yvbolt/main.go

package main

import (
	"errors"
	"fmt"
	"runtime"
	"runtime/debug"
	"strings"
	"unsafe"

	"github.com/pkg/browser"
	"github.com/ying32/govcl/vcl"
	"github.com/ying32/govcl/vcl/types"
	"github.com/ying32/govcl/vcl/types/colors"
)

const (
	APPNAME      = "yvbolt"
	HOMEPAGE_URL = "https://code.ivysaur.me/yvbolt"
)

type TMainForm struct {
	*vcl.TForm

	ImageList *vcl.TImageList
	Menu      *vcl.TMainMenu

	SQLiteUseCliDriver *vcl.TMenuItem

	StatusBar     *vcl.TStatusBar
	Buckets       *vcl.TTreeView
	Tabs          *vcl.TPageControl
	propertiesBox *vcl.TMemo
	contentBox    *vcl.TStringGrid
	insertRows    []int32 // Rows in the StringGrid that are to-be-inserted
	queryInput    *vcl.TMemo
	queryResult   *vcl.TStringGrid

	none *noLoadedDatabase
	dbs  []loadedDatabase
}

var (
	mainForm *TMainForm
)

func main() {
	vcl.RunApp(&mainForm)
}

func (f *TMainForm) OnFormCreate(sender vcl.IObject) {
	f.ImageList = loadImages(f)

	f.SetCaption(APPNAME)
	f.ScreenCenter()
	f.SetWidth(1280)
	f.SetHeight(640)
	f.ImageList.GetIcon(imgDatabaseLightning, f.Icon())

	mnuFile := vcl.NewMenuItem(f)
	mnuFile.SetCaption("File")

	//

	mnuFileBadger := vcl.NewMenuItem(mnuFile)
	mnuFileBadger.SetCaption("Badger")
	mnuFileBadger.SetImageIndex(imgVendorDgraph)
	mnuFile.Add(mnuFileBadger)

	vcl_menuitem(mnuFileBadger, "Open database...", imgDatabaseAdd, f.OnMnuFileBadgerOpenClick)
	vcl_menuitem(mnuFileBadger, "New in-memory database", imgDatabaseAdd, f.OnMnuFileBadgerMemoryClick)

	//

	mnuFileBolt := vcl.NewMenuItem(mnuFile)
	mnuFileBolt.SetCaption("Bolt")
	mnuFileBolt.SetImageIndex(imgVendorGithub)
	mnuFile.Add(mnuFileBolt)

	vcl_menuitem(mnuFileBolt, "New database...", imgDatabaseAdd, f.OnMnuFileBoltNewClick)
	vcl_menuitem(mnuFileBolt, "Open database...", imgDatabaseAdd, f.OnMnuFileBoltOpenClick)
	vcl_menuitem(mnuFileBolt, "Open database (read-only)...", imgDatabaseAdd, f.OnMnuFileBoltOpenReadonlyClick)

	//

	mnuFileDebconf := vcl.NewMenuItem(mnuFile)
	mnuFileDebconf.SetCaption("Debconf")
	mnuFileDebconf.SetImageIndex(imgVendorDebian)
	mnuFile.Add(mnuFileDebconf)

	vcl_menuitem(mnuFileDebconf, "Open database...", imgDatabaseAdd, f.OnMnuFileDebianOpenClick)

	//

	mnuFilePebble := vcl.NewMenuItem(mnuFile)
	mnuFilePebble.SetCaption("Pebble")
	mnuFilePebble.SetImageIndex(imgVendorCockroach)
	mnuFile.Add(mnuFilePebble)

	vcl_menuitem(mnuFilePebble, "Open database...", imgDatabaseAdd, f.OnMnuFilePebbleOpenClick)
	vcl_menuitem(mnuFilePebble, "New in-memory database", imgDatabaseAdd, f.OnMnuFilePebbleMemoryClick)

