs the `allow-passthrough` option to be set to `on`.
+//
+// See: https://github.com/tmux/tmux/wiki/FAQ#what-is-the-passthrough-escape-sequence-and-how-do-i-use-it
+func TmuxPassthrough(seq string) string {
+	var b bytes.Buffer
+	b.WriteString("\x1bPtmux;")
+	for i := 0; i < len(seq); i++ {
+		if seq[i] == ESC {
+			b.WriteByte(ESC)
+		}
+		b.WriteByte(seq[i])
+	}
+	b.WriteString("\x1b\\")
+	return b.String()
+}
diff --git a/exp/term/ansi/passthrough_test.go b/exp/term/ansi/passthrough_test.go
new file mode 100644
index 00000000..0fc8f1e3
--- /dev/null
+++ b/exp/term/ansi/passthrough_test.go
@@ -0,0 +1,63 @@
+package ansi_test
+
+import (
+	"testing"
+
+	"github.com/charmbracelet/x/exp/term/ansi"
+)
+
+var passthroughCases = []struct {
+	name   string
+	seq    string
+	limit  int
+	screen string
+	tmux   string
+}{
+	{
+		name:   "empty",
+		seq:    "",
+		screen: "\x1bP\x1b\\",
+		tmux:   "\x1bPtmux;\x1b\\",
+	},
+	{
+		name:   "short",
+		seq:    "hello",
+		screen: "\x1bPhello\x1b\\",
+		tmux:   "\x1bPtmux;hello\x1b\\",
+	},
+	{
+		name:   "limit",
+		seq:    "foobarbaz",
+		limit:  3,
+		screen: "\x1bPfoo\x1b\\\x1bPbar\x1b\\\x1bPbaz\x1b\\",
+		tmux:   "\x1bPtmux;foobarbaz\x1b\\",
+	},
+	{
+		name:   "escaped",
+		seq:    "\x1b]52;c;Zm9vYmFy\x07",
+		screen: "\x1bP\x1b]52;c;Zm9vYmFy\x07\x1b\\",
+		tmux:   "\x1bPtmux;\x1b\x1b]52;c;Zm9vYmFy\x07\x1b\\",
+	},
+}
+
+func TestScreenPassthrough(t *testing.T) {
+	for i, tt := range passthroughCases {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ansi.ScreenPassthrough(tt.seq, tt.limit)
+			if got != tt.screen {
+				t.Errorf("case: %d, ScreenPassthrough() = %q, want %q", i+1, got, tt.screen)
+			}
+		})
+	}
+}
+
+func TestTmuxPassthrough(t *testing.T) {
+	for i, tt := range passthroughCases {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ansi.TmuxPassthrough(tt.seq)
+			if got != tt.tmux {
+				t.Errorf("case: %d, TmuxPassthrough() = %q, want %q", i+1, got, tt.tmux)
+			}
+		})
+	}
+}