path: root/resources/page/pagination.go

// Copyright 2019 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package page

import (
	"errors"
	"fmt"
	"math"
	"reflect"

	"github.com/gohugoio/hugo/config"

	"github.com/spf13/cast"
)

// PaginatorProvider provides two ways to create a page paginator.
type PaginatorProvider interface {
	// Paginator creates a paginator with the default page set.
	Paginator(options ...any) (*Pager, error)
	// Paginate creates a paginator with the given page set in pages.
	Paginate(pages any, options ...any) (*Pager, error)
}

var _ PaginatorProvider = (*PaginatorNotSupportedFunc)(nil)

type PaginatorNotSupportedFunc func() error

func (f PaginatorNotSupportedFunc) Paginate(pages any, options ...any) (*Pager, error) {
	return nil, f()
}

func (f PaginatorNotSupportedFunc) Paginator(options ...any) (*Pager, error) {
	return nil, f()
}

// Pager represents one of the elements in a paginator.
// The number, starting on 1, represents its place.
type Pager struct {
	number int
	*Paginator
}

func (p Pager) String() string {
	return fmt.Sprintf("Pager %d", p.number)
}

type paginatedElement interface {
	Len() int
}

type pagers []*Pager

var (
	paginatorEmptyPages      Pages
	paginatorEmptyPageGroups PagesGroup
)

type Paginator struct {
	paginatedElements []paginatedElement
	pagers
	paginationURLFactory
	total int
	size  int
}

type paginationURLFactory func(int) string

// PageNumber returns the current page's number in the pager sequence.
func (p *Pager) PageNumber() int {
	return p.number
}

// URL returns the URL to the current page.
func (p *Pager) URL() string {
	return p.paginationURLFactory(p.PageNumber())
}

// Pages returns the Pages on this page.
// Note: If this return a non-empty result, then PageGroups() will return empty.
func (p *Pager) Pages() Pages {
	if len(p.paginatedElements) == 0 {
		return paginatorEmptyPages
	}

	if pages, ok := p.element().(Pages); ok {
		return pages
	}

	return paginatorEmptyPages
}

// PageGroups return Page groups for this page.
// Note: If this return non-empty result, then Pages() will return empty.
func (p *Pager) PageGroups() PagesGroup {
	if len(p.paginatedElements) == 0 {
		return paginatorEmptyPageGroups
	}

	if groups, ok := p.element().(PagesGroup); ok {
		return groups
	}

	return paginatorEmptyPageGroups
}

func (p *Pager) element() paginatedElement {
	if len(p.paginatedElements) == 0 {
		return paginatorEmptyPages
	}
	return p.paginatedElements[p.PageNumber()-1]
}

// page returns the Page with the given index
func (p *Pager) page(index int) (Page, error) {
	if pages, ok := p.element().(Pages); ok {
		if pages != nil && len(pages) > index {
			return pages[index], nil
		}
		return nil, nil
	}

	// must be PagesGroup
	// this construction looks clumsy, but ...
	// ... it is the difference between 99.5% and 100% test coverage :-)
	groups := p.element().(PagesGroup)

	i := 0
	for _, v := range groups {
		for _, page := range v.Pages {
			if i == index {
				return page, nil
			}
			i++
		}
	}
	return nil, nil
}

// NumberOfElements gets the number of elements on this page.
func (p *Pager) NumberOfElements() int {
	return p.element().Len()
}

// HasPrev tests whether there are page(s) before the current.
func (p *Pager) HasPrev() bool {
	return p.PageNumber() > 1
}

// Prev returns the pager for the previous page.
func (p *Pager) Prev() *Pager {
	if !p.HasPrev() {
		return nil
	}
	return p.pagers[p.PageNumber()-2]
}

// HasNext tests whether there are page(s) after the current.
func (p *Pager) HasNext() bool {
	return p.PageNumber() < len(p.paginatedElements)
}

// Next returns the pager for the next page.
func (p *Pager) Next() *Pager {
	if !p.HasNext() {
		return nil
	}
	return p.pagers[p.PageNumber()]
}

// First returns the pager for the first page.
func (p *Pager) First() *Pager {
	return p.pagers[0]
}

// Last returns the pager for the last page.
func (p *Pager) Last() *Pager {
	return p.pagers[len(p.pagers)-1]
}

// Pagers returns a list of pagers that can be used to build a pagination menu.
func (p *Paginator) Pagers() pagers {
	return p.pagers
}

// PageSize returns the size of each paginator page.
func (p *Paginator) PageSize() int {
	return p.size
}

// TotalPages returns the number of pages in the paginator.
func (p *Paginator) TotalPages() int {
	return len(p.paginatedElements)
}

// TotalNumberOfElements returns the number of elements on all pages in this paginator.
func (p *Paginator) TotalNumberOfElements() int {
	return p.total
}

func splitPages(pages Pages, size int) []paginatedElement {
	var split []paginatedElement
	for low, j := 0, len(pages); low < j; low += size {
		high := int(math.Min(float64(low+size), float64(len(pages))))
		split = append(split, pages[low:high])
	}

	return split
}

func splitPageGroups(pageGroups PagesGroup, size int) []paginatedElement {
	type keyPage struct {
		key  any
		page Page
	}

	var (
		split     []paginatedElement
		flattened []keyPage
	)

	for _, g := range pageGroups