// Info: The idea about the ring buffer is that we have a FIFO
// buffer where we store all incomming messages requested by
// operators. Each message processed will also be stored in a DB.
//
// Idea: All incomming messages should be handled from the in-memory
// buffered channel, but when they are put on the buffer they should
// also be written to the DB with a handled flag set to false.
// When a message have left the buffer the handled flag should be
// set to true.
package steward

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
	"sort"
	"strconv"
	"sync"
	"time"

	bolt "go.etcd.io/bbolt"
)

// samValue represents one message with a subject. This
// struct type is used when storing and retreiving from
// db.
type samDBValue struct {
	ID   int
	Data subjectAndMessage
}

// ringBuffer holds the data of the buffer,
type ringBuffer struct {
	bufData            chan samDBValue
	db                 *bolt.DB
	totalMessagesIndex int
	mu                 sync.Mutex
	permStore          chan string
	nodeName           node
	newMessagesCh      chan []subjectAndMessage
}

// newringBuffer is a push/pop storage for values.
func newringBuffer(size int, dbFileName string, nodeName node, newMessagesCh chan []subjectAndMessage) *ringBuffer {
	db, err := bolt.Open(dbFileName, 0600, nil)
	if err != nil {
		log.Printf("error: failed to open db: %v\n", err)
	}
	return &ringBuffer{
		bufData:       make(chan samDBValue, size),
		db:            db,
		permStore:     make(chan string),
		nodeName:      nodeName,
		newMessagesCh: newMessagesCh,
	}
}

// start will process incomming messages through the inCh,
// put the messages on a buffered channel
// and deliver messages out when requested on the outCh.
func (r *ringBuffer) start(inCh chan subjectAndMessage, outCh chan samDBValue, defaultMessageTimeout int, defaultMessageRetries int) {

	// Starting both writing and reading in separate go routines so we
	// can write and read concurrently.

	const samValueBucket string = "samValueBucket"
	const indexValueBucket string = "indexValueBucket"

	r.totalMessagesIndex = r.getIndexValue(indexValueBucket)

	// Fill the buffer when new data arrives into the system
	go r.fillBuffer(inCh, samValueBucket, indexValueBucket, defaultMessageTimeout, defaultMessageRetries)

	// Start the process to permanently store done messages.
	go r.startPermanentStore()

	// Start the process that will handle messages present in the ringbuffer.
	go r.processBufferMessages(samValueBucket, outCh)
}

// fillBuffer will fill the buffer in the ringbuffer  reading from the inchannel.
// It will also store the messages in a K/V DB while being processed.
func (r *ringBuffer) fillBuffer(inCh chan subjectAndMessage, samValueBucket string, indexValueBucket string, defaultMessageTimeout int, defaultMessageRetries int) {
	// At startup get all the values that might be in the K/V store so we can
	// put them into the buffer before we start to fill up with new incomming
	// messages to the system.
	// This is needed when the program have been restarted, and we need to check
	// if there where previously unhandled messages that need to be handled first.
	func() {
		s, err := r.dumpBucket(samValueBucket)
		if err != nil {
			er := fmt.Errorf("error: fillBuffer: retreival of values from k/v store failed: %v", err)
			sendErrorLogMessage(r.newMessagesCh, node(r.nodeName), er)
		}

		for _, v := range s {
			r.bufData <- v
		}
	}()

	// Prepare the map structure to know what values are allowed
	// for the commands or events
	var coe CommandOrEvent
	coeAvailable := coe.GetCommandOrEventAvailable()
	coeAvailableValues := []CommandOrEvent{}
	for v := range coeAvailable.topics {
		coeAvailableValues = append(coeAvailableValues, v)
	}

	// Check for incomming messages. These are typically comming from
	// the go routine who reads msg.pipe.
	for v := range inCh {

		// Check if the command or event exists in commandOrEvent.go
		if !coeAvailable.CheckIfExists(v.CommandOrEvent, v.Subject) {
			er := fmt.Errorf("error: fillBuffer: the event or command type do not exist, so this message will not be put on the buffer to be processed. Check the syntax used in the json file for the message. Allowed values are : %v, where given: coe=%v, with subject=%v", coeAvailableValues, v.CommandOrEvent, v.Subject)
			sendErrorLogMessage(r.newMessagesCh, node(r.nodeName), er)

			fmt.Println()
			// if it was not a valid value, we jump back up, and
			// continue the range iteration.
			continue
		}

