// Adapter is the interface for configuration retrieving.
type Adapter interface {
// Available checks and returns the configuration service is available.
// The optional parameter `resource` specifies certain configuration resource.
//
// It returns true if configuration file is present in default AdapterFile, or else false.
// Note that this function does not return error as it just does simply check for backend configuration service.
Available(ctx context.Context, resource ...string) (ok bool)
// Get retrieves and returns value by specified `pattern`.
Get(ctx context.Context, pattern string) (value interface{}, err error)
// Data retrieves and returns all configuration data as map type.
// Note that this function may lead lots of memory usage if configuration data is too large,
// you can implement this function if necessary.
Data(ctx context.Context) (data map[string]interface{}, err error)
}