/*
 * MinIO Cloud Storage, (C) 2019 MinIO, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package target

import (
	"encoding/json"
	"io/ioutil"
	"os"
	"path/filepath"
	"sort"
	"sync"

	"github.com/minio/minio/pkg/event"
	"github.com/minio/minio/pkg/sys"
)

const (
	maxLimit = 10000 // Max store limit.
	eventExt = ".event"
)

// QueueStore - Filestore for persisting events.
type QueueStore struct {
	sync.RWMutex
	directory string
	eC        uint64
	limit     uint64
}

// NewQueueStore - Creates an instance for QueueStore.
func NewQueueStore(directory string, limit uint64) *QueueStore {
	if limit == 0 {
		limit = maxLimit
		currRlimit, _, err := sys.GetMaxOpenFileLimit()
		if err == nil {
			if currRlimit > limit {
				limit = currRlimit
			}
		}
	}

	queueStore := &QueueStore{
		directory: directory,
		limit:     limit,
	}
	return queueStore
}

// Open - Creates the directory if not present.
func (store *QueueStore) Open() error {
	store.Lock()
	defer store.Unlock()

	if terr := os.MkdirAll(store.directory, os.FileMode(0770)); terr != nil {
		return terr
	}

	eCount := uint64(len(store.list()))
	if eCount >= store.limit {
		return errLimitExceeded
	}

	store.eC = eCount

	return nil
}

// write - writes event to the directory.
func (store *QueueStore) write(directory string, key string, e event.Event) error {

	// Marshalls the event.
	eventData, err := json.Marshal(e)
	if err != nil {
		return err
	}

	path := filepath.Join(store.directory, key+eventExt)
	if err := ioutil.WriteFile(path, eventData, os.FileMode(0770)); err != nil {
		return err
	}

	// Increment the event count.
	store.eC++

	return nil
}

// Put - puts a event to the store.
func (store *QueueStore) Put(e event.Event) error {
	store.Lock()
	defer store.Unlock()
	if store.eC >= store.limit {
		return errLimitExceeded
	}
	key, kErr := getNewUUID()
	if kErr != nil {
		return kErr
	}
	return store.write(store.directory, key, e)
}

// Get - gets a event from the store.
func (store *QueueStore) Get(key string) (event.Event, error) {
	store.RLock()
	defer store.RUnlock()

	var event event.Event

	filepath := filepath.Join(store.directory, key+eventExt)

	eventData, rerr := ioutil.ReadFile(filepath)
	if rerr != nil {
		store.del(key)
		return event, rerr
	}

	if len(eventData) == 0 {
		store.del(key)
	}

	uerr := json.Unmarshal(eventData, &event)
	if uerr != nil {
		store.del(key)
		return event, uerr
	}

	return event, nil
}

// Del - Deletes an entry from the store.
func (store *QueueStore) Del(key string) error {
	store.Lock()
	defer store.Unlock()
	return store.del(key)
}

// lockless call
func (store *QueueStore) del(key string) error {
	p := filepath.Join(store.directory, key+eventExt)

	rerr := os.Remove(p)
	if rerr != nil {
		return rerr
	}

	// Decrement the event count.
	store.eC--

	return nil
}

// List - lists all files from the directory.
func (store *QueueStore) List() []string {
	store.RLock()
	defer store.RUnlock()
	return store.list()
}

// lockless call.
func (store *QueueStore) list() []string {
	var names []string
	storeDir, _ := os.Open(store.directory)
	files, _ := storeDir.Readdir(-1)

	// Sort the dentries.
	sort.Slice(files, func(i, j int) bool {
		return files[i].ModTime().Unix() < files[j].ModTime().Unix()
	})

	for _, file := range files {
		names = append(names, file.Name())
	}

	_ = storeDir.Close()
	return names
}