Add Table.Sort, Table.SetSortFunc and Table.SetSortClicked

Resolves #33.

CHANGELOG

@@ -1,5 +1,6 @@
 v1.4.9 (WIP)
 - Add InputField.GetCursorPosition and InputField.SetCursorPosition
+- Add Table.Sort, Table.SetSortFunc and Table.SetSortClicked
 - Upgrade tcell to v2: includes strikethrough support
 
 v1.4.8 (2020-08-11)

table.go

@@ -285,6 +285,18 @@ type Table struct {
 	// If set to true, the table's last row will always be visible.
 	trackEnd bool
 
+	// The sort function of the table. Defaults to a case-sensitive string comparison.
+	sortFunc func(column, i, j int) bool
+
+	// Whether or not the table should be sorted when a fixed row is clicked.
+	sortClicked bool
+
+	// The last direction the table was sorted by when clicked.
+	sortClickedDescending bool
+
+	// The last column the table was sorted by when clicked.
+	sortClickedColumn int
+
 	// The number of visible rows the last time the table was drawn.
 	visibleRows int
 
@@ -330,6 +342,7 @@ func NewTable() *Table {
 		scrollBarColor:      Styles.ScrollBarColor,
 		bordersColor:        Styles.GraphicsColor,
 		separator:           ' ',
+		sortClicked:         true,
 		lastColumn:          -1,
 	}
 }
@@ -706,7 +719,7 @@ func (t *Table) cellAt(x, y int) (row, column int) {
 		}
 	}
 
-	// Saerch for the clicked column.
+	// Search for the clicked column.
 	column = -1
 	if x >= rectX {
 		columnX := rectX
@@ -752,6 +765,59 @@ func (t *Table) ScrollToEnd() *Table {
 	return t
 }
 
+// SetSortClicked sets a flag which determines whether the table is sorted when
+// a fixed row is clicked. This flag is enabled by default.
+func (t *Table) SetSortClicked(sortClicked bool) *Table {
+	t.Lock()
+	defer t.Unlock()
+
+	t.sortClicked = sortClicked
+	return t
+}
+
+// SetSortFunc sets the sorting function used for the table. When unset, a
+// case-sensitive string comparison is used.
+func (t *Table) SetSortFunc(sortFunc func(column, i, j int) bool) *Table {
+	t.Lock()
+	defer t.Unlock()
+
+	t.sortFunc = sortFunc
+	return t
+}
+
+// Sort sorts the table by the column at the given index. You may set a custom
+// sorting function with SetSortFunc.
+func (t *Table) Sort(column int, descending bool) *Table {
+	t.Lock()
+	defer t.Unlock()
+
+	if len(t.cells) == 0 || column < 0 || column >= len(t.cells[0]) {
+		return t
+	}
+
+	if t.sortFunc == nil {
+		t.sortFunc = func(column, i, j int) bool {
+			return t.cells[i][column].Text < t.cells[j][column].Text
+		}
+	}
+
+	sort.SliceStable(t.cells, func(i, j int) bool {
+		if i < t.fixedRows {
+			return i < j
+		} else if j < t.fixedRows {
+			return j > i
+		}
+
+		if !descending {
+			return t.sortFunc(column, i, j)
+		} else {
+			return t.sortFunc(column, j, i)
+		}
+	})
+
+	return t
+}
+
 // Draw draws this primitive onto the screen.
 func (t *Table) Draw(screen tcell.Screen) {
 	t.Box.Draw(screen)
@@ -1424,9 +1490,31 @@ func (t *Table) MouseHandler() func(action MouseAction, event *tcell.EventMouse,
 
 		switch action {
 		case MouseLeftClick:
-			if t.rowsSelectable || t.columnsSelectable {
+			_, tableY, _, _ := t.GetInnerRect()
+			mul := 1
+			maxY := tableY
+			if t.borders {
+				mul = 2
+				maxY = tableY + 1
+			}
+
+			if t.sortClicked && t.fixedRows > 0 && (y >= tableY && y < maxY+(t.fixedRows*mul)) {
+				_, column := t.cellAt(x, y)
+				if t.sortClickedColumn != column {
+					t.sortClickedColumn = column
+					t.sortClickedDescending = false
+				} else {
+					t.sortClickedDescending = !t.sortClickedDescending
+				}
+				t.Sort(column, t.sortClickedDescending)
+
+				if t.columnsSelectable {
+					t.selectedColumn = column
+				}
+			} else if t.rowsSelectable || t.columnsSelectable {
 				t.Select(t.cellAt(x, y))
 			}
+
 			consumed = true
 			setFocus(t)
 		case MouseScrollUp: