Three-group line numbers

Both the numbers in the left column of the file display, and the line
numbers shown in the page footer.

Fixes #6.

m/numberFormatter.go

@@ -0,0 +1,21 @@
+package m
+
+import "fmt"
+
+// Formats a number into a string with _ between each three-group of digits
+func formatNumber(number uint) string {
+	result := ""
+
+	chars := []rune(fmt.Sprint(number))
+	addCount := 0
+	for i := len(chars) - 1; i >= 0; i-- {
+		char := chars[i]
+		if len(result) > 0 && addCount%3 == 0 {
+			result = "_" + result
+		}
+		result = string(char) + result
+		addCount++
+	}
+
+	return result
+}

m/numberFormatter_test.go

@@ -0,0 +1,18 @@
+package m
+
+import (
+	"testing"
+
+	"gotest.tools/assert"
+)
+
+func TestNumberFormatting(t *testing.T) {
+	assert.Equal(t, "1", formatNumber(1))
+	assert.Equal(t, "10", formatNumber(10))
+	assert.Equal(t, "100", formatNumber(100))
+	assert.Equal(t, "1_000", formatNumber(1000))
+	assert.Equal(t, "10_000", formatNumber(10000))
+	assert.Equal(t, "100_000", formatNumber(100000))
+	assert.Equal(t, "1_000_000", formatNumber(1000000))
+	assert.Equal(t, "10_000_000", formatNumber(10000000))
+}

m/pager.go

@@ -3,7 +3,6 @@ package m
 import (
 	"fmt"
 	"regexp"
-	"strconv"
 	"time"
 	"unicode"
 	"unicode/utf8"
@@ -29,7 +28,7 @@ type eventSpinnerUpdate struct {
 type eventMoreLinesAvailable struct{}
 
 // Styling of line numbers
-var _NumberStyle = twin.StyleDefault.WithAttr(twin.AttrDim)
+var _numberStyle = twin.StyleDefault.WithAttr(twin.AttrDim)
 
 // Pager is the main on-screen pager
 type Pager struct {
@@ -122,7 +121,12 @@ func (p *Pager) _AddLine(fileLineNumber *int, numberPrefixLength int, screenLine
 
 	lineNumberString := ""
 	if numberPrefixLength > 0 && fileLineNumber != nil {
-		lineNumberString = fmt.Sprintf("%*d ", numberPrefixLength-1, *fileLineNumber)
+		lineNumberString = formatNumber(uint(*fileLineNumber))
+		if len(lineNumberString) > numberPrefixLength {
+			panic(fmt.Errorf(
+				"lineNumberString <%s> longer than numberPrefixLength %d",
+				lineNumberString, numberPrefixLength))
+		}
 	} else {
 		numberPrefixLength = 0
 	}
@@ -132,7 +136,7 @@ func (p *Pager) _AddLine(fileLineNumber *int, numberPrefixLength int, screenLine
 			break
 		}
 
-		p.screen.SetCell(column, screenLineNumber, twin.NewCell(digit, _NumberStyle))
+		p.screen.SetCell(column, screenLineNumber, twin.NewCell(digit, _numberStyle))
 	}
 
 	tokens := createScreenLine(p.leftColumnZeroBased, screenWidth-numberPrefixLength, line, p.searchPattern)
@@ -220,7 +224,7 @@ func (p *Pager) _AddLines(spinner string) {
 	//
 	// Offsets figured out through trial-and-error...
 	lastLineOneBased := lines.firstLineOneBased + len(lines.lines) - 1
-	numberPrefixLength := len(strconv.Itoa(lastLineOneBased)) + 1
+	numberPrefixLength := len(formatNumber(uint(lastLineOneBased))) + 1
 	if numberPrefixLength < 4 {
 		// 4 = space for 3 digits followed by one whitespace
 		//

m/reader.go

@@ -456,11 +456,11 @@ func (r *Reader) _CreateStatusUnlocked(firstLineOneBased int, lastLineOneBased i
 
 	percent := int(100 * float64(lastLineOneBased) / float64(len(r.lines)))
 
-	return fmt.Sprintf("%s%d-%d/%d %d%%",
+	return fmt.Sprintf("%s%s-%s/%s %d%%",
 		prefix,
-		firstLineOneBased,
-		lastLineOneBased,
-		len(r.lines),
+		formatNumber(uint(firstLineOneBased)),
+		formatNumber(uint(lastLineOneBased)),
+		formatNumber(uint(len(r.lines))),
 		percent)
 }
 

m/reader_test.go

@@ -261,7 +261,7 @@ func testStatusText(t *testing.T, fromLine int, toLine int, totalLines int, expe
 func TestStatusText(t *testing.T) {
 	testStatusText(t, 1, 10, 20, "1-10/20 50%")
 	testStatusText(t, 1, 5, 5, "1-5/5 100%")
-	testStatusText(t, 998, 999, 1000, "998-999/1000 99%")
+	testStatusText(t, 998, 999, 1000, "998-999/1_000 99%")
 
 	testStatusText(t, 0, 0, 0, "<empty>")
 	testStatusText(t, 1, 1, 1, "1-1/1 100%")