tableview.go

package clui

import (
	"fmt"
	term "github.com/nsf/termbox-go"
)

/*
TableView is control to display a list of items in a table(grid).
Content is scrollable with arrow keys and mouse.
TableView always works in virtual mode - it does not keep table
data and always asks for the cell value using callback OnDrawCell.

Predefined hotkeys:
  Arrows - move cursor
  Home, End - move cursor to first and last column, respectively
  Alt+Home, Alt+End - move cursor to first and last row, respectively
  PgDn, PgUp - move cursor to a screen down and up
  Enter, F2 - emits event TableActionEdit
  Insert - emits event TableActionNew
  Delete - emits event TableActionDelete
  F4 - Change sort mode

Events:
  OnDrawCell - called every time the table is going to draw a cell.
        The argument is ColumnDrawInfo prefilled with the current
        cell attributes. Callback should fill at least the field
        Title. Filling Bg, Fg, and Alignment are optional. Changing
        other fields in callback does not make any difference - they
        are only for caller convenience
  OnAction - called when a user pressed some hotkey(please, see
        above) or clicks any column header(in this case, the control
        sends TableActionSort event and fills column number and
        sorting type - no sort, ascending, descending)
  OnKeyPress - called every time a user presses a key. Callback should
        return true if TableView must skip internal key processing.
        E.g, a user can disable emitting TableActionDelete event by
        adding callback OnKeyPress and retun true in case of Delete
        key is pressed
  OnSelectCell - called in case of the currently selected row or
        column is changed
*/
type TableView struct {
	BaseControl
	// own listbox members
	topRow        int
	topCol        int
	selectedRow   int
	selectedCol   int
	columns       []Column
	rowCount      int
	fullRowSelect bool
	showRowNo     bool
	showVLines    bool

	onDrawCell   func(*ColumnDrawInfo)
	onAction     func(TableEvent)
	onKeyPress   func(term.Key) bool
	onSelectCell func(int, int)

	// internal variable to avoid sending onSelectCell twice or more
	// in case of current cell is unchanged
	lastEventCol int
	lastEventRow int
}

// Column is a information about a table column.
// When one sets a column list, it the fields Title
// and Width should be set. All other fields can be
// undefined.
type Column struct {
	Title     string
	Width     int
	Alignment Align
	Fg, Bg    term.Attribute
	Sort      SortOrder
}

// ColumnDrawInfo is a structure used in OnDrawCell event.
// A callback should assign Text field otherwise the cell
// will be empty. In addition to it, the callback can
// change Bg, Fg, and Alignment to display customizes
// info. All other non-mentioned fields are for a user
// convinience and used to describe the cell more detailed,
// changing that fields affects nothing
type ColumnDrawInfo struct {
	// row number
	Row int
	// column number
	Col int
	// width of the cell
	Width int
	// cell displayed text
	Text string
	// text alignment
	Alignment Align
	// is the row that contains the cell selected(active)
	RowSelected bool
	// is the column that contains the cell selected(active)
	CellSelected bool
	// current text color
	Fg term.Attribute
	// current background color
	Bg term.Attribute
}

// TableEvent is structure to describe the common action that a
// TableView ask for while a user is interacting with the table
type TableEvent struct {
	// requested action: Add, Edit, Delete, Sort data
	Action TableAction
	// Currently selected column
	Col int
	// Currently selected row (it is not used for TableActionSort)
	Row int
	// Sort order (it is used only in TableActionSort event)
	Sort SortOrder
}

/*
NewTableView creates a new frame.
view - is a View that manages the control
parent - is container that keeps the control. The same View can be a view and a parent at the same time.
width and heigth - are minimal size of the control.
scale - the way of scaling the control when the parent is resized. Use DoNotScale constant if the
control should keep its original size.
*/
func CreateTableView(parent Control, width, height int, scale int) *TableView {
	l := new(TableView)
	l.BaseControl = NewBaseControl()

	if height == AutoSize {
		height = 3
	}
	if width == AutoSize {
		width = 10
	}

	l.SetSize(width, height)
	l.SetConstraints(width, height)
	l.selectedCol = 0
	l.selectedRow = 0
	l.parent = parent
	l.columns = make([]Column, 0)
	l.SetScale(scale)

	l.SetTabStop(true)

	l.onDrawCell = nil
	l.onAction = nil
	l.onKeyPress = nil
	l.onSelectCell = nil
	l.lastEventCol = -1
	l.lastEventRow = -1

