// Copyright (C) 2018 The Go-SQLite3 Authors.
//
// Use of this source code is governed by an MIT-style
// license that can be found in the LICENSE file.

// +build cgo

package sqlite3

/*
#ifndef USE_LIBSQLITE3
#include <sqlite3-binding.h>
#else
#include <sqlite3.h>
#endif

#include <stdlib.h>
#include <string.h>

#ifndef SQLITE_OPEN_READWRITE
# define SQLITE_OPEN_READWRITE 0
#endif

#ifndef SQLITE_OPEN_FULLMUTEX
# define SQLITE_OPEN_FULLMUTEX 0
#endif

#ifndef SQLITE_DETERMINISTIC
# define SQLITE_DETERMINISTIC 0
#endif

static int
_sqlite3_open_v2(const char *filename, sqlite3 **ppDb, int flags, const char *zVfs) {
#ifdef SQLITE_OPEN_URI
  return sqlite3_open_v2(filename, ppDb, flags | SQLITE_OPEN_URI, zVfs);
#else
  return sqlite3_open_v2(filename, ppDb, flags, zVfs);
#endif
}
*/
import "C"
import (
	"bytes"
	"database/sql/driver"
	"errors"
	"fmt"
	"net/url"
	"runtime"
	"strconv"
	"strings"
	"time"
	"unsafe"
)

// Mode represents the open open for the database connection
type Mode C.int

func (m Mode) String() string {
	switch m {
	case ModeReadOnly:
		return "ro"
	case ModeReadWrite:
		return "rw"
	case ModeReadWriteCreate:
		return "rwc"
	case ModeMemory:
		return "memory"
	default:
		return ""
	}
}

// C returns the C.int of Mode
func (m Mode) C() C.int {
	return C.int(m)
}

const (
	// ModeReadOnly defines SQLITE_OPEN_READONLY for the database connection.
	ModeReadOnly = Mode(C.SQLITE_OPEN_READONLY)

	// ModeReadWrite defines SQLITE_OPEN_READWRITE for the database connection.
	ModeReadWrite = Mode(C.SQLITE_OPEN_READWRITE)

	// ModeReadWriteCreate defines SQLITE_OPEN_READWRITE and SQLITE_OPEN_CREATE.
	ModeReadWriteCreate = Mode(C.SQLITE_OPEN_READWRITE | C.SQLITE_OPEN_CREATE)

	// ModeMemory defines mode=memory which will
	// create a pure in-memory database that never reads or writes from disk
	ModeMemory = Mode(C.SQLITE_OPEN_MEMORY)
)

// CacheMode represents the current CacheMode
type CacheMode C.int

func (c CacheMode) String() string {
	switch c {
	case CacheModeShared:
		return "shared"
	case CacheModePrivate:
		return "private"
	default:
		return ""
	}
}

// C returns the C.int of CacheMode
func (c CacheMode) C() C.int {
	return C.int(c)
}

const (
	// CacheModeShared sets the cache mode of SQLite to 'shared'
	CacheModeShared = CacheMode(C.SQLITE_OPEN_SHAREDCACHE)

	// CacheModePrivate sets the cache mode of SQLite to 'private'
	CacheModePrivate = CacheMode(C.SQLITE_OPEN_PRIVATECACHE)
)

// Mutex represents how the database opens connections within
// single or multi-threading
type Mutex C.int

func (m Mutex) String() string {
	switch m {
	case MutexNo:
		return "no"
	case MutexFull:
		return "full"
	default:
		return ""
	}
}

// C returns the C.int of Mutex
func (m Mutex) C() C.int {
	return C.int(m)
}

const (
	// MutexNo will force the database connection opens
	// in the multi-thread threading mode as long as the
	// single-thread mode has not been set at compile-time or start-time.
	MutexNo = Mutex(C.SQLITE_OPEN_NOMUTEX)

	// MutexFull will force the database connection opens
	// in the serialized threading mode unless single-thread
	// was previously selected at compile-time or start-time.
	MutexFull = Mutex(C.SQLITE_OPEN_FULLMUTEX)
)

// TxLock defines the Transaction Lock Behaviour.
type TxLock string

func (tx TxLock) String() string {
	switch tx {
	case TxLockDeferred:
		return "deferred"
	case TxLockImmediate:
		return "immediate"
	case TxLockExclusive:
		return "exclusive"
	default:
		return ""
	}
}

// Value returns the Transaction Lock Value
func (tx TxLock) Value() string {
	return string(tx)
}

const (
	// TxLockDeferred deferred transaction behaviour. (Default)
	// Deferred means that no locks are acquired on the database
	// until the database is first accessed.
	// Thus with a deferred transaction,
	// the BEGIN statement itself does nothing to the filesystem.
	// Locks are not acquired until the first read or write operation.
	// The first read operation against a database creates a SHARED lock
	// and the first write operation creates a RESERVED lock.
	// Because the acquisition of locks is deferred until they are needed,
	// it is possible that another thread or process could create a separate transaction
	// and write to the database after the BEGIN on the current thread has executed.
	TxLockDeferred = TxLock("BEGIN")

	// TxLockImmediate immediate transaction behaviour.
	// If the transaction is immediate,
	// then RESERVED locks are acquired on all databases
	// as soon as the BEGIN command is executed,
	// without waiting for the database to be used.
	// After a BEGIN IMMEDIATE, no other database connection
	// will be able to write to the database or do a BEGIN IMMEDIATE or BEGIN EXCLUSIVE.
	// Other processes can continue to read from the database however.
	TxLockImmediate = TxLock("BEGIN IMMEDIATE")

