1 files changed, 168 insertions, 0 deletions
diff --git a/resources/page/taxonomy.go b/resources/page/taxonomy.go
new file mode 100644
index 000000000..f50152f90
--- /dev/null
+++ b/resources/page/taxonomy.go
@@ -0,0 +1,168 @@
+// Copyright 2023 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 (
+	"fmt"
+	"sort"
+
+	"github.com/gohugoio/hugo/compare"
+	"github.com/gohugoio/hugo/langs"
+)
+
+// The TaxonomyList is a list of all taxonomies and their values
+// e.g. List['tags'] => TagTaxonomy (from above)
+type TaxonomyList map[string]Taxonomy
+
+func (tl TaxonomyList) String() string {
+	return fmt.Sprintf("TaxonomyList(%d)", len(tl))
+}
+
+// A Taxonomy is a map of keywords to a list of pages.
+// For example
+//
+//	TagTaxonomy['technology'] = WeightedPages
+//	TagTaxonomy['go']  =  WeightedPages
+type Taxonomy map[string]WeightedPages
+
+// OrderedTaxonomy is another representation of an Taxonomy using an array rather than a map.
+// Important because you can't order a map.
+type OrderedTaxonomy []OrderedTaxonomyEntry
+
+// getOneOPage returns one page in the taxonomy,
+// nil if there is none.
+func (t OrderedTaxonomy) getOneOPage() Page {
+	if len(t) == 0 {
+		return nil
+	}
+	return t[0].Pages()[0]
+}
+
+// OrderedTaxonomyEntry is similar to an element of a Taxonomy, but with the key embedded (as name)
+// e.g:  {Name: Technology, WeightedPages: TaxonomyPages}
+type OrderedTaxonomyEntry struct {
+	Name string
+	WeightedPages
+}
+
+// Get the weighted pages for the given key.
+func (i Taxonomy) Get(key string) WeightedPages {
+	return i[key]
+}
+
+// Count the weighted pages for the given key.
+func (i Taxonomy) Count(key string) int { return len(i[key]) }
+
+// TaxonomyArray returns an ordered taxonomy with a non defined order.
+func (i Taxonomy) TaxonomyArray() OrderedTaxonomy {
+	ies := make([]OrderedTaxonomyEntry, len(i))
+	count := 0
+	for k, v := range i {
+		ies[count] = OrderedTaxonomyEntry{Name: k, WeightedPages: v}
+		count++
+	}
+	return ies
+}
+
+// Alphabetical returns an ordered taxonomy sorted by key name.
+func (i Taxonomy) Alphabetical() OrderedTaxonomy {
+	ia := i.TaxonomyArray()
+	p := ia.getOneOPage()
+	if p == nil {
+		return ia
+	}
+	currentSite := p.Site().Current()
+	coll := langs.GetCollator(currentSite.Language())
+	coll.Lock()
+	defer coll.Unlock()
+	name := func(i1, i2 *OrderedTaxonomyEntry) bool {
+		return coll.CompareStrings(i1.Name, i2.Name) < 0
+	}
+	oiBy(name).Sort(ia)
+	return ia
+}
+
+// ByCount returns an ordered taxonomy sorted by # of pages per key.
+// If taxonomies have the same # of pages, sort them alphabetical
+func (i Taxonomy) ByCount() OrderedTaxonomy {
+	count := func(i1, i2 *OrderedTaxonomyEntry) bool {
+		li1 := len(i1.WeightedPages)
+		li2 := len(i2.WeightedPages)
+
+		if li1 == li2 {
+			return compare.LessStrings(i1.Name, i2.Name)
+		}
+		return li1 > li2
+	}
+
+	ia := i.TaxonomyArray()
+	oiBy(count).Sort(ia)
+	return ia
+}
+
+// Pages returns the Pages for this taxonomy.
+func (ie OrderedTaxonomyEntry) Pages() Pages {
+	return ie.WeightedPages.Pages()
+}
+
+// Count returns the count the pages in this taxonomy.
+func (ie OrderedTaxonomyEntry) Count() int {
+	return len(ie.WeightedPages)
+}
+
+// Term returns the name given to this taxonomy.
+func (ie OrderedTaxonomyEntry) Term() string {
+	return ie.Name
+}
+
+// Reverse reverses the order of the entries in this taxonomy.
+func (t OrderedTaxonomy) Reverse() OrderedTaxonomy {
+	for i, j := 0, len(t)-1; i < j; i, j = i+1, j-1 {
+		t[i], t[j] = t[j], t[i]
+	}
+
+	return t
+}
+
+// A type to implement the sort interface for TaxonomyEntries.
+type orderedTaxonomySorter struct {
+	taxonomy OrderedTaxonomy
+	by       oiBy
+}
+
+// Closure used in the Sort.Less method.
+type oiBy func(i1, i2 *OrderedTaxonomyEntry) bool
+
+func (by oiBy) Sort(taxonomy OrderedTaxonomy) {
+	ps := &orderedTaxonomySorter{
+		taxonomy: taxonomy,
+		by:       by, // The Sort method's receiver is the function (closure) that defines the sort order.
+	}
+	sort.Stable(ps)
+}
+
+// Len is part of sort.Interface.
+func (s *orderedTaxonomySorter) Len() int {
+	return len(s.taxonomy)
+}
+
+// Swap is part of sort.Interface.
+func (s *orderedTaxonomySorter) Swap(i, j int) {
+	s.taxonomy[i], s.taxonomy[j] = s.taxonomy[j], s.taxonomy[i]
+}
+
+// Less is part of sort.Interface. It is implemented by calling the "by" closure in the sorter.
+func (s *orderedTaxonomySorter) Less(i, j int) bool {
+	return s.by(&s.taxonomy[i], &s.taxonomy[j])
+}