	//

	mnuFileRedis := vcl.NewMenuItem(mnuFile)
	mnuFileRedis.SetCaption("Redis")
	mnuFileRedis.SetImageIndex(imgVendorRedis)
	mnuFile.Add(mnuFileRedis)

	vcl_menuitem(mnuFileRedis, "Connect...", imgDatabaseAdd, f.OnMnuFileRedisConnectClick)

	//

	mnuFileSqlite := vcl.NewMenuItem(mnuFile)
	mnuFileSqlite.SetCaption("SQLite")
	mnuFileSqlite.SetImageIndex(imgVendorSqlite)
	mnuFile.Add(mnuFileSqlite)

	vcl_menuitem(mnuFileSqlite, "Open database...", imgDatabaseAdd, f.OnMnuFileSqliteOpenClick)
	vcl_menuitem(mnuFileSqlite, "New in-memory database", imgDatabaseAdd, f.OnMnuFileSqliteMemoryClick)

	vcl_menuseparator(mnuFileSqlite)
	f.SQLiteUseCliDriver = vcl_menuitem(mnuFileSqlite, "Connect using CLI driver (experimental)", -1, nil)
	f.SQLiteUseCliDriver.SetAutoCheck(true)

	//

	vcl_menuseparator(mnuFile)

	mnuFileExit := vcl.NewMenuItem(mnuFile)
	mnuFileExit.SetCaption("Exit")
	mnuFileExit.SetOnClick(f.OnMnuFileExitClick)
	mnuFile.Add(mnuFileExit)

	mnuQuery := vcl.NewMenuItem(f)
	mnuQuery.SetCaption("Query")

	mnuQueryExecute := vcl.NewMenuItem(mnuQuery)
	mnuQueryExecute.SetCaption("Execute")
	mnuQueryExecute.SetShortCutFromString("F5")
	mnuQueryExecute.SetOnClick(f.OnQueryExecute)
	mnuQueryExecute.SetImageIndex(imgLightning)
	mnuQuery.Add(mnuQueryExecute)

	mnuHelp := vcl.NewMenuItem(f)
	mnuHelp.SetCaption("Help")

	mnuHelpVersion := vcl.NewMenuItem(mnuHelp)
	mnuHelpVersion.SetCaption("Driver versions...")
	mnuHelpVersion.SetOnClick(f.OnMenuHelpVersion)
	mnuHelp.Add(mnuHelpVersion)

	mnuHelpHomepage := vcl.NewMenuItem(mnuHelp)
	mnuHelpHomepage.SetCaption("About " + APPNAME)
	mnuHelpHomepage.SetShortCutFromString("F1")
	mnuHelpHomepage.SetOnClick(f.OnMnuHelpHomepage)
	mnuHelp.Add(mnuHelpHomepage)

	f.Menu = vcl.NewMainMenu(f)
	f.Menu.SetImages(f.ImageList)
	f.Menu.Items().Add(mnuFile)
	f.Menu.Items().Add(mnuQuery)
	f.Menu.Items().Add(mnuHelp)

	//

	f.StatusBar = vcl.NewStatusBar(f)
	f.StatusBar.SetParent(f)
	f.StatusBar.SetSimpleText("")

	//

	f.Buckets = vcl.NewTreeView(f)
	f.Buckets.SetParent(f)
	f.Buckets.SetImages(f.ImageList)
	f.Buckets.SetAlign(types.AlLeft)
	f.Buckets.SetWidth(MY_WIDTH)
	f.Buckets.SetReadOnly(true) // prevent click to rename on nodes
	f.Buckets.SetOnExpanding(f.OnNavExpanding)
	f.Buckets.SetOnChange(f.OnNavChange)
	f.Buckets.SetOnContextPopup(f.OnNavContextPopup)

	hsplit := vcl.NewSplitter(f)
	hsplit.SetParent(f)
	hsplit.SetAlign(types.AlLeft)
	hsplit.SetLeft(1) // Just needs to be further "over" than f.Buckets for auto-alignment

