package display

import (
	"context"
	"fmt"
	"log"
	"os/exec"
	"time"

	"github.com/BurntSushi/xgb"
	"github.com/BurntSushi/xgb/xproto"
)

// X11Opener connects to an X server (selected by DISPLAY in the environment)
// and creates the fullscreen kiosk canvas. It is the display target for the
// Viture screen; future targets such as MIPI/touch provide their own Opener
// and templates.
type X11Opener struct {
	// PollInterval is how often X events are drained while waiting, so that
	// cancellation stays responsive. Zero selects 100 ms.
	PollInterval time.Duration
	// Fullscreen applies the fullscreen/below window state. It defaults to
	// shelling out to wmctrl; tests may replace it. A failure is logged and
	// the canvas degrades to a plain window.
	Fullscreen func(args []string) error
}

func (o X11Opener) applyFullscreen(args []string) error {
	if o.Fullscreen != nil {
		return o.Fullscreen(args)
	}
	return exec.Command("wmctrl", args...).Run()
}

func (o X11Opener) pollInterval() time.Duration {
	if o.PollInterval > 0 {
		return o.PollInterval
	}
	return 100 * time.Millisecond
}

// Open connects to the X server and maps the kiosk window. Failure is
// expected while the display manager is starting; the caller retries.
func (o X11Opener) Open(ctx context.Context) (Session, error) {
	conn, err := xgb.NewConn()
	if err != nil {
		return nil, fmt.Errorf("connect X11: %w", err)
	}

	screen := xproto.Setup(conn).DefaultScreen(conn)
	window, err := xproto.NewWindowId(conn)
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("allocate window: %w", err)
	}

	values := uint32(xproto.CwBackPixel | xproto.CwEventMask)
	xproto.CreateWindow(conn, screen.RootDepth, window, screen.Root,
		0, 0, screen.WidthInPixels, screen.HeightInPixels, 0,
		xproto.WindowClassInputOutput, screen.RootVisual, values,
		[]uint32{screen.BlackPixel, xproto.EventMaskExposure})
	xproto.MapWindow(conn, window)
	// Round trip confirms the window is mapped and the server is alive.
	if err := xproto.GetInputFocus(conn).Check(); err != nil {
		conn.Close()
		return nil, fmt.Errorf("map kiosk window: %w", err)
	}

	// Fullscreen on the root screen, but kept below other windows: pilot
	// video owns the rendering priority whenever it is available. The kiosk
	// never raises itself, so video always stays on top. A missing wmctrl
	// only degrades to a plain window and must not kill the kiosk.
	if err := o.applyFullscreen(x11FullscreenArgs(uint32(window))); err != nil {
		log.Printf("kiosk fullscreen state: %v (canvas stays a plain window)", err)
	}

	gc, err := xproto.NewGcontextId(conn)
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("allocate graphics context: %w", err)
	}
	font, err := xproto.NewFontId(conn)
	if err != nil {
		conn.Close()
		return nil, fmt.Errorf("allocate font: %w", err)
	}
	xproto.OpenFont(conn, font, uint16(len("fixed")), "fixed")
	xproto.CreateGC(conn, gc, xproto.Drawable(window),
		xproto.GcForeground|xproto.GcBackground|xproto.GcFont,
		[]uint32{screen.WhitePixel, screen.BlackPixel, uint32(font)})

	return &x11Session{
		conn:   conn,
		window: window,
		gc:     gc,
		width:  int(screen.WidthInPixels),
		height: int(screen.HeightInPixels),
		black:  screen.BlackPixel,
		white:  screen.WhitePixel,
		poll:   o.pollInterval(),
	}, nil
}

func x11FullscreenArgs(window uint32) []string {
	return []string{"-i", "-r", fmt.Sprintf("0x%08x", window), "-b", "add,fullscreen,below"}
}

// x11Session implements both Session and Canvas for one X11 connection.
type x11Session struct {
	conn   *xgb.Conn
	window xproto.Window
	gc     xproto.Gcontext
	width  int
	height int
	black  uint32
	white  uint32
	poll   time.Duration
}

func (s *x11Session) Canvas() Canvas { return s }

func (s *x11Session) Size() (int, int) { return s.width, s.height }

func (s *x11Session) Clear() {
	// ClearArea tiles the window background (black, set at creation); it
	// involves no graphics context.
	xproto.ClearArea(s.conn, false, s.window, 0, 0,
		uint16(s.width), uint16(s.height))
}

func (s *x11Session) Text(x, y int, message string) {
	if len(message) > 255 {
		message = message[:255]
	}
	xproto.ChangeGC(s.conn, s.gc, xproto.GcForeground, []uint32{s.white})
	xproto.ImageText8(s.conn, byte(len(message)), xproto.Drawable(s.window), s.gc,
		int16(x), int16(y), message)
}

func (s *x11Session) Flush() {
	s.conn.Sync()
}

func (s *x11Session) WaitEvent(ctx context.Context) (bool, error) {
	ticker := time.NewTicker(s.poll)
	defer ticker.Stop()
	for {
		for {
			event, err := s.conn.PollForEvent()
			if err != nil {
				return false, err
			}
			if event == nil {
				break
			}
			if x11WantsRedraw(event) {
				return true, nil
			}
		}
		// Round trip keeps the connection liveness visible even without
		// incoming events.
		if err := xproto.GetInputFocus(s.conn).Check(); err != nil {
			return false, err
		}
		select {
		case <-ctx.Done():
			return false, ctx.Err()
		case <-ticker.C:
		}
	}
}

func x11WantsRedraw(event xgb.Event) bool {
	switch event.(type) {
	case xproto.ExposeEvent:
		return true
	default:
		return false
	}
}

func (s *x11Session) Close() error {
	// Closing the connection makes the X server destroy the kiosk window.
	s.conn.Close()
	return nil
}