Refactor indexer (#25174)

Refactor `modules/indexer` to make it more maintainable. And it can be
easier to support more features. I'm trying to solve some of issue
searching, this is a precursor to making functional changes.

Current supported engines and the index versions:

| engines | issues | code |
| - | - | - |
| db | Just a wrapper for database queries, doesn't need version | - |
| bleve | The version of index is **2** | The version of index is **6**
|
| elasticsearch | The old index has no version, will be treated as
version **0** in this PR | The version of index is **1** |
| meilisearch | The old index has no version, will be treated as version
**0** in this PR | - |


## Changes

### Split

Splited it into mutiple packages

```text
indexer
├── internal
│   ├── bleve
│   ├── db
│   ├── elasticsearch
│   └── meilisearch
├── code
│   ├── bleve
│   ├── elasticsearch
│   └── internal
└── issues
    ├── bleve
    ├── db
    ├── elasticsearch
    ├── internal
    └── meilisearch
```

- `indexer/interanal`: Internal shared package for indexer.
- `indexer/interanal/[engine]`: Internal shared package for each engine
(bleve/db/elasticsearch/meilisearch).
- `indexer/code`: Implementations for code indexer.
- `indexer/code/internal`: Internal shared package for code indexer.
- `indexer/code/[engine]`: Implementation via each engine for code
indexer.
- `indexer/issues`: Implementations for issues indexer.

### Deduplication

- Combine `Init/Ping/Close` for code indexer and issues indexer.
- ~Combine `issues.indexerHolder` and `code.wrappedIndexer` to
`internal.IndexHolder`.~ Remove it, use dummy indexer instead when the
indexer is not ready.
- Duplicate two copies of creating ES clients.
- Duplicate two copies of `indexerID()`.


### Enhancement

- [x] Support index version for elasticsearch issues indexer, the old
index without version will be treated as version 0.
- [x] Fix spell of `elastic_search/ElasticSearch`, it should be
`Elasticsearch`.
- [x] Improve versioning of ES index. We don't need `Aliases`:
- Gitea does't need aliases for "Zero Downtime" because it never delete
old indexes.
- The old code of issues indexer uses the orignal name to create issue
index, so it's tricky to convert it to an alias.
- [x] Support index version for meilisearch issues indexer, the old
index without version will be treated as version 0.
- [x] Do "ping" only when `Ping` has been called, don't ping
periodically and cache the status.
- [x] Support the context parameter whenever possible.
- [x] Fix outdated example config.
- [x] Give up the requeue logic of issues indexer: When indexing fails,
call Ping to check if it was caused by the engine being unavailable, and
only requeue the task if the engine is unavailable.
- It is fragile and tricky, could cause data losing (It did happen when
I was doing some tests for this PR). And it works for ES only.
- Just always requeue the failed task, if it caused by bad data, it's a
bug of Gitea which should be fixed.

