screen.go

// Copyright 2024 The TCell Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use file except in compliance with the License.
// You may obtain a copy of the license at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package tcell

import "sync"

// Screen represents the physical (or emulated) screen.
// This can be a terminal window or a physical console.  Platforms implement
// this differently.
type Screen interface {
	// Init initializes the screen for use.
	Init() error

	// Fini finalizes the screen also releasing resources.
	Fini()

	// Clear logically erases the screen.
	// This is effectively a short-cut for Fill(' ', StyleDefault).
	Clear()

	// Fill fills the screen with the given character and style.
	// The effect of filling the screen is not visible until Show
	// is called (or Sync).
	Fill(rune, Style)

	// SetCell is an older API, and will be removed.  Please use
	// SetContent instead; SetCell is implemented in terms of SetContent.
	SetCell(x int, y int, style Style, ch ...rune)

	// GetContent returns the contents at the given location.  If the
	// coordinates are out of range, then the values will be 0, nil,
	// StyleDefault.  Note that the contents returned are logical contents
	// and may not actually be what is displayed, but rather are what will
	// be displayed if Show() or Sync() is called.  The width is the width
	// in screen cells; most often this will be 1, but some East Asian
	// characters and emoji require two cells.
	GetContent(x, y int) (primary rune, combining []rune, style Style, width int)

	// SetContent sets the contents of the given cell location.  If
	// the coordinates are out of range, then the operation is ignored.
	//
	// The first rune is the primary non-zero width rune.  The array
	// that follows is a possible list of combining characters to append,
	// and will usually be nil (no combining characters.)
	//
	// The results are not displayed until Show() or Sync() is called.
	//
	// Note that wide (East Asian full width and emoji) runes occupy two cells,
	// and attempts to place character at next cell to the right will have
	// undefined effects.  Wide runes that are printed in the
	// last column will be replaced with a single width space on output.
	SetContent(x int, y int, primary rune, combining []rune, style Style)

	// SetStyle sets the default style to use when clearing the screen
	// or when StyleDefault is specified.  If it is also StyleDefault,
	// then whatever system/terminal default is relevant will be used.
	SetStyle(style Style)

	// ShowCursor is used to display the cursor at a given location.
	// If the coordinates -1, -1 are given or are otherwise outside the
	// dimensions of the screen, the cursor will be hidden.
	ShowCursor(x int, y int)

	// HideCursor is used to hide the cursor.  It's an alias for
	// ShowCursor(-1, -1).sim
	HideCursor()

	// SetCursorStyle is used to set the cursor style.  If the style
	// is not supported (or cursor styles are not supported at all),
	// then this will have no effect.  Color will be changed if supplied,
	// and the terminal supports doing so.
	SetCursorStyle(CursorStyle, ...Color)

	// Size returns the screen size as width, height.  This changes in
	// response to a call to Clear or Flush.
	Size() (width, height int)

	// ChannelEvents is an infinite loop that waits for an event and
	// channels it into the user provided channel ch.  Closing the
	// quit channel and calling the Fini method are cancellation
	// signals.  When a cancellation signal is received the method
	// returns after closing ch.
	//
	// This method should be used as a goroutine.
	//
	// NOTE: PollEvent should not be called while this method is running.
	ChannelEvents(ch chan<- Event, quit <-chan struct{})

	// PollEvent waits for events to arrive.  Main application loops
	// must spin on this to prevent the application from stalling.
	// Furthermore, this will return nil if the Screen is finalized.
	PollEvent() Event

	// HasPendingEvent returns true if PollEvent would return an event
	// without blocking.  If the screen is stopped and PollEvent would
	// return nil, then the return value from this function is unspecified.
	// The purpose of this function is to allow multiple events to be collected
	// at once, to minimize screen redraws.
	HasPendingEvent() bool

	// PostEvent tries to post an event into the event stream.  This
	// can fail if the event queue is full.  In that case, the event
	// is dropped, and ErrEventQFull is returned.
	PostEvent(ev Event) error