	f.Tabs = vcl.NewPageControl(f)
	f.Tabs.SetParent(f)
	f.Tabs.SetAlign(types.AlClient) // fill remaining space
	f.Tabs.SetImages(f.ImageList)

	propertiesTab := vcl.NewTabSheet(f.Tabs)
	propertiesTab.SetParent(f.Tabs)
	propertiesTab.SetCaption("Properties")
	propertiesTab.SetImageIndex(imgChartBar)

	f.propertiesBox = vcl.NewMemo(propertiesTab)
	f.propertiesBox.SetParent(propertiesTab)
	f.propertiesBox.BorderSpacing().SetAround(MY_SPACING)
	f.propertiesBox.SetAlign(types.AlClient) // fill remaining space
	f.propertiesBox.SetReadOnly(true)
	f.propertiesBox.SetEnabled(true) // Need to leave it enabled so scrolling works
	f.propertiesBox.SetColor(vcl_default_tab_background())

	f.propertiesBox.SetBorderStyle(types.BsNone)
	f.propertiesBox.SetScrollBars(types.SsAutoVertical)

	dataTab := vcl.NewTabSheet(f.Tabs)
	dataTab.SetParent(f.Tabs)
	dataTab.SetCaption("Data")
	dataTab.SetImageIndex(imgTable)

	dataButtonBar := vcl.NewToolBar(dataTab)
	dataButtonBar.SetParent(dataTab)
	dataButtonBar.SetAlign(types.AlTop)
	dataButtonBar.BorderSpacing().SetLeft(MY_SPACING)
	dataButtonBar.BorderSpacing().SetTop(MY_SPACING)
	dataButtonBar.BorderSpacing().SetBottom(1)
	dataButtonBar.BorderSpacing().SetRight(MY_SPACING)
	dataButtonBar.SetEdgeBorders(0)
	dataButtonBar.SetImages(f.ImageList)
	dataButtonBar.SetShowCaptions(true)

	dataRefreshBtn := vcl.NewToolButton(dataButtonBar)
	dataRefreshBtn.SetParent(dataButtonBar)
	dataRefreshBtn.SetCaption("Refresh")
	// dataRefreshBtn.SetImageIndex(imgLightning)
	dataRefreshBtn.SetOnClick(func(sender vcl.IObject) { f.RefreshCurrentItem() })

	dataInsertBtn := vcl.NewToolButton(dataButtonBar)
	dataInsertBtn.SetParent(dataButtonBar)
	dataInsertBtn.SetCaption("Insert")
	dataInsertBtn.SetOnClick(f.OnDataInsertClick)

	f.contentBox = vcl.NewStringGrid(dataTab)
	f.contentBox.SetParent(dataTab)
	f.contentBox.BorderSpacing().SetLeft(MY_SPACING)
	f.contentBox.BorderSpacing().SetRight(MY_SPACING)
	f.contentBox.BorderSpacing().SetBottom(MY_SPACING)
	f.contentBox.SetAlign(types.AlClient) // fill remaining space
	f.contentBox.SetOptions(f.contentBox.Options().Include(types.GoThumbTracking, types.GoColSizing, types.GoDblClickAutoSize))
	f.contentBox.SetOnPrepareCanvas(f.OnDataPrepareCanvas)
	f.contentBox.SetDefaultColWidth(MY_WIDTH)
	vcl_stringgrid_clear(f.contentBox)

	queryTab := vcl.NewTabSheet(f.Tabs)
	queryTab.SetParent(f.Tabs)
	queryTab.SetCaption("Query")
	queryTab.SetImageIndex(imgLightning)