	// TxLockExclusive exclusive transaction behaviour.
	// An exclusive transaction causes EXCLUSIVE locks to be acquired on all databases.
	// After a BEGIN EXCLUSIVE, no other database connection
	// except for read_uncommitted connections will be able to read the database
	// and no other connection without exception will be able to write the database
	// until the transaction is complete.
	TxLockExclusive = TxLock("BEGIN EXCLUSIVE")
)

// LockingMode defines the database locking mode.
// In NORMAL locking-mode (the default unless overridden at compile-time using SQLITE_DEFAULT_LOCKING_MODE),
// a database connection unlocks the database file at the conclusion of each read or write transaction.
// When the locking-mode is set to EXCLUSIVE,
// the database connection never releases file-locks.
// The first time the database is read in EXCLUSIVE mode,
// a shared lock is obtained and held.
// The first time the database is written, an exclusive lock is obtained and held.
//
// Database locks obtained by a connection in EXCLUSIVE mode may be released
// either by closing the database connection,
// or by setting the locking-mode back to NORMAL.
// Simply setting the locking-mode to NORMAL is not enough -
// locks are not released until the next time the database file is accessed.
//
// There are three reasons to set the locking-mode to EXCLUSIVE.
//
// The application wants to prevent other processes from accessing the database file.
// The number of system calls for filesystem operations is reduced,
// possibly resulting in a small performance increase.
// WAL databases can be accessed in EXCLUSIVE mode without the use of shared memory.
// (Additional information)
// When the locking_mode pragma specifies a particular database, for example:
//
// PRAGMA main.locking_mode=EXCLUSIVE;
// Then the locking mode applies only to the named database.
// If no database name qualifier precedes the "locking_mode" keyword
// then the locking mode is applied to all databases,
// including any new databases added by subsequent ATTACH commands.
//
// The "temp" database (in which TEMP tables and indices are stored)
// and in-memory databases always uses exclusive locking mode.
// The locking mode of temp and in-memory databases cannot be changed.
// All other databases use the normal locking mode by default and are affected by this pragma.
//
// If the locking mode is EXCLUSIVE when first entering WAL journal mode,
// then the locking mode cannot be changed to NORMAL until after exiting WAL journal mode.
// If the locking mode is NORMAL when first entering WAL journal mode,
//then the locking mode can be changed between NORMAL and EXCLUSIVE
// and back again at any time and without needing to exit WAL journal mode.
type LockingMode string

func (l LockingMode) String() string {
	return strings.ToLower(string(l))
}

const (
	// LockingModeNormal In NORMAL locking-mode
	// (the default unless overridden at compile-time using SQLITE_DEFAULT_LOCKING_MODE),
	// a database connection unlocks the database file at the conclusion
	// of each read or write transaction.
	LockingModeNormal = LockingMode("NORMAL")

	// LockingModeExclusive When the locking-mode is set to EXCLUSIVE,
	// the database connection never releases file-locks.
	// The first time the database is read in EXCLUSIVE mode,
	// a shared lock is obtained and held.
	// The first time the database is written, an exclusive lock is obtained and held.
	LockingModeExclusive = LockingMode("EXCLUSIVE")
)

// AutoVacuum defines the auto vacuum status of the database.
// The default setting for auto-vacuum is 0 or "none", unless the SQLITE_DEFAULT_AUTOVACUUM compile-time option is used.
// SQLITE_DEFAULT_AUTOVACUUM can be controlled within the package using
// build tags. See README for more information.
//
// Auto-vacuuming is only possible if the database stores some additional information
// that allows each database page to be traced backwards to its referrer.
// Therefore, auto-vacuuming must be turned on before any tables are created.
// It is not possible to enable or disable auto-vacuum after a table has been created.
type AutoVacuum string

func (av AutoVacuum) String() string {
	return strings.ToLower(string(av))
}

const (
	// AutoVacuumNone setting means that auto-vacuum is disabled.
	//
	// When auto-vacuum is disabled and data is deleted data from a database,
	// the database file remains the same size.
	// Unused database file pages are added to a "freelist" and reused for subsequent inserts.
	// So no database file space is lost.
	// However, the database file does not shrink.
	// In this mode the VACUUM command can be used to rebuild the entire database file
	// and thus reclaim unused disk space.
	//
	// The database connection can be changed between full
	// and incremental autovacuum mode at any time.
	// However, changing from "none" to "full" or "incremental"
	// can only occur when the database is new (no tables have yet been created)
	// or by running the VACUUM command. To change auto-vacuum modes,
	// first use the auto_vacuum pragma to set the new desired mode,
	// then invoke the VACUUM command to reorganize the entire database file.
	// To change from "full" or "incremental" back to "none"
	// always requires running VACUUM even on an empty database.
	AutoVacuumNone = AutoVacuum("NONE")

	// AutoVacuumFull sets auto vacuum of the database to FULL.
	//
	// When the auto-vacuum mode is 1 or "full",
	// the freelist pages are moved to the end of the database file and the database file
	// is truncated to remove the freelist pages at every transaction commit.
	// Note, however, that auto-vacuum only truncates the freelist pages from the file.
	// Auto-vacuum does not defragment the database nor repack individual database pages
	// the way that the VACUUM command does.
	// In fact, because it moves pages around within the file,
	// auto-vacuum can actually make fragmentation worse.
	AutoVacuumFull = AutoVacuum("FULL")

