You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: stacks.go
    path of file: ./repos/dry/appui/swarm
    
    the code of the file until where you have to start completion: package swarm

import (
	"sort"
	"strconv"
	"strings"
	"sync"

	"github.com/moncho/dry/appui"
	"github.com/moncho/dry/docker"
	"github.com/moncho/dry/ui/termui"

	gizaktermui "github.com/gizak/termui"
)

var defaultStackTableHeader = stackTableHeader()

var stackTableHeaders = []appui.SortableColumnHeader{
	{Title: "NAME", Mode: appui.SortMode(docker.SortByStackName)},
	{Title: "SERVICES", Mode: appui.SortMode(docker.NoSortStack)},
	{Title: "ORCHESTRATOR", Mode: appui.SortMode(docker.NoSortStack)},
	{Title: "NETWORKS", Mode: appui.SortMode(docker.NoSortStack)},
	{Title: "CONFIGS", Mode: appui.SortMode(docker.NoSortStack)},
	{Title: "SECRETS", Mode: appui.SortMode(docker.NoSortStack)},
}

// StacksWidget shows information about services running on the Swarm
type StacksWidget struct {
	swarmClient          docker.SwarmAPI
    
func (s *StacksWidget) Buffer() gizaktermui.Buffer {
	s.Lock()
	defer s.Unlock()

	buf := gizaktermui.NewBuffer()
	if !s.mounted {
		return buf
	}
	y := s.screen.Bounds().Min.Y

	s.prepareForRendering()
	widgetHeader := appui.NewWidgetHeader()
	widgetHeader.HeaderEntry("Stacks", strconv.Itoa(s.RowCount()))
	if s.filterPattern != "" {
		widgetHeader.HeaderEntry("Active filter", s.filterPattern)
	}
	widgetHeader.Y = y
	buf.Merge(widgetHeader.Buffer())
	y += widgetHeader.GetHeight()
	//Empty line between the header and the rest of the content
	y++
	s.updateHeader()
	s.header.SetY(y)
	buf.Merge(s.header.Buffer())
	y += s.header.GetHeight()

	selected := s.selectedIndex - s.startIndex

	for i, stackRow := range s.visibleRows() {
		stackRow.SetY(y)
		y += stackRow.GetHeight()
		if i != selected {
			stackRow.NotHighlighted()
		} else {
			stackRow.Highlighted()
		}
		buf.Merge(stackRow.Buffer())
	}
	return buf
}