indexOfGroup method
Implementation
MessageIndexOfGroup indexOfGroup(List<Message> messages, item) {
if (messages.length == 1) return MessageIndexOfGroup.none;
if (messages.indexOf(item) == 0) return MessageIndexOfGroup.top;
if (messages.indexOf(item) == messages.length - 1) {
return MessageIndexOfGroup.bottom;
}
return MessageIndexOfGroup.center;
}