Issue 23: Added progress indicators and cancellation (#34)

- Wrapped all table operations in a new foreground job context, which mediates foreground tasks.
- Added cancellation support and partial results for table read operations.
- Added the "mark" command, which can mark, unmark & toggle marked items
- Added support for alias arguments.
- Removed the "unmark" command, and replaced it as an alias to the "marked" command
- Fixed seg faults raised when there is no table shown in the result set.

internal/dynamo-browse/ui/teamodels/dynamotableview/colmodel.go

@@ -5,6 +5,10 @@ type columnModel struct {
 }
 
 func (cm columnModel) Len() int {
+	if len(cm.m.columns) == 0 {
+		return 0
+	}
+
 	return len(cm.m.columns[cm.m.colOffset:]) + 1
 }
 

internal/dynamo-browse/ui/teamodels/dynamotableview/model.go

@@ -118,6 +118,10 @@ func (m *Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 }
 
 func (m *Model) setLeftmostDisplayedColumn(newCol int) {
+	if m.columnsProvider == nil || m.columnsProvider.Columns() == nil {
+		return
+	}
+
 	if newCol < 0 {
 		m.colOffset = 0
 	} else if newCol >= len(m.columnsProvider.Columns().Columns) {
@@ -163,11 +167,8 @@ func (m *Model) rebuildTable(targetTbl *table.Model) {
 
 	// Use the target table model if you can, but if it's nil or the number of rows is smaller than the
 	// existing table, create a new one
-	if targetTbl == nil || len(resultSet.Items()) > len(m.rows) {
+	if targetTbl == nil {
 		tbl = table.New(columnModel{m}, m.w, m.h-m.frameTitle.HeaderHeight())
-		if targetTbl != nil {
-			tbl.GoBottom()
-		}
 	} else {
 		tbl = *targetTbl
 	}
@@ -191,6 +192,7 @@ func (m *Model) rebuildTable(targetTbl *table.Model) {
 
 	m.rows = newRows
 	tbl.SetRows(newRows)
+	tbl.GoTop() // Preserve top and cursor location
 
 	m.table = tbl
 }
@@ -205,6 +207,12 @@ func (m *Model) SelectedItemIndex() int {
 
 func (m *Model) selectedItem() (itemTableRow, bool) {
 	resultSet := m.resultSet
+
+	// Fix bug??
+	if m.table.Cursor() < 0 {
+		return itemTableRow{}, false
+	}
+
 	if resultSet != nil && len(m.rows) > 0 {
 		selectedItem, ok := m.table.SelectedRow().(itemTableRow)
 		if ok {