1 files changed, 404 insertions, 0 deletions
diff --git a/resources/page/pagination.go b/resources/page/pagination.go
new file mode 100644
index 000000000..6d5da966e
--- /dev/null
+++ b/resources/page/pagination.go
@@ -0,0 +1,404 @@
+// 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"
+	"html/template"
+	"math"
+	"reflect"
+
+	"github.com/gohugoio/hugo/config"
+
+	"github.com/spf13/cast"
+)
+
+// PaginatorProvider provides two ways to create a page paginator.
+type PaginatorProvider interface {
+	Paginator(options ...interface{}) (*Pager, error)
+	Paginate(seq interface{}, options ...interface{}) (*Pager, error)
+}
+
+// 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() template.HTML {
+	return template.HTML(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  interface{}
+		page Page
+	}
+
+	var (
+		split     []paginatedElement
+		flattened []keyPage
+	)
+
+	for _, g := range pageGroups {
+		for _, p := range g.Pages {
+			flattened = append(flattened, keyPage{g.Key, p})
+		}
+	}
+
+	numPages := len(flattened)
+
+	for low, j := 0, numPages; low < j; low += size {
+		high := int(math.Min(float64(low+size), float64(numPages)))
+
+		var (
+			pg         PagesGroup
+			key        interface{}
+			groupIndex = -1
+		)
+
+		for k := low; k < high; k++ {
+			kp := flattened[k]
+			if key == nil || key != kp.key {
+				key = kp.key
+				pg = append(pg, PageGroup{Key: key})
+				groupIndex++
+			}
+			pg[groupIndex].Pages = append(pg[groupIndex].Pages, kp.page)
+		}
+		split = append(split, pg)
+	}
+
+	return split
+}
+
+func ResolvePagerSize(cfg config.Provider, options ...interface{}) (int, error) {
+	if len(options) == 0 {
+		return cfg.GetInt("paginate"), nil
+	}
+
+	if len(options) > 1 {
+		return -1, errors.New("too many arguments, 'pager size' is currently the only option")
+	}
+
+	pas, err := cast.ToIntE(options[0])
+
+	if err != nil || pas <= 0 {
+		return -1, errors.New(("'pager size' must be a positive integer"))
+	}
+
+	return pas, nil
+}
+
+func Paginate(td TargetPathDescriptor, seq interface{}, pagerSize int) (*Paginator, error) {
+
+	if pagerSize <= 0 {
+		return nil, errors.New("'paginate' configuration setting must be positive to paginate")
+	}
+
+	urlFactory := newPaginationURLFactory(td)
+
+	var paginator *Paginator
+
+	groups, err := ToPagesGroup(seq)
+	if err != nil {
+		return nil, err
+	}
+	if groups != nil {
+		paginator, _ = newPaginatorFromPageGroups(groups, pagerSize, urlFactory)
+	} else {
+		pages, err := ToPages(seq)
+		if err != nil {
+			return nil, err
+		}
+		paginator, _ = newPaginatorFromPages(pages, pagerSize, urlFactory)
+	}
+
+	return paginator, nil
+}
+
+// probablyEqual checks page lists for probable equality.
+// It may return false positives.
+// The motivation behind this is to avoid potential costly reflect.DeepEqual
+// when "probably" is good enough.
+func probablyEqualPageLists(a1 interface{}, a2 interface{}) bool {
+
+	if a1 == nil || a2 == nil {
+		return a1 == a2
+	}
+
+	t1 := reflect.TypeOf(a1)
+	t2 := reflect.TypeOf(a2)
+
+	if t1 != t2 {
+		return false
+	}
+
+	if g1, ok := a1.(PagesGroup); ok {
+		g2 := a2.(PagesGroup)
+		if len(g1) != len(g2) {
+			return false
+		}
+		if len(g1) == 0 {
+			return true
+		}
+		if g1.Len() != g2.Len() {
+			return false
+		}
+
+		return g1[0].Pages[0] == g2[0].Pages[0]
+	}
+
+	p1, err1 := ToPages(a1)
+	p2, err2 := ToPages(a2)
+
+	// probably the same wrong type
+	if err1 != nil && err2 != nil {
+		return true
+	}
+
+	if len(p1) != len(p2) {
+		return false
+	}
+
+	if len(p1) == 0 {
+		return true
+	}
+
+	return p1[0] == p2[0]
+}
+
+func newPaginatorFromPages(pages Pages, size int, urlFactory paginationURLFactory) (*Paginator, error) {
+
+	if size <= 0 {
+		return nil, errors.New("Paginator size must be positive")
+	}
+
+	split := splitPages(pages, size)
+
+	return newPaginator(split, len(pages), size, urlFactory)
+}
+
+func newPaginatorFromPageGroups(pageGroups PagesGroup, size int, urlFactory paginationURLFactory) (*Paginator, error) {
+
+	if size <= 0 {
+		return nil, errors.New("Paginator size must be positive")
+	}
+
+	split := splitPageGroups(pageGroups, size)
+
+	return newPaginator(split, pageGroups.Len(), size, urlFactory)
+}
+
+func newPaginator(elements []paginatedElement, total, size int, urlFactory paginationURLFactory) (*Paginator, error) {
+	p := &Paginator{total: total, paginatedElements: elements, size: size, paginationURLFactory: urlFactory}
+
+	var ps pagers
+
+	if len(elements) > 0 {
+		ps = make(pagers, len(elements))
+		for i := range p.paginatedElements {
+			ps[i] = &Pager{number: (i + 1), Paginator: p}
+		}
+	} else {
+		ps = make(pagers, 1)
+		ps[0] = &Pager{number: 1, Paginator: p}
+	}
+
+	p.pagers = ps
+
+	return p, nil
+}
+
+func newPaginationURLFactory(d TargetPathDescriptor) paginationURLFactory {
+
+	return func(pageNumber int) string {
+		pathDescriptor := d
+		var rel string
+		if pageNumber > 1 {
+			rel = fmt.Sprintf("/%s/%d/", d.PathSpec.PaginatePath, pageNumber)
+			pathDescriptor.Addends = rel
+		}
+
+		return CreateTargetPaths(pathDescriptor).RelPermalink(d.PathSpec)
+
+	}
+}