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// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package paging
import "golang.org/x/exp/slices"
// Pager provides a means of paging serialized IDs,
// using the terminology of our API endpoint queries.
type Pager struct {
// SinceID will limit the returned
// page of IDs to contain newer than
// since ID (excluding it). Result
// will be returned DESCENDING.
SinceID string
// MinID will limit the returned
// page of IDs to contain newer than
// min ID (excluding it). Result
// will be returned ASCENDING.
MinID string
// MaxID will limit the returned
// page of IDs to contain older
// than (excluding) this max ID.
MaxID string
// Limit will limit the returned
// page of IDs to at most 'limit'.
Limit int
}
// Page will page the given slice of GoToSocial IDs according
// to the receiving Pager's SinceID, MinID, MaxID and Limits.
// NOTE THE INPUT SLICE MUST BE SORTED IN ASCENDING ORDER
// (I.E. OLDEST ITEMS AT LOWEST INDICES, NEWER AT HIGHER).
func (p *Pager) PageAsc(ids []string) []string {
if p == nil {
// no paging.
return ids
}
var asc bool
if p.SinceID != "" {
// If a sinceID is given, we
// page down i.e. descending.
asc = false
for i := 0; i < len(ids); i++ {
if ids[i] == p.SinceID {
// Hit the boundary.
// Reslice to be:
// "from here"
ids = ids[i+1:]
break
}
}
} else if p.MinID != "" {
// We only support minID if
// no sinceID is provided.
//
// If a minID is given, we
// page up, i.e. ascending.
asc = true
for i := 0; i < len(ids); i++ {
if ids[i] == p.MinID {
// Hit the boundary.
// Reslice to be:
// "from here"
ids = ids[i+1:]
break
}
}
}
if p.MaxID != "" {
for i := 0; i < len(ids); i++ {
if ids[i] == p.MaxID {
// Hit the boundary.
// Reslice to be:
// "up to here"
ids = ids[:i]
break
}
}
}
if !asc && len(ids) > 1 {
var (
// Start at front.
i = 0
// Start at back.
j = len(ids) - 1
)
// Clone input IDs before
// we perform modifications.
ids = slices.Clone(ids)
for i < j {
// Swap i,j index values in slice.
ids[i], ids[j] = ids[j], ids[i]
// incr + decr,
// looping until
// they meet in
// the middle.
i++
j--
}
}
if p.Limit > 0 && p.Limit < len(ids) {
// Reslice IDs to given limit.
ids = ids[:p.Limit]
}
return ids
}
// Page will page the given slice of GoToSocial IDs according
// to the receiving Pager's SinceID, MinID, MaxID and Limits.
// NOTE THE INPUT SLICE MUST BE SORTED IN ASCENDING ORDER.
// (I.E. NEWEST ITEMS AT LOWEST INDICES, OLDER AT HIGHER).
func (p *Pager) PageDesc(ids []string) []string {
if p == nil {
// no paging.
return ids
}
var asc bool
if p.MaxID != "" {
for i := 0; i < len(ids); i++ {
if ids[i] == p.MaxID {
// Hit the boundary.
// Reslice to be:
// "from here"
ids = ids[i+1:]
break
}
}
}
if p.SinceID != "" {
// If a sinceID is given, we
// page down i.e. descending.
asc = false
for i := 0; i < len(ids); i++ {
if ids[i] == p.SinceID {
// Hit the boundary.
// Reslice to be:
// "up to here"
ids = ids[:i]
break
}
}
} else if p.MinID != "" {
// We only support minID if
// no sinceID is provided.
//
// If a minID is given, we
// page up, i.e. ascending.
asc = true
for i := 0; i < len(ids); i++ {
if ids[i] == p.MinID {
// Hit the boundary.
// Reslice to be:
// "up to here"
ids = ids[:i]
break
}
}
}
if asc && len(ids) > 1 {
var (
// Start at front.
i = 0
// Start at back.
j = len(ids) - 1
)
// Clone input IDs before
// we perform modifications.
ids = slices.Clone(ids)
for i < j {
// Swap i,j index values in slice.
ids[i], ids[j] = ids[j], ids[i]
// incr + decr,
// looping until
// they meet in
// the middle.
i++
j--
}
}
if p.Limit > 0 && p.Limit < len(ids) {
// Reslice IDs to given limit.
ids = ids[:p.Limit]
}
return ids
}
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