		// Check if message values for timers override default values
		if v.Message.ACKTimeout < 1 {
			v.Message.ACKTimeout = defaultMessageTimeout
		}
		if v.Message.Retries < 1 {
			v.Message.Retries = defaultMessageRetries
		}

		// --- Store the incomming message in the k/v store ---

		// Get a unique number for the message to use when storing
		// it in the databases, and also use when further processing.
		r.mu.Lock()
		dbID := r.totalMessagesIndex
		r.mu.Unlock()

		// Create a structure for JSON marshaling.
		samV := samDBValue{
			ID:   dbID,
			Data: v,
		}

		js, err := json.Marshal(samV)
		if err != nil {
			er := fmt.Errorf("error:fillBuffer gob encoding samValue: %v", err)
			sendErrorLogMessage(r.newMessagesCh, node(r.nodeName), er)
		}

		// Store the incomming message in key/value store
		err = r.dbUpdate(r.db, samValueBucket, strconv.Itoa(dbID), js)
		if err != nil {
			er := fmt.Errorf("error: dbUpdate samValue failed: %v", err)
			sendErrorLogMessage(r.newMessagesCh, node(r.nodeName), er)

		}

		// Put the message on the inmemory buffer.
		r.bufData <- samV

		// Increment index, and store the new value to the database.
		r.mu.Lock()
		r.totalMessagesIndex++
		r.dbUpdate(r.db, indexValueBucket, "index", []byte(strconv.Itoa(r.totalMessagesIndex)))
		r.mu.Unlock()
	}

	// When done close the buffer channel
	close(r.bufData)
}

// processBufferMessages will pick messages from the buffer, and process them
// one by one. The messages will be delivered on the outCh, and it will wait
// until a signal is received on the done channel before it continues with the
// next message.
func (r *ringBuffer) processBufferMessages(samValueBucket string, outCh chan samDBValue) {
	// Range over the buffer of messages to pass on to processes.
	for v := range r.bufData {
		// Create a done channel per message. A process started by the
		// spawnProcess function will handle incomming messages sequentaly.
		// So in the spawnProcess function we put a struct{} value when a
		// message is processed on the "done" channel and an ack is received
		// for a message, and we wait here for the "done" to be received.

		// We start the actual processing of an individual message here within
		// it's own go routine. Reason is that we don't want to block other
		// messages being blocked while waiting for the done signal, or if an
		// error with an individual message occurs.
		go func(v samDBValue) {
			v.Data.Message.done = make(chan struct{})
			outCh <- v

			// Listen on the done channel here , so a go routine handling the
			// message will be able to signal back here that the message have
			// been processed, and that we then can delete it out of the K/V Store.
			<-v.Data.done
			log.Printf("info: processBufferMessages: done with message, deleting key from bucket, %v\n", v.ID)

			// Since we are now done with the specific message we can delete
			// it out of the K/V Store.
			r.deleteKeyFromBucket(samValueBucket, strconv.Itoa(v.ID))

			r.permStore <- fmt.Sprintf("%v : %+v\n", time.Now().UTC(), v)

			// REMOVE: Dump the whole KV store
			err := r.printBucketContent(samValueBucket)
			if err != nil {
				log.Printf("* Error: dump of db failed: %v\n", err)
			}
		}(v)

	}

	close(outCh)
}

// dumpBucket will dump out all they keys and values in the
// specified bucket, and return a sorted []samDBValue
func (r *ringBuffer) dumpBucket(bucket string) ([]samDBValue, error) {
	samDBValues := []samDBValue{}

	err := r.db.View(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))
		if bu == nil {
			return fmt.Errorf("error: dumpBucket: tx.bucket returned nil")
		}

		// For each element found in the DB, unmarshal, and put on slice.
		bu.ForEach(func(k, v []byte) error {
			var vv samDBValue
			err := json.Unmarshal(v, &vv)
			if err != nil {
				log.Printf("error: dumpBucket json.Umarshal failed: %v\n", err)
			}
			samDBValues = append(samDBValues, vv)
			return nil
		})

