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paging_iterator.go
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/
paging_iterator.go
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// The MIT License
//
// Copyright (c) 2020 Temporal Technologies Inc. All rights reserved.
//
// Copyright (c) 2020 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package collection
type (
// PaginationFn is the function which get a page of results
PaginationFn[V any] func(paginationToken []byte) ([]V, []byte, error)
// PagingIteratorImpl is the implementation of PagingIterator
PagingIteratorImpl[V any] struct {
paginationFn PaginationFn[V]
pageToken []byte
pageErr error
pageItems []V
nextPageItemIndex int
}
)
// NewPagingIterator create a new paging iterator
func NewPagingIterator[V any](
paginationFn PaginationFn[V],
) Iterator[V] {
iter := &PagingIteratorImpl[V]{
paginationFn: paginationFn,
pageToken: nil,
pageErr: nil,
pageItems: nil,
nextPageItemIndex: 0,
}
iter.getNextPage() // this will initialize the paging iterator
return iter
}
// NewPagingIteratorWithToken create a new paging iterator with initial token
func NewPagingIteratorWithToken[V any](
paginationFn PaginationFn[V],
pageToken []byte,
) Iterator[V] {
iter := &PagingIteratorImpl[V]{
paginationFn: paginationFn,
pageToken: pageToken,
pageErr: nil,
pageItems: nil,
nextPageItemIndex: 0,
}
iter.getNextPage() // this will initialize the paging iterator
return iter
}
// HasNext return whether has next item or err
func (iter *PagingIteratorImpl[V]) HasNext() bool {
// pagination encounters error
if iter.pageErr != nil {
return true
}
// still have local cached item to return
if iter.nextPageItemIndex < len(iter.pageItems) {
return true
}
if len(iter.pageToken) != 0 {
iter.getNextPage()
return iter.HasNext()
}
return false
}
// Next return next item or err
func (iter *PagingIteratorImpl[V]) Next() (V, error) {
if !iter.HasNext() {
panic("HistoryEventIterator Next() called without checking HasNext()")
}
if iter.pageErr != nil {
err := iter.pageErr
iter.pageErr = nil
var v V
return v, err
}
// we have cached events
if iter.nextPageItemIndex < len(iter.pageItems) {
index := iter.nextPageItemIndex
iter.nextPageItemIndex++
return iter.pageItems[index], nil
}
panic("HistoryEventIterator Next() should return either a history event or a err")
}
func (iter *PagingIteratorImpl[V]) getNextPage() {
items, token, err := iter.paginationFn(iter.pageToken)
if err == nil {
iter.pageItems = items
iter.pageToken = token
iter.pageErr = nil
} else {
iter.pageItems = nil
iter.pageToken = nil
iter.pageErr = err
}
iter.nextPageItemIndex = 0
}