tusd/pkg/handler/composer.mgo

package handler

#define USE_FUNC(TYPE) \
func (store *StoreComposer) Use ## TYPE(ext TYPE ## DataStore) { \
  store.Uses ## TYPE = ext != nil; \
  store.TYPE = ext; \
}

#define USE_FIELD(TYPE) Uses ## TYPE bool; \
  TYPE TYPE ## DataStore

#define USE_FROM(TYPE) if mod, ok := store.(TYPE ## DataStore); ok { \
  composer.Use ## TYPE (mod) \
}

#define USE_CAP(TYPE) str += ` TYPE: `; \
if store.Uses ## TYPE { \
  str += "✓" \
} else { \
  str += "✗" \
}

// StoreComposer represents a composable data store. It consists of the core
// data store and optional extensions. Please consult the package's overview
// for a more detailed introduction in how to use this structure.
type StoreComposer struct {
  Core DataStore

  USE_FIELD(Terminater)
  USE_FIELD(Finisher)
  USE_FIELD(Locker)
  USE_FIELD(GetReader)
  USE_FIELD(Concater)
  USE_FIELD(LengthDeferrer)
}

// NewStoreComposer creates a new and empty store composer.
func NewStoreComposer() *StoreComposer {
  return &StoreComposer{}
}

// newStoreComposerFromDataStore creates a new store composer and attempts to
// extract the extensions for the provided store. This is intended to be used
// for transitioning from data stores to composers.
func newStoreComposerFromDataStore(store DataStore) *StoreComposer {
  composer := NewStoreComposer()
  composer.UseCore(store)

  USE_FROM(Terminater)
  USE_FROM(Finisher)
  USE_FROM(Locker)
  USE_FROM(GetReader)
  USE_FROM(Concater)
  USE_FROM(LengthDeferrer)

  return composer
}

// Capabilities returns a string representing the provided extensions in a
// human-readable format meant for debugging.
func (store *StoreComposer) Capabilities() string {
  str := "Core: "

  if store.Core != nil {
    str += "✓"
  } else {
    str += "✗"
  }

  USE_CAP(Terminater)
  USE_CAP(Finisher)
  USE_CAP(Locker)
  USE_CAP(GetReader)
  USE_CAP(Concater)
  USE_CAP(LengthDeferrer)

  return str
}

// UseCore will set the used core data store. If the argument is nil, the
// property will be unset.
func (store *StoreComposer) UseCore(core DataStore) {
  store.Core = core
}

USE_FUNC(Terminater)
USE_FUNC(Finisher)
USE_FUNC(Locker)
USE_FUNC(GetReader)
USE_FUNC(Concater)
USE_FUNC(LengthDeferrer)