GoToSocial/internal/paging/page.go

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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 (
"net/url"
"strconv"
"golang.org/x/exp/slices"
)
type Page struct {
// Min is the Page's lower limit value.
Min Boundary
// Max is this Page's upper limit value.
Max Boundary
// Limit will limit the returned
// page of items to at most 'limit'.
Limit int
}
// GetMin is a small helper function to return minimum boundary value (checking for nil page).
func (p *Page) GetMin() string {
if p == nil {
return ""
}
return p.Min.Value
}
// GetMax is a small helper function to return maximum boundary value (checking for nil page).
func (p *Page) GetMax() string {
if p == nil {
return ""
}
return p.Max.Value
}
// GetLimit is a small helper function to return limit (checking for nil page and unusable limit).
func (p *Page) GetLimit() int {
if p == nil || p.Limit < 0 {
return 0
}
return p.Limit
}
// GetOrder is a small helper function to return page sort ordering (checking for nil page).
func (p *Page) GetOrder() Order {
if p == nil {
return 0
}
return p.order()
}
func (p *Page) order() Order {
switch {
case p.Min.Order != 0:
return p.Min.Order
case p.Max.Order != 0:
return p.Max.Order
default:
return 0
}
}
// Page will page the given slice of input according
// to the receiving Page's minimum, maximum and limit.
// NOTE: input slice MUST be sorted according to the order is
// expected to be paged in, i.e. it is currently sorted
// according to Page.Order(). Sorted data isn't always according
// to string inequalities so this CANNOT be checked here.
func (p *Page) Page(in []string) []string {
if p == nil {
// no paging.
return in
}
if p.order().Ascending() {
// Sort type is ascending, input
// data is assumed to be ascending.
if minIdx := p.Min.Find(in); minIdx != -1 {
// Reslice skipping up to min.
in = in[minIdx+1:]
}
if maxIdx := p.Max.Find(in); maxIdx != -1 {
// Reslice stripping past max.
in = in[:maxIdx]
}
if p.Limit > 0 && p.Limit < len(in) {
// Reslice input to limit.
in = in[:p.Limit]
}
if len(in) > 1 {
// Clone input before
// any modifications.
in = slices.Clone(in)
// Output slice must
// ALWAYS be descending.
in = Reverse(in)
}
} else {
// Default sort is descending,
// catching all cases when NOT
// ascending (even zero value).
if maxIdx := p.Max.Find(in); maxIdx != -1 {
// Reslice skipping up to max.
in = in[maxIdx+1:]
}
if minIdx := p.Min.Find(in); minIdx != -1 {
// Reslice stripping past min.
in = in[:minIdx]
}
if p.Limit > 0 && p.Limit < len(in) {
// Reslice input to limit.
in = in[:p.Limit]
}
}
return in
}
// Next creates a new instance for the next returnable page, using
// given max value. This preserves original limit and max key name.
func (p *Page) Next(lo, hi string) *Page {
if p == nil || lo == "" || hi == "" {
// no paging.
return nil
}
// Create new page.
p2 := new(Page)
// Set original limit.
p2.Limit = p.Limit
if p.order().Ascending() {
// When ascending, next page
// needs to start with min at
// the next highest value.
p2.Min = p.Min.new(hi)
p2.Max = p.Max.new("")
} else {
// When descending, next page
// needs to start with max at
// the next lowest value.
p2.Min = p.Min.new("")
p2.Max = p.Max.new(lo)
}
return p2
}
// Prev creates a new instance for the prev returnable page, using
// given min value. This preserves original limit and min key name.
func (p *Page) Prev(lo, hi string) *Page {
if p == nil || lo == "" || hi == "" {
// no paging.
return nil
}
// Create new page.
p2 := new(Page)
// Set original limit.
p2.Limit = p.Limit
if p.order().Ascending() {
// When ascending, prev page
// needs to start with max at
// the next lowest value.
p2.Min = p.Min.new("")
p2.Max = p.Max.new(lo)
} else {
// When descending, next page
// needs to start with max at
// the next lowest value.
p2.Min = p.Min.new(hi)
p2.Max = p.Max.new("")
}
return p2
}
// ToLink builds a URL link for given endpoint information and extra query parameters,
// appending this Page's minimum / maximum boundaries and available limit (if any).
func (p *Page) ToLink(proto, host, path string, queryParams url.Values) string {
if p == nil {
// no paging.
return ""
}
if queryParams == nil {
// Allocate new query parameters.
queryParams = make(url.Values)
}
if p.Min.Value != "" {
// A page-minimum query parameter is available.
queryParams.Add(p.Min.Name, p.Min.Value)
}
if p.Max.Value != "" {
// A page-maximum query parameter is available.
queryParams.Add(p.Max.Name, p.Max.Value)
}
if p.Limit > 0 {
// A page limit query parameter is available.
queryParams.Add("limit", strconv.Itoa(p.Limit))
}
// Build URL string.
return (&url.URL{
Scheme: proto,
Host: host,
Path: path,
RawQuery: queryParams.Encode(),
}).String()
}