	// AutoVacuumIncremental sets the auto vacuum of the database to INCREMENTAL.
	//
	// When the value of auto-vacuum is 2 or "incremental"
	// then the additional information needed to do auto-vacuuming is stored
	// in the database file but auto-vacuuming does not occur automatically
	// at each commit as it does with auto_vacuum=full.
	// In incremental mode, the separate incremental_vacuum pragma must be invoked
	//  to cause the auto-vacuum to occur.
	AutoVacuumIncremental = AutoVacuum("INCREMENTAL")
)

// JournalMode defines the journal mode associated with the current database connection.
//
// Note that the journal_mode for an in-memory database is either
// MEMORY or OFF and can not be changed to a different value.
// An attempt to change the journal_mode of an in-memory database
// to any setting other than MEMORY or OFF is ignored.
// Note also that the journal_mode cannot be changed while a transaction is active.
type JournalMode string

func (j JournalMode) String() string {
	return strings.ToLower(string(j))
}

const (
	// JournalModeDelete  is the normal behavior.
	// In the DELETE mode, the rollback journal is deleted at the conclusion
	// of each transaction.
	// Indeed, the delete operation is the action that causes the transaction to commit.
	// (See the document titled Atomic Commit In SQLite for additional detail.)
	JournalModeDelete = JournalMode("DELETE")

	// JournalModeTruncate commits transactions by truncating the rollback journal
	// to zero-length instead of deleting it.
	// On many systems, truncating a file is much faster
	// than deleting the file since the containing directory does not need to be changed.
	JournalModeTruncate = JournalMode("TRUNCATE")

	// JournalModePersist prevents the rollback journal from being deleted
	// at the end of each transaction.
	// Instead, the header of the journal is overwritten with zeros.
	// This will prevent other database connections from rolling the journal back.
	// The PERSIST journaling mode is useful as an optimization on platforms
	// where deleting or truncating a file is much more expensive
	// than overwriting the first block of a file with zeros.
	// See also: PRAGMA journal_size_limit and SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT.
	JournalModePersist = JournalMode("PERSIST")

	// JournalModeMemory stores the rollback journal in volatile RAM.
	// This saves disk I/O but at the expense of database safety and integrity.
	// If the application using SQLite crashes in the middle of a transaction
	// when the MEMORY journaling mode is set,
	// then the database file will very likely go corrupt.
	JournalModeMemory = JournalMode("MEMORY")

	// JournalModeWAL uses a write-ahead log instead of a rollback journal
	// to implement transactions.
	// The WAL journaling mode is persistent;
	// after being set it stays in effect across multiple database connections
	// and after closing and reopening the database.
	JournalModeWAL = JournalMode("WAL")

	// JournalModeOff disables the rollback journal completely.
	// No rollback journal is ever created and hence there is never a rollback journal to delete.
	// The OFF journaling mode disables the atomic commit and rollback capabilities of SQLite. The ROLLBACK command no longer works; it behaves in an undefined way. Applications must avoid using the ROLLBACK command when the journal mode is OFF. If the application crashes in the middle of a transaction when the OFF journaling mode is set, then the database file will very likely go corrupt.
	JournalModeOff = JournalMode("OFF")
)

// SecureDelete defines the secure-delete setting.
//
// When secure_delete is on, SQLite overwrites deleted content with zeros.
// The default setting for secure_delete is determined by the SQLITE_SECURE_DELETE
// compile-time option and is normally off.
// The off setting for secure_delete improves performance by reducing
// the number of CPU cycles and the amount of disk I/O.
// Applications that wish to avoid leaving forensic traces after content is deleted
// or updated should enable the secure_delete pragma prior to performing the delete or update,
// or else run VACUUM after the delete or update.
type SecureDelete string

func (sd SecureDelete) String() string {
	return strings.ToLower(string(sd))
}

const (
	// SecureDeleteOff disables secure deletion of content.
	SecureDeleteOff = SecureDelete("OFF")

	// SecureDeleteOn will cause SQLite overwrites deleted content with zeros.
	SecureDeleteOn = SecureDelete("ON")

	// SecureDeleteFast defines the "fast" setting for secure_delete (added circa 2017-08-01) is an intermediate setting
	// in between "on" and "off". When secure_delete is set to "fast",
	// SQLite will overwrite deleted content with zeros only if doing so
	// does not increase the amount of I/O. In other words,
	// the "fast" setting uses more CPU cycles but does not use more I/O.
	// This has the effect of purging all old content from b-tree pages,
	// but leaving forensic traces on freelist pages.
	SecureDeleteFast = SecureDelete("FAST")
)

// Synchronous sync setting of the database connection.
type Synchronous string

func (s Synchronous) String() string {
	return strings.ToLower(string(s))
}

const (
	// SynchronousOff sets synchronous to OFF (0),
	// SQLite continues without syncing as soon as it has handed data off to the operating system.
	// If the application running SQLite crashes, the data will be safe,
	// but the database might become corrupted if the operating system crashes
	// or the computer loses power before that data has been written to the disk surface.
	// On the other hand, commits can be orders of magnitude faster with synchronous OFF.
	SynchronousOff = Synchronous("OFF")

