15 files changed, 882 insertions, 0 deletions

diff --git a/modules/indexer/internal/base32.go b/modules/indexer/internal/base32.go
new file mode 100644
index 00000000..aca756c6
--- /dev/null
+++ b/modules/indexer/internal/base32.go
@@ -0,0 +1,21 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func Base36(i int64) string {
+	return strconv.FormatInt(i, 36)
+}
+
+func ParseBase36(s string) (int64, error) {
+	i, err := strconv.ParseInt(s, 36, 64)
+	if err != nil {
+		return 0, fmt.Errorf("invalid base36 integer %q: %w", s, err)
+	}
+	return i, nil
+}
diff --git a/modules/indexer/internal/bleve/batch.go b/modules/indexer/internal/bleve/batch.go
new file mode 100644
index 00000000..ed5ef077
--- /dev/null
+++ b/modules/indexer/internal/bleve/batch.go
@@ -0,0 +1,58 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"github.com/blevesearch/bleve/v2"
+)
+
+// FlushingBatch is a batch of operations that automatically flushes to the
+// underlying index once it reaches a certain size.
+type FlushingBatch struct {
+	maxBatchSize int
+	batch        *bleve.Batch
+	index        bleve.Index
+}
+
+// NewFlushingBatch creates a new flushing batch for the specified index. Once
+// the number of operations in the batch reaches the specified limit, the batch
+// automatically flushes its operations to the index.
+func NewFlushingBatch(index bleve.Index, maxBatchSize int) *FlushingBatch {
+	return &FlushingBatch{
+		maxBatchSize: maxBatchSize,
+		batch:        index.NewBatch(),
+		index:        index,
+	}
+}
+
+// Index add a new index to batch
+func (b *FlushingBatch) Index(id string, data any) error {
+	if err := b.batch.Index(id, data); err != nil {
+		return err
+	}
+	return b.flushIfFull()
+}
+
+// Delete add a delete index to batch
+func (b *FlushingBatch) Delete(id string) error {
+	b.batch.Delete(id)
+	return b.flushIfFull()
+}
+
+func (b *FlushingBatch) flushIfFull() error {
+	if b.batch.Size() < b.maxBatchSize {
+		return nil
+	}
+	return b.Flush()
+}
+
+// Flush submit the batch and create a new one
+func (b *FlushingBatch) Flush() error {
+	err := b.index.Batch(b.batch)
+	if err != nil {
+		return err
+	}
+	b.batch = b.index.NewBatch()
+	return nil
+}
diff --git a/modules/indexer/internal/bleve/indexer.go b/modules/indexer/internal/bleve/indexer.go
new file mode 100644
index 00000000..1435d2f5
--- /dev/null
+++ b/modules/indexer/internal/bleve/indexer.go
@@ -0,0 +1,102 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"context"
+	"fmt"
+
+	"code.gitea.io/gitea/modules/indexer/internal"
+	"code.gitea.io/gitea/modules/log"
+
+	"github.com/blevesearch/bleve/v2"
+	"github.com/blevesearch/bleve/v2/mapping"
+)
+
+var _ internal.Indexer = &Indexer{}
+
+// Indexer represents a basic bleve indexer implementation
+type Indexer struct {
+	Indexer bleve.Index
+
+	indexDir      string
+	version       int
+	mappingGetter MappingGetter
+}
+
+type MappingGetter func() (mapping.IndexMapping, error)
+
+func NewIndexer(indexDir string, version int, mappingGetter func() (mapping.IndexMapping, error)) *Indexer {
