From d75ec2013df66acc106a4b924e6e3e1a11b0ef43 Mon Sep 17 00:00:00 2001
From: Charlie Groves <c@sevorg.org>
Date: Fri, 22 Jul 2022 17:00:41 -0400
Subject: [PATCH] Emit focus events

---
 examples/event-read.rs      | 11 ++++++----
 src/event.rs                | 44 +++++++++++++++++++++++++++++++++++++
 src/event/source/windows.rs |  4 ++++
 src/event/sys/unix/parse.rs | 10 +++++++++
 4 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/examples/event-read.rs b/examples/event-read.rs
index 7de5f42ca..6162141b9 100644
--- a/examples/event-read.rs
+++ b/examples/event-read.rs
@@ -7,7 +7,10 @@ use std::io::stdout;
 use crossterm::event::poll;
 use crossterm::{
     cursor::position,
-    event::{read, DisableMouseCapture, EnableMouseCapture, Event, KeyCode},
+    event::{
+        read, DisableFocusChange, DisableMouseCapture, EnableFocusChange, EnableMouseCapture,
+        Event, KeyCode
+    },
     execute,
     terminal::{disable_raw_mode, enable_raw_mode},
     Result,
@@ -15,7 +18,7 @@ use crossterm::{
 use std::time::Duration;
 
 const HELP: &str = r#"Blocking read()
- - Keyboard, mouse and terminal resize events enabled
+ - Keyboard, mouse, focus and terminal resize events enabled
  - Hit "c" to print current cursor position
  - Use Esc to quit
 "#;
@@ -67,13 +70,13 @@ fn main() -> Result<()> {
     enable_raw_mode()?;
 
     let mut stdout = stdout();
-    execute!(stdout, EnableMouseCapture)?;
+    execute!(stdout, EnableFocusChange, EnableMouseCapture)?;
 
     if let Err(e) = print_events() {
         println!("Error: {:?}\r", e);
     }
 
-    execute!(stdout, DisableMouseCapture)?;
+    execute!(stdout, DisableFocusChange, DisableMouseCapture)?;
 
     disable_raw_mode()
 }
diff --git a/src/event.rs b/src/event.rs
index accc19c1d..d3b30a9a7 100644
--- a/src/event.rs
+++ b/src/event.rs
@@ -34,6 +34,8 @@
 //!     loop {
 //!         // `read()` blocks until an `Event` is available
 //!         match read()? {
+//!             Event::FocusGained => println!("FocusGained"),
+//!             Event::FocusLost => println!("FocusLost"),
 //!             Event::Key(event) => println!("{:?}", event),
 //!             Event::Mouse(event) => println!("{:?}", event),
 //!             Event::Resize(width, height) => println!("New size {}x{}", width, height),
@@ -57,6 +59,8 @@
 //!             // It's guaranteed that the `read()` won't block when the `poll()`
 //!             // function returns `true`
 //!             match read()? {
+//!                 Event::FocusGained => println!("FocusGained"),
+//!                 Event::FocusLost => println!("FocusLost"),
 //!                 Event::Key(event) => println!("{:?}", event),
 //!                 Event::Mouse(event) => println!("{:?}", event),
 //!                 Event::Resize(width, height) => println!("New size {}x{}", width, height),
@@ -409,10 +413,50 @@ impl Command for PopKeyboardEnhancementFlags {
     }
 }
 
+/// A command that enables focus event emission.
+///
+/// Focus events can be captured with [read](./fn.read.html)/[poll](./fn.poll.html).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct EnableFocusChange;
+
+impl Command for EnableFocusChange {
+    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
+        f.write_str(csi!("?1004h"))
+    }
+
+    #[cfg(windows)]
+    fn execute_winapi(&self) -> Result<()> {
+        // Focus events are always enabled on Windows
+        Ok(())
+    }
+}
+
+/// A command that disables focus event emission.
+///
+/// Focus events can be captured with [read](./fn.read.html)/[poll](./fn.poll.html).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct DisableFocusChange;
+
+impl Command for DisableFocusChange {
+    fn write_ansi(&self, f: &mut impl fmt::Write) -> fmt::Result {
+        f.write_str(csi!("?1004l"))
+    }
+
+    #[cfg(windows)]
+    fn execute_winapi(&self) -> Result<()> {
+        // Focus events can't be disabled on Windows
+        Ok(())
+    }
+}
+
 /// Represents an event.
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[derive(Debug, PartialOrd, PartialEq, Eq, Clone, Copy, Hash)]
 pub enum Event {
+    /// The terminal gained focus
+    FocusGained,
+    /// The terminal lost focus
+    FocusLost,
     /// A single key event with additional pressed modifiers.
     Key(KeyEvent),
     /// A single mouse event with additional pressed modifiers.
diff --git a/src/event/source/windows.rs b/src/event/source/windows.rs
index 669272d48..fa4bdca62 100644
--- a/src/event/source/windows.rs
+++ b/src/event/source/windows.rs
@@ -66,6 +66,10 @@ impl EventSource for WindowsEventSource {
                         InputRecord::WindowBufferSizeEvent(record) => {
                             Some(Event::Resize(record.size.x as u16, record.size.y as u16))
                         }
+                        InputRecord::FocusEvent(record) => {
+                            let event = if record.set_focus { Event::FocusGained } else { Event::FocusLost };
+                            Some(event)
+                        }
                         _ => None,
                     };
 
diff --git a/src/event/sys/unix/parse.rs b/src/event/sys/unix/parse.rs
index 4e127cac8..89cfeb537 100644
--- a/src/event/sys/unix/parse.rs
+++ b/src/event/sys/unix/parse.rs
@@ -167,6 +167,8 @@ pub(crate) fn parse_csi(buffer: &[u8]) -> Result<Option<InternalEvent>> {
         })),
         b'M' => return parse_csi_normal_mouse(buffer),
         b'<' => return parse_csi_sgr_mouse(buffer),
+        b'I' => Some(Event::FocusGained),
+        b'O' => Some(Event::FocusLost),
         b'0'..=b'9' => {
             // Numbered escape code.
             if buffer.len() == 3 {
@@ -745,6 +747,14 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_parse_csi_focus() {
+        assert_eq!(
+            parse_csi(b"\x1B[O").unwrap(),
+            Some(InternalEvent::Event(Event::FocusLost))
+        );
+    }
+
     #[test]
     fn test_parse_csi_rxvt_mouse() {
         assert_eq!(