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/code/internal/indexer.go

@@ -0,0 +1,43 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"context"
+	"fmt"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/indexer/internal"
+)
+
+// Indexer defines an interface to index and search code contents
+type Indexer interface {
+	internal.Indexer
+	Index(ctx context.Context, repo *repo_model.Repository, sha string, changes *RepoChanges) error
+	Delete(ctx context.Context, repoID int64) error
+	Search(ctx context.Context, repoIDs []int64, language, keyword string, page, pageSize int, isMatch bool) (int64, []*SearchResult, []*SearchResultLanguages, error)
+}
+
+// NewDummyIndexer returns a dummy indexer
+func NewDummyIndexer() Indexer {
+	return &dummyIndexer{
+		Indexer: internal.NewDummyIndexer(),
+	}
+}
+
+type dummyIndexer struct {
+	internal.Indexer
+}
+
+func (d *dummyIndexer) Index(ctx context.Context, repo *repo_model.Repository, sha string, changes *RepoChanges) error {
+	return fmt.Errorf("indexer is not ready")
+}
+
+func (d *dummyIndexer) Delete(ctx context.Context, repoID int64) error {
+	return fmt.Errorf("indexer is not ready")
+}
+
+func (d *dummyIndexer) Search(ctx context.Context, repoIDs []int64, language, keyword string, page, pageSize int, isMatch bool) (int64, []*SearchResult, []*SearchResultLanguages, error) {
+	return 0, nil, nil, fmt.Errorf("indexer is not ready")
+}

modules/indexer/code/internal/model.go

@@ -0,0 +1,44 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import "code.gitea.io/gitea/modules/timeutil"
+
+type FileUpdate struct {
+	Filename string
+	BlobSha  string
+	Size     int64
+	Sized    bool
+}
+
+// RepoChanges changes (file additions/updates/removals) to a repo
+type RepoChanges struct {
+	Updates          []FileUpdate
+	RemovedFilenames []string
+}
+
+// IndexerData represents data stored in the code indexer
+type IndexerData struct {
+	RepoID int64
+}
+
+// SearchResult result of performing a search in a repo
+type SearchResult struct {
+	RepoID      int64
+	StartIndex  int
+	EndIndex    int
+	Filename    string
+	Content     string
+	CommitID    string
+	UpdatedUnix timeutil.TimeStamp
+	Language    string
+	Color       string
+}
+
+// SearchResultLanguages result of top languages count in search results
+type SearchResultLanguages struct {
+	Language string
+	Color    string
+	Count    int
+}

modules/indexer/code/internal/util.go

@@ -0,0 +1,32 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"strings"
+
+	"code.gitea.io/gitea/modules/indexer/internal"
+	"code.gitea.io/gitea/modules/log"
+)
+
+func FilenameIndexerID(repoID int64, filename string) string {
+	return internal.Base36(repoID) + "_" + filename
+}
+
+func ParseIndexerID(indexerID string) (int64, string) {
+	index := strings.IndexByte(indexerID, '_')
+	if index == -1 {
+		log.Error("Unexpected ID in repo indexer: %s", indexerID)
+	}
+	repoID, _ := internal.ParseBase36(indexerID[:index])
+	return repoID, indexerID[index+1:]
+}
+
+func FilenameOfIndexerID(indexerID string) string {
+	index := strings.IndexByte(indexerID, '_')
+	if index == -1 {
+		log.Error("Unexpected ID in repo indexer: %s", indexerID)
+	}
+	return indexerID[index+1:]
+}