+	return &Indexer{
+		indexDir:      indexDir,
+		version:       version,
+		mappingGetter: mappingGetter,
+	}
+}
+
+// Init initializes the indexer
+func (i *Indexer) Init(_ context.Context) (bool, error) {
+	if i == nil {
+		return false, fmt.Errorf("cannot init nil indexer")
+	}
+
+	if i.Indexer != nil {
+		return false, fmt.Errorf("indexer is already initialized")
+	}
+
+	indexer, version, err := openIndexer(i.indexDir, i.version)
+	if err != nil {
+		return false, err
+	}
+	if indexer != nil {
+		i.Indexer = indexer
+		return true, nil
+	}
+
+	if version != 0 {
+		log.Warn("Found older bleve index with version %d, Forgejo will remove it and rebuild", version)
+	}
+
+	indexMapping, err := i.mappingGetter()
+	if err != nil {
+		return false, err
+	}
+
+	indexer, err = bleve.New(i.indexDir, indexMapping)
+	if err != nil {
+		return false, err
+	}
+
+	if err = writeIndexMetadata(i.indexDir, &IndexMetadata{
+		Version: i.version,
+	}); err != nil {
+		return false, err
+	}
+
+	i.Indexer = indexer
+
+	return false, nil
+}
+
+// Ping checks if the indexer is available
+func (i *Indexer) Ping(_ context.Context) error {
+	if i == nil {
+		return fmt.Errorf("cannot ping nil indexer")
+	}
+	if i.Indexer == nil {
+		return fmt.Errorf("indexer is not initialized")
+	}
+	return nil
+}
+
+func (i *Indexer) Close() {
+	if i == nil || i.Indexer == nil {
+		return
+	}
+
+	if err := i.Indexer.Close(); err != nil {
+		log.Error("Failed to close bleve indexer in %q: %v", i.indexDir, err)
+	}
+	i.Indexer = nil
+}
diff --git a/modules/indexer/internal/bleve/metadata.go b/modules/indexer/internal/bleve/metadata.go
new file mode 100644
index 00000000..3c570ab4
--- /dev/null
+++ b/modules/indexer/internal/bleve/metadata.go
@@ -0,0 +1,55 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+// Copied and modified from https://github.com/ethantkoenig/rupture (MIT License)
+
+package bleve
+
+import (
+	"os"
+	"path/filepath"
+
+	"code.gitea.io/gitea/modules/json"
+)
+
+const metaFilename = "rupture_meta.json"
+
+func indexMetadataPath(dir string) string {
+	return filepath.Join(dir, metaFilename)
+}
+
+// IndexMetadata contains metadata about a bleve index.
+type IndexMetadata struct {
+	// The version of the data in the index. This can be useful for tracking
+	// schema changes or data migrations.
+	Version int `json:"version"`
+}
+
+// readIndexMetadata returns the metadata for the index at the specified path.
+// If no such index metadata exists, an empty metadata and a nil error are
+// returned.
+func readIndexMetadata(path string) (*IndexMetadata, error) {
+	meta := &IndexMetadata{}
+	metaPath := indexMetadataPath(path)
+	if _, err := os.Stat(metaPath); os.IsNotExist(err) {
+		return meta, nil
+	} else if err != nil {
+		return nil, err
+	}
+
+	metaBytes, err := os.ReadFile(metaPath)
+	if err != nil {
+		return nil, err
+	}
+	return meta, json.Unmarshal(metaBytes, &meta)
+}
+
+// writeIndexMetadata writes metadata for the index at the specified path.
