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pagination.go
128 lines (104 loc) · 2.16 KB
/
pagination.go
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package eventline
const (
MinPageSize = 1
MaxPageSize = 100
)
type PageElement interface {
SortKey(string) string
}
type Page struct {
Elements []PageElement `json:"elements"`
Previous *Cursor `json:"previous,omitempty"`
Next *Cursor `json:"next,omitempty"`
}
func ReversePageElements(elts []PageElement) {
for i := 0; i < len(elts)/2; i++ {
j := len(elts) - i - 1
elts[i], elts[j] = elts[j], elts[i]
}
}
func NewPage(cursor *Cursor, elements []PageElement, sorts Sorts) *Page {
if len(elements) == 0 {
return &Page{
Elements: elements,
}
}
size := cursor.Size
if size == 0 {
size = DefaultCursorSize
}
order := cursor.Order
if order == "" {
order = OrderAsc
}
sort := cursor.Sort
if sort == "" {
sort = sorts.Default
}
var page Page
firstElement := elements[0]
if cursor.Before != "" {
page.Next = &Cursor{
After: firstElement.SortKey(sort),
Size: size,
Order: order,
Sort: sort,
}
if len(elements) > size {
elements = elements[:len(elements)-1]
lastElement := elements[len(elements)-1]
ReversePageElements(elements)
page.Elements = elements
page.Previous = &Cursor{
Before: lastElement.SortKey(sort),
Size: size,
Order: order,
Sort: sort,
}
} else {
ReversePageElements(elements)
page.Elements = elements
}
} else {
if cursor.After != "" {
page.Previous = &Cursor{
Before: firstElement.SortKey(sort),
Size: size,
Order: order,
Sort: sort,
}
}
if len(elements) > size {
elements = elements[:len(elements)-1]
lastElement := elements[len(elements)-1]
page.Elements = elements
page.Next = &Cursor{
After: lastElement.SortKey(sort),
Size: size,
Order: order,
Sort: sort,
}
} else {
page.Elements = elements
}
}
return &page
}
func (p *Page) IsEmpty() bool {
return len(p.Elements) == 0
}
func (p *Page) HasPreviousOrNextURI() bool {
return p.Previous != nil || p.Next != nil
}
func (p *Page) PreviousURI() string {
if p.Previous == nil {
return ""
}
return p.Previous.URL().String()
}
func (p *Page) NextURI() string {
if p.Next == nil {
return ""
}
return p.Next.URL().String()
}