Refactor the code by adding State type

filter.go

@@ -43,6 +43,7 @@ type State struct {
 	InSelectionMode bool
 	UpperBound      int
 	LowerBound      int
+	Screen          *tcell.Screen
 }
 
 // Draws the given `text` to the screen `s` at the given coordinates. Remember that
@@ -64,11 +65,11 @@ func drawText(s tcell.Screen, x1, y1, x2, y2 int, style tcell.Style, text string
 }
 
 // Main render function that gets called during the event loop.
-func Render(s tcell.Screen, inputs Items, lowerBound int, upperBound int, current int) {
+func Render(s State, inputs Items) {
 	y := 2
-	status := fmt.Sprintf("Navigation: [UP or C-p] [Down or C-n] | Select: SPACE | Cancel: [q ESC] | Done: [Enter] | Line: %d", current+1)
-	drawText(s, 0, 0, xmax-1, 1, helpStyle, status)
-	for i, item := range (*inputs)[lowerBound:upperBound] {
+	status := fmt.Sprintf("Navigation: [UP or C-p] [Down or C-n] | Select: SPACE | Cancel: [q ESC] | Done: [Enter] | Line: %d", s.Current+1)
+	drawText(*s.Screen, 0, 0, xmax-1, 1, helpStyle, status)
+	for i, item := range (*inputs)[s.LowerBound:s.UpperBound] {
 		style := tcell.StyleDefault
 		var txt string
 
@@ -79,16 +80,16 @@ func Render(s tcell.Screen, inputs Items, lowerBound int, upperBound int, curren
 			txt = fmt.Sprintf("    %s", item.Text)
 		}
 
-		if current == lowerBound+i {
+		if s.Current == s.LowerBound+i {
 			style = highlight
 		}
 
-		drawText(s, 0, y, xmax-1, y+1, style, txt)
+		drawText(*s.Screen, 0, y, xmax-1, y+1, style, txt)
 		// Clean up the rest of the line that might've been filled with a previous render.
 		// This is a hack to NOT use `Clear` on each loop
-		drawText(s, len(txt), y, xmax-1, y+1, style, strings.Repeat(" ", xmax-1-len(txt)))
-		if current == lowerBound+i {
-			drawText(s, 0, y, 1, y+1, tcell.StyleDefault.Foreground(tcell.ColorGreen).Bold(true), ">")
+		drawText(*s.Screen, len(txt), y, xmax-1, y+1, style, strings.Repeat(" ", xmax-1-len(txt)))
+		if s.Current == s.LowerBound+i {
+			drawText(*s.Screen, 0, y, 1, y+1, tcell.StyleDefault.Foreground(tcell.ColorGreen).Bold(true), ">")
 		}
 
 		y += 1
@@ -108,7 +109,6 @@ func main() {
 	selectedStyle = tcell.StyleDefault.Foreground(tcell.ColorYellow)
 	helpStyle = tcell.StyleDefault.Foreground(tcell.ColorDefault)
 
-	currentLine := 0
 	done := false
 
 	// Initialize screen
@@ -140,14 +140,19 @@ func main() {
 	}
 	defer quit()
 
-	lowerBound := 0
-	upperBound := min(ymax-3, len(*input))
-	inSelectedMode := false
 	startOfSelection := 0
 
+	state := State{
+		Current:         0,
+		Screen:          &s,
+		LowerBound:      0,
+		UpperBound:      min(ymax-3, len(*input)),
+		InSelectionMode: false,
+	}
+
 	// Event loop
 	for !done {
-		Render(s, input, lowerBound, upperBound, currentLine)
+		Render(state, input)
 
 		// Update screen
 		s.Show()
@@ -169,42 +174,44 @@ func main() {
 				s.Sync()
 			} else if ev.Rune() == ' ' {
 				// Mark the current line as selected
-				item := (*input)[currentLine]
+				item := (*input)[state.Current]
 				item.Selected = !item.Selected
 
 			} else if ev.Key() == tcell.KeyUp || ev.Key() == tcell.KeyCtrlP {
-				if currentLine > 0 {
-					currentLine -= 1
+				if state.Current > 0 {
+					state.Current -= 1
 				}
-				if currentLine <= lowerBound && currentLine != 0 {
-					lowerBound -= 1
-					upperBound -= 1
+				if state.Current <= state.LowerBound && state.Current != 0 {
+					state.LowerBound -= 1
+					state.UpperBound -= 1
 				}
 
 			} else if ev.Key() == tcell.KeyDown || ev.Key() == tcell.KeyCtrlN {
-				if currentLine < len(*input)-1 {
-					currentLine += 1
+				if state.Current < len(*input)-1 {
+					state.Current += 1
 				}
 
-				if currentLine >= upperBound && currentLine != len(*input)-1 {
-					lowerBound += 1
-					upperBound += 1
+				if state.Current >= state.UpperBound && state.Current != len(*input)-1 {
+					state.LowerBound += 1
+					state.UpperBound += 1
 				}
 			} else if ev.Key() == tcell.KeyCtrlE || ev.Key() == tcell.KeyEnd {
-				upperBound = len(*input)
-				lowerBound = upperBound - ymax + 2
-				currentLine = len(*input) - 1
+				state.UpperBound = len(*input)
+				state.LowerBound = state.UpperBound - ymax + 2
+				state.Current = len(*input) - 1
 			} else if ev.Key() == tcell.KeyCtrlA || ev.Key() == tcell.KeyHome {
-				upperBound = ymax - 2
-				lowerBound = 0
-				currentLine = 0
+				state.UpperBound = ymax - 2
+				state.LowerBound = 0
+				state.Current = 0
 			} else if ev.Key() == tcell.KeyCtrlSpace {
-				if inSelectedMode {
-					toggleItems(input, startOfSelection, currentLine)
+				if state.InSelectionMode {
+					start := min(startOfSelection, state.Current)
+					end := max(startOfSelection, state.Current)
+					toggleItems(input, start, end)
 				} else {
-					startOfSelection = currentLine
+					startOfSelection = state.Current
 				}
-				inSelectedMode = !inSelectedMode
+				state.InSelectionMode = !state.InSelectionMode
 			}
 		}
 	}

utils.go

@@ -50,6 +50,13 @@ func min(a, b int) int {
 	return b
 }
 
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
 // Reads the input from stdin and makes sure that the current
 // process is being run in a pipeline and converts the data
 // to an array of items.