+func writeIndexMetadata(path string, meta *IndexMetadata) error {
+	metaBytes, err := json.Marshal(meta)
+	if err != nil {
+		return err
+	}
+
+	return os.WriteFile(indexMetadataPath(path), metaBytes, 0o644)
+}
diff --git a/modules/indexer/internal/bleve/metadata_test.go b/modules/indexer/internal/bleve/metadata_test.go
new file mode 100644
index 00000000..31603a92
--- /dev/null
+++ b/modules/indexer/internal/bleve/metadata_test.go
@@ -0,0 +1,28 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+// Copied and modified from https://github.com/ethantkoenig/rupture (MIT License)
+
+package bleve
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMetadata(t *testing.T) {
+	dir := t.TempDir()
+
+	meta, err := readIndexMetadata(dir)
+	require.NoError(t, err)
+	assert.Equal(t, &IndexMetadata{}, meta)
+
+	meta.Version = 24
+	require.NoError(t, writeIndexMetadata(dir, meta))
+
+	meta, err = readIndexMetadata(dir)
+	require.NoError(t, err)
+	assert.EqualValues(t, 24, meta.Version)
+}
diff --git a/modules/indexer/internal/bleve/query.go b/modules/indexer/internal/bleve/query.go
new file mode 100644
index 00000000..21422b28
--- /dev/null
+++ b/modules/indexer/internal/bleve/query.go
@@ -0,0 +1,56 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"code.gitea.io/gitea/modules/optional"
+
+	"github.com/blevesearch/bleve/v2"
+	"github.com/blevesearch/bleve/v2/search/query"
+)
+
+// NumericEqualityQuery generates 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
+}
+
+// MatchPhraseQuery generates a match phrase query for the given phrase, field and analyzer
+func MatchPhraseQuery(matchPhrase, field, analyzer string, fuzziness int) *query.MatchPhraseQuery {
+	q := bleve.NewMatchPhraseQuery(matchPhrase)
+	q.FieldVal = field
+	q.Analyzer = analyzer
+	q.Fuzziness = fuzziness
+	return q
+}
+
+// BoolFieldQuery generates a bool field query for the given value and field
+func BoolFieldQuery(value bool, field string) *query.BoolFieldQuery {
+	q := bleve.NewBoolFieldQuery(value)
+	q.SetField(field)
+	return q
+}
+
+func NumericRangeInclusiveQuery(min, max optional.Option[int64], field string) *query.NumericRangeQuery {
+	var minF, maxF *float64
+	var minI, maxI *bool
+	if min.Has() {
+		minF = new(float64)
+		*minF = float64(min.Value())
+		minI = new(bool)
+		*minI = true
+	}
+	if max.Has() {
+		maxF = new(float64)
+		*maxF = float64(max.Value())
+		maxI = new(bool)
+		*maxI = true
+	}
+	q := bleve.NewNumericRangeInclusiveQuery(minF, maxF, minI, maxI)
+	q.SetField(field)
+	return q
+}
diff --git a/modules/indexer/internal/bleve/util.go b/modules/indexer/internal/bleve/util.go
new file mode 100644
index 00000000..d05b6797
--- /dev/null
+++ b/modules/indexer/internal/bleve/util.go
@@ -0,0 +1,48 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package bleve
+
+import (
+	"errors"
+	"os"
+
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/util"
+
+	"github.com/blevesearch/bleve/v2"
+	"github.com/blevesearch/bleve/v2/index/upsidedown"
+)
+
+// openIndexer open the index at the specified path, checking for metadata
+// updates and bleve version updates.  If index needs to be created (or
+// re-created), returns (nil, nil)
+func openIndexer(path string, latestVersion int) (bleve.Index, int, error) {
+	_, err := os.Stat(path)
+	if err != nil && os.IsNotExist(err) {
+		return nil, 0, nil
+	} else if err != nil {
+		return nil, 0, err
+	}
+
+	metadata, err := readIndexMetadata(path)
+	if err != nil {
+		return nil, 0, err
+	}
+	if metadata.Version < latestVersion {
+		// the indexer is using a previous version, so we should delete it and
+		// re-populate
+		return nil, metadata.Version, util.RemoveAll(path)
+	}
+
+	index, err := bleve.Open(path)
+	if err != nil {
+		if errors.Is(err, upsidedown.IncompatibleVersion) {
+			log.Warn("Indexer was built with a previous version of bleve, deleting and rebuilding")
+			return nil, 0, util.RemoveAll(path)
+		}
+		return nil, 0, err
+	}
+
+	return index, 0, nil
+}
diff --git a/modules/indexer/internal/db/indexer.go b/modules/indexer/internal/db/indexer.go
new file mode 100644
index 00000000..3deec836
--- /dev/null
+++ b/modules/indexer/internal/db/indexer.go
@@ -0,0 +1,34 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package db
+
+import (
+	"context"
+
+	"code.gitea.io/gitea/modules/indexer/internal"
+)
+
+var _ internal.Indexer = &Indexer{}
+
+// Indexer represents a basic db indexer implementation
+type Indexer struct{}
+
+// Init initializes the indexer
+func (i *Indexer) Init(_ context.Context) (bool, error) {
+	// Return true to indicate that the index was opened/existed.
