//go:build linux

package evidence

import (
	"context"
	"time"

	"github.com/jezek/xgbutil"
	"github.com/jezek/xgbutil/ewmh"
	"github.com/jezek/xgbutil/icccm"
)

// pollInterval is how often the X11 sensor samples the active window. ~1s
// latency on a switch is immaterial for a focus tracker, and polling is what
// catches a title change inside the same window — e.g. switching a browser tab,
// which changes the title but not the active window, so an _NET_ACTIVE_WINDOW
// event subscription would miss it and credit the stale title. Mirrors the
// Windows sensor's polling cadence.
const pollInterval = 750 * time.Millisecond

// NewSource returns the real X11 active-window sensor.
func NewSource() Source { return &x11Source{} }

type x11Source struct{}

// Watch opens one long-lived X connection and samples the active window every
// pollInterval, emitting a snapshot whenever the active window OR its title
// changes. Any failure degrades to an Unavailable snapshot; it never panics the
// daemon.
func (s *x11Source) Watch(ctx context.Context, onChange func(WindowSnapshot)) {
	X, err := xgbutil.NewConn()
	if err != nil {
		onChange(unavailable("cannot connect to X server: " + err.Error()))
		<-ctx.Done()
		return
	}
	defer X.Conn().Close()

	pollLoop(ctx, pollInterval, func() WindowSnapshot { return snapshot(X) }, onChange)
}

// snapshot reads the current active window's title and class. A missing active
// window (or read error) yields an Unavailable snapshot.
func snapshot(X *xgbutil.XUtil) WindowSnapshot {
	active, err := ewmh.ActiveWindowGet(X)
	if err != nil || active == 0 {
		return unavailable("no active window")
	}
	title, err := ewmh.WmNameGet(X, active)
	if err != nil || title == "" {
		// Fall back to ICCCM WM_NAME.
		if t, e := icccm.WmNameGet(X, active); e == nil {
			title = t
		}
	}
	var class string
	if wmClass, err := icccm.WmClassGet(X, active); err == nil && wmClass != nil {
		class = wmClass.Class
	}
	return WindowSnapshot{
		Title:  title,
		Class:  class,
		Health: EvidenceHealth{Available: true},
	}
}