package backends

// This backend is presented here as an example only, please modify it to your needs.
// The backend stores the email data in Redis.
// Other meta-information is stored in MySQL to be joined later.
// A lot of email gets discarded without viewing on Guerrilla Mail,
// so it's much faster to put in Redis, where other programs can
// process it later, without touching the disk.
// Short history:
// Started with issuing an insert query for each single email and another query to update the tally
// Then applied the following optimizations:
// - Moved tally updates to another background process which does the tallying in a single query
// - Changed the MySQL queries to insert in batch
// - Made a Compressor that recycles buffers using sync.Pool
// The result was around 400% speed improvement. If you know of any more improvements, please share!
import (
	"fmt"

	"time"

	log "github.com/Sirupsen/logrus"
	"github.com/garyburd/redigo/redis"

	"bytes"
	"compress/zlib"
	"github.com/flashmob/go-guerrilla/envelope"
	"github.com/ziutek/mymysql/autorc"
	_ "github.com/ziutek/mymysql/godrv"
	"io"
	"sync"
)

// how many rows to batch at a time
const GuerrillaDBAndRedisBatchMax = 500

// tick on every...
const GuerrillaDBAndRedisBatchTimeout = time.Second * 3

func init() {
	backends["guerrilla-db-redis"] = &AbstractBackend{
		extend: &GuerrillaDBAndRedisBackend{}}
}

type GuerrillaDBAndRedisBackend struct {
	AbstractBackend
	config    guerrillaDBAndRedisConfig
	batcherWg sync.WaitGroup
	// cache prepared queries
	cache stmtCache
}

// statement cache. It's an array, not slice
type stmtCache [GuerrillaDBAndRedisBatchMax]*autorc.Stmt

type guerrillaDBAndRedisConfig struct {
	NumberOfWorkers    int    `json:"save_workers_size"`
	MysqlTable         string `json:"mail_table"`
	MysqlDB            string `json:"mysql_db"`
	MysqlHost          string `json:"mysql_host"`
	MysqlPass          string `json:"mysql_pass"`
	MysqlUser          string `json:"mysql_user"`
	RedisExpireSeconds int    `json:"redis_expire_seconds"`
	RedisInterface     string `json:"redis_interface"`
	PrimaryHost        string `json:"primary_mail_host"`
}

func convertError(name string) error {
	return fmt.Errorf("failed to load backend config (%s)", name)
}

// Load the backend config for the backend. It has already been unmarshalled
// from the main config file 'backend' config "backend_config"
// Now we need to convert each type and copy into the guerrillaDBAndRedisConfig struct
func (g *GuerrillaDBAndRedisBackend) loadConfig(backendConfig BackendConfig) (err error) {
	configType := baseConfig(&guerrillaDBAndRedisConfig{})
	bcfg, err := g.extractConfig(backendConfig, configType)
	if err != nil {
		return err
	}
	m := bcfg.(*guerrillaDBAndRedisConfig)
	g.config = *m
	return nil
}

func (g *GuerrillaDBAndRedisBackend) getNumberOfWorkers() int {
	return g.config.NumberOfWorkers
}

func (g *GuerrillaDBAndRedisBackend) Process(mail *envelope.Envelope) BackendResult {
	to := mail.RcptTo
	log.Info("(g *GuerrillaDBAndRedisBackend) Process called")
	if len(to) == 0 {
		return NewBackendResult("554 Error: no recipient")
	}
	return nil
}

type redisClient struct {
	isConnected bool
	conn        redis.Conn
	time        int
}

// compressedData struct will be compressed using zlib when printed via fmt
type compressedData struct {
	extraHeaders []byte
	data         *bytes.Buffer
	pool         sync.Pool
}

// newCompressedData returns a new CompressedData
func newCompressedData() *compressedData {
	var p = sync.Pool{
		New: func() interface{} {
			var b bytes.Buffer
			return &b
		},
	}
	return &compressedData{
		pool: p,
	}
}

// Set the extraheaders and buffer of data to compress
func (c *compressedData) set(b []byte, d *bytes.Buffer) {
	c.extraHeaders = b
	c.data = d
}