+	// So that the indexer will not try to populate the index, the data is already there.
+	return true, nil
+}
+
+// Ping checks if the indexer is available
+func (i *Indexer) Ping(_ context.Context) error {
+	// No need to ping database to check if it is available.
+	// If the database goes down, Gitea will go down, so nobody will care if the indexer is available.
+	return nil
+}
+
+// Close closes the indexer
+func (i *Indexer) Close() {
+	// nothing to do
+}
diff --git a/modules/indexer/internal/elasticsearch/indexer.go b/modules/indexer/internal/elasticsearch/indexer.go
new file mode 100644
index 00000000..395eea3b
--- /dev/null
+++ b/modules/indexer/internal/elasticsearch/indexer.go
@@ -0,0 +1,93 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package elasticsearch
+
+import (
+	"context"
+	"fmt"
+
+	"code.gitea.io/gitea/modules/indexer/internal"
+
+	"github.com/olivere/elastic/v7"
+)
+
+var _ internal.Indexer = &Indexer{}
+
+// Indexer represents a basic elasticsearch indexer implementation
+type Indexer struct {
+	Client *elastic.Client
+
+	url       string
+	indexName string
+	version   int
+	mapping   string
+}
+
+func NewIndexer(url, indexName string, version int, mapping string) *Indexer {
+	return &Indexer{
+		url:       url,
+		indexName: indexName,
+		version:   version,
+		mapping:   mapping,
+	}
+}
+
+// Init initializes the indexer
+func (i *Indexer) Init(ctx context.Context) (bool, error) {
+	if i == nil {
+		return false, fmt.Errorf("cannot init nil indexer")
+	}
+	if i.Client != nil {
+		return false, fmt.Errorf("indexer is already initialized")
+	}
+
+	client, err := i.initClient()
+	if err != nil {
+		return false, err
+	}
+	i.Client = client
+
+	exists, err := i.Client.IndexExists(i.VersionedIndexName()).Do(ctx)
+	if err != nil {
+		return false, err
+	}
+	if exists {
+		return true, nil
+	}
+
+	if err := i.createIndex(ctx); err != nil {
+		return false, err
+	}
+
+	return exists, nil
+}
+
+// Ping checks if the indexer is available
+func (i *Indexer) Ping(ctx context.Context) error {
+	if i == nil {
+		return fmt.Errorf("cannot ping nil indexer")
+	}
+	if i.Client == nil {
+		return fmt.Errorf("indexer is not initialized")
+	}
+
+	resp, err := i.Client.ClusterHealth().Do(ctx)
+	if err != nil {
+		return err
+	}
+	if resp.Status != "green" && resp.Status != "yellow" {
+		// It's healthy if the status is green, and it's available if the status is yellow,
+		// see https://www.elastic.co/guide/en/elasticsearch/reference/current/cluster-health.html
+		return fmt.Errorf("status of elasticsearch cluster is %s", resp.Status)
+	}
+	return nil
+}
+
+// Close closes the indexer
+func (i *Indexer) Close() {
+	if i == nil {
+		return
+	}
+	i.Client = nil
+}
diff --git a/modules/indexer/internal/elasticsearch/util.go b/modules/indexer/internal/elasticsearch/util.go
new file mode 100644
index 00000000..18cb152d
--- /dev/null
+++ b/modules/indexer/internal/elasticsearch/util.go
@@ -0,0 +1,68 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package elasticsearch
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"code.gitea.io/gitea/modules/log"
+
+	"github.com/olivere/elastic/v7"
+)
+
+// VersionedIndexName returns the full index name with version
