const (
	EnvVerifyValueLock verify.VerificationType = "lock"
)

var (

	// InitialMmapSize is the initial size of the mmapped region. Setting this larger than
	// the potential max db size can prevent writer from blocking reader.
	// This only works for linux.
	InitialMmapSize = uint64(10 * 1024 * 1024 * 1024)
)

type Backend interface {
	// ReadTx returns a read transaction. It is replaced by ConcurrentReadTx in the main data path, see #10523.
	ReadTx() ReadTx
	BatchTx() BatchTx
	// ConcurrentReadTx returns a non-blocking read transaction.
	ConcurrentReadTx() ReadTx

	Snapshot() Snapshot
	Hash(ignores func(bucketName, keyName []byte) bool) (uint32, error)
	// Size returns the current size of the backend physically allocated.
	// The backend can hold DB space that is not utilized at the moment,
	// since it can conduct pre-allocation or spare unused space for recycling.
	// Use SizeInUse() instead for the actual DB size.
	Size() int64
	// SizeInUse returns the current size of the backend logically in use.
	// Since the backend can manage free space in a non-byte unit such as
	// number of pages, the returned value can be not exactly accurate in bytes.
	SizeInUse() int64
	// OpenReadTxN returns the number of currently open read transactions in the backend.
	OpenReadTxN() int64
	Defrag() error
	ForceCommit()
	Close() error

	// SetTxPostLockInsideApplyHook sets a txPostLockInsideApplyHook.
	SetTxPostLockInsideApplyHook(func())
}

type BackendConfig struct {
	// Path is the file path to the backend file.
	Path string
	// BatchInterval is the maximum time before flushing the BatchTx.
	BatchInterval time.Duration
	// BatchLimit is the maximum puts before flushing the BatchTx.
	BatchLimit int
	// BackendFreelistType is the backend boltdb's freelist type.
	BackendFreelistType bolt.FreelistType
	// MmapSize is the number of bytes to mmap for the backend.
	MmapSize uint64
	// Logger logs backend-side operations.
	Logger *zap.Logger
	// UnsafeNoFsync disables all uses of fsync.
	UnsafeNoFsync bool `json:"unsafe-no-fsync"`
	// Mlock prevents backend database file to be swapped
	Mlock bool
	// Timeout is the amount of time to wait to obtain a file lock.
	// When set to zero it will wait indefinitely.
	Timeout time.Duration

	// Hooks are getting executed during lifecycle of Backend's transactions.
	Hooks Hooks
}

type BackendConfigOption func(*BackendConfig)

type BatchTx interface {
	Lock()
	Unlock()
	// Commit commits a previous tx and begins a new writable one.
	Commit()
	// CommitAndStop commits the previous tx and does not create a new one.
	CommitAndStop()
	LockInsideApply()
	LockOutsideApply()
	UnsafeReadWriter
}

type Bucket interface {
	// ID returns a unique identifier of a bucket.
	// The id must NOT be persisted and can be used as lightweight identificator
	// in the in-memory maps.
	ID() BucketID
	Name() []byte
	// String implements Stringer (human readable name).
	String() string

	// IsSafeRangeBucket is a hack to avoid inadvertently reading duplicate keys;
	// overwrites on a bucket should only fetch with limit=1, but safeRangeBucket
	// is known to never overwrite any key so range is safe.
	IsSafeRangeBucket() bool
}

type BucketID int

type HookFunc func(tx UnsafeReadWriter)

type Hooks interface {
	// OnPreCommitUnsafe is executed before Commit of transactions.
	// The given transaction is already locked.
	OnPreCommitUnsafe(tx UnsafeReadWriter)
}

type ReadTx interface {
	RLock()
	RUnlock()
	UnsafeReader
}

type Snapshot interface {
	// Size gets the size of the snapshot.
	Size() int64
	// WriteTo writes the snapshot into the given writer.
	WriteTo(w io.Writer) (n int64, err error)
	// Close closes the snapshot.
	Close() error
}

type UnsafeReadWriter interface {
	UnsafeReader
	UnsafeWriter
}

type UnsafeReader interface {
	UnsafeRange(bucket Bucket, key, endKey []byte, limit int64) (keys [][]byte, vals [][]byte)
	UnsafeForEach(bucket Bucket, visitor func(k, v []byte) error) error
}

type UnsafeWriter interface {
	UnsafeCreateBucket(bucket Bucket)
	UnsafeDeleteBucket(bucket Bucket)
	UnsafePut(bucket Bucket, key []byte, value []byte)
	UnsafeSeqPut(bucket Bucket, key []byte, value []byte)
	UnsafeDelete(bucket Bucket, key []byte)
}