feat: preserve line breaks from original input (#412)

* feat: preserve line breaks from original input
* docs: fix spelling error in comment

---------

Co-authored-by: Hilmar Falkenberg <hilmar.falkenberg@sap.com>

ast/ast.go

@@ -278,6 +278,49 @@ func readNode(p []byte, node Node) (int, error) {
 	return size, nil
 }
 
+func checkLineBreak(t *token.Token) bool {
+	if t.Prev != nil {
+		lbc := "\n"
+		prev := t.Prev
+		var adjustment int
+		// if the previous type is sequence entry use the previous type for that
+		if prev.Type == token.SequenceEntryType {
+			// as well as switching to previous type count any new lines in origin to account for:
+			// -
+			//   b: c
+			adjustment = strings.Count(strings.TrimRight(t.Origin, lbc), lbc)
+			if prev.Prev != nil {
+				prev = prev.Prev
+			}
+		}
+		lineDiff := t.Position.Line - prev.Position.Line - 1
+		if lineDiff > 0 {
+			if prev.Type == token.StringType {
+				// Remove any line breaks included in multiline string
+				adjustment += strings.Count(strings.TrimRight(strings.TrimSpace(prev.Origin), lbc), lbc)
+			}
+			// Due to the way that comment parsing works its assumed that when a null value does not have new line in origin
+			// it was squashed therefore difference is ignored.
+			//foo:
+			//  bar:
+			//  # comment
+			//  baz: 1
+			//becomes
+			//foo:
+			//  bar: null # comment
+			//
+			//  baz: 1
+			if prev.Type == token.NullType {
+				return strings.Count(prev.Origin, lbc) > 0
+			}
+			if lineDiff-adjustment > 0 {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // Null create node for null value
 func Null(tk *token.Token) *NullNode {
 	return &NullNode{
@@ -1390,6 +1433,9 @@ func (n *MappingValueNode) String() string {
 
 func (n *MappingValueNode) toString() string {
 	space := strings.Repeat(" ", n.Key.GetToken().Position.Column-1)
+	if checkLineBreak(n.Key.GetToken()) {
+		space = fmt.Sprintf("%s%s", "\n", space)
+	}
 	keyIndentLevel := n.Key.GetToken().Position.IndentLevel
 	valueIndentLevel := n.Value.GetToken().Position.IndentLevel
 	keyComment := n.Key.GetComment()
@@ -1563,6 +1609,11 @@ func (n *SequenceNode) blockStyleString() string {
 
 	for idx, value := range n.Values {
 		valueStr := value.String()
+		newLinePrefix := ""
+		if strings.HasPrefix(valueStr, "\n") {
+			valueStr = valueStr[1:]
+			newLinePrefix = "\n"
+		}
 		splittedValues := strings.Split(valueStr, "\n")
 		trimmedFirstValue := strings.TrimLeft(splittedValues[0], " ")
 		diffLength := len(splittedValues[0]) - len(trimmedFirstValue)
@@ -1585,9 +1636,10 @@ func (n *SequenceNode) blockStyleString() string {
 		}
 		newValue := strings.Join(newValues, "\n")
 		if len(n.ValueHeadComments) == len(n.Values) && n.ValueHeadComments[idx] != nil {
-			values = append(values, n.ValueHeadComments[idx].StringWithSpace(n.Start.Position.Column-1))
+			values = append(values, fmt.Sprintf("%s%s", newLinePrefix, n.ValueHeadComments[idx].StringWithSpace(n.Start.Position.Column-1)))
+			newLinePrefix = ""
 		}
-		values = append(values, fmt.Sprintf("%s- %s", space, newValue))
+		values = append(values, fmt.Sprintf("%s%s- %s", newLinePrefix, space, newValue))
 	}
 	if n.FootComment != nil {
 		values = append(values, n.FootComment.StringWithSpace(n.Start.Position.Column-1))
@@ -1880,10 +1932,13 @@ func (n *CommentGroupNode) StringWithSpace(col int) string {
 	values := []string{}
 	space := strings.Repeat(" ", col)
 	for _, comment := range n.Comments {
+		space := space
+		if checkLineBreak(comment.Token) {
+			space = fmt.Sprintf("%s%s", "\n", space)
+		}
 		values = append(values, space+comment.String())
 	}
 	return strings.Join(values, "\n")
-
 }
 
 // MarshalYAML encodes to a YAML text