	// Deprecated: PostEventWait is unsafe, and will be removed
	// in the future.
	//
	// PostEventWait is like PostEvent, but if the queue is full, it
	// blocks until there is space in the queue, making delivery
	// reliable.  However, it is VERY important that this function
	// never be called from within whatever event loop is polling
	// with PollEvent(), otherwise a deadlock may arise.
	//
	// For this reason, when using this function, the use of a
	// Goroutine is recommended to ensure no deadlock can occur.
	PostEventWait(ev Event)

	// EnableMouse enables the mouse.  (If your terminal supports it.)
	// If no flags are specified, then all events are reported, if the
	// terminal supports them.
	EnableMouse(...MouseFlags)

	// DisableMouse disables the mouse.
	DisableMouse()

	// EnablePaste enables bracketed paste mode, if supported.
	EnablePaste()

	// DisablePaste disables bracketed paste mode.
	DisablePaste()

	// EnableFocus enables reporting of focus events, if your terminal supports it.
	EnableFocus()

	// DisableFocus disables reporting of focus events.
	DisableFocus()

	// HasMouse returns true if the terminal (apparently) supports a
	// mouse.  Note that the return value of true doesn't guarantee that
	// a mouse/pointing device is present; a false return definitely
	// indicates no mouse support is available.
	HasMouse() bool

	// Colors returns the number of colors.  All colors are assumed to
	// use the ANSI color map.  If a terminal is monochrome, it will
	// return 0.
	Colors() int

	// Show makes all the content changes made using SetContent() visible
	// on the display.
	//
	// It does so in the most efficient and least visually disruptive
	// manner possible.
	Show()

	// Sync works like Show(), but it updates every visible cell on the
	// physical display, assuming that it is not synchronized with any
	// internal model.  This may be both expensive and visually jarring,
	// so it should only be used when believed to actually be necessary.
	//
	// Typically, this is called as a result of a user-requested redraw
	// (e.g. to clear up on-screen corruption caused by some other program),
	// or during a resize event.
	Sync()

	// CharacterSet returns information about the character set.
	// This isn't the full locale, but it does give us the input/output
	// character set.  Note that this is just for diagnostic purposes,
	// we normally translate input/output to/from UTF-8, regardless of
	// what the user's environment is.
	CharacterSet() string

	// RegisterRuneFallback adds a fallback for runes that are not
	// part of the character set -- for example one could register
	// o as a fallback for ø.  This should be done cautiously for
	// characters that might be displayed ordinarily in language
	// specific text -- characters that could change the meaning of
	// written text would be dangerous.  The intention here is to
	// facilitate fallback characters in pseudo-graphical applications.
	//
	// If the terminal has fallbacks already in place via an alternate
	// character set, those are used in preference.  Also, standard
	// fallbacks for graphical characters in the alternate character set
	// terminfo string are registered implicitly.
	//
	// The display string should be the same width as original rune.
	// This makes it possible to register two character replacements
	// for full width East Asian characters, for example.
	//
	// It is recommended that replacement strings consist only of
	// 7-bit ASCII, since other characters may not display everywhere.
	RegisterRuneFallback(r rune, subst string)

	// UnregisterRuneFallback unmaps a replacement.  It will unmap
	// the implicit ASCII replacements for alternate characters as well.
	// When an unmapped char needs to be displayed, but no suitable
	// glyph is available, '?' is emitted instead.  It is not possible
	// to "disable" the use of alternate characters that are supported
	// by your terminal except by changing the terminal database.
	UnregisterRuneFallback(r rune)

	// CanDisplay returns true if the given rune can be displayed on
	// this screen.  Note that this is a best-guess effort -- whether
	// your fonts support the character or not may be questionable.
	// Mostly this is for folks who work outside of Unicode.
	//
	// If checkFallbacks is true, then if any (possibly imperfect)
	// fallbacks are registered, this will return true.  This will
	// also return true if the terminal can replace the glyph with
	// one that is visually indistinguishable from the one requested.
	CanDisplay(r rune, checkFallbacks bool) bool

