from __future__ import annotations

from datetime import datetime
from typing import TYPE_CHECKING

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

from app.core.database import Base
from app.utils.ids import prefixed_id

if TYPE_CHECKING:
    from app.models.document import Document


class DocumentChunk(Base):
    __tablename__ = "document_chunks"
    __table_args__ = (
        UniqueConstraint("document_id", "chunk_index", name="uq_document_chunk_index"),
    )

    id: Mapped[str] = mapped_column(
        String(40),
        primary_key=True,
        default=lambda: prefixed_id("chunk"),
    )
    document_id: Mapped[str] = mapped_column(
        String(40),
        ForeignKey("documents.id", ondelete="CASCADE"),
        index=True,
        nullable=False,
    )
    chunk_index: Mapped[int] = mapped_column(Integer, nullable=False)
    chunk_text: Mapped[str] = mapped_column(Text, nullable=False)
    token_estimate: Mapped[int] = mapped_column(Integer, nullable=False)
    page_number: Mapped[int | None] = mapped_column(Integer, nullable=True)
    heading: Mapped[str | None] = mapped_column(String(255), nullable=True)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        server_default=func.now(),
        nullable=False,
    )
    embedding: Mapped[str | None] = mapped_column(Text, nullable=True)

    document: Mapped["Document"] = relationship("Document", back_populates="chunks")