+func (i *Indexer) VersionedIndexName() string {
+	return versionedIndexName(i.indexName, i.version)
+}
+
+func versionedIndexName(indexName string, version int) string {
+	if version == 0 {
+		// Old index name without version
+		return indexName
+	}
+	return fmt.Sprintf("%s.v%d", indexName, version)
+}
+
+func (i *Indexer) createIndex(ctx context.Context) error {
+	createIndex, err := i.Client.CreateIndex(i.VersionedIndexName()).BodyString(i.mapping).Do(ctx)
+	if err != nil {
+		return err
+	}
+	if !createIndex.Acknowledged {
+		return fmt.Errorf("create index %s with %s failed", i.VersionedIndexName(), i.mapping)
+	}
+
+	i.checkOldIndexes(ctx)
+
+	return nil
+}
+
+func (i *Indexer) initClient() (*elastic.Client, error) {
+	opts := []elastic.ClientOptionFunc{
+		elastic.SetURL(i.url),
+		elastic.SetSniff(false),
+		elastic.SetHealthcheckInterval(10 * time.Second),
+		elastic.SetGzip(false),
+	}
+
+	logger := log.GetLogger(log.DEFAULT)
+
+	opts = append(opts, elastic.SetTraceLog(&log.PrintfLogger{Logf: logger.Trace}))
+	opts = append(opts, elastic.SetInfoLog(&log.PrintfLogger{Logf: logger.Info}))
+	opts = append(opts, elastic.SetErrorLog(&log.PrintfLogger{Logf: logger.Error}))
+
+	return elastic.NewClient(opts...)
+}
+
+func (i *Indexer) checkOldIndexes(ctx context.Context) {
+	for v := 0; v < i.version; v++ {
+		indexName := versionedIndexName(i.indexName, v)
+		exists, err := i.Client.IndexExists(indexName).Do(ctx)
+		if err == nil && exists {
+			log.Warn("Found older elasticsearch index named %q, Forgejo will keep the old NOT DELETED. You can delete the old version after the upgrade succeed.", indexName)
+		}
+	}
+}
diff --git a/modules/indexer/internal/indexer.go b/modules/indexer/internal/indexer.go
new file mode 100644
index 00000000..c7f356da
--- /dev/null
+++ b/modules/indexer/internal/indexer.go
@@ -0,0 +1,37 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"context"
+	"fmt"
+)
+
+// Indexer defines an basic indexer interface
+type Indexer interface {
+	// Init initializes the indexer
+	// returns true if the index was opened/existed (with data populated), false if it was created/not-existed (with no data)
+	Init(ctx context.Context) (bool, error)
+	// Ping checks if the indexer is available
+	Ping(ctx context.Context) error
+	// Close closes the indexer
+	Close()
+}
+
+// NewDummyIndexer returns a dummy indexer
+func NewDummyIndexer() Indexer {
+	return &dummyIndexer{}
+}
+
+type dummyIndexer struct{}
+
+func (d *dummyIndexer) Init(ctx context.Context) (bool, error) {
+	return false, fmt.Errorf("indexer is not ready")
+}
+
+func (d *dummyIndexer) Ping(ctx context.Context) error {
+	return fmt.Errorf("indexer is not ready")
+}
+
+func (d *dummyIndexer) Close() {}
diff --git a/modules/indexer/internal/meilisearch/filter.go b/modules/indexer/internal/meilisearch/filter.go
new file mode 100644
index 00000000..593177f1
--- /dev/null
+++ b/modules/indexer/internal/meilisearch/filter.go
@@ -0,0 +1,119 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package meilisearch
+
+import (
+	"fmt"
+	"strings"
+)
+
+// Filter represents a filter for meilisearch queries.
+// It's just a simple wrapper around a string.
+// DO NOT assume that it is a complete implementation.
