package sqlite

import (
	"database/sql"
	"errors"
	"fmt"
	"os"

	_ "github.com/mutecomm/go-sqlcipher" // We require go sqlcipher that overrides default implementation
)

const (
	// The reduced number of kdf iterations (for performance reasons) which is
	// currently used for derivation of the database key
	// https://github.com/status-im/status-go/pull/1343
	// https://notes.status.im/i8Y_l7ccTiOYq09HVgoFwA
	kdfIterationsNumber = 3200
	// WALMode for sqlite.
	WALMode      = "wal"
	inMemoryPath = ":memory:"
)

// DecryptDB completely removes the encryption from the db
func DecryptDB(oldPath, newPath, key string) error {

	db, err := openDB(oldPath, key)
	if err != nil {
		return err
	}

	_, err = db.Exec(`ATTACH DATABASE '` + newPath + `' AS plaintext KEY ''`)
	if err != nil {
		return err
	}

	_, err = db.Exec(`SELECT sqlcipher_export('plaintext')`)
	if err != nil {
		return err
	}
	_, err = db.Exec(`DETACH DATABASE plaintext`)
	return err
}

// EncryptDB takes a plaintext database and adds encryption
func EncryptDB(unencryptedPath, encryptedPath, key string) error {

	_ = os.Remove(encryptedPath)

	db, err := OpenUnecryptedDB(unencryptedPath)
	if err != nil {
		return err
	}

	_, err = db.Exec(`ATTACH DATABASE '` + encryptedPath + `' AS encrypted KEY '` + key + `'`)
	if err != nil {
		return err
	}

	_, err = db.Exec(fmt.Sprintf("PRAGMA encrypted.kdf_iter = '%d'", kdfIterationsNumber))
	if err != nil {
		return err
	}

	_, err = db.Exec(`SELECT sqlcipher_export('encrypted')`)
	if err != nil {
		return err
	}
	_, err = db.Exec(`DETACH DATABASE encrypted`)
	return err
}

func openDB(path, key string) (*sql.DB, error) {
	db, err := sql.Open("sqlite3", path)
	if err != nil {
		return nil, err
	}

	// Disable concurrent access as not supported by the driver
	db.SetMaxOpenConns(1)

	if _, err = db.Exec("PRAGMA foreign_keys=ON"); err != nil {
		return nil, err
	}
	keyString := fmt.Sprintf("PRAGMA key = '%s'", key)
	if _, err = db.Exec(keyString); err != nil {
		return nil, errors.New("failed to set key pragma")
	}

	if _, err = db.Exec(fmt.Sprintf("PRAGMA kdf_iter = '%d'", kdfIterationsNumber)); err != nil {
		return nil, err
	}

	// readers do not block writers and faster i/o operations
	// https://www.sqlite.org/draft/wal.html
	// must be set after db is encrypted
	var mode string
	err = db.QueryRow("PRAGMA journal_mode=WAL").Scan(&mode)
	if err != nil {
		return nil, err
	}
	if mode != WALMode && path != inMemoryPath {
		return nil, fmt.Errorf("unable to set journal_mode to WAL. actual mode %s", mode)
	}

	return db, nil
}

// OpenDB opens not-encrypted database.
func OpenDB(path, key string) (*sql.DB, error) {
	return openDB(path, key)
}

// OpenUnecryptedDB opens database with setting PRAGMA key.
func OpenUnecryptedDB(path string) (*sql.DB, error) {
	db, err := sql.Open("sqlite3", path)
	if err != nil {
		return nil, err
	}

	// Disable concurrent access as not supported by the driver
	db.SetMaxOpenConns(1)

	if _, err = db.Exec("PRAGMA foreign_keys=ON"); err != nil {
		return nil, err
	}
	// readers do not block writers and faster i/o operations
	// https://www.sqlite.org/draft/wal.html
	// must be set after db is encrypted
	var mode string
	err = db.QueryRow("PRAGMA journal_mode=WAL").Scan(&mode)
	if err != nil {
		return nil, err
	}
	if mode != WALMode {
		return nil, fmt.Errorf("unable to set journal_mode to WAL. actual mode %s", mode)
	}

	return db, nil
}

func ChangeEncryptionKey(path, key, newKey string) error {
	db, err := openDB(path, key)

	if err != nil {
		return err
	}

	resetKeyString := fmt.Sprintf("PRAGMA rekey = '%s'", newKey)
	if _, err = db.Exec(resetKeyString); err != nil {
		return errors.New("failed to set rekey pragma")
	}

	return nil
}