hugolib: Implement "related content"

This closes #98, even if this commit does not do full content text search.

We may revisit that problem in the future, but that deserves its own issue.

Fixes #98

2 files changed, 726 insertions, 0 deletions

diff --git a/related/inverted_index.go b/related/inverted_index.go
new file mode 100644
index 000000000..f0d598d33
--- /dev/null
+++ b/related/inverted_index.go
@@ -0,0 +1,450 @@
+// Copyright 2017-present 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 related holds code to help finding related content.
+package related
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/gohugoio/hugo/common/types"
+	"github.com/mitchellh/mapstructure"
+)
+
+var (
+	_        Keyword = (*StringKeyword)(nil)
+	zeroDate         = time.Time{}
+
+	// DefaultConfig is the default related config.
+	DefaultConfig = Config{
+		Threshold: 80,
+		Indices: IndexConfigs{
+			IndexConfig{Name: "keywords", Weight: 100},
+			IndexConfig{Name: "date", Weight: 10},
+		},
+	}
+)
+
+/*
+Config is the top level configuration element used to configure how to retrieve
+related content in Hugo.
+
+An example site config.toml:
+
+	[related]
+	threshold = 1
+	[[related.indices]]
+	name = "keywords"
+	weight = 200
+	[[related.indices]]
+	name  = "tags"
+	weight = 100
+	[[related.indices]]
+	name  = "date"
+	weight = 1
+	pattern = "2006"
+*/
+type Config struct {
+	// Only include matches >= threshold, a normalized rank between 0 and 100.
+	Threshold int
+
+	// To get stable "See also" sections we, by default, exclude newer related pages.
+	IncludeNewer bool
+
+	// Will lower case all string values and queries to the indices.
+	// May get better results, but at a slight performance cost.
+	ToLower bool
+
+	Indices IndexConfigs
+}
+
+func (c *Config) Add(index IndexConfig) {
+	if c.ToLower {
+		index.ToLower = true
+	}
+	c.Indices = append(c.Indices, index)
+}
+
+// IndexConfigs holds a set of index configurations.
+type IndexConfigs []IndexConfig
+
+// IndexConfig configures an index.
+type IndexConfig struct {
+	// The index name. This directly maps to a field or Param name.
+	Name string
+
+	// Contextual pattern used to convert the Param value into a string.
+	// Currently only used for dates. Can be used to, say, bump posts in the same
+	// time frame when searching for related documents.
+	// For dates it follows Go's time.Format patterns, i.e.
+	// "2006" for YYYY and "200601" for YYYYMM.
+	Pattern string
+
+	// This field's weight when doing multi-index searches. Higher is "better".
+	Weight int
+
+	// Will lower case all string values in and queries tothis index.
+	// May get better accurate results, but at a slight performance cost.
+	ToLower bool
+}
+
+// Document is the interface an indexable document in Hugo must fulfill.
+type Document interface {
+	// SearchKeywords returns a list of keywords for the given index config.
+	SearchKeywords(cfg IndexConfig) ([]Keyword, error)
+
+	// When this document was or will be published.
+	PubDate() time.Time
+}
+
+// InvertedIndex holds an inverted index, also sometimes named posting list, which
+// lists, for every possible search term, the documents that contain that term.
+type InvertedIndex struct {
+	cfg   Config
+	index map[string]map[Keyword][]Document
+
+	minWeight int
+	maxWeight int
+}
+
+func (idx *InvertedIndex) getIndexCfg(name string) (IndexConfig, bool) {
+	for _, conf := range idx.cfg.Indices {
+		if conf.Name == name {
+			return conf, true
+		}
+	}
+
+	return IndexConfig{}, false
+}
+
+// NewInvertedIndex creates a new InvertedIndex.
+// Documents to index must be added in Add.
+func NewInvertedIndex(cfg Config) *InvertedIndex {
+	idx := &InvertedIndex{index: make(map[string]map[Keyword][]Document), cfg: cfg}
+	for _, conf := range cfg.Indices {
+		idx.index[conf.Name] = make(map[Keyword][]Document)
+		if conf.Weight < idx.minWeight {
+			// By default, the weight scale starts at 0, but we allow
+			// negative weights.