+type Filter interface {
+	Statement() string
+}
+
+type FilterAnd struct {
+	filters []Filter
+}
+
+func (f *FilterAnd) Statement() string {
+	var statements []string
+	for _, filter := range f.filters {
+		if s := filter.Statement(); s != "" {
+			statements = append(statements, fmt.Sprintf("(%s)", s))
+		}
+	}
+	return strings.Join(statements, " AND ")
+}
+
+func (f *FilterAnd) And(filter Filter) *FilterAnd {
+	f.filters = append(f.filters, filter)
+	return f
+}
+
+type FilterOr struct {
+	filters []Filter
+}
+
+func (f *FilterOr) Statement() string {
+	var statements []string
+	for _, filter := range f.filters {
+		if s := filter.Statement(); s != "" {
+			statements = append(statements, fmt.Sprintf("(%s)", s))
+		}
+	}
+	return strings.Join(statements, " OR ")
+}
+
+func (f *FilterOr) Or(filter Filter) *FilterOr {
+	f.filters = append(f.filters, filter)
+	return f
+}
+
+type FilterIn string
+
+// NewFilterIn creates a new FilterIn.
+// It supports int64 only, to avoid extra works to handle strings with special characters.
+func NewFilterIn[T int64](field string, values ...T) FilterIn {
+	if len(values) == 0 {
+		return ""
+	}
+	vs := make([]string, len(values))
+	for i, v := range values {
+		vs[i] = fmt.Sprintf("%v", v)
+	}
+	return FilterIn(fmt.Sprintf("%s IN [%v]", field, strings.Join(vs, ", ")))
+}
+
+func (f FilterIn) Statement() string {
+	return string(f)
+}
+
+type FilterEq string
+
+// NewFilterEq creates a new FilterEq.
+// It supports int64 and bool only, to avoid extra works to handle strings with special characters.
+func NewFilterEq[T bool | int64](field string, value T) FilterEq {
+	return FilterEq(fmt.Sprintf("%s = %v", field, value))
+}
+
+func (f FilterEq) Statement() string {
+	return string(f)
+}
+
+type FilterNot string
+
+func NewFilterNot(filter Filter) FilterNot {
+	return FilterNot(fmt.Sprintf("NOT (%s)", filter.Statement()))
+}
+
+func (f FilterNot) Statement() string {
+	return string(f)
+}
+
+type FilterGte string
+
+// NewFilterGte creates a new FilterGte.
+// It supports int64 only, to avoid extra works to handle strings with special characters.
+func NewFilterGte[T int64](field string, value T) FilterGte {
+	return FilterGte(fmt.Sprintf("%s >= %v", field, value))
+}
+
+func (f FilterGte) Statement() string {
+	return string(f)
+}
+
+type FilterLte string
+
+// NewFilterLte creates a new FilterLte.
+// It supports int64 only, to avoid extra works to handle strings with special characters.
+func NewFilterLte[T int64](field string, value T) FilterLte {
+	return FilterLte(fmt.Sprintf("%s <= %v", field, value))
+}
+
+func (f FilterLte) Statement() string {
+	return string(f)
+}
diff --git a/modules/indexer/internal/meilisearch/indexer.go b/modules/indexer/internal/meilisearch/indexer.go
new file mode 100644
index 00000000..f4004849
--- /dev/null
+++ b/modules/indexer/internal/meilisearch/indexer.go
@@ -0,0 +1,91 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package meilisearch
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/meilisearch/meilisearch-go"
+)
+
+// Indexer represents a basic meilisearch indexer implementation
+type Indexer struct {
+	Client *meilisearch.Client
+
+	url, apiKey string
+	indexName   string
+	version     int
+	settings    *meilisearch.Settings
+}
+
+func NewIndexer(url, apiKey, indexName string, version int, settings *meilisearch.Settings) *Indexer {
+	return &Indexer{
+		url:       url,
+		apiKey:    apiKey,
+		indexName: indexName,
+		version:   version,
+		settings:  settings,
+	}
+}
+
+// Init initializes the indexer
+func (i *Indexer) Init(_ context.Context) (bool, error) {
+	if i == nil {
+		return false, fmt.Errorf("cannot init nil indexer")
+	}
+
+	if i.Client != nil {
