refactor: windows: clean up, tidy and improve windows key handling (#…

…1163)

This fixes a bunch of issues on Windows bringing improvements and
reliability to the implementation. It replaces the existing key events
hack with a key state that keeps track of previous key events to parse
the incoming ANSI escape sequences. It also decodes unicode utf16 pairs
at the parser level instead of the driver level.

Related: #1126

TODO:
- [x] Windows API tests
  - [x] Key events
  - [x] Mouse events
  - [x] Resize events
  - [x] Focus events

driver.go

@@ -8,6 +8,23 @@ import (
 	"github.com/muesli/cancelreader"
 )
 
+// win32InputState is a state machine for parsing key events from the Windows
+// Console API into escape sequences and utf8 runes, and keeps track of the last
+// control key state to determine modifier key changes. It also keeps track of
+// the last mouse button state and window size changes to determine which mouse
+// buttons were released and to prevent multiple size events from firing.
+//
+//nolint:unused
+type win32InputState struct {
+	ansiBuf                    [256]byte
+	ansiIdx                    int
+	utf16Buf                   [2]rune
+	utf16Half                  bool
+	lastCks                    uint32 // the last control key state for the previous event
+	lastMouseBtns              uint32 // the last mouse button state for the previous event
+	lastWinsizeX, lastWinsizeY int16  // the last window size for the previous event to prevent multiple size events from firing
+}
+
 // driver represents an ANSI terminal input driver.
 // It reads input events and parses ANSI sequences from the terminal input
 // buffer.
@@ -23,13 +40,9 @@ type driver struct {
 
 	buf [256]byte // do we need a larger buffer?
 
-	// prevMouseState keeps track of the previous mouse state to determine mouse
-	// up button events.
-	prevMouseState uint32 // nolint: unused
-
-	// lastWinsizeEvent keeps track of the last window size event to prevent
-	// multiple size events from firing.
-	lastWinsizeEventX, lastWinsizeEventY int16 // nolint: unused
+	// keyState keeps track of the current Windows Console API key events state.
+	// It is used to decode ANSI escape sequences and utf16 sequences.
+	keyState win32InputState //nolint:unused
 
 	flags int // control the behavior of the driver.
 }

driver_other.go

@@ -9,3 +9,9 @@ package tea
 func (d *driver) ReadEvents() ([]Msg, error) {
 	return d.readEvents()
 }
+
+// parseWin32InputKeyEvent parses a Win32 input key events. This function is
+// only available on Windows.
+func parseWin32InputKeyEvent(*win32InputState, uint16, uint16, rune, bool, uint32, uint16) Msg {
+	return nil
+}