	if parent != nil {
		parent.AddChild(l)
	}

	return l
}

func (l *TableView) drawHeader() {
	PushAttributes()
	defer PopAttributes()

	fg, bg := RealColor(l.fg, l.Style(), ColorTableHeaderText), RealColor(l.bg, l.Style(), ColorTableHeaderBack)
	fgLine := RealColor(l.fg, l.Style(), ColorTableLineText)
	x, y := l.Pos()
	w, _ := l.Size()
	SetTextColor(fg)
	SetBackColor(bg)
	FillRect(x, y, w, 1, ' ')
	parts := []rune(SysObject(ObjTableView))

	for i := 0; i < w; i++ {
		PutChar(x+i, y+1, parts[0])
	}
	w-- // scrollbar

	dx := 0
	if l.showVLines {
		dx = 1
	}

	pos := 0
	SetBackColor(bg)
	if l.showRowNo {
		cW := l.counterWidth()
		shift, str := AlignText("#", cW, AlignRight)
		SetTextColor(fg)
		DrawRawText(x+pos+shift, y, str)
		if l.showVLines {
			SetTextColor(fgLine)
			PutChar(x+pos+cW, y, parts[1])
			PutChar(x+pos+cW, y+1, parts[2])
			pos++
		}
		pos = cW + dx
	}

	idx := l.topCol
	for pos < w && idx < len(l.columns) {
		w := l.columns[idx].Width
		if l.width-1-pos < w {
			w = l.width - 1 - pos
		}
		if w <= 0 {
			break
		}

		dw := 0
		if l.columns[idx].Sort != SortNone {
			dw = -1
			ch := parts[3]
			if l.columns[idx].Sort == SortDesc {
				ch = parts[4]
			}
			SetTextColor(fg)
			PutChar(x+pos+w-1, y, ch)
		}

		shift, str := AlignColorizedText(l.columns[idx].Title, w+dw, l.columns[idx].Alignment)
		SetTextColor(fg)
		DrawText(x+pos+shift, y, str)
		pos += w

		if l.showVLines && idx < len(l.columns)-1 {
			SetTextColor(fgLine)
			PutChar(x+pos, y, parts[1])
			PutChar(x+pos, y+1, parts[2])
			pos++
		}

		idx++
	}
}

func (l *TableView) counterWidth() int {
	width := 0

	if l.showRowNo {
		s := fmt.Sprintf("%v", l.rowCount)
		if s == "" {
			s = " "
		}
		width = len(s)
	}

	return width
}

func (l *TableView) drawScroll() {

	pos := ThumbPosition(l.selectedRow, l.rowCount, l.height-1)
	DrawScrollBar(l.x+l.width-1, l.y, 1, l.height-1, pos)

	pos = ThumbPosition(l.selectedCol, len(l.columns), l.width-1)
	DrawScrollBar(l.x, l.y+l.height-1, l.width-1, 1, pos)
	PutChar(l.x+l.width-1, l.y+l.height-1, ' ')
}

func (l *TableView) drawCells() {
	PushAttributes()
	defer PopAttributes()

	maxRow := l.rowCount - 1
	rowNo := l.topRow
	dy := 2
	maxDy := l.height - 2

	fg, bg := RealColor(l.fg, l.Style(), ColorTableText), RealColor(l.bg, l.Style(), ColorTableBack)
	fgRow, bgRow := RealColor(l.fg, l.Style(), ColorTableSelectedText), RealColor(l.bg, l.Style(), ColorTableSelectedBack)
	fgCell, bgCell := RealColor(l.fg, l.Style(), ColorTableActiveCellText), RealColor(l.bg, l.Style(), ColorTableActiveCellBack)
	fgLine := RealColor(l.fg, l.Style(), ColorTableLineText)
	parts := []rune(SysObject(ObjTableView))

	start := 0
	if l.showRowNo {
		start = l.counterWidth()
		for idx := 1; idx < l.height-2; idx++ {
			if l.topRow+idx > l.rowCount {
				break
			}
			s := fmt.Sprintf("%v", idx+l.topRow)
			shift, str := AlignText(s, start, AlignRight)
			SetTextColor(fg)
			SetBackColor(bg)
			DrawText(l.x+shift, l.y+dy+idx-1, str)
			if l.showVLines {
				SetTextColor(fgLine)
				PutChar(l.x+start, l.y+dy+idx-1, parts[1])
			}
		}
		if l.showVLines {
			start++
		}
	}

