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offset.go
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offset.go
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package pagination
import (
"context"
"encoding/base64"
"fmt"
"strconv"
)
var SafeDefaultLast = 10
func DiffOffsetCursor(offset int, count int) OffsetCursor {
return OffsetCursor(offset + count)
}
type OffsetCursor int
func (c OffsetCursor) GetCursor() string {
return base64.StdEncoding.EncodeToString([]byte(strconv.Itoa(int(c))))
}
func NewOffsetPaginator(f OffsetPaginator) Paginator {
return func(ctx context.Context, first, last *int, before, after Cursor) (*Connection, error) {
var limit *int
if first != nil {
limit = first
}
if last != nil {
limit = last
}
// Using backwards pagination and the limit has not been provided
if before != nil && last == nil {
limit = &SafeDefaultLast
}
var offset = 0
if after != nil {
after, err := GetOffsetCursor(after)
if err != nil {
return nil, fmt.Errorf("expected offset cursor: %+v", err)
}
offset = int(*after)+1
}
//log.Printf("Bla offset: %+v", offset)
if before != nil {
before, err := GetOffsetCursor(before)
if err != nil {
return nil, fmt.Errorf("expected offset cursor: %+v", err)
}
// When the client requests nodes that exist before another but lower than the limit, reset the
// limit so that the client won't get duplicate nodes.
if limit != nil && before != nil && *limit > int(*before) {
limit = (*int)(before)
}
offset = int(*before)-*limit
}
if offset < 0 {
offset = 0
}
// Call the offset paginator
r, err := f(ctx, offset, limit)
if err != nil {
return nil, err
}
count := len(r.Nodes)
connection := &Connection{}
connection.PageInfo = PageInfo{}
connection.PageInfo.HasNextPage = r.HasNextPage
connection.PageInfo.HasPreviousPage = r.HasPreviousPage
connection.PageInfo.StartCursor = OffsetCursor(offset)
connection.PageInfo.EndCursor = DiffOffsetCursor(offset, count-1)
connection.Edges = []Edge{}
for i, n := range r.Nodes {
connection.Edges = append(connection.Edges, Edge{
Cursor: DiffOffsetCursor(offset, i),
Node: n,
})
}
return connection, nil
}
}
type OffsetPaginator func(ctx context.Context, offset int, limit *int) (*ResultSet, error)
type ResultSet struct {
HasNextPage bool
HasPreviousPage bool
Nodes []Node
}