	// SynchronousNormal sets synchronous to NORMAL (1),
	// the SQLite database engine will still sync at the most critical moments,
	// but less often than in FULL mode.
	// There is a very small (though non-zero) chance that a power failure
	// at just the wrong time could corrupt the database in journal_mode=DELETE
	// on an older filesystem. WAL mode is safe from corruption with synchronous=NORMAL,
	// and probably DELETE mode is safe too on modern filesystems.
	// WAL mode is always consistent with synchronous=NORMAL,
	// but WAL mode does lose durability.
	// A transaction committed in WAL mode with synchronous=NORMAL
	// might roll back following a power loss or system crash.
	// Transactions are durable across application crashes regardless
	// of the synchronous setting or journal mode.
	// The synchronous=NORMAL setting is a good choice for most applications running in WAL mode.
	SynchronousNormal = Synchronous("NORMAL")

	// SynchronousFull sets synchronous to FULL (2),
	// the SQLite database engine will use the xSync method of the VFS
	// to ensure that all content is safely written to the disk surface prior to continuing.
	// This ensures that an operating system crash or power failure
	// will not corrupt the database. FULL synchronous is very safe,
	// but it is also slower.
	///FULL is the most commonly used synchronous setting when not in WAL mode.
	SynchronousFull = Synchronous("FULL")

	// SynchronousExtra is like FULL with the addition that the directory containing
	// a rollback journal is synced after that journal is unlinked to commit a transaction
	// in DELETE mode. EXTRA provides additional durability if the commit
	// is followed closely by a power loss.
	SynchronousExtra = Synchronous("EXTRA")
)

// Config is configuration parsed from a DSN string.
// If a new Config is created instead of being parsed from a DSN string,
// the NewConfig function should be used, which sets default values.
// Manual usage is allowed
type Config struct {
	// Database
	Database string

	// Mode of the SQLite database
	Mode Mode

	// CacheMode of the SQLite Connection
	Cache CacheMode

	// Mutex flag SQLITE_OPEN_MUTEX_NO, SQLITE_OPEN_MUTEX_FULL
	// Defaults to SQLITE_OPEN_MUTEX_FULL
	Mutex Mutex

	// The immutable parameter is a boolean query parameter that indicates
	// that the database file is stored on read-only media. When immutable is set,
	// SQLite assumes that the database file cannot be changed,
	// even by a process with higher privilege,
	// and so the database is opened read-only and all locking and change detection is disabled.
	// Caution: Setting the immutable property on a database file that
	// does in fact change can result in incorrect query results and/or SQLITE_CORRUPT errors.
	Immutable bool

	// TimeZone location
	TimeZone *time.Location

	// TransactionLock behaviour
	TransactionLock TxLock

	// LockingMode behaviour
	LockingMode LockingMode

	// Authentication holds the UserAuth configuration
	Authentication *Auth

	// AutoVacuum sets the auto vacuum status of the database
	// Defaults to NONE
	AutoVacuum AutoVacuum

	// BusyTimeout defines the time a connection will wait when the
	// connection is BUSY and locked by an other connection.
	// BusyTimeout is defined in milliseconds
	BusyTimeout time.Duration

	// CaseSensitiveLike controls the behaviour of the LIKE operator.
	// Default or disabled the LIKE operation is case-insensitive.
	// When enabling this options behaviour of LIKE will become case-sensitive.
	CaseSensitiveLike bool

	// DeferForeignKeys when enabled will cause the enforcement
	// of all foreign key constraints is delayed until
	// the outermost transaction is committed.
	// The defer_foreign_keys pragma defaults to false
	// so that foreign key constraints are only deferred
	// if they are created as "DEFERRABLE INITIALLY DEFERRED".
	// The defer_foreign_keys pragma is automatically switched off at each COMMIT or ROLLBACK.
	// Hence, the defer_foreign_keys pragma must be separately enabled for each transaction.
	// This pragma is only meaningful if foreign key constraints are enabled, of course.
	DeferForeignKeys bool

	// ForeignKeyConstraints enable or disable the enforcement of foreign key constraints.
	ForeignKeyConstraints bool

	// IgnoreCheckConstraints enables or disables the enforcement of CHECK constraints.
	// The default setting is off, meaning that CHECK constraints are enforced by default.
	IgnoreCheckConstraints bool

	// JournalMode sets the journal mode for databases associated with the current database connection.
	JournalMode JournalMode

	// QueryOnly prevents all changes to the database when set to true.
	QueryOnly bool

	// RecursiveTriggers enable or disable the recursive trigger capability.
	RecursiveTriggers bool

	// SecureDelete enables or disables or sets the secure deletion within the database.
	SecureDelete SecureDelete

	// Synchronous Mode of the database
	Synchronous Synchronous

	// WriteableSchema enables of disables the ability to using UPDATE, INSERT, DELETE
	// Warning: misuse of this pragma can easily result in a corrupt database file.
	WriteableSchema bool

	// Extensions
	Extensions []string

	// ConnectHook
	ConnectHook func(*SQLiteConn) error
}

// Auth holds the authentication configuration for the SQLite UserAuth module.
type Auth struct {
	// Username for authentication
	Username string

	// Password for authentication
	Password string

	// Salt for encryption
	Salt string

	// CryptEncoder used for the password encryption
	Encoder CryptEncoder
}

// NewConfig creates a new Config and sets default values.
func NewConfig() *Config {
	return &Config{
		Database:               ":memory:",
		Mode:                   ModeReadWriteCreate,
		Cache:                  CacheModePrivate,
		Immutable:              false,
		Mutex:                  MutexFull,
		TransactionLock:        TxLockDeferred,
		LockingMode:            LockingModeNormal,
		AutoVacuum:             AutoVacuumNone,
		CaseSensitiveLike:      false,
		DeferForeignKeys:       false,
		ForeignKeyConstraints:  false,
		IgnoreCheckConstraints: false,
		JournalMode:            JournalModeDelete,
		QueryOnly:              false,
		RecursiveTriggers:      false,
		SecureDelete:           SecureDeleteOff,
		Synchronous:            SynchronousNormal,
		WriteableSchema:        false,
		Authentication: &Auth{
			Encoder: NewSHA1Encoder(),
		},
	}
}

