leveldb

type Batch struct {
	// contains filtered or unexported fields
}

type Comparator interface {
	// Name returns the name of this comparator. A DB created with one comparator
	// can't be opened using a comparator with different name.
	//
	// Client should switch to a new name if the comparator implementation changes
	// in a way that cause the relative order of any two keys varied.
	//
	// Names starting with "leveldb." are reserved and should not used by clients.
	Name() string

	// Compare returns a value 'less than', 'equal to' or 'greater than' 0 depending
	// on whether a is 'less than', 'equal to' or 'greater than' b.
	Compare(a, b []byte) int

	// AppendSuccessor appends a possibly shortest byte sequence in range [start, limit)
	// to dst. Empty limit acts as infinite large. In particularly, if limit equals to
	// start, it returns append(dst, start).
	AppendSuccessor(dst, start, limit []byte) []byte

	// MakePrefixSuccessor returns a byte sequence 'limit' such that all byte sequences
	// falling in [prefix, limit) have 'prefix' as prefix. Zero length 'limit' acts as
	// infinite large.
	MakePrefixSuccessor(prefix []byte) []byte
}

type CompressionType int

type DB struct {
	// contains filtered or unexported fields
}

type File interface {
	io.Reader
	io.Writer
	io.Seeker
	io.Closer
	io.ReaderAt
	Truncate(size int64) error
	Sync() error
}

type FileSystem interface {
	// Open opens a file using specified flag.
	Open(name string, flag int) (File, error)

	// Lock locks a file for exclusive usage. If the file is locked by
	// someone else, failed with an error instead of blocking. If ok,
	// returns an io.Closer to let caller to release underly locker.
	Lock(name string) (io.Closer, error)

	// Exists returns true if the named file exists.
	Exists(name string) bool

	// MkdirAll creates a directory and all necessary parents.
	MkdirAll(path string) error

	// Lists returns all contents of the directory.
	List(dir string) ([]string, error)

	// Remove removes named file or directory.
	Remove(filename string) error

	// Rename renames(moves) oldpath to newpath. If newpath already exists,
	// Rename replaces it.
	Rename(oldpath, newpath string) error
}

type Filter interface {
	// Name returns the name of this filter.
	//
	// Note that if the encoding of filter data changes in an incompatible
	// way, the name returned by this method must be changed. Otherwise,
	// old incompatible filter data may be passed to methods of this filter.
	Name() string

	// Append appends filter data summarized from keys to buf.
	Append(buf *bytes.Buffer, keys [][]byte)

	// Contains returns a boolean indicating whether key is possibly
	// falling in 'data', which is generated by Generator.
	Contains(data, key []byte) bool

	// NewGenerator creates a new generator to generate filter data
	// for bunch of keys. This method is optional, an implementation
	// can safely return nil, in this case, a fallback generator is
	// created.
	NewGenerator() Generator
}

type Generator interface {
	// Name returns the name of underlying filter.
	Name() string

	// Reset resets generator to its initial state.
	Reset()

	// Empty returns whether any key has been added to this generator.
	Empty() bool

	// Add adds key to this generator for summarization.
	Add(key []byte)

	// Append appends filter data summarized from keys added before.
	Append(buf *bytes.Buffer)
}

type Iterator interface {
	// Next moves to next entry. It returns whether such entry exists.
	// If it is the first seek method called, it behaves as First().
	Next() bool

	// Prev moves to previous entry. It returns whether such entry exists.
	// If it is the first seek method called, it behaves as Last().
	Prev() bool

	// First moves to the first entry. It returns whether such entry exists.
	First() bool

	// Last moves to the last entry. It returns whether such entry exists.
	Last() bool

	// Seek moves the iterator to the first key that equal to or greater than
	// key. It returns whether such entry exists.
	Seek(key []byte) bool

	// Valid returns whether the iterator is point to a valid entry.
	Valid() bool

	// Key returns the key of current entry. The behaviour is undefined if
	// current status of iterator is invalid.
	Key() []byte

	// Value returns the value of current entry. The behaviour is undefined
	// if current status of iterator is invalid.
	Value() []byte

	// Err returns error we encounters so far. Seek methods, First, Last and Seek may
	// clear this error.
	Err() error

	// Closes releases any resources hold by this iterator, and returns
	// any error it encounters so far. The behaviour is undefined if you
	// call any methods after this iterator has been closed.
	Close() error
}

type Logger interface {
	Debugf(format string, args ...interface{})
	Infof(format string, args ...interface{})
	Warnf(format string, args ...interface{})
	Errorf(format string, args ...interface{})
}

type Options struct {
	// Comparator defines the total order over keys in the database.
	//
	// The default comparator is BytewiseComparator, which uses the same ordering
	// as bytes.Compare.
	Comparator Comparator

	// Compression type used to compress blocks.
	//
	// The default value points to SnappyCompression.
	Compression CompressionType

	// MaxFileSize enforces size limitation for files created by LevelDB.
	//
	// Defaults to 2MiB.
	MaxFileSize int64

	// MaxGrandparentOverlapBytes limits number of overlap bytes with level+2 a
	// compacted file produced in compaction level => level+1 can have.
	//
	// Defaults to 10 * MaxFileSize.
	MaxGrandparentOverlapBytes int64

	// MaxExpandedCompactionBytes limits number of bytes of input files when expanding
	// input files in compacting level.
	//
	// Defaults to 25 * MaxFileSize.
	MaxExpandedCompactionBytes int64

