Some basic TextArea code.

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/lucasb-eyer/go-colorful v1.2.0
 	github.com/mattn/go-runewidth v0.0.13
 	github.com/rivo/uniseg v0.2.0
-	golang.org/x/sys v0.0.0-20210309074719-68d13333faf2 // indirect
+	golang.org/x/sys v0.0.0-20211019181941-9d821ace8654 // indirect
 	golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d // indirect
+	golang.org/x/text v0.3.7 // indirect
 )

go.sum

@@ -9,12 +9,13 @@ github.com/mattn/go-runewidth v0.0.13/go.mod h1:Jdepj2loyihRzMpdS35Xk/zdY8IAYHsh
 github.com/rivo/uniseg v0.2.0 h1:S1pD9weZBuJdFmowNwbpi7BJ8TNftyUImj/0WQi72jY=
 github.com/rivo/uniseg v0.2.0/go.mod h1:J6wj4VEh+S6ZtnVlnTBMWIodfgj8LQOQFoIToxlJtxc=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210309074719-68d13333faf2 h1:46ULzRKLh1CwgRq2dC5SlBzEqqNCi8rreOZnNrbqcIY=
-golang.org/x/sys v0.0.0-20210309074719-68d13333faf2/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20211019181941-9d821ace8654 h1:id054HUawV2/6IGm2IV8KZQjqtwAOo2CYlOToYqa0d0=
+golang.org/x/sys v0.0.0-20211019181941-9d821ace8654/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201210144234-2321bbc49cbf/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d h1:SZxvLBoTP5yHO3Frd4z4vrF+DBX9vMVanchswa69toE=
 golang.org/x/term v0.0.0-20210220032956-6a3ed077a48d/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
 golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=