+		return false, fmt.Errorf("indexer is already initialized")
+	}
+
+	i.Client = meilisearch.NewClient(meilisearch.ClientConfig{
+		Host:   i.url,
+		APIKey: i.apiKey,
+	})
+
+	_, err := i.Client.GetIndex(i.VersionedIndexName())
+	if err == nil {
+		return true, nil
+	}
+	_, err = i.Client.CreateIndex(&meilisearch.IndexConfig{
+		Uid:        i.VersionedIndexName(),
+		PrimaryKey: "id",
+	})
+	if err != nil {
+		return false, err
+	}
+
+	i.checkOldIndexes()
+
+	_, err = i.Client.Index(i.VersionedIndexName()).UpdateSettings(i.settings)
+	return false, err
+}
+
+// Ping checks if the indexer is available
+func (i *Indexer) Ping(ctx context.Context) error {
+	if i == nil {
+		return fmt.Errorf("cannot ping nil indexer")
+	}
+	if i.Client == nil {
+		return fmt.Errorf("indexer is not initialized")
+	}
+	resp, err := i.Client.Health()
+	if err != nil {
+		return err
+	}
+	if resp.Status != "available" {
+		// See https://docs.meilisearch.com/reference/api/health.html#status
+		return fmt.Errorf("status of meilisearch is not available: %s", resp.Status)
+	}
+	return nil
+}
+
+// Close closes the indexer
+func (i *Indexer) Close() {
+	if i == nil {
+		return
+	}
+	i.Client = nil
+}
diff --git a/modules/indexer/internal/meilisearch/util.go b/modules/indexer/internal/meilisearch/util.go
new file mode 100644
index 00000000..845bdb6e
--- /dev/null
+++ b/modules/indexer/internal/meilisearch/util.go
@@ -0,0 +1,38 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package meilisearch
+
+import (
+	"fmt"
+
+	"code.gitea.io/gitea/modules/log"
+)
+
+// VersionedIndexName returns the full index name with version
+func (i *Indexer) VersionedIndexName() string {
+	return versionedIndexName(i.indexName, i.version)
+}
+
+func versionedIndexName(indexName string, version int) string {
+	if version == 0 {
+		// Old index name without version
+		return indexName
+	}
+
+	// The format of the index name is <index_name>_v<version>, not <index_name>.v<version> like elasticsearch.
+	// Because meilisearch does not support "." in index name, it should contain only alphanumeric characters, hyphens (-) and underscores (_).
+	// See https://www.meilisearch.com/docs/learn/core_concepts/indexes#index-uid
+
+	return fmt.Sprintf("%s_v%d", indexName, version)
+}
+
+func (i *Indexer) checkOldIndexes() {
+	for v := 0; v < i.version; v++ {
+		indexName := versionedIndexName(i.indexName, v)
+		_, err := i.Client.GetIndex(indexName)
+		if err == nil {
+			log.Warn("Found older meilisearch index named %q, Forgejo will keep the old NOT DELETED. You can delete the old version after the upgrade succeed.", indexName)
+		}
+	}
+}
diff --git a/modules/indexer/internal/paginator.go b/modules/indexer/internal/paginator.go
new file mode 100644
index 00000000..ee204bf0
--- /dev/null
+++ b/modules/indexer/internal/paginator.go
@@ -0,0 +1,34 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package internal
+
+import (
+	"math"
+
+	"code.gitea.io/gitea/models/db"
+)
+
+// ParsePaginator parses a db.Paginator into a skip and limit
+func ParsePaginator(paginator *db.ListOptions, max ...int) (int, int) {
+	// Use a very large number to indicate no limit
+	unlimited := math.MaxInt32
+	if len(max) > 0 {
+		// Some indexer engines have a limit on the page size, respect that
+		unlimited = max[0]
+	}
+
+	if paginator == nil || paginator.IsListAll() {
+		// It shouldn't happen. In actual usage scenarios, there should not be requests to search all.
+		// But if it does happen, respect it and return "unlimited".
+		// And it's also useful for testing.
+		return 0, unlimited
+	}
+
+	if paginator.PageSize == 0 {
+		// Do not return any results when searching, it's used to get the total count only.
+		return 0, 0
+	}
+
+	return paginator.GetSkipTake()
+}