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Diffstat (limited to 'internal/paging/paging.go')
| -rw-r--r-- | internal/paging/paging.go | 227 |
1 files changed, 227 insertions, 0 deletions
diff --git a/internal/paging/paging.go b/internal/paging/paging.go new file mode 100644 index 000000000..0323f40bc --- /dev/null +++ b/internal/paging/paging.go @@ -0,0 +1,227 @@ +// 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 +} |