	queryButtonBar := vcl.NewToolBar(queryTab)
	queryButtonBar.SetParent(queryTab)
	queryButtonBar.SetAlign(types.AlTop)
	queryButtonBar.BorderSpacing().SetLeft(MY_SPACING)
	queryButtonBar.BorderSpacing().SetTop(MY_SPACING)
	//queryButtonBar.BorderSpacing().SetBottom(1)
	queryButtonBar.BorderSpacing().SetRight(MY_SPACING)
	queryButtonBar.SetEdgeBorders(0)
	queryButtonBar.SetImages(f.ImageList)
	queryButtonBar.SetShowCaptions(true)

	queryExecBtn := vcl.NewToolButton(queryButtonBar)
	queryExecBtn.SetParent(queryButtonBar)
	queryExecBtn.SetCaption("Execute")
	// queryExecBtn.SetImageIndex(imgLightning)
	queryExecBtn.SetOnClick(f.OnQueryExecute)

	f.queryInput = vcl.NewMemo(queryTab)
	f.queryInput.SetParent(queryTab)
	f.queryInput.SetHeight(MY_HEIGHT)
	f.queryInput.SetAlign(types.AlTop)
	f.queryInput.SetTop(1)
	if runtime.GOOS == "windows" {
		f.queryInput.Font().SetName("Consolas")
	} else {
		f.queryInput.Font().SetName("monospace")
	}
	f.queryInput.BorderSpacing().SetLeft(MY_SPACING)
	//f.queryInput.BorderSpacing().SetTop(1)
	f.queryInput.BorderSpacing().SetRight(MY_SPACING)
	f.queryInput.SetBorderStyle(types.BsFrame)

	vsplit := vcl.NewSplitter(queryTab)
	vsplit.SetParent(queryTab)
	vsplit.SetAlign(types.AlTop)
	vsplit.SetTop(2)

	f.queryResult = vcl.NewStringGrid(queryTab)
	f.queryResult.SetParent(queryTab)
	f.queryResult.SetAlign(types.AlClient) // fill remaining space
	f.queryResult.BorderSpacing().SetLeft(MY_SPACING)
	f.queryResult.BorderSpacing().SetRight(MY_SPACING)
	f.queryResult.BorderSpacing().SetBottom(MY_SPACING)
	f.queryResult.SetOptions(f.queryResult.Options().Include(types.GoThumbTracking))
	f.queryResult.SetDefaultColWidth(MY_WIDTH)
	vcl_stringgrid_clear(f.queryResult)

	f.none = &noLoadedDatabase{}
	f.OnNavChange(f, nil) // calls f.none.RenderForNav and sets up status bar content
}

func (f *TMainForm) OnMnuFileBoltNewClick(sender vcl.IObject) {
	dlg := vcl.NewSaveDialog(f)
	dlg.SetTitle("Save database as...")
	dlg.SetFilter("Bolt database|*.db|All files|*.*")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.boltAddDatabaseFromFile(dlg.FileName(), false)
	}
}

func (f *TMainForm) OnMnuFileBoltOpenClick(sender vcl.IObject) {
	dlg := vcl.NewOpenDialog(f)
	dlg.SetTitle("Select a database file...")
	dlg.SetFilter("Bolt database|*.db|All files|*.*")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.boltAddDatabaseFromFile(dlg.FileName(), false)
	}
}

func (f *TMainForm) OnMnuFileBoltOpenReadonlyClick(sender vcl.IObject) {
	dlg := vcl.NewOpenDialog(f)
	dlg.SetTitle("Select a database file...")
	dlg.SetFilter("Bolt database|*.db|All files|*.*")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.boltAddDatabaseFromFile(dlg.FileName(), true)
	}
}

func (f *TMainForm) OnMnuFileSqliteOpenClick(sender vcl.IObject) {
	cliDriver := f.SQLiteUseCliDriver.Checked()

	dlg := vcl.NewOpenDialog(f)
	dlg.SetTitle("Select a database file...")
	dlg.SetFilter("SQLite database|*.db;*.db3;*.sqlite;*.sqlite3|All files|*.*")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.sqliteAddDatabaseFromFile(dlg.FileName(), cliDriver)
	}
}