	for rowNo <= maxRow && dy <= maxDy {
		colNo := l.topCol
		dx := start
		for colNo < len(l.columns) && dx < l.width-1 {
			c := l.columns[colNo]
			info := ColumnDrawInfo{Row: rowNo, Col: colNo, Width: c.Width, Alignment: c.Alignment}
			if l.selectedRow == rowNo && l.selectedCol == colNo {
				info.RowSelected = true
				info.CellSelected = true
				info.Bg = bgCell
				info.Fg = fgCell
			} else if l.selectedRow == rowNo && l.fullRowSelect {
				info.RowSelected = true
				info.Bg = bgRow
				info.Fg = fgRow
			} else {
				info.Fg = fg
				info.Bg = bg
			}

			if l.onDrawCell != nil {
				l.onDrawCell(&info)
			}

			length := c.Width
			if length+dx >= l.width-1 {
				length = l.width - 1 - dx
			}
			SetTextColor(info.Fg)
			SetBackColor(info.Bg)
			FillRect(l.x+dx, l.y+dy, length, 1, ' ')
			shift, text := AlignColorizedText(info.Text, length, info.Alignment)
			DrawText(l.x+dx+shift, l.y+dy, text)

			dx += c.Width
			if l.showVLines && dx < l.width-1 && colNo < len(l.columns)-1 {
				SetTextColor(fg)
				SetBackColor(bg)
				PutChar(l.x+dx, l.y+dy, parts[1])
				dx++
			}

			colNo++
		}

		rowNo++
		dy++
	}
}

// Repaint draws the control on its View surface
func (l *TableView) Draw() {
	if l.hidden {
		return
	}

	l.mtx.RLock()
	defer l.mtx.RUnlock()
	PushAttributes()
	defer PopAttributes()

	x, y := l.Pos()
	w, h := l.Size()

	bg := RealColor(l.bg, l.Style(), ColorTableBack)
	SetBackColor(bg)
	FillRect(x, y+2, w, h-2, ' ')
	l.drawHeader()
	l.drawScroll()
	l.drawCells()
}

func (l *TableView) emitSelectionChange() {
	if l.lastEventRow == l.selectedRow && l.lastEventCol == l.selectedCol {
		return
	}

	if l.selectedCol != -1 && l.selectedRow != -1 && l.onSelectCell != nil {
		l.onSelectCell(l.selectedCol, l.selectedRow)
		l.lastEventRow = l.selectedRow
		l.lastEventCol = l.selectedCol
	}
}

func (l *TableView) home() {
	if len(l.columns) > 0 {
		l.selectedCol = 0
	}
	l.topCol = 0
	l.EnsureColVisible()
	l.emitSelectionChange()
}

func (l *TableView) end() {
	length := len(l.columns)

	if length == 0 {
		return
	}

	l.selectedCol = length - 1
	l.EnsureColVisible()
	l.emitSelectionChange()
}

func (l *TableView) firstRow() {
	if l.rowCount > 0 {
		l.selectedRow = 0
	}
	l.topRow = 0
	l.EnsureRowVisible()
	l.emitSelectionChange()
}

func (l *TableView) lastRow() {
	if l.rowCount == 0 {
		return
	}

	l.selectedRow = l.rowCount - 1
	l.EnsureColVisible()
	l.emitSelectionChange()
}

func (l *TableView) moveUp(dy int) {
	if l.topRow == 0 && l.selectedRow == 0 {
		return
	}

	if l.selectedRow == -1 {
		if l.rowCount != 0 {
			l.selectedRow = 0
			l.emitSelectionChange()
		}
		return
	}

	if l.selectedRow < dy {
		l.selectedRow = 0
	} else {
		l.selectedRow -= dy
	}

	l.EnsureRowVisible()
	l.emitSelectionChange()
}

func (l *TableView) moveDown(dy int) {
	length := l.rowCount

	if length == 0 || l.selectedRow == length-1 {
		return
	}

	if l.selectedRow+dy >= length {
		l.selectedRow = length - 1
	} else {
		l.selectedRow += dy
	}

	l.EnsureRowVisible()
	l.emitSelectionChange()
}

func (l *TableView) moveRight(dx int) {
	colCnt := len(l.columns)
	if l.selectedCol == colCnt-1 || colCnt == 0 {
		return
	}