// FormatDSN formats the given Config into a DSN string which can be passed to
// the driver.
func (cfg *Config) FormatDSN() string {
	var buf bytes.Buffer

	params := url.Values{}
	if len(cfg.Cache.String()) > 0 {
		params.Set("cache", cfg.Cache.String())
	}

	if len(cfg.Mode.String()) > 0 {
		params.Set("mode", cfg.Mode.String())
	}

	if len(cfg.Mutex.String()) > 0 {
		params.Set("mutex", cfg.Mutex.String())
	}

	if cfg.Immutable {
		params.Set("immutable", "true")
	}

	if cfg.TimeZone != nil {
		if cfg.TimeZone == time.Local {
			params.Set("tz", "auto")
		} else {
			params.Set("tz", cfg.TimeZone.String())
		}
	}

	if len(cfg.TransactionLock.String()) > 0 && cfg.TransactionLock != TxLockDeferred {
		params.Set("txlock", cfg.TransactionLock.String())
	}

	if len(cfg.LockingMode) > 0 && cfg.LockingMode != LockingModeNormal {
		params.Set("lock", cfg.LockingMode.String())
	}

	if len(cfg.AutoVacuum) > 0 && cfg.AutoVacuum != AutoVacuumNone {
		params.Set("vacuum", cfg.AutoVacuum.String())
	}

	if cfg.CaseSensitiveLike {
		params.Set("cslike", "true")
	}

	if cfg.DeferForeignKeys {
		params.Set("defer_fk", "true")
	}

	if cfg.ForeignKeyConstraints {
		params.Set("fk", "true")
	}

	if cfg.IgnoreCheckConstraints {
		params.Set("ignore_check_contraints", "true")
	}

	if len(cfg.JournalMode) > 0 && cfg.JournalMode != JournalModeDelete {
		params.Set("journal", cfg.JournalMode.String())
	}

	if cfg.QueryOnly {
		params.Set("query_only", "true")
	}

	if cfg.RecursiveTriggers {
		params.Set("recursive_triggers", "true")
	}

	if len(cfg.SecureDelete) > 0 && cfg.SecureDelete != SecureDeleteOff {
		params.Set("secure_delete", cfg.SecureDelete.String())
	}

	if len(cfg.Synchronous) > 0 && cfg.Synchronous != SynchronousNormal {
		params.Set("sync", cfg.Synchronous.String())
	}

	if cfg.WriteableSchema {
		params.Set("writable_schema", "true")
	}

	if cfg.Authentication != nil {
		if len(cfg.Authentication.Username) > 0 && len(cfg.Authentication.Password) > 0 {
			params.Set("user", cfg.Authentication.Username)
			params.Set("pass", cfg.Authentication.Password)

			if len(cfg.Authentication.Salt) > 0 {
				params.Set("salt", cfg.Authentication.Salt)
			}

			if cfg.Authentication.Encoder != nil {
				params.Set("crypt", cfg.Authentication.Encoder.String())
			}
		}
	}

	if !strings.HasPrefix(cfg.Database, "file:") {
		buf.WriteString("file:")
	}
	buf.WriteString(cfg.Database)

	// Append Options
	if len(params) > 0 {
		buf.WriteRune('?')
		buf.WriteString(params.Encode())
	}

	return buf.String()
}

// Create connection from Configuration
func (cfg *Config) createConnection() (driver.Conn, error) {
	if C.sqlite3_threadsafe() == 0 {
		return nil, errors.New("sqlite library was not compiled for thread-safe operation")
	}

	if len(cfg.Database) == 0 || cfg.Database == "file:" {
		return nil, fmt.Errorf("No database configured")
	}

	var db *C.sqlite3

	// Configure Database URI
	// Because we are adding the 'immutable' flag to the database file
	// We are required to conform the database path to an URI
	// The immutable flag is an query parameter which means that the URI needs
	// to start with 'file:'. Regardless if it is an in-memory database or not.
	uri := cfg.Database
	if !strings.HasPrefix(uri, "file:") {
		uri = fmt.Sprintf("file:%s", uri)
	}
	if !strings.Contains(uri, ":memory:") {
		uri = fmt.Sprintf("%s?immutable=%t", uri, cfg.Immutable)
	}
	database := C.CString(uri)

	// Free CString on return
	defer C.free(unsafe.Pointer(database))

	// Open the database
	// https://www.sqlite.org/c3ref/open.html
	rv := C._sqlite3_open_v2(
		database,
		&db,
		cfg.Mutex.C()|cfg.Cache.C()|cfg.Mode.C(),
		nil)

	// Check if the database was opened succesful.
	if rv != C.SQLITE_OK {
		return nil, Error{Code: ErrNo(rv)}
	}

	// Verify we have a database pointer
	if db == nil {
		return nil, errors.New("sqlite succeeded without returning a database")
	}