---------

Co-authored-by: Giteabot <teabot@gitea.io>

modules/indexer/issues/bleve/bleve.go

@@ -0,0 +1,187 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"context"
+
+	indexer_internal "code.gitea.io/gitea/modules/indexer/internal"
+	inner_bleve "code.gitea.io/gitea/modules/indexer/internal/bleve"
+	"code.gitea.io/gitea/modules/indexer/issues/internal"
+
+	"github.com/blevesearch/bleve/v2"
+	"github.com/blevesearch/bleve/v2/analysis/analyzer/custom"
+	"github.com/blevesearch/bleve/v2/analysis/token/camelcase"
+	"github.com/blevesearch/bleve/v2/analysis/token/lowercase"
+	"github.com/blevesearch/bleve/v2/analysis/token/unicodenorm"
+	"github.com/blevesearch/bleve/v2/analysis/tokenizer/unicode"
+	"github.com/blevesearch/bleve/v2/mapping"
+	"github.com/blevesearch/bleve/v2/search/query"
+)
+
+const (
+	issueIndexerAnalyzer      = "issueIndexer"
+	issueIndexerDocType       = "issueIndexerDocType"
+	issueIndexerLatestVersion = 2
+)
+
+// numericEqualityQuery a numeric equality query for the given value and field
+func numericEqualityQuery(value int64, field string) *query.NumericRangeQuery {
+	f := float64(value)
+	tru := true
+	q := bleve.NewNumericRangeInclusiveQuery(&f, &f, &tru, &tru)
+	q.SetField(field)
+	return q
+}
+
+func newMatchPhraseQuery(matchPhrase, field, analyzer string) *query.MatchPhraseQuery {
+	q := bleve.NewMatchPhraseQuery(matchPhrase)
+	q.FieldVal = field
+	q.Analyzer = analyzer
+	return q
+}
+
+const unicodeNormalizeName = "unicodeNormalize"
+
+func addUnicodeNormalizeTokenFilter(m *mapping.IndexMappingImpl) error {
+	return m.AddCustomTokenFilter(unicodeNormalizeName, map[string]interface{}{
+		"type": unicodenorm.Name,
+		"form": unicodenorm.NFC,
+	})
+}
+
+const maxBatchSize = 16
+
+// IndexerData an update to the issue indexer
+type IndexerData internal.IndexerData
+
+// Type returns the document type, for bleve's mapping.Classifier interface.
+func (i *IndexerData) Type() string {
+	return issueIndexerDocType
+}
+
+// generateIssueIndexMapping generates the bleve index mapping for issues
+func generateIssueIndexMapping() (mapping.IndexMapping, error) {
+	mapping := bleve.NewIndexMapping()
+	docMapping := bleve.NewDocumentMapping()
+
+	numericFieldMapping := bleve.NewNumericFieldMapping()
+	numericFieldMapping.IncludeInAll = false
+	docMapping.AddFieldMappingsAt("RepoID", numericFieldMapping)
+
+	textFieldMapping := bleve.NewTextFieldMapping()
+	textFieldMapping.Store = false
+	textFieldMapping.IncludeInAll = false
+	docMapping.AddFieldMappingsAt("Title", textFieldMapping)
+	docMapping.AddFieldMappingsAt("Content", textFieldMapping)
+	docMapping.AddFieldMappingsAt("Comments", textFieldMapping)
+
+	if err := addUnicodeNormalizeTokenFilter(mapping); err != nil {
+		return nil, err
+	} else if err = mapping.AddCustomAnalyzer(issueIndexerAnalyzer, map[string]interface{}{
+		"type":          custom.Name,
+		"char_filters":  []string{},
+		"tokenizer":     unicode.Name,
+		"token_filters": []string{unicodeNormalizeName, camelcase.Name, lowercase.Name},
+	}); err != nil {
+		return nil, err
+	}
+
+	mapping.DefaultAnalyzer = issueIndexerAnalyzer
+	mapping.AddDocumentMapping(issueIndexerDocType, docMapping)
+	mapping.AddDocumentMapping("_all", bleve.NewDocumentDisabledMapping())
+
+	return mapping, nil
+}
+
+var _ internal.Indexer = &Indexer{}
+
+// Indexer implements Indexer interface
+type Indexer struct {
+	inner                    *inner_bleve.Indexer
+	indexer_internal.Indexer // do not composite inner_bleve.Indexer directly to avoid exposing too much
+}
+
+// NewIndexer creates a new bleve local indexer
+func NewIndexer(indexDir string) *Indexer {
+	inner := inner_bleve.NewIndexer(indexDir, issueIndexerLatestVersion, generateIssueIndexMapping)
+	return &Indexer{
+		Indexer: inner,
+		inner:   inner,
+	}
+}
+
+// Index will save the index data
+func (b *Indexer) Index(_ context.Context, issues []*internal.IndexerData) error {
+	batch := inner_bleve.NewFlushingBatch(b.inner.Indexer, maxBatchSize)
+	for _, issue := range issues {
+		if err := batch.Index(indexer_internal.Base36(issue.ID), struct {
+			RepoID   int64
+			Title    string
+			Content  string
+			Comments []string
+		}{
+			RepoID:   issue.RepoID,
+			Title:    issue.Title,
+			Content:  issue.Content,
+			Comments: issue.Comments,
+		}); err != nil {
+			return err
+		}
+	}
+	return batch.Flush()
+}
+
+// Delete deletes indexes by ids
+func (b *Indexer) Delete(_ context.Context, ids ...int64) error {
+	batch := inner_bleve.NewFlushingBatch(b.inner.Indexer, maxBatchSize)
+	for _, id := range ids {
+		if err := batch.Delete(indexer_internal.Base36(id)); err != nil {
+			return err
+		}
+	}
+	return batch.Flush()
+}
+
+// Search searches for issues by given conditions.
+// Returns the matching issue IDs
+func (b *Indexer) Search(ctx context.Context, keyword string, repoIDs []int64, limit, start int) (*internal.SearchResult, error) {
+	var repoQueriesP []*query.NumericRangeQuery
+	for _, repoID := range repoIDs {
+		repoQueriesP = append(repoQueriesP, numericEqualityQuery(repoID, "RepoID"))
+	}
+	repoQueries := make([]query.Query, len(repoQueriesP))
+	for i, v := range repoQueriesP {
+		repoQueries[i] = query.Query(v)
+	}
+
+	indexerQuery := bleve.NewConjunctionQuery(
+		bleve.NewDisjunctionQuery(repoQueries...),
+		bleve.NewDisjunctionQuery(
+			newMatchPhraseQuery(keyword, "Title", issueIndexerAnalyzer),
+			newMatchPhraseQuery(keyword, "Content", issueIndexerAnalyzer),
+			newMatchPhraseQuery(keyword, "Comments", issueIndexerAnalyzer),
+		))
+	search := bleve.NewSearchRequestOptions(indexerQuery, limit, start, false)
+	search.SortBy([]string{"-_score"})
+
+	result, err := b.inner.Indexer.SearchInContext(ctx, search)
+	if err != nil {
+		return nil, err
+	}
+
+	ret := internal.SearchResult{
+		Hits: make([]internal.Match, 0, len(result.Hits)),
+	}
+	for _, hit := range result.Hits {
+		id, err := indexer_internal.ParseBase36(hit.ID)
+		if err != nil {
+			return nil, err
+		}
+		ret.Hits = append(ret.Hits, internal.Match{
+			ID: id,
+		})
+	}
+	return &ret, nil
+}