WIP Restart heading parsing implementation

m/textstyles/manPageHeading.go

@@ -1,29 +1,20 @@
 package textstyles
 
 import (
-	"unicode"
-	"unicode/utf8"
-
 	"github.com/walles/moar/twin"
 )
 
 func manPageHeadingFromString(s string) *CellsWithTrailer {
-	if !isManPageHeading(s) {
+	if !parseManPageHeading(s, func(_ twin.Cell) {}) {
 		return nil
 	}
 
-	cells := make([]twin.Cell, 0, len(s)/3)
-	cellIndex := -1
-	for _, char := range s {
-		cellIndex++
-		if cellIndex%3 > 0 {
-			continue
-		}
-
-		cells = append(
-			cells,
-			twin.Cell{Rune: char, Style: ManPageHeading},
-		)
+	cells := make([]twin.Cell, 0, len(s)/2)
+	ok := parseManPageHeading(s, func(cell twin.Cell) {
+		cells = append(cells, cell)
+	})
+	if !ok {
+		panic("man page heading state changed")
 	}
 
 	return &CellsWithTrailer{
@@ -32,53 +23,21 @@ func manPageHeadingFromString(s string) *CellsWithTrailer {
 	}
 }
 
+// Reports back one cell at a time. Returns true if the entire string was a man
+// page heading.
+//
+// If it was not, false will be returned and the cell reporting will be
+// interrupted.
+//
 // A man page heading is all caps. Also, each character is encoded as
-// char+backspace+char, where both chars need to be the same.
-func isManPageHeading(s string) bool {
+// char+backspace+char, where both chars need to be the same. Whitespace is an
+// exception, they can be not bold.
+func parseManPageHeading(s string, reportCell func(twin.Cell)) bool {
 	if len(s) < 3 {
 		// We don't want to match empty strings. Also, strings of length 1 and 2
 		// cannot be man page headings since "char+backspace+char" is 3 bytes.
 		return false
 	}
 
-	var currentChar rune
-	nextCharNumber := 0
-	for _, char := range s {
-		currentCharNumber := nextCharNumber
-		nextCharNumber++
-		switch currentCharNumber % 3 {
-		case 0:
-			if !isManPageHeadingChar(char) {
-				return false
-			}
-			currentChar = char
-		case 1:
-			if char != '\b' {
-				return false
-			}
-		case 2:
-			if char != currentChar {
-				return false
-			}
-		default:
-			panic("Impossible")
-		}
-	}
-
-	firstChar, _ := utf8.DecodeRuneInString(s)
-	if unicode.IsSpace(firstChar) {
-		// Headings are not indented
-		return false
-	}
-
-	return nextCharNumber%3 == 0
-}
-
-// Alphabetic chars must be upper case, all others are fine.
-func isManPageHeadingChar(char rune) bool {
-	if !unicode.IsLetter(char) {
-		return true
-	}
-
-	return unicode.IsUpper(char)
+	Johan: Write code here
 }