type App interface {
    // ReadCode requests the App to read code from the terminal by running an
    // event loop. This function is not re-entrant.
    ReadCode() (string, error)

    // MutateState mutates the state of the app.
    MutateState(f func(*State))
    // CopyState returns a copy of the a state.
    CopyState() State
    // CodeArea returns the codearea widget of the app.
    CodeArea() tk.CodeArea
    // SetAddon sets the current addon to the given widget. If there is an
    // existing addon, it is closed first. If the existing addon implements
    // interface{ Close(bool) }, the Close method is called with the accept
    // argument. To close the current addon without setting a new one, call
    // SetAddon(nil, accept).
    SetAddon(w tk.Widget, accept bool)

    // CommitEOF causes the main loop to exit with EOF. If this method is called
    // when an event is being handled, the main loop will exit after the handler
    // returns.
    CommitEOF()
    // CommitCode causes the main loop to exit with the current code content. If
    // this method is called when an event is being handled, the main loop will
    // exit after the handler returns.
    CommitCode()

    // Redraw requests a redraw. It never blocks and can be called regardless of
    // whether the App is active or not.
    Redraw()
    // RedrawFull requests a full redraw. It never blocks and can be called
    // regardless of whether the App is active or not.
    RedrawFull()
    // Notify adds a note and requests a redraw.
    Notify(note string)
}

type AppSpec struct {
    TTY               TTY
    MaxHeight         func() int
    RPromptPersistent func() bool
    BeforeReadline    []func()
    AfterReadline     []func(string)

    Highlighter Highlighter
    Prompt      Prompt
    RPrompt     Prompt

    GlobalBindings   tk.Bindings
    CodeAreaBindings tk.Bindings
    Abbreviations    func(f func(abbr, full string))
    QuotePaste       func() bool

    SmallWordAbbreviations func(f func(abbr, full string))

    CodeAreaState tk.CodeAreaState
    State         State
}

type Highlighter interface {
    // Get returns the highlighted code and any static errors.
    Get(code string) (ui.Text, []error)
    // LateUpdates returns a channel for delivering late updates.
    LateUpdates() <-chan struct{}
}

type Prompt interface {
    // Trigger requests a re-computation of the prompt. The force flag is set
    // when triggered for the first time during a ReadCode session or after a
    // SIGINT that resets the editor.
    Trigger(force bool)
    // Get returns the current prompt.
    Get() ui.Text
    // LastUpdates returns a channel for notifying late updates.
    LateUpdates() <-chan struct{}
}

type State struct {
    // Notes that have been added since the last redraw.
    Notes []string
    // An addon widget. When non-nil, it is shown under the codearea widget and
    // terminal events are handled by it.
    //
    // The cursor is placed on the addon by default. If the addon widget
    // implements interface{ Focus() bool }, the Focus method is called to
    // determine that instead.
    Addon tk.Widget
}

type TTY interface {
    // Setup sets up the terminal for the CLI app.
    //
    // This method returns a restore function that undoes the setup, and any
    // error during setup. It only returns fatal errors that make the terminal
    // unsuitable for later operations; non-fatal errors may be reported by
    // showing a warning message, but not returned.
    //
    // This method should be called before any other method is called.
    Setup() (restore func(), err error)

    // ReadEvent reads a terminal event.
    ReadEvent() (term.Event, error)
    // SetRawInput requests the next n ReadEvent calls to read raw events. It
    // is applicable to environments where events are represented as a special
    // sequences, such as VT100. It is a no-op if events are delivered as whole
    // units by the terminal, such as Windows consoles.
    SetRawInput(n int)

    // StopInput causes input delivery to be stopped. When this function
    // returns, the channel previously returned by StartInput will no longer
    // deliver input events.
    StopInput()

    // NotifySignals start relaying signals and returns a channel on which
    // signals are delivered.
    NotifySignals() <-chan os.Signal
    // StopSignals stops the relaying of signals. After this function returns,
    // the channel returned by NotifySignals will no longer deliver signals.
    StopSignals()

    // Size returns the height and width of the terminal.
    Size() (h, w int)

    // Buffer returns the current buffer. The initial value of the current
    // buffer is nil.
    Buffer() *term.Buffer
    // ResetBuffer resets the current buffer to nil without actuating any redraw.
    ResetBuffer()
    // UpdateBuffer updates the current buffer and draw it to the terminal.
    UpdateBuffer(bufNotes, bufMain *term.Buffer, full bool) error
    // ClearScreen clears the terminal screen and places the cursor at the top
    // left corner.
    ClearScreen()
}