func (f *TMainForm) OnMnuFileBadgerOpenClick(sender vcl.IObject) {
	dlg := vcl.NewSelectDirectoryDialog(f)
	dlg.SetTitle("Select a database directory...")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.badgerAddDatabaseFromDirectory(dlg.FileName())
	}
}

func (f *TMainForm) OnMnuFileBadgerMemoryClick(sender vcl.IObject) {
	f.badgerAddDatabaseFromMemory()
}

func (f *TMainForm) OnMnuFilePebbleOpenClick(sender vcl.IObject) {
	dlg := vcl.NewSelectDirectoryDialog(f)
	dlg.SetTitle("Select a database directory...")
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.pebbleAddDatabaseFrom(dlg.FileName(), nil)
	}
}

func (f *TMainForm) OnMnuFileDebianOpenClick(sender vcl.IObject) {
	dlg := vcl.NewOpenDialog(f)
	dlg.SetTitle("Select a database file...")
	dlg.SetFilter("Debconf database|*.dat|All files|*.*")
	if runtime.GOOS == "linux" {
		dlg.SetInitialDir(`/var/cache/debconf/`)
	}
	ret := dlg.Execute() // Fake blocking
	if ret {
		f.debconfAddDatabaseFrom(dlg.FileName())
	}
}

func (f *TMainForm) OnMnuFilePebbleMemoryClick(sender vcl.IObject) {
	f.pebbleAddDatabaseFromMemory()
}

func (f *TMainForm) OnMnuFileSqliteMemoryClick(sender vcl.IObject) {
	cliDriver := f.SQLiteUseCliDriver.Checked()

	f.sqliteAddDatabaseFromFile(`:memory:`, cliDriver)
}

func (f *TMainForm) OnMnuFileRedisConnectClick(sender vcl.IObject) {

	var child *TRedisConnectionDialog
	vcl.Application.CreateForm(&child)
	defer child.Free()

	var ret TRedisConnectionDialogResult
	child.CustomReturn = &ret

	mr := child.ShowModal() // Fake blocking
	if mr != types.MrOk || ret == nil {
		return // Cancelled
	}

	// Connect
	f.redisConnect(ret)
}

func (f *TMainForm) OnMnuFileExitClick(sender vcl.IObject) {
	f.Close()
}

func (f *TMainForm) OnMnuHelpHomepage(sender vcl.IObject) {
	err := browser.OpenURL(HOMEPAGE_URL)
	if err != nil {
		vcl.ShowMessage("Opening browser: " + err.Error())
	}
}

func (f *TMainForm) OnMenuHelpVersion(sender vcl.IObject) {

	bi, ok := debug.ReadBuildInfo()
	if !ok {
		return
	}

	info := "This version of " + APPNAME + " was compiled with:\n\n"
	for _, dep := range bi.Deps {

		// Filter to only interesting things
		switch dep.Path {
		case `github.com/cockroachdb/pebble`,
			`github.com/dgraph-io/badger/v4`,
			`github.com/mattn/go-sqlite3`,
			`github.com/redis/go-redis/v9`,
			`go.etcd.io/bbolt`,
			`modernc.org/sqlite`:
			info += fmt.Sprintf("- %s %s\n", dep.Path, dep.Version)
		}
	}

	vcl.ShowMessage(info)
}

func (f *TMainForm) OnNavContextPopup(sender vcl.IObject, mousePos types.TPoint, handled *bool) {
	*handled = true

	curItem := f.Buckets.Selected()
	if curItem == nil {
		// Nothing is selected at all
		return
	}

	ndata := (*navData)(curItem.Data())

	mnu := vcl.NewPopupMenu(f.Buckets)
	mnu.SetImages(f.ImageList)

	mnuRefresh := vcl.NewMenuItem(mnu)
	mnuRefresh.SetCaption("Refresh")
	mnuRefresh.SetImageIndex(imgArrowRefresh)
	mnuRefresh.SetOnClick(func(sender vcl.IObject) { f.OnNavContextRefresh(curItem, ndata) })
	mnu.Items().Add(mnuRefresh)

