import enum
from datetime import datetime

from sqlalchemy import DateTime, Enum, ForeignKey, String, Text, UniqueConstraint, func
from sqlalchemy.orm import Mapped, mapped_column, relationship

from app.core.database import Base


class FitLabel(enum.StrEnum):
    POSSIBLE = "possible"
    EXACT = "exact"
    NONE = "none"


class Fit(Base):
    """A candidate or confirmed fit between two attachment points on different parts."""

    __tablename__ = "fits"
    __table_args__ = (
        UniqueConstraint("attachment_point_a_id", "attachment_point_b_id"),
    )

    id: Mapped[int] = mapped_column(primary_key=True)

    # Canonical ordering (attachment_point_a_id < attachment_point_b_id) is enforced
    # by app.crud.fit so an unordered pair only ever has one row.
    attachment_point_a_id: Mapped[int] = mapped_column(
        ForeignKey("attachment_points.id", ondelete="CASCADE"), nullable=False
    )
    attachment_point_b_id: Mapped[int] = mapped_column(
        ForeignKey("attachment_points.id", ondelete="CASCADE"), nullable=False
    )

    # Denormalized from the attachment points' augmented_part_id, for querying
    # "fits for this part" without joining through attachment_points.
    augmented_part_a_id: Mapped[int] = mapped_column(
        ForeignKey("augmented_parts.id", ondelete="CASCADE"), nullable=False
    )
    augmented_part_b_id: Mapped[int] = mapped_column(
        ForeignKey("augmented_parts.id", ondelete="CASCADE"), nullable=False
    )

    label: Mapped[FitLabel] = mapped_column(
        Enum(FitLabel, values_callable=lambda enum_cls: [e.value for e in enum_cls]),
        nullable=False,
        default=FitLabel.POSSIBLE,
    )

    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), server_default=func.now()
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
    )

    attachment_point_a = relationship(
        "AttachmentPoint", foreign_keys=[attachment_point_a_id], lazy="selectin"
    )
    attachment_point_b = relationship(
        "AttachmentPoint", foreign_keys=[attachment_point_b_id], lazy="selectin"
    )
    notes: Mapped[list["FitNote"]] = relationship(
        back_populates="fit",
        lazy="selectin",
        order_by="FitNote.created_at",
        cascade="all, delete-orphan",
    )


class FitNote(Base):
    __tablename__ = "fit_notes"

    id: Mapped[int] = mapped_column(primary_key=True)
    fit_id: Mapped[int] = mapped_column(
        ForeignKey("fits.id", ondelete="CASCADE"), nullable=False
    )
    user_id: Mapped[int | None] = mapped_column(
        ForeignKey("users.id", ondelete="SET NULL"), nullable=True
    )
    # Denormalized snapshot of who wrote the note (mirrors AuditLog.user_email),
    # so the note stays attributable even if the user is later deleted.
    username: Mapped[str] = mapped_column(String(255), nullable=False)
    body: Mapped[str] = mapped_column(Text, nullable=False)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), server_default=func.now()
    )

    fit: Mapped[Fit] = relationship(back_populates="notes")