Add dispute system

backend/app/models/dispute.py

@@ -0,0 +1,66 @@
+from datetime import datetime
+from enum import Enum
+from sqlalchemy import String, Text, DateTime, ForeignKey, Boolean, UniqueConstraint
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from app.core.database import Base
+
+
+class DisputeStatus(str, Enum):
+    OPEN = "open"
+    RESOLVED_VALID = "valid"
+    RESOLVED_INVALID = "invalid"
+
+
+class Dispute(Base):
+    """Dispute against a completed assignment's proof"""
+    __tablename__ = "disputes"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    assignment_id: Mapped[int] = mapped_column(ForeignKey("assignments.id", ondelete="CASCADE"), unique=True, index=True)
+    raised_by_id: Mapped[int] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"))
+    reason: Mapped[str] = mapped_column(Text, nullable=False)
+    status: Mapped[str] = mapped_column(String(20), default=DisputeStatus.OPEN.value)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+    resolved_at: Mapped[datetime | None] = mapped_column(DateTime, nullable=True)
+
+    # Relationships
+    assignment: Mapped["Assignment"] = relationship("Assignment", back_populates="dispute")
+    raised_by: Mapped["User"] = relationship("User", foreign_keys=[raised_by_id])
+    comments: Mapped[list["DisputeComment"]] = relationship("DisputeComment", back_populates="dispute", cascade="all, delete-orphan")
+    votes: Mapped[list["DisputeVote"]] = relationship("DisputeVote", back_populates="dispute", cascade="all, delete-orphan")
+
+
+class DisputeComment(Base):
+    """Comment in a dispute discussion"""
+    __tablename__ = "dispute_comments"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    dispute_id: Mapped[int] = mapped_column(ForeignKey("disputes.id", ondelete="CASCADE"), index=True)
+    user_id: Mapped[int] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"))
+    text: Mapped[str] = mapped_column(Text, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+
+    # Relationships
+    dispute: Mapped["Dispute"] = relationship("Dispute", back_populates="comments")
+    user: Mapped["User"] = relationship("User")
+
+
+class DisputeVote(Base):
+    """Vote in a dispute (valid or invalid)"""
+    __tablename__ = "dispute_votes"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    dispute_id: Mapped[int] = mapped_column(ForeignKey("disputes.id", ondelete="CASCADE"), index=True)
+    user_id: Mapped[int] = mapped_column(ForeignKey("users.id", ondelete="CASCADE"))
+    vote: Mapped[bool] = mapped_column(Boolean, nullable=False)  # True = valid, False = invalid
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow)
+
+    # Unique constraint: one vote per user per dispute
+    __table_args__ = (
+        UniqueConstraint("dispute_id", "user_id", name="uq_dispute_vote_user"),
+    )
+
+    # Relationships
+    dispute: Mapped["Dispute"] = relationship("Dispute", back_populates="votes")
+    user: Mapped["User"] = relationship("User")