	// Check what custom actions the ndata->db itself wants to add
	actions, err := ndata.ld.NavContext(ndata)
	if err != nil {
		vcl.ShowMessage(err.Error())
		return
	}

	if len(actions) > 0 {
		mnuSep := vcl.NewMenuItem(mnu)
		mnuSep.SetCaption("-")
		mnu.Items().Add(mnuSep)

		for _, action := range actions {
			mnuAction := vcl.NewMenuItem(mnu)
			mnuAction.SetCaption(action.Name)
			cb := action.Callback // Copy to avoid reuse of loop variable
			mnuAction.SetOnClick(func(sender vcl.IObject) {
				cb(ndata)
				f.OnNavContextRefresh(curItem, ndata)
			})
			mnu.Items().Add(mnuAction)
		}
	}

	if curItem.Parent() == nil {
		// Top-level item (database connection). Allow closing by right-click.
		mnuSep := vcl.NewMenuItem(mnu)
		mnuSep.SetCaption("-")
		mnu.Items().Add(mnuSep)

		mnuClose := vcl.NewMenuItem(mnu)
		mnuClose.SetCaption("Close")
		mnuClose.SetOnClick(f.OnNavContextClose)
		mnuClose.SetImageIndex(imgDatabaseDelete)
		mnu.Items().Add(mnuClose)
	}

	// Show popup
	mnu.Popup2()
}

func (f *TMainForm) RefreshCurrentItem() {
	item := f.Buckets.Selected()
	if item == nil {
		return // nothing to do
	}

	ndata := (*navData)(item.Data())

	f.OnNavContextRefresh(item, ndata)
}

func (f *TMainForm) OnNavContextRefresh(item *vcl.TTreeNode, ndata *navData) {
	isExpanded := item.Expanded()

	// Reset nav node to 'unloaded' state
	item.Collapse(true)
	item.DeleteChildren()
	item.SetHasChildren(true)
	ndata.childrenLoaded = false

	// Trigger a virtual reload
	item.Expand(false) // Calls OnNavExpanding to dynamically detect children

	// Restore previous gui state
	item.SetExpanded(isExpanded)
}

func (f *TMainForm) OnDataPrepareCanvas(sender vcl.IObject, aCol, aRow int32, aState types.TGridDrawState) {
	if len(f.insertRows) == 0 {
		return // fast-path
	}

	isInsertRow := false
	for _, rr := range f.insertRows {
		if rr == aRow {
			isInsertRow = true
			break
		}
	}

	if isInsertRow {
		/*sender.(*vcl.TStringGrid)*/
		f.contentBox.Canvas().Brush().SetColor(colors.ClYellow)
	}
}

func (f *TMainForm) OnDataInsertClick(sender vcl.IObject) {
	if !f.contentBox.Enabled() {
		return // Not an active data view
	}

	rpos := f.contentBox.RowCount()
	f.contentBox.SetRowCount(rpos + 1)

	f.insertRows = append(f.insertRows, rpos)

	// Scroll to bottom
	f.contentBox.SetTopRow(rpos)
}

func (f *TMainForm) OnNavContextClose(sender vcl.IObject) {
	curItem := f.Buckets.Selected()
	if curItem == nil {
		return // Nothing selected (shouldn't happen)
	}
	if curItem.Parent() != nil {
		return // Selection is not top-level DB connection (shouldn't happen)
	}

	ndata := (*navData)(curItem.Data())

	ndata.ld.Close()
	curItem.Delete()

	// n.b. This triggers OnNavChange, which will then re-render from noLoadedDatabase{}
}

func (f *TMainForm) OnQueryExecute(sender vcl.IObject) {
	// If query tab is not selected, switch to it, but do not exec
	if f.Tabs.ActivePageIndex() != 2 {
		f.Tabs.SetActivePageIndex(2)
		return
	}

	queryString := f.queryInput.Text()
	if f.queryInput.SelLength() > 0 {
		queryString = f.queryInput.SelText() // Just the selected text
	}