	// Resize does nothing, since it's generally not possible to
	// ask a screen to resize, but it allows the Screen to implement
	// the View interface.
	Resize(int, int, int, int)

	// HasKey returns true if the keyboard is believed to have the
	// key.  In some cases a keyboard may have keys with this name
	// but no support for them, while in others a key may be reported
	// as supported but not actually be usable (such as some emulators
	// that hijack certain keys).  Its best not to depend to strictly
	// on this function, but it can be used for hinting when building
	// menus, displayed hot-keys, etc.  Note that KeyRune (literal
	// runes) is always true.
	HasKey(Key) bool

	// Suspend pauses input and output processing.  It also restores the
	// terminal settings to what they were when the application started.
	// This can be used to, for example, run a sub-shell.
	Suspend() error

	// Resume resumes after Suspend().
	Resume() error

	// Beep attempts to sound an OS-dependent audible alert and returns an error
	// when unsuccessful.
	Beep() error

	// SetSize attempts to resize the window.  It also invalidates the cells and
	// calls the resize function.  Note that if the window size is changed, it will
	// not be restored upon application exit.
	//
	// Many terminals cannot support this.  Perversely, the "modern" Windows Terminal
	// does not support application-initiated resizing, whereas the legacy terminal does.
	// Also, some emulators can support this but may have it disabled by default.
	SetSize(int, int)

	// LockRegion sets or unsets a lock on a region of cells. A lock on a
	// cell prevents the cell from being redrawn.
	LockRegion(x, y, width, height int, lock bool)

	// Tty returns the underlying Tty. If the screen is not a terminal, the
	// returned bool will be false
	Tty() (Tty, bool)

	// SetTitle sets a window title on the screen.
	// Terminals may be configured to ignore this, or unable to.
	// Tcell may attempt to save and restore the window title on entry and exit, but
	// the results may vary.  Use of unicode characters may not be supported.
	SetTitle(string)

	// SetClipboard is used to post arbitrary data to the system clipboard.
	// This need not be UTF-8 string data.  It's up to the recipient to decode the
	// data meaningfully.  Terminals may prevent this for security reasons.
	SetClipboard([]byte)

	// GetClipboard is used to request the clipboard contents.  It may be ignored.
	// If the terminal is willing, it will be post the clipboard contents using an
	// EventPaste with the clipboard content as the Data() field.  Terminals may
	// prevent this for security reasons.
	GetClipboard()
}

// NewScreen returns a default Screen suitable for the user's terminal
// environment.
func NewScreen() (Screen, error) {
	// Windows is happier if we try for a console screen first.
	if s, _ := NewConsoleScreen(); s != nil {
		return s, nil
	} else if s, e := NewTerminfoScreen(); s != nil {
		return s, nil
	} else {
		return nil, e
	}
}

// MouseFlags are options to modify the handling of mouse events.
// Actual events can be ORed together.
type MouseFlags int

const (
	MouseButtonEvents = MouseFlags(1) // Click events only
	MouseDragEvents   = MouseFlags(2) // Click-drag events (includes button events)
	MouseMotionEvents = MouseFlags(4) // All mouse events (includes click and drag events)
)

// CursorStyle represents a given cursor style, which can include the shape and
// whether the cursor blinks or is solid.  Support for changing this is not universal.
type CursorStyle int

const (
	CursorStyleDefault = CursorStyle(iota) // The default
	CursorStyleBlinkingBlock
	CursorStyleSteadyBlock
	CursorStyleBlinkingUnderline
	CursorStyleSteadyUnderline
	CursorStyleBlinkingBar
	CursorStyleSteadyBar
)