	// Set SQLITE Busy Timeout Handler
	rv = C.sqlite3_busy_timeout(db, C.int(cfg.BusyTimeout))
	if rv != C.SQLITE_OK {
		// Failed to set busy timeout
		// close the database and return the error
		C.sqlite3_close_v2(db)

		return nil, Error{Code: ErrNo(rv)}
	}

	// Create basic connection
	conn := &SQLiteConn{
		db:     db,
		tz:     cfg.TimeZone,
		txlock: cfg.TransactionLock.Value(),
	}

	// At this point we have the following
	// - database pointer
	// - basic connection
	//
	// Now we need to configure the connection according to the *Config

	// USER AUTHENTICATION
	//
	// User Authentication is always performed even when
	// sqlite_userauth is not compiled in, because without user authentication
	// the authentication is a no-op.
	//
	// Workflow
	//	- Authenticate
	//		ON::SUCCESS		=> Continue
	//		ON::SQLITE_AUTH => Return error and exit Open(...)
	//
	//  - Activate User Authentication
	//		Check if the user wants to activate User Authentication.
	//		If so then first create a temporary AuthConn to the database
	//		This is possible because we are already succesfully authenticated.
	//
	//	- Check if `sqlite_user`` table exists
	//		YES				=> Add the provided user from DSN as Admin User and
	//						   activate user authentication.
	//		NO				=> Continue
	//
	//
	// Because we need to perform authentication we need to register
	// the required functions on the connection.

	// Register sqlite_crypt function with the CryptEncoder provided
	// within *Config.Authentication
	if err := conn.RegisterFunc("sqlite_crypt", cfg.Authentication.Encoder.Encode, true); err != nil {
		return nil, fmt.Errorf("CryptEncoder: %s", err)
	}

	// Register: authenticate
	// Authenticate will perform an authentication of the provided username
	// and password against the database.
	//
	// If a database contains the SQLITE_USER table, then the
	// call to Authenticate must be invoked with an
	// appropriate username and password prior to enable read and write
	// access to the database.
	//
	// Return SQLITE_OK on success or SQLITE_ERROR if the username/password
	// combination is incorrect or unknown.
	//
	// If the SQLITE_USER table is not present in the database file, then
	// this interface is a harmless no-op returnning SQLITE_OK.
	if err := conn.RegisterFunc("authenticate", conn.authenticate, true); err != nil {
		return nil, err
	}

	// Register: auth_user_add
	// auth_user_add can be used (by an admin user only)
	// to create a new user. When called on a no-authentication-required
	// database, this routine converts the database into an authentication-
	// required database, automatically makes the added user an
	// administrator, and logs in the current connection as that user.
	// The AuthUserAdd only works for the "main" database, not
	// for any ATTACH-ed databases. Any call to AuthUserAdd by a
	// non-admin user results in an error.
	if err := conn.RegisterFunc("auth_user_add", conn.authUserAdd, true); err != nil {
		return nil, err
	}

	// Register: auth_user_change
	// auth_user_change can be used to change a users
	// login credentials or admin privilege.  Any user can change their own
	// login credentials. Only an admin user can change another users login
	// credentials or admin privilege setting. No user may change their own
	// admin privilege setting.
	if err := conn.RegisterFunc("auth_user_change", conn.authUserChange, true); err != nil {
		return nil, err
	}

	// Register: auth_user_delete
	// auth_user_delete can be used (by an admin user only)
	// to delete a user. The currently logged-in user cannot be deleted,
	// which guarantees that there is always an admin user and hence that
	// the database cannot be converted into a no-authentication-required
	// database.
	if err := conn.RegisterFunc("auth_user_delete", conn.authUserDelete, true); err != nil {
		return nil, err
	}

	// Register: auth_enabled
	// auth_enabled can be used to check if user authentication is enabled
	if err := conn.RegisterFunc("auth_enabled", conn.authEnabled, true); err != nil {
		return nil, err
	}

	// Preform Authentication only if username and password are provided
	// If authentication is not enabled on the database
	// this call is a NO-OP.
	// Only call this when Username and Password are provided in the *Config
	if len(cfg.Authentication.Username) > 0 && len(cfg.Authentication.Password) > 0 {
		if err := conn.Authenticate(cfg.Authentication.Username, cfg.Authentication.Password); err != nil {
			return nil, err
		}
	}

	// AUTO VACUUM
	// The user preference for auto_vacuum needs to be implemented directly after
	// the authentication and before the sqlite_user table gets created if the user
	// decides to activate User Authentication because
	// auto_vacuum needs to be set before any tables are created
	// and activating user authentication creates the internal table `sqlite_user`.
	if err := conn.PRAGMA(PRAGMA_AUTO_VACUUM, cfg.AutoVacuum.String()); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Check if authentication is enabled
	// This can now be succesfully checked because we are successfully connected.
	// Only issue this when Username and Password are configured.
	// If this is an unauthenticated database
	// the provided user will be created as Admin.
	if len(cfg.Authentication.Username) > 0 && len(cfg.Authentication.Password) > 0 {
		authExists := conn.AuthEnabled()
		if !authExists {
			if err := conn.AuthUserAdd(cfg.Authentication.Username, cfg.Authentication.Password, true); err != nil {
				return nil, err
			}
		}
	}

