Initial patterm project

internal/vt/emulator.go

@@ -0,0 +1,62 @@
+// Package vt wraps a headless virtual terminal emulator behind a small
+// Go interface. The intent is that all cgo to libghostty-vt is confined
+// to the GhosttyEmulator implementation in this package.
+package vt
+
+// Screen identifies which buffer is currently displayed.
+type Screen uint8
+
+const (
+	ScreenPrimary Screen = iota
+	ScreenAlternate
+)
+
+// CursorState is a snapshot of cursor position and visibility.
+type CursorState struct {
+	Col, Row uint16
+	Visible  bool
+}
+
+// Emulator is the headless VT used by the daemon (and by the milestone-1 spike).
+//
+// Implementations are not required to be safe for concurrent use. The spike
+// CLI funnels all calls through a single goroutine.
+type Emulator interface {
+	// Write feeds bytes from the PTY master into the emulator. It returns
+	// the number of bytes consumed (always len(p) on success).
+	Write(p []byte) (int, error)
+
+	// Resize updates the emulator's cell grid. The caller is responsible
+	// for issuing TIOCSWINSZ on the PTY itself.
+	Resize(cols, rows uint16) error
+
+	// PlainText returns the active screen rendered as plain text, with
+	// soft-wrapped lines unwrapped and trailing whitespace trimmed.
+	PlainText() (string, error)
+
+	// ScreenText returns the active screen as fixed screen rows. Unlike
+	// PlainText, this preserves row boundaries so a host UI can repaint
+	// into a clipped viewport.
+	ScreenText() (string, error)
+
+	// SerializeVT returns the active screen as a VT byte sequence that, when
+	// written to a fresh terminal, reproduces the visible state (colours,
+	// styles, cursor, hyperlinks, etc.). Used as the daemon's "catch-up
+	// frame" for newly-attached clients.
+	SerializeVT() ([]byte, error)
+
+	// Cursor returns cursor position and visibility on the active screen.
+	Cursor() (CursorState, error)
+
+	// ActiveScreen reports whether we are on the primary or alternate buffer.
+	ActiveScreen() (Screen, error)
+
+	// OnWritePTY registers a callback that fires when the emulator wants
+	// to write bytes back to the PTY master (e.g. responses to DA / DSR
+	// queries). The callback runs synchronously inside Write and must not
+	// recurse into the emulator.
+	OnWritePTY(fn func([]byte))
+
+	// Close releases any underlying resources.
+	Close() error
+}