	if l.selectedCol == -1 {
		l.selectedCol = 0
	} else {
		if l.selectedCol+dx >= colCnt {
			l.selectedCol = colCnt - 1
		} else {
			l.selectedCol += dx
		}
	}

	l.EnsureColVisible()
	l.emitSelectionChange()
}

func (l *TableView) moveLeft(dx int) {
	colCnt := len(l.columns)
	if l.selectedCol == 0 || colCnt == 0 {
		return
	}

	if l.selectedCol == -1 {
		l.selectedCol = 0
	} else {
		if l.selectedCol-dx < 0 {
			l.selectedCol = 0
		} else {
			l.selectedCol -= dx
		}
	}

	l.EnsureColVisible()
	l.emitSelectionChange()
}

func (l *TableView) isColVisible(idx int) bool {
	if idx < l.topCol {
		return false
	}

	width := l.width - 1
	width -= l.counterWidth()
	if l.showVLines && l.showRowNo {
		width--
	}

	for i := l.topCol; i < len(l.columns); i++ {
		if i == idx && l.columns[i].Width <= width {
			return true
		}

		width -= l.columns[i].Width
	}

	return false
}

// EnsureColVisible scrolls the table horizontally
// to make the curently selected column fully visible
func (l *TableView) EnsureColVisible() {
	if l.isColVisible(l.selectedCol) {
		return
	}

	if l.selectedCol < l.topCol {
		l.topCol = l.selectedCol
		return
	}

	width := l.width - 1 - l.counterWidth()
	if l.showRowNo && l.showVLines {
		width--
	}

	toShow := l.selectedCol
	for width > 0 {
		if l.columns[toShow].Width > width {
			if toShow == l.selectedCol {
				break
			} else {
				toShow++
				break
			}
		} else if l.columns[toShow].Width == width {
			break
		} else {
			width -= l.columns[toShow].Width
			if width < 0 {
				break
			}
			toShow--
			if toShow == 0 {
				break
			}
		}
	}

	l.topCol = toShow
}

// EnsureRowVisible scrolls the table vertically
// to make the curently selected row visible
func (l *TableView) EnsureRowVisible() {
	length := l.rowCount

	hgt := l.height - 3

	if length <= hgt || l.selectedRow == -1 {
		return
	}

	diff := l.selectedRow - l.topRow
	if diff >= 0 && diff < hgt {
		return
	}

	if diff < 0 {
		l.topRow = l.selectedRow
	} else {
		top := l.selectedRow - hgt + 1
		if length-top > hgt {
			l.topRow = top
		} else {
			l.topRow = length - hgt
		}
	}
}

func (l *TableView) mouseToCol(dx int) int {
	shift := l.counterWidth()
	if l.showVLines {
		shift++
	}

	if dx < shift {
		return -1
	}

	idx := l.topCol
	selectedCol := l.selectedCol
	for {
		if shift+l.columns[idx].Width > dx {
			selectedCol = idx
			break
		}

		if idx == len(l.columns)-1 {
			selectedCol = idx
			break
		}

		shift += l.columns[idx].Width
		if l.showVLines {
			shift++
		}
		idx++
	}

	return selectedCol
}

func (l *TableView) horizontalScrollClick(dx int) {
	if dx == 0 {
		l.moveLeft(1)
		return
	} else if dx == l.width-2 {
		l.moveRight(1)
	} else if dx > 0 && dx < l.width-2 {
		pos := ThumbPosition(l.selectedCol, len(l.columns), l.width-1)
		if pos < dx {
			l.moveRight(1)
		} else if pos > dx {
			l.moveLeft(1)
		}
	}
}

func (l *TableView) verticalScrollClick(dy int) {
	if dy == 0 {
		l.moveUp(1)
		return
	} else if dy == l.height-2 {
		l.moveDown(1)
	} else if dy > 0 && dy < l.height-2 {
		pos := ThumbPosition(l.selectedRow, l.rowCount, l.height-1)
		if pos > dy {
			l.moveUp(l.height - 3)
		} else if pos < dy {
			l.moveDown(l.height - 3)
		}
	}
}

func (l *TableView) processMouseClick(ev Event) bool {
	if ev.Key != term.MouseLeft {
		return false
	}

	dx := ev.X - l.x
	dy := ev.Y - l.y

	if l.topRow+dy-2 >= l.rowCount && dy != l.height-1 && dx != l.width-1 {
		return false
	}

