// Copyright 2014 by Sascha L. Teichmann
// Use of this source code is governed by the MIT license
// that can be found in the LICENSE file.

package main

import (
	"database/sql"
	"log"
	"sync"

	_ "github.com/mattn/go-sqlite3"

	"bitbucket.org/s_l_teichmann/mtredisalize/common"
)

var globalLock sync.RWMutex

const (
	fetchSql  = "SELECT data FROM blocks WHERE pos = ?"
	existsSql = "SELECT 1 FROM blocks WHERE pos = ?"
	updateSql = "UPDATE blocks SET data = ? WHERE pos = ?"
	insertSql = "INSERT INTO blocks (pos, data) VALUES (?, ?)"
	countSql  = "SELECT count(*) FROM blocks"
	keysSql   = "SELECT pos FROM blocks"
)

type SqliteBackend struct {
	db         *sql.DB
	existsStmt *sql.Stmt
	fetchStmt  *sql.Stmt
	insertStmt *sql.Stmt
	updateStmt *sql.Stmt
	countStmt  *sql.Stmt
	keysStmt   *sql.Stmt
}

type SqliteSession struct {
	backend *SqliteBackend
	tx      *sql.Tx
}

func (ss *SqliteBackend) NewSession() (Session, error) {
	return &SqliteSession{ss, nil}, nil
}

func (ss *SqliteSession) Close() error {
	t := ss.tx
	if t != nil {
		ss.tx = nil
		return t.Rollback()
	}
	return nil
}

func NewSqliteBackend(path string) (sqlb *SqliteBackend, err error) {

	res := SqliteBackend{}

	if res.db, err = sql.Open("sqlite3", path); err != nil {
		return
	}

	if res.existsStmt, err = res.db.Prepare(existsSql); err != nil {
		res.closeAll()
		return
	}

	if res.fetchStmt, err = res.db.Prepare(fetchSql); err != nil {
		res.closeAll()
		return
	}

	if res.insertStmt, err = res.db.Prepare(insertSql); err != nil {
		res.closeAll()
		return
	}

	if res.updateStmt, err = res.db.Prepare(updateSql); err != nil {
		res.closeAll()
		return
	}

	if res.countStmt, err = res.db.Prepare(countSql); err != nil {
		res.closeAll()
		return
	}

	if res.keysStmt, err = res.db.Prepare(keysSql); err != nil {
		res.closeAll()
		return
	}

	sqlb = &res
	return
}

func closeStmt(stmt **sql.Stmt) error {
	s := *stmt
	if s != nil {
		*stmt = nil
		return s.Close()
	}
	return nil
}

func closeDB(db **sql.DB) error {
	d := *db
	if d != nil {
		*db = nil
		return d.Close()
	}
	return nil
}

func (sqlb *SqliteBackend) closeAll() error {
	closeStmt(&sqlb.fetchStmt)
	closeStmt(&sqlb.insertStmt)
	closeStmt(&sqlb.updateStmt)
	closeStmt(&sqlb.existsStmt)
	closeStmt(&sqlb.countStmt)
	closeStmt(&sqlb.keysStmt)
	return closeDB(&sqlb.db)
}

func (sqlb *SqliteBackend) Shutdown() error {
	globalLock.Lock()
	defer globalLock.Unlock()

	return sqlb.closeAll()
}

func (ss *SqliteSession) txStmt(stmt *sql.Stmt) *sql.Stmt {
	if ss.tx != nil {
		return ss.tx.Stmt(stmt)
	}
	return stmt
}

func (ss *SqliteSession) Fetch(hash, key []byte) (data []byte, err error) {
	var pos int64
	if pos, err = common.DecodeStringFromBytes(key); err != nil {
		return
	}

	globalLock.RLock()
	defer globalLock.RUnlock()

	fetchStmt := ss.txStmt(ss.backend.fetchStmt)
	err2 := fetchStmt.QueryRow(pos).Scan(&data)
	if err2 == sql.ErrNoRows {
		return
	}
	err = err2
	return
}

func (ss *SqliteSession) InTransaction() bool {
	return ss.tx != nil
}

func (ss *SqliteSession) Store(hash, key, value []byte) (exists bool, err error) {
	var pos int64
	if pos, err = common.DecodeStringFromBytes(key); err != nil {
		return
	}

	globalLock.Lock()
	defer globalLock.Unlock()

	existsStmt := ss.txStmt(ss.backend.existsStmt)
	var x int
	err2 := existsStmt.QueryRow(pos).Scan(&x)

	if err2 == sql.ErrNoRows {
		exists = false
	} else if err2 != nil {
		err = err2
		return
	} else {
		exists = true
	}

	if exists {
		updateStmt := ss.txStmt(ss.backend.updateStmt)
		_, err = updateStmt.Exec(value, pos)
	} else {
		insertStmt := ss.txStmt(ss.backend.insertStmt)
		_, err = insertStmt.Exec(pos, value)
	}
	return
}

func (ss *SqliteSession) BeginTransaction() (err error) {
	if ss.tx != nil {
		log.Println("WARN: Already running transaction.")
		return nil
	}

	globalLock.Lock()
	defer globalLock.Unlock()
	ss.tx, err = ss.backend.db.Begin()
	return
}

func (ss *SqliteSession) CommitTransaction() error {

	tx := ss.tx
	if tx == nil {
		log.Println("WARN: No transaction running.")
		return nil
	}

	globalLock.Lock()
	defer globalLock.Unlock()
	ss.tx = nil
	return tx.Commit()
}

func (ss *SqliteSession) AllKeys(hash []byte) (keys chan []byte, n int, err error) {
	globalLock.RLock()

	countStmt := ss.txStmt(ss.backend.countStmt)
	if err = countStmt.QueryRow().Scan(&n); err != nil {
		if err == sql.ErrNoRows {
			err = nil
		}
		globalLock.RUnlock()
		return
	}

	keysStmt := ss.txStmt(ss.backend.keysStmt)
	var rows *sql.Rows
	if rows, err = keysStmt.Query(); err != nil {
		globalLock.RUnlock()
		return
	}

	keys = make(chan []byte)
	go func() {
		defer globalLock.RUnlock()
		defer rows.Close()
		defer close(keys)
		var err error
		for rows.Next() {
			var key int64
			if err := rows.Scan(&key); err != nil {
				log.Printf("WARN: %s", err)
				break
			}
			var encoded []byte
			if encoded, err = common.EncodeStringToBytes(key); err != nil {
				log.Printf("Cannot encode key: %d %s\n", key, err)
				break
			}

			keys <- encoded
		}
	}()

	return
}