antidrift/internal/evidence/windows.go

//go:build windows

package evidence

import (
	"context"
	"time"

	"keel/internal/winapi"
)

// pollInterval is how often the Windows sensor samples the foreground window.
// ~1s latency on a window switch is immaterial for a focus tracker, and polling
// avoids the message-loop/callback machinery a SetWinEventHook source needs.
const pollInterval = 750 * time.Millisecond

// NewSource returns the Windows active-window sensor (polling).
func NewSource() Source { return windowsSource{} }

type windowsSource struct{}

// Watch emits the current window immediately, then samples every pollInterval,
// emitting only when the foreground window or its title changes. A read with no
// foreground window yields an Unavailable snapshot (once, until it recovers). It
// runs until ctx is cancelled. It never panics the daemon.
func (windowsSource) Watch(ctx context.Context, onChange func(WindowSnapshot)) {
	var tr foregroundTracker
	poll := func() {
		hwnd, title, class, ok := winapi.ForegroundWindow()
		if !tr.changed(ok, hwnd, title) {
			return
		}
		if !ok {
			onChange(unavailable("no foreground window"))
			return
		}
		onChange(WindowSnapshot{Title: title, Class: class, Health: EvidenceHealth{Available: true}})
	}

	poll() // immediate current window
	ticker := time.NewTicker(pollInterval)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			poll()
		}
	}
}