+			idx.minWeight = conf.Weight
+		}
+		if conf.Weight > idx.maxWeight {
+			idx.maxWeight = conf.Weight
+		}
+	}
+	return idx
+}
+
+// Add documents to the inverted index.
+// The value must support == and !=.
+func (idx *InvertedIndex) Add(docs ...Document) error {
+	var err error
+	for _, config := range idx.cfg.Indices {
+		if config.Weight == 0 {
+			// Disabled
+			continue
+		}
+		setm := idx.index[config.Name]
+
+		for _, doc := range docs {
+			var words []Keyword
+			words, err = doc.SearchKeywords(config)
+			if err != nil {
+				continue
+			}
+
+			for _, keyword := range words {
+				setm[keyword] = append(setm[keyword], doc)
+			}
+		}
+	}
+
+	return err
+
+}
+
+// queryElement holds the index name and keywords that can be used to compose a
+// search for related content.
+type queryElement struct {
+	Index    string
+	Keywords []Keyword
+}
+
+func newQueryElement(index string, keywords ...Keyword) queryElement {
+	return queryElement{Index: index, Keywords: keywords}
+}
+
+type ranks []*rank
+
+type rank struct {
+	Doc     Document
+	Weight  int
+	Matches int
+}
+
+func (r *rank) addWeight(w int) {
+	r.Weight += w
+	r.Matches++
+}
+
+func newRank(doc Document, weight int) *rank {
+	return &rank{Doc: doc, Weight: weight, Matches: 1}
+}
+
+func (r ranks) Len() int      { return len(r) }
+func (r ranks) Swap(i, j int) { r[i], r[j] = r[j], r[i] }
+func (r ranks) Less(i, j int) bool {
+	if r[i].Weight == r[j].Weight {
+		return r[i].Doc.PubDate().After(r[j].Doc.PubDate())
+	}
+	return r[i].Weight > r[j].Weight
+}
+
+// SearchDoc finds the documents matching any of the keywords in the given indices
+// against the given document.
+// The resulting document set will be sorted according to number of matches
+// and the index weights, and any matches with a rank below the configured
+// threshold (normalize to 0..100) will be removed.
+// If an index name is provided, only that index will be queried.
+func (idx *InvertedIndex) SearchDoc(doc Document, indices ...string) ([]Document, error) {
+	var q []queryElement
+
+	var configs IndexConfigs
+
+	if len(indices) == 0 {
+		configs = idx.cfg.Indices
+	} else {
+		configs = make(IndexConfigs, len(indices))
+		for i, indexName := range indices {
+			cfg, found := idx.getIndexCfg(indexName)
+			if !found {
+				return nil, fmt.Errorf("index %q not found", indexName)
+			}
+			configs[i] = cfg
+		}
+	}
+
+	for _, cfg := range configs {
+		keywords, err := doc.SearchKeywords(cfg)
+		if err != nil {
+			return nil, err
+		}
+
+		q = append(q, newQueryElement(cfg.Name, keywords...))
+
+	}
+
+	return idx.searchDate(doc.PubDate(), q...)
+}
+
+func (cfg IndexConfig) ToKeywords(v interface{}) ([]Keyword, error) {
+	var (
+		keywords []Keyword
+		toLower  = cfg.ToLower
+	)
+	switch vv := v.(type) {
+	case string:
+		if toLower {
+			vv = strings.ToLower(vv)
+		}
+		keywords = append(keywords, StringKeyword(vv))
+	case []string:
+		if toLower {
+			for i := 0; i < len(vv); i++ {
+				vv[i] = strings.ToLower(vv[i])
+			}
+		}
+		keywords = append(keywords, StringsToKeywords(vv...)...)
+	case time.Time:
+		layout := "2006"
+		if cfg.Pattern != "" {
+			layout = cfg.Pattern
+		}
+		keywords = append(keywords, StringKeyword(vv.Format(layout)))
+	case nil:
+		return keywords, nil
+	default:
+		return keywords, fmt.Errorf("indexing currently not supported for for index %q and type %T", cfg.Name, vv)
+	}
+
+	return keywords, nil
+}
+
+// SearchKeyValues finds the documents matching any of the keywords in the given indices.
+// The resulting document set will be sorted according to number of matches
+// and the index weights, and any matches with a rank below the configured
+// threshold (normalize to 0..100) will be removed.