	if dy == l.height-1 && dx == l.width-1 {
		l.selectedRow = l.rowCount - 1
		l.selectedCol = len(l.columns) - 1
		return true
	}

	if dy == l.height-1 {
		l.horizontalScrollClick(dx)
		return true
	}

	if dx == l.width-1 {
		l.verticalScrollClick(dy)
		return true
	}

	if dy < 2 {
		l.headerClicked(dx)
		return true
	}

	dy -= 2
	newRow := l.topRow + dy

	newCol := l.mouseToCol(dx)
	if newCol == -1 && newRow != l.selectedRow {
		l.selectedRow = newRow
		l.EnsureColVisible()
		l.emitSelectionChange()
	} else if newCol != -1 && (newCol != l.selectedCol || newRow != l.selectedRow) {
		l.selectedCol = newCol
		l.selectedRow = newRow
		l.EnsureColVisible()
		l.emitSelectionChange()
	}

	return true
}

func (l *TableView) headerClicked(dx int) {
	colID := l.mouseToCol(dx)
	if colID == -1 {
		if l.onAction != nil {
			ev := TableEvent{Action: TableActionSort, Col: -1, Row: -1}
			l.onAction(ev)
		}
	} else {
		sort := l.columns[colID].Sort

		for idx := range l.columns {
			l.columns[idx].Sort = SortNone
		}

		if sort == SortAsc {
			sort = SortDesc
		} else if sort == SortNone {
			sort = SortAsc
		} else {
			sort = SortNone
		}
		l.columns[colID].Sort = sort

		if l.onAction != nil {
			ev := TableEvent{Action: TableActionSort, Col: colID, Row: -1, Sort: sort}
			l.onAction(ev)
		}
	}
}

/*
ProcessEvent processes all events come from the control parent. If a control
processes an event it should return true. If the method returns false it means
that the control do not want or cannot process the event and the caller sends
the event to the control parent
*/
func (l *TableView) ProcessEvent(event Event) bool {
	if !l.Active() || !l.Enabled() {
		return false
	}

	switch event.Type {
	case EventKey:
		if l.onKeyPress != nil {
			res := l.onKeyPress(event.Key)
			if res {
				return true
			}
		}

		switch event.Key {
		case term.KeyHome:
			if event.Mod == term.ModAlt {
				l.selectedRow = 0
				l.EnsureRowVisible()
				l.emitSelectionChange()
			} else {
				l.home()
			}
			return true
		case term.KeyEnd:
			if event.Mod == term.ModAlt {
				l.selectedRow = l.rowCount - 1
				l.EnsureRowVisible()
				l.emitSelectionChange()
			} else {
				l.end()
			}
			return true
		case term.KeyArrowUp:
			l.moveUp(1)
			return true
		case term.KeyArrowDown:
			l.moveDown(1)
			return true
		case term.KeyArrowLeft:
			l.moveLeft(1)
			return true
		case term.KeyArrowRight:
			l.moveRight(1)
			return true
		case term.KeyPgdn:
			l.moveDown(l.height - 3)
			return true
		case term.KeyPgup:
			l.moveUp(l.height - 3)
			return true
		case term.KeyCtrlM:
		case term.KeyF2:
			if l.selectedRow != -1 && l.selectedCol != -1 && l.onAction != nil {
				ev := TableEvent{Action: TableActionEdit, Col: l.selectedCol, Row: l.selectedRow}
				l.onAction(ev)
			}
		case term.KeyDelete:
			if l.selectedRow != -1 && l.onAction != nil {
				ev := TableEvent{Action: TableActionDelete, Col: l.selectedCol, Row: l.selectedRow}
				l.onAction(ev)
			}
		case term.KeyInsert:
			if l.onAction != nil {
				ev := TableEvent{Action: TableActionNew, Col: l.selectedCol, Row: l.selectedRow}
				l.onAction(ev)
			}
		case term.KeyF4:
			if l.onAction != nil {
				colID := l.selectedCol
				sort := l.columns[colID].Sort

				for idx := range l.columns {
					l.columns[idx].Sort = SortNone
				}

				if sort == SortAsc {
					sort = SortDesc
				} else if sort == SortNone {
					sort = SortAsc
				} else {
					sort = SortNone
				}
				l.columns[colID].Sort = sort

				ev := TableEvent{Action: TableActionSort, Col: colID, Row: -1, Sort: sort}
				l.onAction(ev)
			}
		default:
			return false
		}
	case EventMouse:
		return l.processMouseClick(event)
	}

	return false
}

// own methods

// ShowLines returns true if table displays vertical
// lines to separate columns
func (l *TableView) ShowLines() bool {
	return l.showVLines
}