	// Case Sensitive LIKE
	if err := conn.PRAGMA(PRAGMA_CASE_SENSITIVE_LIKE, strconv.FormatBool(cfg.CaseSensitiveLike)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Defer Foreign Keys
	if err := conn.PRAGMA(PRAGMA_DEFER_FOREIGN_KEYS, strconv.FormatBool(cfg.DeferForeignKeys)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Foreign Keys
	if err := conn.PRAGMA(PRAGMA_FOREIGN_KEYS, strconv.FormatBool(cfg.ForeignKeyConstraints)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Ignore CHECK constraints
	if err := conn.PRAGMA(PRAGMA_IGNORE_CHECK_CONTRAINTS, strconv.FormatBool(cfg.IgnoreCheckConstraints)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Journal Mode
	if err := conn.PRAGMA(PRAGMA_JOURNAL_MODE, cfg.JournalMode.String()); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Locking Mode
	if err := conn.PRAGMA(PRAGMA_LOCKING_MODE, cfg.LockingMode.String()); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Query Only
	if err := conn.PRAGMA(PRAGMA_QUERY_ONLY, strconv.FormatBool(cfg.QueryOnly)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Recursive Triggers
	if err := conn.PRAGMA(PRAGMA_RECURSIVE_TRIGGERS, strconv.FormatBool(cfg.RecursiveTriggers)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Secure Delete
	if err := conn.PRAGMA(PRAGMA_SECURE_DELETE, cfg.SecureDelete.String()); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Synchronous
	if err := conn.PRAGMA(PRAGMA_SYNCHRONOUS, cfg.SecureDelete.String()); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Writable Schema
	if err := conn.PRAGMA(PRAGMA_WRITABLE_SCHEMA, strconv.FormatBool(cfg.WriteableSchema)); err != nil {
		C.sqlite3_close_v2(db)
		return nil, err
	}

	// Load Extensions
	if len(cfg.Extensions) > 0 {
		if err := conn.loadExtensions(cfg.Extensions); err != nil {
			conn.Close()
			return nil, err
		}
	}

	// Configure Connect Hooks
	if cfg.ConnectHook != nil {
		if err := cfg.ConnectHook(conn); err != nil {
			conn.Close()
			return nil, err
		}
	}

	// Configure Finalizer
	runtime.SetFinalizer(conn, (*SQLiteConn).Close)

	return conn, nil
}

// ParseDSN parses the DSN string to a Config
func ParseDSN(dsn string) (cfg *Config, err error) {
	// New default with default values
	cfg = NewConfig()

	cfg.Database = dsn

	pos := strings.IndexRune(dsn, '?')
	if pos >= 1 {
		// Update DatabaseURI
		cfg.Database = dsn[0:pos]

		// Parse Options
		params, err := url.ParseQuery(dsn[pos+1:])
		if err != nil {
			return nil, err
		}

		// Normalize Params
		normalizeParams(params)

		if !strings.HasPrefix(dsn, "file:") {
			dsn = dsn[:pos]
		}

		// Parse Autentication
		if val := params.Get("user"); val != "" {
			cfg.Authentication.Username = val
		}

		if val := params.Get("pass"); val != "" {
			cfg.Authentication.Password = val
		}

		if val := params.Get("salt"); val != "" {
			cfg.Authentication.Salt = val
		}

		if val := params.Get("crypt"); val != "" {
			var enc CryptEncoder
			var ok bool

			if enc, ok = cryptEncoders[val]; !ok {
				return nil, fmt.Errorf("Unknown CryptEncoder(%s); please register first with 'RegisterCryptEncoder()'", val)
			}

			cfg.Authentication.Encoder = enc
		}

		// Parse Multi name options
		// Multi name options are options which has multiple aliases for the same option
		for k := range params {
			// Cache
			if k == "cache" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "shared":
					cfg.Cache = CacheModeShared
				case "private":
					cfg.Cache = CacheModePrivate
				default:
					return nil, fmt.Errorf("Unknown cache mode: %v, expecting value of 'shared, private'", val)
				}
			}

			// Immutable
			if k == "immutable" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.Immutable = false
				case "1", "yes", "true", "on":
					cfg.Immutable = true
				default:
					return nil, fmt.Errorf("Unknown immutable: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Mode
			if k == "mode" {
				val := params.Get(k)
				switch strings.ToUpper(val) {
				case "RO":
					cfg.Mode = ModeReadOnly
				case "RW":
					cfg.Mode = ModeReadWrite
				case "RWC":
					cfg.Mode = ModeReadWriteCreate
				case "MEMORY":
					cfg.Mode = ModeMemory
				default:
					return nil, fmt.Errorf("Unknown mode: %v, expecting value of 'ro, rw, rwc, memory'", val)
				}
			}

			// Mutex
			if k == "mutex" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "no":
					cfg.Mutex = MutexNo
				case "full":
					cfg.Mutex = MutexFull
				default:
					return nil, fmt.Errorf("Invalid mutex: %v, expecting value of 'no, full", val)
				}
			}

			// Timezone
			if k == "tz" || k == "timezone" || k == "loc" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "auto":
					cfg.TimeZone = time.Local
				default:
					cfg.TimeZone, err = time.LoadLocation(val)
					if err != nil {
						return nil, fmt.Errorf("Invalid tz: %v: %v", val, err)
					}
				}
			}

			// Transaction Lock
			if k == "txlock" || k == "transaction_lock" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "immediate":
					cfg.TransactionLock = TxLockImmediate
				case "exclusive":
					cfg.TransactionLock = TxLockExclusive
				case "deferred":
					cfg.TransactionLock = TxLockDeferred
				default:
					return nil, fmt.Errorf("Invalid txlock: %v, expecting value of 'deferred, immediate, exclusive'", val)
				}
			}