		// Sort the order of the slice items based on ID, since they where retreived from a map.
		sort.SliceStable(samDBValues, func(i, j int) bool {
			return samDBValues[i].ID > samDBValues[j].ID
		})

		for _, v := range samDBValues {
			log.Printf("info: k/v store: %#v\n", v)
		}

		return nil
	})

	if err != nil {
		return nil, err
	}

	return samDBValues, err
}

// printBuckerContent will print out all they keys and values in the
// specified bucket.
func (r *ringBuffer) printBucketContent(bucket string) error {
	err := r.db.View(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))

		fmt.Println("-- K/V STORE DUMP--")
		bu.ForEach(func(k, v []byte) error {
			var vv samDBValue
			err := json.Unmarshal(v, &vv)
			if err != nil {
				log.Printf("error: printBucketContent json.Umarshal failed: %v\n", err)
			}
			log.Printf("k: %s, v: %v\n", k, vv)
			return nil
		})
		fmt.Println("--")

		return nil
	})

	return err
}

// deleteKeyFromBucket will delete the specified key from the specified
// bucket if it exists.
func (r *ringBuffer) deleteKeyFromBucket(bucket string, key string) error {
	err := r.db.Update(func(tx *bolt.Tx) error {
		bu := tx.Bucket([]byte(bucket))

		err := bu.Delete([]byte(key))
		if err != nil {
			log.Printf("error: delete key in bucket %v failed: %v\n", bucket, err)
		}

		return nil
	})

	return err
}

// getIndexValue will get the last index value stored in DB.
func (r *ringBuffer) getIndexValue(indexBucket string) int {
	const indexKey string = "index"
	indexB, err := r.dbView(r.db, indexBucket, indexKey)
	if err != nil {
		log.Printf("error: getIndexValue: dbView: %v\n", err)
	}

	index, err := strconv.Atoi(string(indexB))
	if err != nil {
		log.Printf("error: getIndexValue: strconv.Atoi : %v\n", err)
	}

	// fmt.Printf("ringBuffer.getIndexValue: got index value = %v\n", index)

	return index
}

// dbView will look up a specific value for a key in a bucket in a DB.
func (r *ringBuffer) dbView(db *bolt.DB, bucket string, key string) ([]byte, error) {
	var value []byte
	//View is a help function to get values out of the database.
	err := db.View(func(tx *bolt.Tx) error {
		//Open a bucket to get key's and values from.
		bu := tx.Bucket([]byte(bucket))
		if bu == nil {
			log.Printf("info: no such bucket exist: %v\n", bucket)
			return nil
		}

		v := bu.Get([]byte(key))
		if len(v) == 0 {
			log.Printf("info: view: key not found\n")
			return nil
		}

		value = v

		return nil
	})

	return value, err

}

//dbUpdate will update the specified bucket with a key and value.
func (r *ringBuffer) dbUpdate(db *bolt.DB, bucket string, key string, value []byte) error {
	err := db.Update(func(tx *bolt.Tx) error {
		//Create a bucket
		bu, err := tx.CreateBucketIfNotExists([]byte(bucket))
		if err != nil {
			return fmt.Errorf("error: CreateBuckerIfNotExists failed: %v", err)
		}

		//Put a value into the bucket.
		if err := bu.Put([]byte(key), []byte(value)); err != nil {
			return err
		}

		//If all was ok, we should return a nil for a commit to happen. Any error
		// returned will do a rollback.
		return nil
	})
	return err
}

// startPermStore will start the process that will handle writing of
// handled message to a permanent file.
// To store a message in the store, send what to store on the
// ringbuffer.permStore channel.
func (r *ringBuffer) startPermanentStore() {
	const storeFile string = "store.log"
	f, err := os.OpenFile(storeFile, os.O_APPEND|os.O_RDWR|os.O_CREATE, 0600)
	if err != nil {
		log.Printf("error: startPermanentStore: failed to open file: %v\n", err)
	}
	defer f.Close()

	for {
		d := <-r.permStore
		_, err := f.WriteString(d)
		if err != nil {
			log.Printf("error:failed to write entry: %v\n", err)
		}

		// REMOVED: time
		// time.Sleep(time.Second * 1)
	}

}