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>

1 files changed, 0 insertions, 104 deletions

diff --git a/modules/indexer/code/wrapped.go b/modules/indexer/code/wrapped.go
deleted file mode 100644
index 7eed3e8557..0000000000
--- a/modules/indexer/code/wrapped.go
+++ /dev/null
@@ -1,104 +0,0 @@
-// Copyright 2019 The Gitea Authors. All rights reserved.
-// SPDX-License-Identifier: MIT
-
-package code
-
-import (
-	"context"
-	"fmt"
-	"sync"
-
-	repo_model "code.gitea.io/gitea/models/repo"
-	"code.gitea.io/gitea/modules/log"
-)
-
-var indexer = newWrappedIndexer()
-
-// ErrWrappedIndexerClosed is the error returned if the indexer was closed before it was ready
-var ErrWrappedIndexerClosed = fmt.Errorf("Indexer closed before ready")
-
-type wrappedIndexer struct {
-	internal Indexer
-	lock     sync.RWMutex
-	cond     *sync.Cond
-	closed   bool
-}
-
-func newWrappedIndexer() *wrappedIndexer {
-	w := &wrappedIndexer{}
-	w.cond = sync.NewCond(w.lock.RLocker())
-	return w
-}
-
-func (w *wrappedIndexer) set(indexer Indexer) {
-	w.lock.Lock()
-	defer w.lock.Unlock()
-	if w.closed {
-		// Too late!
-		indexer.Close()
-	}
-	w.internal = indexer
-	w.cond.Broadcast()
-}
-
-func (w *wrappedIndexer) get() (Indexer, error) {
-	w.lock.RLock()
-	defer w.lock.RUnlock()
-	if w.internal == nil {
-		if w.closed {
-			return nil, ErrWrappedIndexerClosed
-		}
-		w.cond.Wait()
-		if w.closed {
-			return nil, ErrWrappedIndexerClosed
-		}
-	}
-	return w.internal, nil
-}
-
-// Ping checks if elastic is available
-func (w *wrappedIndexer) Ping() bool {
-	indexer, err := w.get()
-	if err != nil {
-		log.Warn("Failed to get indexer: %v", err)
-		return false
-	}
-	return indexer.Ping()
-}
-
-func (w *wrappedIndexer) Index(ctx context.Context, repo *repo_model.Repository, sha string, changes *repoChanges) error {
-	indexer, err := w.get()
-	if err != nil {
-		return err
-	}
-	return indexer.Index(ctx, repo, sha, changes)
-}
-
-func (w *wrappedIndexer) Delete(repoID int64) error {
-	indexer, err := w.get()
-	if err != nil {
-		return err
-	}
-	return indexer.Delete(repoID)
-}
-
-func (w *wrappedIndexer) Search(ctx context.Context, repoIDs []int64, language, keyword string, page, pageSize int, isMatch bool) (int64, []*SearchResult, []*SearchResultLanguages, error) {
-	indexer, err := w.get()
-	if err != nil {
-		return 0, nil, nil, err
-	}
-	return indexer.Search(ctx, repoIDs, language, keyword, page, pageSize, isMatch)
-}
-
-func (w *wrappedIndexer) Close() {
-	w.lock.Lock()
-	defer w.lock.Unlock()
-	if w.closed {
-		return
-	}
-	w.closed = true
-	w.cond.Broadcast()
-	if w.internal != nil {
-		w.internal.Close()
-	}
-}