// screenImpl is a subset of Screen that can be used with baseScreen to formulate
// a complete implementation of Screen.  See Screen for doc comments about methods.
type screenImpl interface {
	Init() error
	Fini()
	SetStyle(style Style)
	ShowCursor(x int, y int)
	HideCursor()
	SetCursor(CursorStyle, Color)
	Size() (width, height int)
	EnableMouse(...MouseFlags)
	DisableMouse()
	EnablePaste()
	DisablePaste()
	EnableFocus()
	DisableFocus()
	HasMouse() bool
	Colors() int
	Show()
	Sync()
	CharacterSet() string
	RegisterRuneFallback(r rune, subst string)
	UnregisterRuneFallback(r rune)
	CanDisplay(r rune, checkFallbacks bool) bool
	Resize(int, int, int, int)
	HasKey(Key) bool
	Suspend() error
	Resume() error
	Beep() error
	SetSize(int, int)
	SetTitle(string)
	Tty() (Tty, bool)
	SetClipboard([]byte)
	GetClipboard()

	// Following methods are not part of the Screen api, but are used for interaction with
	// the common layer code.

	// Locker locks the underlying data structures so that we can access them
	// in a thread-safe way.
	sync.Locker

	// GetCells returns a pointer to the underlying CellBuffer that the implementation uses.
	// Various methods will write to these for performance, but will use the lock to do so.
	GetCells() *CellBuffer

	// StopQ is closed when the screen is shut down via Fini.  It remains open if the screen
	// is merely suspended.
	StopQ() <-chan struct{}

	// EventQ delivers events.  Events are posted to this by the screen in response to
	// key presses, resizes, etc.  Application code receives events from this via the
	// Screen.PollEvent, Screen.ChannelEvents APIs.
	EventQ() chan Event
}

type baseScreen struct {
	screenImpl
}

func (b *baseScreen) SetCell(x int, y int, style Style, ch ...rune) {
	if len(ch) > 0 {
		b.SetContent(x, y, ch[0], ch[1:], style)
	} else {
		b.SetContent(x, y, ' ', nil, style)
	}
}

func (b *baseScreen) Clear() {
	b.Fill(' ', StyleDefault)
}

func (b *baseScreen) Fill(r rune, style Style) {
	cb := b.GetCells()
	b.Lock()
	cb.Fill(r, style)
	b.Unlock()
}

func (b *baseScreen) SetContent(x, y int, mainc rune, combc []rune, st Style) {

	cells := b.GetCells()
	b.Lock()
	cells.SetContent(x, y, mainc, combc, st)
	b.Unlock()
}

func (b *baseScreen) GetContent(x, y int) (rune, []rune, Style, int) {
	var primary rune
	var combining []rune
	var style Style
	var width int
	cells := b.GetCells()
	b.Lock()
	primary, combining, style, width = cells.GetContent(x, y)
	b.Unlock()
	return primary, combining, style, width
}

func (b *baseScreen) LockRegion(x, y, width, height int, lock bool) {
	cells := b.GetCells()
	b.Lock()
	for j := y; j < (y + height); j += 1 {
		for i := x; i < (x + width); i += 1 {
			switch lock {
			case true:
				cells.LockCell(i, j)
			case false:
				cells.UnlockCell(i, j)
			}
		}
	}
	b.Unlock()
}

func (b *baseScreen) ChannelEvents(ch chan<- Event, quit <-chan struct{}) {
	defer close(ch)
	for {
		select {
		case <-quit:
			return
		case <-b.StopQ():
			return
		case ev := <-b.EventQ():
			select {
			case <-quit:
				return
			case <-b.StopQ():
				return
			case ch <- ev:
			}
		}
	}
}

func (b *baseScreen) PollEvent() Event {
	select {
	case <-b.StopQ():
		return nil
	case ev := <-b.EventQ():
		return ev
	}
}

func (b *baseScreen) HasPendingEvent() bool {
	return len(b.EventQ()) > 0
}

func (b *baseScreen) PostEventWait(ev Event) {
	select {
	case b.EventQ() <- ev:
	case <-b.StopQ():
	}
}

func (b *baseScreen) PostEvent(ev Event) error {
	select {
	case b.EventQ() <- ev:
		return nil
	default:
		return ErrEventQFull
	}
}

func (b *baseScreen) SetCursorStyle(cs CursorStyle, ccs ...Color) {
	if len(ccs) > 0 {
		b.SetCursor(cs, ccs[0])
	} else {
		b.SetCursor(cs, ColorNone)
	}
}