// SetShowLines disables and enables displaying vertical
// lines inside TableView
func (l *TableView) SetShowLines(show bool) {
	l.showVLines = show
}

// ShowRowNumber returns true if the table shows the
// row number as the first table column. This virtual
// column is always fixed and a user cannot change
// displayed text
func (l *TableView) ShowRowNumber() bool {
	return l.showRowNo
}

// SetShowRowNumber turns on and off the first fixed
// column of the table that displays the row number
func (l *TableView) SetShowRowNumber(show bool) {
	l.showRowNo = show
}

// Columns returns the current list of table columns
func (l *TableView) Columns() []Column {
	c := make([]Column, len(l.columns))
	copy(c, l.columns)
	return c
}

// SetColumns replaces existing table column list with
// a new one. Be sure that every item has correct
// Title and Width, all other column properties may
// be undefined
func (l *TableView) SetColumns(cols []Column) {
	l.columns = cols
}

// SetColumnInfo replaces the existing column info
func (l *TableView) SetColumnInfo(id int, col Column) {
	if id < len(l.columns) {
		l.columns[id] = col
	}
}

// RowCount returns current row count
func (l *TableView) RowCount() int {
	return l.rowCount
}

// SetRowCount sets the new row count
func (l *TableView) SetRowCount(count int) {
	l.rowCount = count
}

// FullRowSelect returns if TableView hilites the selected
// cell only or the whole row that contains the selected
// cell. By default the colors for selected row and cell
// are different
func (l *TableView) FullRowSelect() bool {
	return l.fullRowSelect
}

// SetFullRowSelect enables or disables hiliting of the
// full row that contains the selected cell
func (l *TableView) SetFullRowSelect(fullRow bool) {
	l.fullRowSelect = fullRow
}

// OnSelectCell sets a callback that is called every time
// the selected cell is changed
func (l *TableView) OnSelectCell(fn func(int, int)) {
	l.onSelectCell = fn
}

// OnKeyPress sets the callback that is called when a user presses a Key while
// the controls is active. If a handler processes the key it should return
// true. If handler returns false it means that the default handler has to
// process the key
func (l *TableView) OnKeyPress(fn func(term.Key) bool) {
	l.onKeyPress = fn
}

// OnDrawCell is called every time the table is going to display
// a cell
func (l *TableView) OnDrawCell(fn func(*ColumnDrawInfo)) {
	l.mtx.Lock()
	defer l.mtx.Unlock()

	l.onDrawCell = fn
}

// OnAction is called when the table wants a user application to
// do some job like add, delete, edit or sort data
func (l *TableView) OnAction(fn func(TableEvent)) {
	l.onAction = fn
}

// SelectedRow returns currently selected row number or
// -1 if no row is selected
func (l *TableView) SelectedRow() int {
	return l.selectedRow
}

// SelectedCol returns currently selected column number or
// -1 if no column is selected
func (l *TableView) SelectedCol() int {
	return l.selectedCol
}

// SetSelectedRow changes the currently selected row.
// If row is greater than number of row the last row
// is selected. Set row to -1 to turn off selection.
// The table scrolls automatically to display the column
func (l *TableView) SetSelectedRow(row int) {
	oldSelection := l.selectedRow
	if row >= l.rowCount {
		l.selectedRow = l.rowCount - 1
	} else if row < -1 {
		l.selectedRow = -1
	}

	if l.selectedRow != oldSelection {
		l.EnsureRowVisible()
		l.emitSelectionChange()
	}
}

// SetSelectedCol changes the currently selected column.
// If column is greater than number of columns the last
// column is selected. Set row to -1 to turn off selection.
// The table scrolls automatically to display the column
func (l *TableView) SetSelectedCol(col int) {
	oldSelection := l.selectedCol
	if col >= len(l.columns) {
		l.selectedCol = len(l.columns) - 1
	} else if col < -1 {
		l.selectedCol = -1
	}

	if l.selectedCol != oldSelection {
		l.EnsureColVisible()
		l.emitSelectionChange()
	}
}