add database models and session factory

.pylintrc

@@ -0,0 +1,2 @@
+[FORMAT]
+max-line-length = 120

harvester/db/models.py

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+# harvester/db/models.py
+
+from sqlalchemy import Column, Integer, String, DateTime
+from sqlalchemy.ext.declarative import declarative_base
+
+Base = declarative_base()
+
+
+class Proxy(Base):
+    __tablename__ = 'proxies'
+
+    id = Column(Integer, primary_key=True)
+    host = Column(String, nullable=False)
+    port = Column(Integer, nullable=False)
+    asn = Column(String)
+    egress_ip = Column(String)
+    egress_asn = Column(String)
+    date_added = Column(DateTime, nullable=False)
+    date_validated = Column(DateTime)
+
+    def __repr__(self):
+        return (
+            f'Proxy(id={self.id}, host={self.host}, port={self.port}, '
+            f'egress={self.egress}, created_at={self.created_at})'
+        )

harvester/db/session.py

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+# harvester/db/session.py
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+
+class SessionFactory:
+    def __init__(self, engine_url):
+        self.engine = create_engine(engine_url)
+        self.Session = sessionmaker(bind=self.engine)
+
+    def create_session(self):
+        return self.Session()
+
+
+# Create a singleton instance of the SessionFactory
+session_factory = None
+
+
+def get_session_factory(engine_url):
+    global session_factory
+    if session_factory is None:
+        session_factory = SessionFactory(engine_url)
+    return session_factory
+
+
+def get_session(engine_url):
+    return get_session_factory(engine_url).create_session()

requirements.txt

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 requests
 requests[socks]
+sqlalchemy