// implement Stringer interface
func (c *compressedData) String() string {
	if c.data == nil {
		return ""
	}
	//borrow a buffer form the pool
	b := c.pool.Get().(*bytes.Buffer)
	// put back in the pool
	defer func() {
		b.Reset()
		c.pool.Put(b)
	}()

	var r *bytes.Reader
	w, _ := zlib.NewWriterLevel(b, zlib.BestSpeed)
	r = bytes.NewReader(c.extraHeaders)
	io.Copy(w, r)
	io.Copy(w, c.data)
	w.Close()
	return b.String()
}

// clear it, without clearing the pool
func (c *compressedData) clear() {
	c.extraHeaders = []byte{}
	c.data = nil
}

// prepares the sql query with the number of rows that can be batched with it
func (g *GuerrillaDBAndRedisBackend) prepareInsertQuery(rows int, db *autorc.Conn) *autorc.Stmt {
	if rows == 0 {
		panic("rows argument cannot be 0")
	}
	if g.cache[rows-1] != nil {
		return g.cache[rows-1]
	}
	sql := "INSERT INTO " + g.config.MysqlTable + " "
	sql += "(`date`, `to`, `from`, `subject`, `body`, `charset`, `mail`, `spam_score`, `hash`, `content_type`, `recipient`, `has_attach`, `ip_addr`, `return_path`, `is_tls`)"
	sql += " values "
	values := "(NOW(), ?, ?, ?, ? , 'UTF-8' , ?, 0, ?, '', ?, 0, ?, ?, ?)"
	// add more rows
	comma := ""
	for i := 0; i < rows; i++ {
		sql += comma + values
		if comma == "" {
			comma = ","
		}
	}
	//log.Debug("Prepared SQL", rows, sql)
	stmt, sqlErr := db.Prepare(sql)
	if sqlErr != nil {
		log.WithError(sqlErr).Fatalf("failed while db.Prepare(INSERT...)")
	}
	// cache it
	g.cache[rows-1] = stmt
	return stmt
}

// Batches the rows from the feeder chan in to a single INSERT statement.
// Execute the batches query when:
// - number of batched rows reaches a threshold, i.e. count n = threshold
// - or, no new rows within a certain time, i.e. times out
func (g *GuerrillaDBAndRedisBackend) insertQueryBatcher(feeder chan []interface{}, db *autorc.Conn) {
	// controls shutdown
	defer g.batcherWg.Done()
	g.batcherWg.Add(1)
	// vals is where values are batched to
	var vals []interface{}
	// how many rows were batched
	count := 0
	// The timer will tick every second.
	// Interrupting the select clause when there's no data on the feeder channel
	t := time.NewTimer(GuerrillaDBAndRedisBatchTimeout)
	// prepare the query used to insert when rows reaches batchMax
	insertStmt := g.prepareInsertQuery(GuerrillaDBAndRedisBatchMax, db)
	// inserts executes a batched insert query, clears the vals and resets the count
	insert := func(c int) {
		if c > 0 {
			insertStmt = g.prepareInsertQuery(c, db)
			insertStmt.Bind(vals...)
			_, _, err := insertStmt.Exec()
			if err != nil {
				log.WithError(err).Error("There was a problem the insert")
			} else {
				//log.Debugf("Inserted %d rows ", count)
			}
		}
		vals = nil
		count = 0
	}
	// Keep getting values from feeder and add to batch.
	// if feeder times out, execute the batched query
	// otherwise, execute the batched query once it reaches the GuerrillaDBAndRedisBatchMax threshold
	for {
		select {
		case row := <-feeder:
			log.Info("row form chan is", row, "cols:", len(row))
			if row == nil {
				log.Debug("Query batchaer exiting")
				// Insert any remaining rows
				insert(count)
				return
			}
			vals = append(vals, row...)
			count++
			//log.Debug("apend vals", count, vals)
			if count == GuerrillaDBAndRedisBatchMax {
				insert(GuerrillaDBAndRedisBatchMax)
			}
			// stop timer from firing (reset the interrupt)
			if !t.Stop() {
				<-t.C
			}
			t.Reset(GuerrillaDBAndRedisBatchTimeout)
		case <-t.C:
			//log.Debugf("Query batcher timer fired! [%d]", len(vals))
			//log.Debug("Contents:", count, vals)
			// anything to insert?
			if n := len(vals); n > 0 {
				insert(count)
			}
			t.Reset(GuerrillaDBAndRedisBatchTimeout)
		}
	}
}