+func (idx *InvertedIndex) SearchKeyValues(args ...types.KeyValues) ([]Document, error) {
+	q := make([]queryElement, len(args))
+
+	for i, arg := range args {
+		var keywords []Keyword
+		key := arg.KeyString()
+		if key == "" {
+			return nil, fmt.Errorf("index %q not valid", arg.Key)
+		}
+		conf, found := idx.getIndexCfg(key)
+		if !found {
+			return nil, fmt.Errorf("index %q not found", key)
+		}
+
+		for _, val := range arg.Values {
+			k, err := conf.ToKeywords(val)
+			if err != nil {
+				return nil, err
+			}
+			keywords = append(keywords, k...)
+		}
+
+		q[i] = newQueryElement(conf.Name, keywords...)
+
+	}
+
+	return idx.search(q...)
+}
+
+func (idx *InvertedIndex) search(query ...queryElement) ([]Document, error) {
+	return idx.searchDate(zeroDate, query...)
+}
+
+func (idx *InvertedIndex) searchDate(upperDate time.Time, query ...queryElement) ([]Document, error) {
+	matchm := make(map[Document]*rank, 200)
+	applyDateFilter := !idx.cfg.IncludeNewer && !upperDate.IsZero()
+
+	for _, el := range query {
+		setm, found := idx.index[el.Index]
+		if !found {
+			return []Document{}, fmt.Errorf("index for %q not found", el.Index)
+		}
+
+		config, found := idx.getIndexCfg(el.Index)
+		if !found {
+			return []Document{}, fmt.Errorf("index config for %q not found", el.Index)
+		}
+
+		for _, kw := range el.Keywords {
+			if docs, found := setm[kw]; found {
+				for _, doc := range docs {
+					if applyDateFilter {
+						// Exclude newer than the limit given
+						if doc.PubDate().After(upperDate) {
+							continue
+						}
+					}
+					r, found := matchm[doc]
+					if !found {
+						matchm[doc] = newRank(doc, config.Weight)
+					} else {
+						r.addWeight(config.Weight)
+					}
+				}
+			}
+		}
+	}
+
+	if len(matchm) == 0 {
+		return []Document{}, nil
+	}
+
+	matches := make(ranks, 0, 100)
+
+	for _, v := range matchm {
+		avgWeight := v.Weight / v.Matches
+		weight := norm(avgWeight, idx.minWeight, idx.maxWeight)
+		threshold := idx.cfg.Threshold / v.Matches
+
+		if weight >= threshold {
+			matches = append(matches, v)
+		}
+	}
+
+	sort.Stable(matches)
+
+	result := make([]Document, len(matches))
+
+	for i, m := range matches {
+		result[i] = m.Doc
+	}
+
+	return result, nil
+}
+
+// normalizes num to a number between 0 and 100.
+func norm(num, min, max int) int {
+	if min > max {
+		panic("min > max")
+	}
+	return int(math.Floor((float64(num-min) / float64(max-min) * 100) + 0.5))
+}
+
+// DecodeConfig decodes a slice of map into Config.
+func DecodeConfig(in interface{}) (Config, error) {
+	if in == nil {
+		return Config{}, errors.New("no related config provided")
+	}
+
+	m, ok := in.(map[string]interface{})
+	if !ok {
+		return Config{}, fmt.Errorf("expected map[string]interface {} got %T", in)
+	}
+
+	if len(m) == 0 {
+		return Config{}, errors.New("empty related config provided")
+	}
+
+	var c Config
+
+	if err := mapstructure.WeakDecode(m, &c); err != nil {
+		return c, err
+	}
+
+	if c.Threshold < 0 || c.Threshold > 100 {
+		return Config{}, errors.New("related threshold must be between 0 and 100")
+	}
+
+	if c.ToLower {
+		for i, _ := range c.Indices {
+			c.Indices[i].ToLower = true
+		}
+	}
+
+	return c, nil
+}
+
+// StringKeyword is a string search keyword.
+type StringKeyword string
+
+func (s StringKeyword) String() string {
+	return string(s)
+}
+
+// Keyword is the interface a keyword in the search index must implement.
+type Keyword interface {
+	String() string
+}
+
+// StringsToKeywords converts the given slice of strings to a slice of Keyword.