	// BlockSize specifies the minimum uncompressed size in bytes for a table block.
	//
	// The default value is 4KiB.
	BlockSize int

	// BlockRestartInterval specifies the number of keys between restart points
	// for delta encoding of keys in a block.
	//
	// The default value is 16.
	BlockRestartInterval int

	// BlockCompressionRatio specifies a minimal compression ratio for table blocks.
	// Uncompressed block will be written to table file if its compression ratio is
	// this value.
	//
	// The default value is 8.0/7.0, which means that uncompressed block will be written
	// to table file unless at least 1/8 of raw data were compressed out.
	BlockCompressionRatio float64

	// WriteBufferSize is the amount of data to build up in memory (backed by
	// an unsorted log on disk) before converting to a sorted on-disk file.
	//
	// Larger values increase performance, especially during bulk loads. Up to two
	// write buffers may be held in memory at the same time, so you may wish to
	// adjust this parameter to control memory usage. Also, a larger write buffer
	// will result in a longer recovery time the next time the database is opened.
	//
	// The default value is 4MiB.
	WriteBufferSize int

	// MaxOpenFiles is the number of open files that can be used this db instance.
	// You may need to increase this if your database has a large number of files.
	//
	// The default value is 1000.
	MaxOpenFiles int

	// BlockCacheCapacity specifies the capacity in bytes for block cache.
	//
	// The default value is 8MiB.
	BlockCacheCapacity int

	// CompactionConcurrency specifies max allowed concurrent compactions.
	//
	// The default value is 1, use MaxCompactionConcurrency to maximize compaction
	// concurrency as poosible.
	CompactionConcurrency int

	// CompactionBytesPerSeek states that one seek cost approximately equal time
	// to compact specified number of data.
	//
	// We decide to compact a file after a certain number of overlap seeks, this
	// way for keys in range we reduce potential seeks by one after compaction.
	// We use CompactionBytesPerSeek and MinimalAllowedOverlapSeeks to calculate
	// the number of allowed overlap seeks for a file.
	//
	// The default value is 16KiB, which means that one seek cost approximately
	// equal time to compact 16KiB data.
	CompactionBytesPerSeek int

	// MinimalAllowedOverlapSeeks specifies minimal allowed overlap seeks per table file.
	//
	// The default value is 100.
	MinimalAllowedOverlapSeeks int

	// IterationBytesPerSampleSeek specifies average iteration bytes for one sample
	// seek to detect overlap file.
	//
	// The default value is 1MiB.
	IterationBytesPerSampleSeek int

	// Level0CompactionFiles specifies that a compaction for level-0 is triggered if
	// there are more than this number of files in level-0.
	//
	// The default value is 4.
	Level0CompactionFiles int

	// Level0SlowdownWriteFiles specifies that writes will be slowdown if there are
	// more than this number of files in level-0.
	//
	// The default value is Level0CompactionFiles + 4.
	Level0SlowdownWriteFiles int

	// Level0StopWriteFiles specifies that writes will be stopped if there are more
	// than this number of files in level-0.
	//
	// The default value is Level0SlowdownWriteFiles + 4.
	Level0StopWriteFiles int

	// Filter specifies a Filter to filter out unnecessary disk reads when looking for
	// a specific key. The filter is also used to generate filter data when building
	// table files.
	//
	// The default value is nil.
	Filter Filter

	// Logger specifies a place that all internal progress/error information generated
	// by this db instance will be written to.
	//
	// The default value is a file named "LOG" stored under this db directory. You can
	// suppress logging by using DiscardLogger.
	Logger Logger

	// FileSystem defines a hierarchical file storage interface.
	//
	// The default file system is built around os package.
	FileSystem FileSystem

	// CreateIfMissing specifies whether to create one if the database does not exist.
	//
	// The default value is false.
	CreateIfMissing bool

	// ErrorIfExists specifies whether to report a error if the database already exists.
	//
	// The default value is false.
	ErrorIfExists bool
}

type ReadOptions struct {
	// DontFillCache specifies whether data read in this operation
	// should be cached in memory. If true, data read from underlying
	// storage will not be cahced in memory for later reading, but
	// if the data is already cached in memory, it will be used by
	// this operation.
	DontFillCache bool

	// VerifyChecksums specifies whether data read from underlying
	// storage should be verified against saved checksums. Note that
	// it never verify data cached in memory.
	VerifyChecksums bool
}

type Reader interface {
	Get(key []byte, opts *ReadOptions) ([]byte, error)

	All(opts *ReadOptions) Iterator

	Find(start []byte, opts *ReadOptions) Iterator

	Range(start, limit []byte, opts *ReadOptions) Iterator

	Prefix(prefix []byte, opts *ReadOptions) Iterator

	Snapshot() *Snapshot
}

type Snapshot struct {
	// contains filtered or unexported fields
}

type WriteOptions struct {
	// Sync specifies whether to synchronize the write from OS cache to
	// underlying storage before the write is considered complete.
	// Setting Sync to true may result in slower writes.
	//
	// If Sync is false, and the machine crashes, some recent writes may
	// be lost. Note that if it is just the process crashes, no writes will
	// be lost.
	//
	// In other words, a write with false Sync has similar crash semantics
	// as the "write()" system call. A write with true Sync has similar crash
	// semantics to a "write()" system call followed by "fsync()".
	Sync bool
}