package gs.config.v0

/** Defines some piece of configuration.
  *
  * See:
  *
  *   - [[ConfigKey.Required]]
  *   - [[ConfigKey.WithDefaultValue]]
  *
  * @tparam A
  *   The type of data referenced by this key. This type must be
  *   [[Configurable]].
  */
sealed trait ConfigKey[A: Configurable]:
  def name: ConfigName

object ConfigKey:

  /** Defines a piece of configuration that is required and does not have any
    * default value. If the value referenced by the name cannot be found, an
    * [[ConfigError.MissingValue]] is returned.
    *
    * @param name
    *   The name of this configuration.
    */
  case class Required[A: Configurable](
    name: ConfigName
  ) extends ConfigKey[A]

  /** Defines a piece of configuration that has a default value. If the value
    * referenced by the name cannot be found, the default is used.
    *
    * @param name
    *   The name of this piece of configuration.
    * @param defaultValue
    *   The default value for this configuration.
    */
  case class WithDefaultValue[A: Configurable](
    name: ConfigName,
    defaultValue: () => A
  ) extends ConfigKey[A]