"""
This file contains the database schema in SQLAlchemy format.
"""
from sqlalchemy import event
from sqlalchemy import Column, ForeignKey, Integer, String
from sqlalchemy.engine import Engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship as sqlalchemy_relationship

Base = declarative_base()


@event.listens_for(Engine, "connect")
def set_sqlite_pragma(dbapi_connection, connection_record):
    """
    Auto enable foreign keys for SQLite.
    """
    cursor = dbapi_connection.cursor()
    cursor.execute("PRAGMA foreign_keys=ON")
    cursor.close()


# TODO: Backref
class Association(Base):
    # Relationships are to be read "left RELATION right"
    __tablename__ = "association"
    id = Column(Integer, primary_key=True)
    left_id = Column(Integer, ForeignKey("papers.id", ondelete="CASCADE"))
    right_id = Column(Integer, ForeignKey("papers.id", ondelete="CASCADE"))
    relationship_id = Column(Integer,
                             ForeignKey("relationships.id",
                                        ondelete="CASCADE"))
    right_paper = sqlalchemy_relationship("Paper", foreign_keys=right_id)
    relationship = sqlalchemy_relationship("Relationship")


class Paper(Base):
    __tablename__ = "papers"
    id = Column(Integer, primary_key=True)
    doi = Column(String(), nullable=True, unique=True)
    arxiv_id = Column(String(25), nullable=True, unique=True)
    related = sqlalchemy_relationship("Association",
                                      foreign_keys="Association.left_id")

    def __repr__(self):
        return "<Paper(id='%d', doi='%s', arxiv_id='%s')>" % (
            self.id,
            self.doi,
            self.arxiv_id,
        )

    def json_api_repr(self):
        """
        Dict to dump for the JSON API.
        """
        return {
            "types": self.__tablename__,
            "id": self.id,
            "attributes": {
                "doi": self.doi,
                "arxiv_id": self.arxiv_id,
            },
            "links": {
                "self": "/papers/%d" % (self.id,)
            },
            "relationships": {
                # TODO
            }
        }


class Relationship(Base):
    __tablename__ = "relationships"
    id = Column(Integer, primary_key=True)
    name = Column(String(), unique=True)
    associations = sqlalchemy_relationship("Association",
                                           back_populates="relationship")