	// Execute
	node := f.Buckets.Selected()
	if node == nil {
		vcl.ShowMessage("No database selected")
		return
	}

	ndata := (*navData)(node.Data())
	ndata.ld.ExecQuery(queryString, f.queryResult)
}

func (f *TMainForm) OnNavChange(sender vcl.IObject, node *vcl.TTreeNode) {

	var ld loadedDatabase = f.none
	var ndata *navData = nil

	if node != nil && node.Data() != nil {
		ndata = (*navData)(node.Data())
		ld = ndata.ld
	}

	// Reset some controls that the render function is expected to populate
	f.insertRows = nil
	f.propertiesBox.Clear()
	vcl_stringgrid_clear(f.contentBox)

	ld.RenderForNav(f, ndata) // Handover to the database type's own renderer function

	// We're in charge of common status bar text updates
	f.StatusBar.SetSimpleText(ld.DisplayName() + " | " + ld.DriverName())
}

func (f *TMainForm) OnNavExpanding(sender vcl.IObject, node *vcl.TTreeNode, allowExpansion *bool) {

	if node.Data() == nil {
		vcl.ShowMessage("unexpected nil data")
		*allowExpansion = false
		return
	}

	ndata := (*navData)(node.Data())

	err := f.NavLoadChildren(node, ndata)
	if err != nil {

		if errors.Is(err, ErrNavNotExist) {
			// The nav entry has been deleted.
			// This is a normal thing to happen when e.g. deleting a table
			// f.StatusBar.SetSimpleText(err.Error()) // Just gets overridden when the selection changes
			node.Delete()
			return
		}

		vcl.ShowMessage(err.Error())
		*allowExpansion = false // Permanently block
		return
	}

	*allowExpansion = node.HasChildren()

	// While we're here - preload one single level deep (not any deeper)

	if node.HasChildren() {

		// This node has children that we haven't processed. Process them now
		cc := node.GetFirstChild()

		for {
			ndataChild := (*navData)(cc.Data())
			if ndataChild.childrenLoaded {
				break // We always do them together, so if one's done, no need to keep looking
			}

			f.NavLoadChildren(cc, ndataChild)

			cc = cc.GetNextSibling()
			if cc == nil {
				break
			}
		}

	}
}

func (f *TMainForm) NavLoadChildren(node *vcl.TTreeNode, ndata *navData) error {

	if ndata.childrenLoaded {
		return nil // Nothing to do
	}

	// Find the child buckets from this point under the element
	nextBucketNames, err := ndata.ld.NavChildren(ndata)
	if err != nil {
		return fmt.Errorf("Failed to find child buckets under %q: %w", strings.Join(ndata.bucketPath, `/`), err)
	}

	ndata.childrenLoaded = true // don't repeat this work

	if len(nextBucketNames) == 0 {
		node.SetHasChildren(false)

	} else {
		node.SetHasChildren(true)

		// Populate LCL child nodes
		for _, bucketName := range nextBucketNames {

			node := f.Buckets.Items().AddChild(node, formatUtf8([]byte(bucketName)))
			node.SetHasChildren(true) // dynamically populate in OnNavExpanding
			node.SetImageIndex(imgTable)
			node.SetSelectedIndex(imgTable)
			navData := &navData{
				ld:             ndata.ld,
				childrenLoaded: false,      // will be loaded dynamically
				bucketPath:     []string{}, // empty = root
			}
			navData.bucketPath = append(navData.bucketPath, ndata.bucketPath...)
			navData.bucketPath = append(navData.bucketPath, bucketName)
			node.SetData(unsafe.Pointer(navData))

			ndata.ld.Keepalive(navData)
		}
	}

	return nil
}