Open a file picker and load the result

Dialogs.fileDialog is a presentational overlay — like Dialogs.confirm, it returns an Overlay and doesn't take callbacks. The app owns the current path, the directory listing, the selected index, and rebuilds the listing when the user steps into a subdirectory.

Pattern

1. Hold a picker: Option[PickerState] on the model with the path, entries, and selected index.
2. On Open, list the start directory and store it in the picker.
3. Route keys to the picker while it's open — Enter dives into a directory or returns the selected file; Esc cancels.
4. On commit, close the picker and dispatch a domain Msg carrying the chosen path.

Code

import java.nio.file.{Files, Path}
import scala.jdk.CollectionConverters.*

import termflow.tui.{Dialogs, FileEntry, Theme}
import termflow.tui.KeyDecoder.InputKey.*

final case class PickerState(
  path:          Path,
  entries:       Seq[FileEntry],
  selectedIndex: Int,
  okFocused:     Boolean = true
)

final case class Model(
  loadedFile: Option[Path],
  picker:     Option[PickerState]
)

enum Msg:
  case OpenPicker
  case PickerKey(k: InputKey)
  case FileChosen(p: Path)
  case PickerCancelled

def listDir(p: Path): Seq[FileEntry] =
  // FileEntry has fields name, path, isDir, sizeBytes — see
  // termflow.tui.FileEntry. Skipping sort/hidden filtering for brevity.
  Files.list(p).iterator.asScala.toList.map(FileEntry.fromPath).sortBy(e => (!e.isDir, e.name))

def update(m: Model, msg: Msg, ctx: RuntimeCtx[Msg]): Tui[Model, Msg] =
  msg match
    case Msg.OpenPicker =>
      val cwd = Path.of(System.getProperty("user.dir"))
      m.copy(picker = Some(PickerState(cwd, listDir(cwd), 0))).tui

    case Msg.PickerKey(k) =>
      m.picker match
        case None => m.tui
        case Some(p) =>
          k match
            case ArrowDown =>
              val next = math.min(p.entries.size - 1, p.selectedIndex + 1)
              m.copy(picker = Some(p.copy(selectedIndex = next))).tui

            case ArrowUp =>
              val next = math.max(0, p.selectedIndex - 1)
              m.copy(picker = Some(p.copy(selectedIndex = next))).tui

            case Enter | CharKey(' ') =>
              p.entries.lift(p.selectedIndex) match
                case Some(entry) if entry.isDir =>
                  // Step in: rebuild listing
                  m.copy(picker = Some(p.copy(
                    path          = entry.path,
                    entries       = listDir(entry.path),
                    selectedIndex = 0
                  ))).tui
                case Some(entry) =>
                  m.copy(picker = None).gCmd(Msg.FileChosen(entry.path))
                case None => m.tui

            case Escape =>
              m.copy(picker = None).gCmd(Msg.PickerCancelled)

            case _ => m.tui

    case Msg.FileChosen(p) =>
      m.copy(loadedFile = Some(p)).tui

    case Msg.PickerCancelled =>
      m.tui

def view(m: Model): RootNode =
  given Theme = Theme.dark
  val baseChildren = /* … */
  val overlays = m.picker.toList.map { p =>
    Dialogs.fileDialog(
      title         = "Open file",
      currentPath   = p.path,
      entries       = p.entries,
      selectedIndex = p.selectedIndex,
      okFocused     = p.okFocused,
      maxVisible    = 12,
      showSizes     = true
    )
  }
  RootNode(80, 24, children = baseChildren, input = None, overlays = overlays)

Notes

• FileEntry is a small case class shipped in termflow.tui with name, path, isDir, sizeBytes. Build your own list any way you like — flat directory listing, recursive search, pre-filtered globs. The dialog only renders.
• Hidden / dotfiles. Filter at the listDir level so the dialog never shows them. Adding a showHidden: Boolean to PickerState is straightforward.
• Read the file inside FileChosen if it's small. For larger loads, hand it to Cmd.asyncResult(future, Msg.LoadDone.apply, Msg.LoadFailed.apply) and treat it as async work — the Async tutorial covers the pattern.
• Symlink loops are not detected by listDir above — guard with Files.readAttributes(..., LinkOption.NOFOLLOW_LINKS) if you walk user-supplied trees.

For a working example, see apps.dialog.FileDialogDemoApp.