major refactoring adding vendor and customer features

models/database/inventory.py

@@ -0,0 +1,41 @@
+# models/database/inventory.py
+from datetime import datetime
+from sqlalchemy import Column, ForeignKey, Index, Integer, String, UniqueConstraint
+from sqlalchemy.orm import relationship
+
+from app.core.database import Base
+from models.database.base import TimestampMixin
+
+
+class Inventory(Base, TimestampMixin):
+    __tablename__ = "inventory"
+
+    id = Column(Integer, primary_key=True, index=True)
+    product_id = Column(Integer, ForeignKey("products.id"), nullable=False, index=True)
+    vendor_id = Column(Integer, ForeignKey("vendors.id"), nullable=False, index=True)
+
+    location = Column(String, nullable=False, index=True)
+    quantity = Column(Integer, nullable=False, default=0)
+    reserved_quantity = Column(Integer, default=0)
+
+    # Optional: Keep GTIN for reference/reporting
+    gtin = Column(String, index=True)
+
+    # Relationships
+    product = relationship("Product", back_populates="inventory_entries")
+    vendor = relationship("Vendor")
+
+    # Constraints
+    __table_args__ = (
+        UniqueConstraint("product_id", "location", name="uq_inventory_product_location"),
+        Index("idx_inventory_vendor_product", "vendor_id", "product_id"),
+        Index("idx_inventory_product_location", "product_id", "location"),
+    )
+
+    def __repr__(self):
+        return f"<Inventory(product_id={self.product_id}, location='{self.location}', quantity={self.quantity})>"
+
+    @property
+    def available_quantity(self):
+        """Calculate available quantity (total - reserved)."""
+        return max(0, self.quantity - self.reserved_quantity)