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/**
 * Capable of converting T to/from a String that can be persisted in the varchar column of a database. 
 * E.g. a date would be stored as yyyy-mm-dd and an image might be stored as a uri pointing to a 
 * PACS system. Also capable of validating T, e.g. so we can use a plain java.util.Date to represent 
 * "date-in-past" but limit its possible values.
 * Defines a String "datatypeHandled", e.g. "date", "regex-validated-string")
 */
interface CustomDatatypeHandler<T> {
  T fromPersistedString(String);
  String toPersistedString(T);
  void validate(T);
  String render(String persistedValue, String view);
  // can be configured with setHandlerConfiguration(String);
}

/**
 * holds the definition of a custom datatype (which is handled by a handler of the above interface). 
 * For example VisitAttributeType and Setting (formerly global properties 1.8 and GlobalPropertybelow) (we're able to do typed GPs trivially now)
 */
interface CustomDatatyped {
  String getDatatype(); // required
  /**
   * if specified, will be handled by this specific CustomDatatypeHandler, otherwise it will be handled 
   * by the default handler for this thing's datatype
   */
  String getPreferredHandlerClassname(); // optional
  String getHandlerConfig(); // optional
}

/**
 * for user-defined extensions to core domain objects, which would be handled by adding custom 
 * database columns in a less generic system. E.g. VisitAttributeType implements AttributeType<Visit>
 * datatype/handler specified via CustomDatatyped superinterface
 */
interface AttributeType<OwningType extends Customizable> extends CustomDatatyped, OpenmrsMetadata {
  Integer getMinOccurs();
  Integer getMaxOccurs();
}

/**
 * trivial implementations of AttributeType (via BaseAttributeType)
 */
class VisitAttributeType
class LocationAttributeType
class ProviderAttributeType

/**
 * Implemented by domain classes that may be customized by the user via custom attributes. 
 * E.g. Visit implements Customizable<VisitAttribute>, Location implements Customizable<LocationAttribute>
 * Has convenience methods for dealing with a collection of attributes, of different types:
 */
interface Customizable<AttrClass extends Attribute> {
  Collection<AttrClass> getAttributes();  //includes voided
  Collection<AttrClass> getActiveAttributes();  //non-voided
  void addAttribute(AttrClass);
  void setAttribute(AttrClass);  // voids other attributes of the given type
}

/**
* holds a value managed by a CustomDatatypeHandler. E.g. VisitAttribute, GlobalProperty Setting (formerly global properties 1.8 and below). 
* Any implementation of this has a corresponding CustomDatatyped implementation. "persistedValue"
* is a String suitable for persisting in a db varchar column; "objectValue" is what you'd want 
* to work with in the API.
*/
interface CustomValue {
  String getPersistedValue();
  void setPersistedValue();
  Object getObjectValue();  // don't remember why this isn't <T>
  void setObjectValue(Object);
}

/**
* value corresponding to an AttributeType (which defines its datatype, whether it's 
* required, whether it can repeat, etc), e.g. VisitAttribute corresponds to VisitAttributeType
*/
interface Attribute<OwningType extends Customizable> implements CustomValue, OpenmrsData {
  OwningType getOwner();
  void setOwner(OwningType);
  AttributeType<OwningType> getAttributeType();
}

/**
* trivial implementation of Attribute (via BaseAttribute)
*/
class VisitAttribute
class LocationAttribute
class ProviderAttribute

/**
* this is interesting in that it both defines a custom datatype and stores its value
*/
class GlobalPropertySetting (formerly global properties 1.8 and below) implements CustomDatatyped, CustomValue