+func StringsToKeywords(s ...string) []Keyword {
+	kw := make([]Keyword, len(s))
+
+	for i := 0; i < len(s); i++ {
+		kw[i] = StringKeyword(s[i])
+	}
+
+	return kw
+}
diff --git a/related/inverted_index_test.go b/related/inverted_index_test.go
new file mode 100644
index 000000000..781a969fb
--- /dev/null
+++ b/related/inverted_index_test.go
@@ -0,0 +1,276 @@
+// Copyright 2017-present 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 related
+
+import (
+	"fmt"
+	"math/rand"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+type testDoc struct {
+	keywords map[string][]Keyword
+	date     time.Time
+}
+
+func (k *testDoc) String() string {
+	s := "\n"
+	for k, v := range k.keywords {
+		s += k + ":\t\t"
+		for _, vv := range v {
+			s += "  " + vv.String()
+		}
+		s += "\n"
+	}
+	return s
+}
+
+func newTestDoc(name string, keywords ...string) *testDoc {
+	km := make(map[string][]Keyword)
+
+	time.Sleep(1 * time.Millisecond)
+	kw := &testDoc{keywords: km, date: time.Now()}
+
+	kw.addKeywords(name, keywords...)
+	return kw
+}
+
+func (t *testDoc) addKeywords(name string, keywords ...string) *testDoc {
+	keywordm := createTestKeywords(name, keywords...)
+
+	for k, v := range keywordm {
+		keywords := make([]Keyword, len(v))
+		for i := 0; i < len(v); i++ {
+			keywords[i] = StringKeyword(v[i])
+		}
+		t.keywords[k] = keywords
+	}
+	return t
+}
+
+func createTestKeywords(name string, keywords ...string) map[string][]string {
+	return map[string][]string{
+		name: keywords,
+	}
+}
+
+func (k *testDoc) SearchKeywords(cfg IndexConfig) ([]Keyword, error) {
+	return k.keywords[cfg.Name], nil
+}
+
+func (k *testDoc) PubDate() time.Time {
+	return k.date
+}
+
+func TestSearch(t *testing.T) {
+
+	config := Config{
+		Threshold:    90,
+		IncludeNewer: false,
+		Indices: IndexConfigs{
+			IndexConfig{Name: "tags", Weight: 50},
+			IndexConfig{Name: "keywords", Weight: 65},
+		},
+	}
+
+	idx := NewInvertedIndex(config)
+	//idx.debug = true
+
+	docs := []Document{
+		newTestDoc("tags", "a", "b", "c", "d"),
+		newTestDoc("tags", "b", "d", "g"),
+		newTestDoc("tags", "b", "h").addKeywords("keywords", "a"),
+		newTestDoc("tags", "g", "h").addKeywords("keywords", "a", "b"),
+	}
+
+	idx.Add(docs...)
+
+	t.Run("count", func(t *testing.T) {
+		assert := require.New(t)
+		assert.Len(idx.index, 2)
+		set1, found := idx.index["tags"]
+		assert.True(found)
+		// 6 tags
+		assert.Len(set1, 6)
+
+		set2, found := idx.index["keywords"]
+		assert.True(found)
+		assert.Len(set2, 2)
+
+	})
+
+	t.Run("search-tags", func(t *testing.T) {
+		assert := require.New(t)
+		m, err := idx.search(newQueryElement("tags", StringsToKeywords("a", "b", "d", "z")...))
+		assert.NoError(err)
+		assert.Len(m, 2)
+		assert.Equal(docs[0], m[0])
+		assert.Equal(docs[1], m[1])
+	})
+
+	t.Run("search-tags-and-keywords", func(t *testing.T) {
+		assert := require.New(t)
+		m, err := idx.search(
+			newQueryElement("tags", StringsToKeywords("a", "b", "z")...),
+			newQueryElement("keywords", StringsToKeywords("a", "b")...))
