synchronizator-go/pkg/node.go

package synchronizator

// A user representation of a node, this interface should be implemented by the user
// to provide the ability to parse the database node into a user defined
// struct that fulfills it's requirements.
//
// Example usage:
//
//	type Library struct {
//		Name     string                 `json:"name"`
//		Category string                 `json:"category"`
//		Metadata map[string]interface{} `json:"metadata"`
//	}
//
//	func (library *Library) ToNode() (string, string, []byte, error) {
//		metadata, err := json.Marshal(library.Metadata)
//		if err != nil {
//			return "", "", nil, err
//		}
//		return "LIBRARY", library.Name, metadata, nil
//	}
//
//	func (library *Library) FromNode(_class string, name string, metadata []byte) error {
//		if _class != "LIBRARY" {
//			return fmt.Errorf("invalid class %s", _class)
//		}
//		if err := json.Unmarshal(metadata, &library.Metadata); err != nil {
//			return err
//		}
//		library.Name = name
//		return nil
//	}
type NodeClass interface {
	// How to transform the struct into a node. It needs to return the class,
	// name and a []byte representation of the metadata.
	//
	// - class: Is used for classification and query pourposes. It's recomended to provide a constante string to increase consistency.
	// - name: A user friendly name
	// - metadata: Arbitrary data. This will be stored as a jsonb in the database
	//
	ToNode() (string, string, []byte, error)

	// How to transform a node into the struct. This method should modify the
	// struct directly as it receives a pointer.
	//
	// - class: Is used for classification and query pourposes.
	// - name: A user friendly name
	// - metadata: Arbitrary data. This is stored as a jsonb in the database
	FromNode(string, string, []byte) error
}

// A node in the database.
// It adds some helper methods to easily manage the node.
type Node struct {
	_conn          *DB             // Underlaying connection to the database.
	_class         string          // The class of the node, should not be modified to avoid inconsistencies.
	_relationships []*Relationship // Relationships of the node
	Id             int64           // The id of the node
	name           string          // The name of the node
	metadata       []byte          // Arbitrary data. This is stored as a jsonb in the database
}

// Creates a new relation of type RelationshipClass to the node with the
// provided id. An error is returned if the relation already exists.
//
// This method is a wrapper around the AddRelation method of the connection.
func (node *Node) AddRelation(relation RelationshipClass, to int64) (*Relationship, error) {
	return node._conn.AddRelation(node.Id, relation, to)
}

// Update a relation with the node of the provided id.
//
// This method is a wrapper around the UpdateRelation method of the connection.
func (node *Node) UpdateRelation(metadata any, to int64) error {
	return node._conn.UpdateRelation(node.Id, metadata, to)
}

// Delete a relation with the node of the provided id.
//
// This method is a wrapper around the DeleteRelation method of the connection.
func (node *Node) DeleteRelation(to int64) error {
	return node._conn.DeleteRelation(node.Id, to)
}

// Fetch all the outgoing relations for this node. This method will return a
// slice of relationships pointers and also store them in the node for further
// use.
func (node *Node) GetOutRelations() ([]*Relationship, error) {
	sql := `
WITH RECURSIVE NodeRelationships AS (
  SELECT
    *,
    relationships._class AS relationship_class,
    relationships.metadata AS relationship_metadata
  FROM
    nodes as src
    JOIN relationships ON src.id = relationships.node_from
		WHERE src.id = $1
)
SELECT
  NodeRelationships.id as src_node,
  NodeRelationships.relationship_class,
  NodeRelationships.relationship_metadata,
  dst.id as dst_id
FROM
  NodeRelationships
  JOIN nodes as dst ON dst.id = NodeRelationships.node_to
	`

	rows, err := node._conn.Query(sql, node.Id)
	if err != nil {
		return nil, err
	}

	defer rows.Close()

	node._relationships = make([]*Relationship, 0)
	for rows.Next() {
		relationship := &Relationship{
			_conn: node._conn,
		}

		if err := rows.Scan(&relationship.From, &relationship._class, &relationship.Metadata, &relationship.To); err != nil {
			return nil, err
		}

		node._relationships = append(node._relationships, relationship)
	}

	return node._relationships, nil
}

// Deletes this node from the database.
// This method is a wrapper around the DeleteNode method of the connection.
func (node *Node) Delete() error {
	return node._conn.DeleteNode(node.Id)
}

// Allows to retreive the saved information back into the user struct. This
// method will call the [NodeClass.FromNode] of the provided struct.
//
// Example:
//
//	data := &Library{}
//	if err := node.Unmarshall(data); err != nil {
//		println(err)
//	}
func (node *Node) Unmarshall(dst NodeClass) error {
	return dst.FromNode(node._class, node.name, node.metadata)
}