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/indexer_test.go

@@ -5,11 +5,15 @@ package code
 
 import (
 	"context"
+	"os"
 	"path/filepath"
 	"testing"
 
 	"code.gitea.io/gitea/models/unittest"
 	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/indexer/code/bleve"
+	"code.gitea.io/gitea/modules/indexer/code/elasticsearch"
+	"code.gitea.io/gitea/modules/indexer/code/internal"
 
 	_ "code.gitea.io/gitea/models"
 
@@ -22,7 +26,7 @@ func TestMain(m *testing.M) {
 	})
 }
 
-func testIndexer(name string, t *testing.T, indexer Indexer) {
+func testIndexer(name string, t *testing.T, indexer internal.Indexer) {
 	t.Run(name, func(t *testing.T) {
 		var repoID int64 = 1
 		err := index(git.DefaultContext, indexer, repoID)
@@ -81,6 +85,48 @@ func testIndexer(name string, t *testing.T, indexer Indexer) {
 			})
 		}
 
-		assert.NoError(t, indexer.Delete(repoID))
+		assert.NoError(t, indexer.Delete(context.Background(), repoID))
 	})
 }
+
+func TestBleveIndexAndSearch(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+
+	dir := t.TempDir()
+
+	idx := bleve.NewIndexer(dir)
+	_, err := idx.Init(context.Background())
+	if err != nil {
+		assert.Fail(t, "Unable to create bleve indexer Error: %v", err)
+		if idx != nil {
+			idx.Close()
+		}
+		return
+	}
+	defer idx.Close()
+
+	testIndexer("beleve", t, idx)
+}
+
+func TestESIndexAndSearch(t *testing.T) {
+	unittest.PrepareTestEnv(t)
+
+	u := os.Getenv("TEST_INDEXER_CODE_ES_URL")
+	if u == "" {
+		t.SkipNow()
+		return
+	}
+
+	indexer := elasticsearch.NewIndexer(u, "gitea_codes")
+	if _, err := indexer.Init(context.Background()); err != nil {
+		assert.Fail(t, "Unable to init ES indexer Error: %v", err)
+		if indexer != nil {
+			indexer.Close()
+		}
+		return
+	}
+
+	defer indexer.Close()
+
+	testIndexer("elastic_search", t, indexer)
+}