+		assert.NoError(err)
+		assert.Len(m, 3)
+		assert.Equal(docs[3], m[0])
+		assert.Equal(docs[2], m[1])
+		assert.Equal(docs[0], m[2])
+	})
+
+	t.Run("searchdoc-all", func(t *testing.T) {
+		assert := require.New(t)
+		doc := newTestDoc("tags", "a").addKeywords("keywords", "a")
+		m, err := idx.SearchDoc(doc)
+		assert.NoError(err)
+		assert.Len(m, 2)
+		assert.Equal(docs[3], m[0])
+		assert.Equal(docs[2], m[1])
+	})
+
+	t.Run("searchdoc-tags", func(t *testing.T) {
+		assert := require.New(t)
+		doc := newTestDoc("tags", "a", "b", "d", "z").addKeywords("keywords", "a", "b")
+		m, err := idx.SearchDoc(doc, "tags")
+		assert.NoError(err)
+		assert.Len(m, 2)
+		assert.Equal(docs[0], m[0])
+		assert.Equal(docs[1], m[1])
+	})
+
+	t.Run("searchdoc-keywords-date", func(t *testing.T) {
+		assert := require.New(t)
+		doc := newTestDoc("tags", "a", "b", "d", "z").addKeywords("keywords", "a", "b")
+		// This will get a date newer than the others.
+		newDoc := newTestDoc("keywords", "a", "b")
+		idx.Add(newDoc)
+
+		m, err := idx.SearchDoc(doc, "keywords")
+		assert.NoError(err)
+		assert.Len(m, 2)
+		assert.Equal(docs[3], m[0])
+	})
+
+}
+
+func BenchmarkRelatedNewIndex(b *testing.B) {
+
+	pages := make([]*testDoc, 100)
+	numkeywords := 30
+	allKeywords := make([]string, numkeywords)
+	for i := 0; i < numkeywords; i++ {
+		allKeywords[i] = fmt.Sprintf("keyword%d", i+1)
+	}
+
+	for i := 0; i < len(pages); i++ {
+		start := rand.Intn(len(allKeywords))
+		end := start + 3
+		if end >= len(allKeywords) {
+			end = start + 1
+		}
+
+		kw := newTestDoc("tags", allKeywords[start:end]...)
+		if i%5 == 0 {
+			start := rand.Intn(len(allKeywords))
+			end := start + 3
+			if end >= len(allKeywords) {
+				end = start + 1
+			}
+			kw.addKeywords("keywords", allKeywords[start:end]...)
+		}
+
+		pages[i] = kw
+	}
+
+	cfg := Config{
+		Threshold: 50,
+		Indices: IndexConfigs{
+			IndexConfig{Name: "tags", Weight: 100},
+			IndexConfig{Name: "keywords", Weight: 200},
+		},
+	}
+
+	b.Run("singles", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			idx := NewInvertedIndex(cfg)
+			for _, doc := range pages {
+				idx.Add(doc)
+			}
+		}
+	})
+
+	b.Run("all", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			idx := NewInvertedIndex(cfg)
+			docs := make([]Document, len(pages))
+			for i := 0; i < len(pages); i++ {
+				docs[i] = pages[i]
+			}
+			idx.Add(docs...)
+		}
+	})
+
+}
+
+func BenchmarkRelatedMatchesIn(b *testing.B) {
+
+	q1 := newQueryElement("tags", StringsToKeywords("keyword2", "keyword5", "keyword32", "asdf")...)
+	q2 := newQueryElement("keywords", StringsToKeywords("keyword3", "keyword4")...)
+
+	docs := make([]*testDoc, 1000)
+	numkeywords := 20
+	allKeywords := make([]string, numkeywords)
+	for i := 0; i < numkeywords; i++ {
+		allKeywords[i] = fmt.Sprintf("keyword%d", i+1)
+	}
+
+	cfg := Config{
+		Threshold: 20,
+		Indices: IndexConfigs{
+			IndexConfig{Name: "tags", Weight: 100},
+			IndexConfig{Name: "keywords", Weight: 200},
+		},
+	}
+
+	idx := NewInvertedIndex(cfg)
+
+	for i := 0; i < len(docs); i++ {
+		start := rand.Intn(len(allKeywords))
+		end := start + 3
+		if end >= len(allKeywords) {
+			end = start + 1
+		}
+
+		index := "tags"
+		if i%5 == 0 {
+			index = "keywords"
+		}
+
+		idx.Add(newTestDoc(index, allKeywords[start:end]...))
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if i%10 == 0 {
+			idx.search(q2)
+		} else {
+			idx.search(q1)
+		}
+	}
+}