package evidence

import (
	"context"
	"time"
)

// pollLoop samples the active window via read and forwards snapshots through
// onChange, but only when the observation changes — a different window OR a
// different title. The title case is the one that matters: switching a browser
// tab changes the window title without changing the active window, so a sensor
// that re-reads only on active-window events never sees it and credits the stale
// title. Polling re-reads on a fixed cadence, so a tab switch is caught within
// one interval.
//
// It emits once immediately, then samples every interval, until ctx is
// cancelled. WindowSnapshot is comparable, so the change check is a plain
// equality. Factoring the loop here keeps the change-dedup identical across
// sensors and lets it be tested without a display. (The Windows sensor predates
// this and keeps its own equivalent loop.)
func pollLoop(ctx context.Context, interval time.Duration, read func() WindowSnapshot, onChange func(WindowSnapshot)) {
	var last WindowSnapshot
	var haveLast bool
	emit := func() {
		s := read()
		if haveLast && s == last {
			return
		}
		last, haveLast = s, true
		onChange(s)
	}

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