			// AutoVacuum
			if k == "auto_vacuum" || k == "vacuum" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "none":
					cfg.AutoVacuum = AutoVacuumNone
				case "1", "full":
					cfg.AutoVacuum = AutoVacuumFull
				case "2", "incremental":
					cfg.AutoVacuum = AutoVacuumIncremental
				default:
					return nil, fmt.Errorf("Invalid auto_vacuum: %v, expecting value of '0 NONE 1 FULL 2 INCREMENTAL'", val)
				}
			}

			// Busy Timeout
			if k == "busy_timeout" || k == "timeout" {
				val := params.Get(k)
				iv, err := strconv.ParseInt(val, 10, 64)
				if err != nil {
					return nil, fmt.Errorf("Invalid busy_timeout: %v: %v", val, err)
				}

				cfg.BusyTimeout, _ = time.ParseDuration(fmt.Sprintf("%dms", iv))
			}

			// Case Sensitive LIKE
			if k == "case_sensitive_like" || k == "cslike" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.CaseSensitiveLike = false
				case "1", "yes", "true", "on":
					cfg.CaseSensitiveLike = true
				default:
					return nil, fmt.Errorf("Invalid case_sensitive_like: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Defer Foreign Keys
			if k == "defer_foreign_keys" || k == "defer_fk" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.DeferForeignKeys = false
				case "1", "yes", "true", "on":
					cfg.DeferForeignKeys = true
				default:
					return nil, fmt.Errorf("Invalid defer_foreign_keys: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Foreign Keys
			if k == "foreign_keys" || k == "fk" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.ForeignKeyConstraints = false
				case "1", "yes", "true", "on":
					cfg.ForeignKeyConstraints = true
				default:
					return nil, fmt.Errorf("Invalid foreign_keys: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Ignore Check Constraints
			if k == "ignore_check_constraints" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.IgnoreCheckConstraints = false
				case "1", "yes", "true", "on":
					cfg.IgnoreCheckConstraints = true
				default:
					return nil, fmt.Errorf("Invalid ignore_check_constraints: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Parse Synchronous before Journal Mode
			// Because if WAL mode is selected for Journal
			// This will change the Synchronous mode
			if k == "synchronous" || k == "sync" {
				val := params.Get(k)
				switch strings.ToUpper(val) {
				case "0", "OFF":
					cfg.Synchronous = SynchronousOff
				case "1", "NORMAL":
					cfg.Synchronous = SynchronousNormal
				case "2", "FULL":
					cfg.Synchronous = SynchronousFull
				case "3", "EXTRA":
					cfg.Synchronous = SynchronousExtra
				default:
					return nil, fmt.Errorf("Invalid synchronous: %v, expecting value of '0 OFF 1 NORMAL 2 FULL 3 EXTRA'", val)
				}
			}

			// Journal Mode
			if k == "journal_mode" || k == "journal" {
				val := params.Get(k)
				switch strings.ToUpper(val) {
				case "DELETE", "TRUNCATE", "PERSIST", "MEMORY", "OFF":
					cfg.JournalMode = JournalMode(strings.ToUpper(val))
				case "WAL":
					cfg.JournalMode = JournalModeWAL

					// For WAL Mode set Synchronous Mode to 'NORMAL'
					// See https://www.sqlite.org/pragma.html#pragma_synchronous
					cfg.Synchronous = SynchronousNormal
				default:
					return nil, fmt.Errorf("Invalid journal: %v, expecting value of 'DELETE TRUNCATE PERSIST MEMORY WAL OFF'", val)
				}
			}

			// Locking Mode
			if k == "locking_mode" || k == "locking" || k == "lock" {
				val := params.Get(k)
				switch strings.ToUpper(val) {
				case "NORMAL":
					cfg.LockingMode = LockingModeNormal
				case "EXCLUSIVE":
					cfg.LockingMode = LockingModeExclusive
				default:
					return nil, fmt.Errorf("Invalid locking_mode: %v, expecting value of 'NORMAL EXCLUSIVE", val)
				}
			}

			// Query Only
			if k == "query_only" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.QueryOnly = false
				case "1", "yes", "true", "on":
					cfg.QueryOnly = true
				default:
					return nil, fmt.Errorf("Invalid query_only: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Recursive Triggers
			if k == "rt" || k == "recursive_triggers" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.RecursiveTriggers = false
				case "1", "yes", "true", "on":
					cfg.RecursiveTriggers = true
				default:
					return nil, fmt.Errorf("Invalid recursive_triggers: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}

			// Secure Delete
			if k == "secure_delete" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.SecureDelete = SecureDeleteOff
				case "1", "yes", "true", "on":
					cfg.SecureDelete = SecureDeleteOn
				case "fast":
					cfg.SecureDelete = SecureDeleteFast
				default:
					return nil, fmt.Errorf("Invalid secure_delete: %v, expecting boolean value of '0 1 false true no yes off on fast'", val)
				}
			}

			if k == "writable_schema" {
				val := params.Get(k)
				switch strings.ToLower(val) {
				case "0", "no", "false", "off":
					cfg.WriteableSchema = false
				case "1", "yes", "true", "on":
					cfg.WriteableSchema = true
				default:
					return nil, fmt.Errorf("Invalid writable_schema: %v, expecting boolean value of '0 1 false true no yes off on'", val)
				}
			}
		}
	}

	return cfg, nil
}

func normalizeParams(params url.Values) {
	for k, v := range params {
		params[strings.ToLower(k)] = v
	}
}