Complete code of insert into span buffer. Looks complicated and needs testing.

common/spans.go

@@ -59,6 +59,7 @@ func (sp *SpanPool) FreeAll(s *Span) {
 
 func (sp *SpanPool) Insert(s *Span, pos, value int32) *Span {
 
+	// No head -> create.
 	if s == nil {
 		s = sp.Alloc()
 		s.From = pos
@@ -71,10 +72,10 @@ func (sp *SpanPool) Insert(s *Span, pos, value int32) *Span {
 	if pos < s.From {
 		// Same value and directly neighbored -> extend head.
 		if value == s.Value && pos == s.From-1 {
-			s.From--
+			s.From = pos
 			return s
 		}
-		// Disjunct -> create new.
+		// Disjunct -> create new head.
 		prev := sp.Alloc()
 		prev.From = pos
 		prev.To = pos
@@ -83,7 +84,103 @@ func (sp *SpanPool) Insert(s *Span, pos, value int32) *Span {
 		return prev
 	}
 
-	// TODO: Implement the more complicated cases.
-
-	return nil
+	head := s
+	for prev := s; s != nil; s = s.Next {
+		switch {
+		case pos < s.From: // before span
+			if pos == s.From-1 && value == s.Value { // directly neighbored
+				s.From = pos
+				// Check if a gap has to be closed.
+				if prev.To == s.From-1 && value == prev.Value {
+					prev.To = s.To
+					prev.Next = s.Next
+					sp.Free(s)
+					return head
+				}
+			}
+			// Extend prev?
+			if prev.To == pos-1 && value == prev.Value {
+				prev.To = pos
+				return head
+			}
+			// New between prev and current.
+			sn := sp.Alloc()
+			sn.From = pos
+			sn.To = pos
+			sn.Value = value
+			sn.Next = s
+			prev.Next = sn
+			return head
+
+		case pos > s.To: // after span
+			if pos == s.To+1 && value == s.Value { // directly neighbored
+				s.To = pos
+				// Check if a gap has to be closed
+				next := s.Next
+				if next != nil {
+					if next.From == s.To-1 && value == next.Value {
+						s.To = next.To
+						s.Next = next.Next
+						sp.Free(next)
+						return head
+					}
+					// Extend next?
+					if pos == next.From-1 && value == next.Value {
+						next.From = pos
+						return head
+					}
+					// Before next -> New between current and next
+					if pos < next.From {
+						sn := sp.Alloc()
+						sn.From = pos
+						sn.To = pos
+						sn.Value = value
+						sn.Next = next
+						s.Next = sn
+						return head
+					}
+				} else { // No next -> new at tail
+					sn := sp.Alloc()
+					sn.From = pos
+					sn.To = pos
+					sn.Value = value
+					sn.Next = nil
+					s.Next = sn
+					return head
+				}
+			} else { // Not directly connected and/or values do not match.
+				next := s.Next
+				if next != nil {
+					if pos == next.From-1 && value == next.Value {
+						next.From = pos
+						return head
+					}
+					// Before next -> New between current and next
+					if pos < next.From {
+						sn := sp.Alloc()
+						sn.From = pos
+						sn.To = pos
+						sn.Value = value
+						sn.Next = next
+						s.Next = sn
+						return head
+					}
+				} else { // No next -> new at tail
+					sn := sp.Alloc()
+					sn.From = pos
+					sn.To = pos
+					sn.Value = value
+					sn.Next = nil
+					s.Next = sn
+					return head
+				}
+			}
+
+		default: // pos in span -> do not modify.
+			return head
+		}
+		prev = s
+	}
+
+	return head
 }