/*
 * Copyright 2019 Intel Corporation, 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 namegenerator

import (
	"encoding/json"
	"log"
	"strings"
	"sync"

	"github.com/onap/multicloud-k8s/src/k8splugin/internal/db"

	"github.com/docker/engine/pkg/namesgenerator"
	pkgerrors "github.com/pkg/errors"
)

const (
	storeName = "instanceNames"
	tag       = "names"
)

var (
	nameCache      = &cache{}
	cacheKeyGlobal = cacheKey{"k8sPluginCacheKey"}
)

type cache struct {
	cache map[string]bool
	mux   sync.Mutex
}

type cacheKey struct {
	Key string `json:"key"`
}

func (c cacheKey) String() string {

	out, err := json.Marshal(c)
	if err != nil {
		return ""
	}

	return string(out)
}

func (c *cache) init() {

	// We have either restarted or this is the first time
	// that a name is being requested since the service came
	// up.
	if c.cache == nil {
		c.cache = make(map[string]bool)
		err := c.readCacheFromDB()
		if err != nil {
			log.Println("Error Reading from DB: ", err.Error())
			return
		}
	}
}

func (c *cache) isAlreadyUsed(name string) bool {

	if _, ok := c.cache[name]; ok {
		return true
	}
	return false
}

func (c *cache) readCacheFromDB() error {

	// Read the latest from cache
	data, err := db.DBconn.Read(storeName, cacheKeyGlobal, tag)
	if err != nil {
		log.Println("Error reading name cache from Database: ", err)
		return pkgerrors.Wrap(err, "Reading cache from DB")
	}

	err = db.DBconn.Unmarshal(data, &c.cache)
	if err != nil {
		log.Println("Error unmarshaling data into cache: ", err)
		return pkgerrors.Wrap(err, "Unmarshaling cache from DB")
	}

	return nil
}

// writeCacheToDB will update the DB with the updated cache
func (c *cache) writeCacheToDB() {

	//Update the database as well
	err := db.DBconn.Update(storeName, cacheKeyGlobal, tag, c.cache)
	if err != nil {
		// TODO: Replace with DBconn variable
		if strings.Contains(err.Error(), "Error finding master table") {
			err = db.DBconn.Create(storeName, cacheKeyGlobal, tag, c.cache)
			if err != nil {
				log.Println("Error creating the entry in DB. Will try later...")
				return
			}
		} else {
			log.Println("Error updating DB: ", err.Error())
			return
		}
	}
}

func (c *cache) generateName() string {
	c.mux.Lock()
	defer c.mux.Unlock()

	c.init()

	for {
		//Call moby package here to generate name
		name := namesgenerator.GetRandomName(0)
		if c.isAlreadyUsed(name) {
			// Generate another name
			log.Printf("Name %s already used", name)
			continue
		}

		c.cache[name] = true

		// Update the cache and db
		c.writeCacheToDB()
		return name
	}
}

func (c *cache) releaseName(name string) {
	c.mux.Lock()
	defer c.mux.Unlock()

	c.init()

	if c.isAlreadyUsed(name) {
		c.cache[name] = false

		// Update the cache and db
		c.writeCacheToDB()
	}
}

// Generate returns an autogenerated name
func Generate() string {

	return nameCache.generateName()
}

// Release name from cache
func Release(name string) {

	nameCache.releaseName(name)
}