storage

type Backupable interface {
	// BackupTo backs up the entire state of the underlying store
	// as one or more files into the given `path`.
	// Note that it is upto the implementation to interpret the
	// provided path as a file or a folder.
	BackupTo(path string) error
	// RestoreFrom restores the entire state of the underlying store
	// from one or more files belonging to the given `path`. Typically
	// these files must have been generated by a previous invocation
	// of the `BackupTo` method using this `path` by the same
	// implementation of this interface.
	// Note that it is upto the implementation to interpret the
	// provided path as a file or a folder.
	// Returns the various traits of the newly restored store upon
	// successful restoration, else an error
	RestoreFrom(path string) (KVStore, Backupable, ChangePropagator, ChangeApplier, error)
}

type ChangeApplier interface {
	// GetLatestAppliedChangeNumber retrieves the change number of
	// the latest committed change applied. Returns an error if unable
	// to load this number.
	GetLatestAppliedChangeNumber() (uint64, error)
	// SaveChanges commits to local key space the given changes and
	// returns the change number of the last committed change along
	// with an error that might have occurred during the process.
	// Note that implementors must treat every change on its own and
	// return the first error that occurs during the process. Remaining
	// changes if any must NOT be applied in order to ensure sequential
	// consistency.
	SaveChanges(changes []*serverpb.ChangeRecord) (uint64, error)
}

type ChangePropagator interface {
	// GetLatestCommittedChangeNumber retrieves the change number of
	// the latest committed change. Returns an error if unable to
	// load this number.
	GetLatestCommittedChangeNumber() (uint64, error)
	// LoadChanges retrieves all the changes committed since the given
	// `fromChangeNumber`. Also, `maxChanges` can be used to limit the
	// number of changes returned in the response.
	LoadChanges(fromChangeNumber uint64, maxChanges int) ([]*serverpb.ChangeRecord, error)
}

type Iteration interface {
	ForEach(func(*serverpb.KVPair) error) error
}

type IterationOption func(*iterOpts)

type IterationOptions interface {
	KeyPrefix() ([]byte, bool)
	StartKey() ([]byte, bool)
}

type Iterator interface {
	io.Closer
	HasNext() bool
	Next() *serverpb.KVPair
	Err() error
}

type KVStore interface {
	io.Closer
	// Put stores the association between the given key and value and
	// optionally sets the expireTS of the key to the provided epoch in seconds
	Put(pairs ...*serverpb.KVPair) error
	// Get bulk fetches the associated values for the given keys.
	// Note that during partial failures, any successful results
	// are discarded and an error is returned instead.
	Get(keys ...[]byte) ([]*serverpb.KVPair, error)
	// Delete deletes the given key.
	Delete(key []byte) error
	// GetSnapshot retrieves the entire keyspace representation
	// with latest value against every key.
	GetSnapshot() (io.ReadCloser, error)
	// PutSnapshot ingests the given keyspace representation wholly
	// into the current state. Any existing state will be discarded
	// or replaced with the given state.
	PutSnapshot(io.ReadCloser) error
	// Iterate iterates through the entire keyspace in no particular
	// order. IterationOptions can be used to control where to begin
	// iteration as well as what keys are iterated by their prefix.
	Iterate(IterationOptions) Iterator
	// CompareAndSet compares the current value of the given key with
	// that of the given value. In case of a match, it updates that
	// key with the new value and returns true. Else, it returns false.
	// All this is done atomically from the caller's point of view and
	// hence is safe from a concurrency perspective.
	// If the expected value is `nil`, then the key is created and
	// initialized with the given value, atomically.
	CompareAndSet(request *serverpb.CompareAndSetRequest) (bool, error)
}

type Stat struct {
	RequestLatency        *prometheus.SummaryVec
	ResponseError         *prometheus.CounterVec
	StoreMetricsCollector prometheus.Collector
}