From 0daf8c2849844ac66bcea8349b9c733f98feff1e Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Tue, 2 Jun 2026 12:30:16 -0400
Subject: [PATCH] Add Windows polling active-window sensor

---
 internal/evidence/source_other.go |  2 +-
 internal/evidence/windows.go      | 51 +++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)
 create mode 100644 internal/evidence/windows.go

diff --git a/internal/evidence/source_other.go b/internal/evidence/source_other.go
index d9edd74..5cec967 100644
--- a/internal/evidence/source_other.go
+++ b/internal/evidence/source_other.go
@@ -1,4 +1,4 @@
-//go:build !linux
+//go:build !linux && !windows
 
 package evidence
 
diff --git a/internal/evidence/windows.go b/internal/evidence/windows.go
new file mode 100644
index 0000000..79aae4f
--- /dev/null
+++ b/internal/evidence/windows.go
@@ -0,0 +1,51 @@
+//go:build windows
+
+package evidence
+
+import (
+	"context"
+	"time"
+
+	"antidrift/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(WindowSnapshot{Health: EvidenceHealth{Available: false, Reason: "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()
+		}
+	}
+}