package chat

type List struct {
	root      *ListNode
	length    int
	maxLength int
}

type ListNode struct {
	next *ListNode
	data Message
}

func newList(maxLength int) List {
	return List{nil, 0, maxLength}
}

func (l *List) add(node *ListNode) {
	if l.root == nil {
		l.root = node
	} else {
		var n *ListNode
		for n = l.root; n.next != nil; n = n.next {
		}
		n.next = node
		l.length++
	}
	if l.length >= l.maxLength {
		l.trimFirst()
		l.length = l.maxLength
	}
}

func (l *List) trimFirst() {
	l.root = l.root.next
}

func (l *List) toMessageSlice(offset, count int) (messages []Message) {
	messages = make([]Message, 0)
	if l.root == nil {
		return
	}
	for node, i := l.root, 0; node != nil; node, i = node.next, i+1 {
		if i < offset {
			continue
		}
		if i-offset >= count {
			break
		}
		messages = append(messages, node.data)
	}
	return
}

func (l *List) fromMessageSlice(messages []Message) {
	for i := len(messages) - 1; i >= 0; i-- { // expected order is in reverse i.e. latest first
		l.add(&ListNode{nil, messages[i]})
	}
}