textarea.go

@@ -0,0 +1,161 @@
+package tview
+
+import "github.com/gdamore/tcell/v2"
+
+var (
+	// NewLine is the string sequence to be inserted when hitting the Enter key
+	// in a TextArea. The default is "\n" but you may change it to "\r\n" if
+	// required.
+	NewLine = "\n"
+)
+
+// TextArea implements a simple text editor for multi-line text. Multi-color
+// text is not supported. Text can be optionally word-wrapped to fit the
+// available width.
+//
+// Navigation and Editing
+//
+// A text area is always in editing mode and no other mode exists. The following
+// keys can be used to move the cursor:
+//
+//   - Left arrow: Move left.
+//   - Right arrow: Move right.
+//   - Down arrow: Move down.
+//   - Up arrow: Move up.
+//   - Ctrl-A, Home: Move to the beginning of the current line.
+//   - Ctrl-E, End: Move to the end of the current line.
+//   - Ctrl-F, page down: Move down by one page.
+//   - Ctrl-B, page up: Move up by one page.
+//   - TODO (Shift+Ctrl-/Alt-Up arrow): Scroll the page up, leaving the cursor in its position.
+//   - TODO (Shift+Ctrl-/Alt-Down arrow): Scroll the page down, leaving the cursor in its position.
+//
+// If the mouse is enabled, clicking on a screen cell will move the cursor to
+// that location or to the end of the line if past the last character. Turning
+// the scroll wheel will scroll the text. Text can also be selected by moving
+// the mouse while pressing the left mouse button (see below for details).
+//
+// Entering a character (rune) will insert it at the current cursor location.
+// Subsequent characters are moved accordingly. If the cursor is outside the
+// visible area, any changes to the text will move it into the visible area. The
+// following keys can also be used to modify the text:
+//
+//   - Enter: Insert a newline character (see NewLine).
+//   - Tab: Insert TabSize spaces.
+//   - Ctrl-H, Backspace: Delete one character to the left of the cursor.
+//   - Ctrl-D, Delete: Delete the character under the cursor (or the first
+//     character on the next line if the cursor is at the end of a line).
+//   - Ctrl-K: Delete everything under and to the right of the cursor.
+//   - Ctrl-W: Delete from the start of the current word to the left of the
+//     cursor.
+//   - Ctrl-U: Delete the current line, i.e. everything after the last newline
+//     character before the cursor up until the next newline character. This may
+//     span multiple lines if wrapping is enabled.
+//
+// Text can be selected by moving the cursor while holding the Shift key or
+// dragging the mouse. When text is selected:
+//
+//   - Entering a character (rune) will replace the selected text with the new
+//     character. (The Enter key is an exception, see further below.)
+//   - Backspace, delete: Delete the selected text.
+//   - Enter: Copy the selected text into the clipboard, unselect the text.
+//   - Ctrl-X: Copy the selected text into the clipboard and delete it.
+//   - Ctrl-V: Replace the selected text with the clipboard text. If no text is
+//     selected, the clipboard text will be inserted at the cursor location.
+//
+// The default clipboard is an internal text buffer, i.e. the operating system's
+// clipboard is not used. The Enter key was chosen for the "copy" function
+// because the Ctrl-C key is the default key to stop the application. If your
+// application frees up the global Ctrl-C key and you want to bind it to the
+// "copy to clipboard" function, you may use SetInputCapture() to override the
+// Enter/Ctrl-C keys to implement copying to the clipboard.
+//
+// Similarly, if you want to implement your own clipboard (or make use of your
+// operating system's clipboard), you can also use SetInputCapture() to override
+// the key binds for copy, cut, and paste. The GetSelection(), ReplaceText(),
+// and SetSelection() provide all the functionality needed for your own
+// clipboard.
+type TextArea struct {
+	*Box
+
+	// The text to be shown in the text area when it is empty.
+	placeholder string
+
+	// If set to true, lines that are longer than the available width are
+	// wrapped onto the next line. If set to false, any characters beyond the
+	// available width are discarded.
+	wrap bool
+
+	// If set to true and if wrap is also true, lines are split at spaces or
+	// after punctuation characters.
+	wordWrap bool
+
+	// The maximum number of bytes allowed in the text area. If 0, there is no
+	// limit.
+	maxLength int
+
+	// The index of the first line shown in the text area.
+	lineOffset int
+
+	// The number of cells to be skipped on each line (not used in wrap mode).
+	columnOffset int
+
+	// The height of the content the last time the text area was drawn.
+	pageSize int
+
+	// The style of the text. Background colors different from the Box's
+	// background color may lead to unwanted artefacts.
+	textStyle tcell.Style
+}
+
+// NewTextArea returns a new text area.
+func NewTextArea() *TextArea {
+	return &TextArea{
+		Box:       NewBox(),
+		wrap:      true,
+		wordWrap:  true,
+		textStyle: tcell.StyleDefault.Background(Styles.PrimitiveBackgroundColor).Foreground(Styles.PrimaryTextColor),
+	}
+}
+
+// SetWrap sets the flag that, if true, leads to lines that are longer than the
+// available width being wrapped onto the next line. If false, any characters
+// beyond the available width are not displayed.
+func (t *TextArea) SetWrap(wrap bool) *TextArea {
+	//TODO: Existing text needs reformatting.
+	t.wrap = wrap
+	return t
+}
+
+// SetWordWrap sets the flag that, if true and if the "wrap" flag is also true
+// (see SetWrap()), wraps the line at spaces or after punctuation marks.
+//
+// This flag is ignored if the "wrap" flag is false.
+func (t *TextArea) SetWordWrap(wrapOnWords bool) *TextArea {
+	//TODO: Existing text needs reformatting.
+	t.wordWrap = wrapOnWords
+	return t
+}
+
+// SetSelection selects the text starting at index "start" and ending just
+// before the index "end". Any previous selection is discarded. If "start" and
+// "end" are the same, currently selected text is unselected.
+func (t *TextArea) SetSelection(start, end int) *TextArea {
+	//TODO
+	return t
+}
+
+// GetSelection returns the currently selected text or an empty string if no
+// text is currently selected. The start and end indices (a half-open range)
+// into the text area's text are also returned.
+func (t *TextArea) GetSelection() (string, int, int) {
+	return "", 0, 0 //TODO
+}
+
+// ReplaceText replaces the text in the given range with the given text. The
+// range is half-open, that is, the character at the "end" index is not
+// replaced. If the provided range overlaps with a selection, the selected text
+// will be unselected.
+func (t *TextArea) ReplaceText(start, end int, text string) *TextArea {
+	//TODO
+	return t
+}

textview.go

@@ -75,8 +75,12 @@ func (w TextViewWriter) HasFocus() bool {
 	return w.t.hasFocus
 }
 
-// TextView is a box which displays text. It implements the io.Writer interface
-// so you can stream text to it. This does not trigger a redraw automatically
+// TextView is a box which displays text. While the text to be displayed can be
+// changed or appended to, there is no functionality that allows the user to
+// edit text. For that, TextArea should be used.
+//
+// TextView implements the io.Writer interface so you can stream text to it,
+// appending to the existing text. This does not trigger a redraw automatically
 // but if a handler is installed via SetChangedFunc(), you can cause it to be
 // redrawn. (See SetChangedFunc() for more details.)
 //
@@ -179,7 +183,8 @@ type TextView struct {
 	// If set to true, the text view will always remain at the end of the content.
 	trackEnd bool
 
-	// The number of characters to be skipped on each line (not in wrap mode).
+	// The number of characters to be skipped on each line (not used in wrap
+	// mode).
 	columnOffset int
 
 	// The maximum number of lines kept in the line index, effectively the