func (g *GuerrillaDBAndRedisBackend) saveMailWorker(saveMailChan chan *savePayload) {
	var to, body string
	//var length int
	//var err error

	var redisErr error

	redisClient := &redisClient{}
	db := autorc.New(
		"tcp",
		"",
		g.config.MysqlHost,
		g.config.MysqlUser,
		g.config.MysqlPass,
		g.config.MysqlDB)
	db.Register("set names utf8")
	// start the query SQL batching where we will send data via the feeder channel
	feeder := make(chan []interface{}, 1)
	go g.insertQueryBatcher(feeder, db)

	defer func() {
		if r := recover(); r != nil {
			//recover form closed channel
			fmt.Println("Recovered in f", r)
		}
		if db.Raw != nil {
			db.Raw.Close()
		}
		if redisClient.conn != nil {
			log.Infof("closed redis")
			redisClient.conn.Close()
		}
		// close the feeder & wait for query batcher to exit.
		close(feeder)
		g.batcherWg.Wait()

	}()
	var vals []interface{}
	data := newCompressedData()
	//  receives values from the channel repeatedly until it is closed.

	for {
		payload := <-saveMailChan
		if payload == nil {
			log.Debug("No more saveMailChan payload")
			return
		}
		to = payload.recipient.User + "@" + g.config.PrimaryHost

		ts := fmt.Sprintf("%d", time.Now().UnixNano())
		payload.mail.ParseHeaders()
		hash := MD5Hex(
			to,
			payload.mail.MailFrom.String(),
			payload.mail.Subject,
			ts)
		// Add extra headers
		var addHead string
		addHead += "Delivered-To: " + to + "\r\n"
		addHead += "Received: from " + payload.mail.Helo + " (" + payload.mail.Helo + "  [" + payload.mail.RemoteAddress + "])\r\n"
		addHead += "	by " + payload.recipient.Host + " with SMTP id " + hash + "@" + payload.recipient.Host + ";\r\n"
		addHead += "	" + time.Now().Format(time.RFC1123Z) + "\r\n"

		// data will be compressed when printed, with addHead added to beginning

		data.set([]byte(addHead), &payload.mail.Data)
		body = "gzencode"

		// data will be written to redis - it implements the Stringer interface, redigo uses fmt to
		// print the data to redis.

		redisErr = redisClient.redisConnection(g.config.RedisInterface)
		if redisErr == nil {
			_, doErr := redisClient.conn.Do("SETEX", hash, g.config.RedisExpireSeconds, data)
			if doErr == nil {
				//payload.mail.Data = ""
				//payload.mail.Data.Reset()
				body = "redis" // the backend system will know to look in redis for the message data
				data.clear()   // blank
			}
		} else {
			log.WithError(redisErr).Warn("Error while SETEX on redis")
		}

		vals = []interface{}{} // clear the vals
		vals = append(vals,
			to,
			payload.mail.MailFrom.String(),
			payload.mail.Subject,
			body,
			data.String(),
			hash,
			to,
			payload.mail.RemoteAddress,
			payload.mail.MailFrom.String(),
			payload.mail.TLS)
		feeder <- vals
		payload.savedNotify <- &saveStatus{nil, hash}

	}
}

func (c *redisClient) redisConnection(redisInterface string) (err error) {
	if c.isConnected == false {
		c.conn, err = redis.Dial("tcp", redisInterface)
		if err != nil {
			// handle error
			return err
		}
		c.isConnected = true
	}
	return nil
}

// test database connection settings
func (g *GuerrillaDBAndRedisBackend) testSettings() (err error) {
	db := autorc.New(
		"tcp",
		"",
		g.config.MysqlHost,
		g.config.MysqlUser,
		g.config.MysqlPass,
		g.config.MysqlDB)

	if mysqlErr := db.Raw.Connect(); mysqlErr != nil {
		err = fmt.Errorf("MySql cannot connect, check your settings: %s", mysqlErr)
	} else {
		db.Raw.Close()
	}

	redisClient := &redisClient{}
	if redisErr := redisClient.redisConnection(g.config.RedisInterface); redisErr != nil {
		err = fmt.Errorf("Redis cannot connect, check your settings: %s", redisErr)
	}

	return
}