// 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
}

// newringBuffer is a push/pop storage for values.
func newringBuffer(size int) *ringBuffer {
	db, err := bolt.Open("./incommmingBuffer.db", 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),
	}
}

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

	// TODO: At startup, check if there are unprocessed messages in
	// the K/V store, and process them.

	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)

	// 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) {
	// 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 {
			log.Printf("error: retreival of values from k/v store failed: %v\n", err)
		}

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

	// Check for incomming messages. These are typically comming from
	// the go routine who reads inmsg.txt.
	for v := range inCh {
		// --- 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 {
			log.Printf("error: gob encoding samValue: %v\n", err)
		}

		// Store the incomming message in key/value store
		err = r.dbUpdate(r.db, samValueBucket, strconv.Itoa(dbID), js)
		if err != nil {
			// TODO: Handle error
			log.Printf("error: dbUpdate samValue failed: %v\n", err)
		}

		// 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++
		fmt.Printf("*** NEXT INDEX NUMBER INCREMENTED: %v\n", r.totalMessagesIndex)
		fmt.Println("---------------------------------------------------------")
		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
			fmt.Println("-----------------------------------------------------------")
			fmt.Printf("### DONE WITH THE MESSAGE\n")
			fmt.Println("-----------------------------------------------------------")

			// 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))
			fmt.Printf("******* DELETED KEY %v FROM BUCKET*******\n", v.ID)

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

			// TODO: Write the Key/Value we just deleted to a file acting
			// as the transaction log for the system.

			// REMOVE: Dump the whole KV store
			err := r.printBucketContent(samValueBucket)
			if err != nil {
				fmt.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
		})

		fmt.Println("--------------------------K/V DUMP TO VARIABLE SORTED---------------------------")
		for _, v := range samDBValues {
			fmt.Printf("%#v\n", v)
		}
		fmt.Println("----------------------------------------------------------------------------------")
		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)
			}
			fmt.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("**** RETURNING INDEX, WITH 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("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)
		}

		time.Sleep(time.Second * 1)
	}

}