From 85dc29bf8ad0aaed9e3f2b0889e73f226fdf25e9 Mon Sep 17 00:00:00 2001
From: stk <stk@ableton.com>
Date: Sat, 11 Mar 2023 18:05:12 +0100
Subject: [PATCH] Implement focus events

---
 _demos/mouse.go | 12 +++++++++++-
 focus.go        | 28 ++++++++++++++++++++++++++++
 tscreen.go      | 45 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+), 1 deletion(-)
 create mode 100644 focus.go

diff --git a/_demos/mouse.go b/_demos/mouse.go
index 394808f..7b41238 100644
--- a/_demos/mouse.go
+++ b/_demos/mouse.go
@@ -135,6 +135,7 @@ func main() {
 	btnfmt := "Buttons: %s"
 	keyfmt := "Keys: %s"
 	pastefmt := "Paste: [%d] %s"
+	focusfmt := "Focus: %s"
 	white := tcell.StyleDefault.
 		Foreground(tcell.ColorMidnightBlue).Background(tcell.ColorLightCoral)
 
@@ -148,9 +149,10 @@ func main() {
 	pstr := ""
 	ecnt := 0
 	pasting := false
+	focus := true // assume we are focused when we start
 
 	for {
-		drawBox(s, 1, 1, 42, 7, white, ' ')
+		drawBox(s, 1, 1, 42, 8, white, ' ')
 		emitStr(s, 2, 2, white, "Press ESC twice to exit, C to clear.")
 		emitStr(s, 2, 3, white, fmt.Sprintf(posfmt, mx, my))
 		emitStr(s, 2, 4, white, fmt.Sprintf(btnfmt, bstr))
@@ -162,6 +164,12 @@ func main() {
 		}
 		emitStr(s, 2, 6, white, fmt.Sprintf(pastefmt, len(pstr), ps))
 
+		fstr := "false"
+		if focus {
+			fstr = "true"
+		}
+		emitStr(s, 2, 7, white, fmt.Sprintf(focusfmt, fstr))
+
 		s.Show()
 		bstr = ""
 		ev := s.PollEvent()
@@ -315,6 +323,8 @@ func main() {
 			lchar = ch
 			s.SetContent(w-1, h-1, 'M', nil, st)
 			mx, my = x, y
+		case *tcell.EventFocus:
+			focus = ev.Focused
 		default:
 			s.SetContent(w-1, h-1, 'X', nil, st)
 		}
diff --git a/focus.go b/focus.go
new file mode 100644
index 0000000..e9b93ef
--- /dev/null
+++ b/focus.go
@@ -0,0 +1,28 @@
+// Copyright 2023 The TCell Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use file except in compliance with the License.
+// You may obtain a copy of the license at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcell
+
+// EventFocus is a focus event. It is sent when the terminal window (or tab)
+// gets or loses focus.
+type EventFocus struct {
+	*EventTime
+
+	// True if the window received focus, false if it lost focus
+	Focused bool
+}
+
+func NewEventFocus(focused bool) *EventFocus {
+	return &EventFocus{Focused: focused}
+}
diff --git a/tscreen.go b/tscreen.go
index 8fc8866..78f3975 100644
--- a/tscreen.go
+++ b/tscreen.go
@@ -1043,6 +1043,14 @@ func (t *tScreen) enablePasting(on bool) {
 	}
 }
 
+func (t *tScreen) enableFocusReporting() {
+	t.TPuts("\x1b[?1004h")
+}
+
+func (t *tScreen) disableFocusReporting() {
+	t.TPuts("\x1b[?1004l")
+}
+
 func (t *tScreen) Size() (int, int) {
 	t.Lock()
 	w, h := t.w, t.h
@@ -1382,6 +1390,35 @@ func (t *tScreen) parseSgrMouse(buf *bytes.Buffer, evs *[]Event) (bool, bool) {
 	return true, false
 }
 
+func (t *tScreen) parseFocus(buf *bytes.Buffer, evs *[]Event) (bool, bool) {
+	state := 0
+	b := buf.Bytes()
+	for i := range b {
+		switch state {
+		case 0:
+			if b[i] != '\x1b' {
+				return false, false
+			}
+			state = 1
+		case 1:
+			if b[i] != '[' {
+				return false, false
+			}
+			state = 2
+		case 2:
+			if b[i] != 'I' && b[i] != 'O' {
+				return false, false
+			}
+			*evs = append(*evs, NewEventFocus(b[i] == 'I'))
+			_, _ = buf.ReadByte()
+			_, _ = buf.ReadByte()
+			_, _ = buf.ReadByte()
+			return true, true
+		}
+	}
+	return true, false
+}
+
 // parseXtermMouse is like parseSgrMouse, but it parses a legacy
 // X11 mouse record.
 func (t *tScreen) parseXtermMouse(buf *bytes.Buffer, evs *[]Event) (bool, bool) {
@@ -1558,6 +1595,12 @@ func (t *tScreen) collectEventsFromInput(buf *bytes.Buffer, expire bool) []Event
 			partials++
 		}
 
+		if part, comp := t.parseFocus(buf, &res); comp {
+			continue
+		} else if part {
+			partials++
+		}
+
 		// Only parse mouse records if this term claims to have
 		// mouse support
 
@@ -1806,6 +1849,7 @@ func (t *tScreen) engage() error {
 	t.stopQ = stopQ
 	t.enableMouse(t.mouseFlags)
 	t.enablePasting(t.pasteEnabled)
+	t.enableFocusReporting()
 
 	ti := t.ti
 	t.TPuts(ti.EnterCA)
@@ -1855,6 +1899,7 @@ func (t *tScreen) disengage() {
 	t.TPuts(ti.ExitKeypad)
 	t.enableMouse(0)
 	t.enablePasting(false)
+	t.disableFocusReporting()
 
 	_ = t.tty.Stop()
 }