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

	// PushAddon pushes a widget to the addon stack.
	PushAddon(w tk.Widget)
	// PopAddon pops the last widget from the addon stack. If the widget
	// implements interface{ Dismiss() }, the Dismiss method is called
	// first. This method does nothing if the addon stack is empty.
	PopAddon()

	// ActiveWidget returns the currently active widget. If the addon stack is
	// non-empty, it returns the last addon. Otherwise it returns the main code
	// area widget.
	ActiveWidget() tk.Widget
	// FocusedWidget returns the currently focused widget. It is searched like
	// ActiveWidget, but skips widgets that implement interface{ Focus() bool }
	// and return false when .Focus() is called.
	FocusedWidget() tk.Widget

	// 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 ui.Text)
}

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
	QuotePaste       func() bool

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

	CodeAreaState tk.CodeAreaState
	State         State
}

type Highlighter interface {
	// Get returns the highlighted code and any tips.
	Get(code string) (ui.Text, []ui.Text)
	// 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 []ui.Text
	// The addon stack. All widgets are shown under the codearea widget. The
	// last widget handles terminal events.
	Addons []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)
	// CloseReader releases resources allocated for reading terminal events.
	CloseReader()

	term.Writer

	// 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)
}