import uuid
from datetime import datetime, timezone

from sqlalchemy import DateTime, ForeignKey, Index, Text
from sqlalchemy.orm import Mapped, mapped_column

from app.db import Base

# The wire cap. Enforced in three places on purpose: the Pydantic schema
# (rejects with a clear 422/400 before touching the DB), the route's own
# check (so a body built any other way still can't slip through), and the
# column type below — Text, because Postgres VARCHAR(n) truncation/erroring
# is a worse failure mode than a validated length, and a future cap change
# then needs no migration.
BODY_MAX_CHARS = 1000


class Message(Base):
    """One plain-text message from one hunter to another.

    Deliberately minimal (hunters-and-messages spec, Workstream S): no
    attachments, no editing, no groups, no threads-as-rows — a "thread" is
    simply every row between two user ids, ordered by time.

    `read_at` is null until the *recipient* opens the thread; the sender
    never marks anything read, so this doubles as the unread signal.
    """

    __tablename__ = "messages"
    # Both directions are queried: the conversation list and thread view each
    # need "sent by me" OR'd with "sent to me", and the unread aggregate
    # scans (recipient_id, read_at). The composite indexes below serve those
    # ordered scans; the per-column indexes on the FKs come from
    # index=True and keep single-sided lookups cheap.
    __table_args__ = (
        Index("ix_messages_sender_recipient_created", "sender_id", "recipient_id", "created_at"),
        Index("ix_messages_recipient_sender_created", "recipient_id", "sender_id", "created_at"),
    )

    id: Mapped[uuid.UUID] = mapped_column(primary_key=True, default=uuid.uuid4)
    sender_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), index=True)
    recipient_id: Mapped[uuid.UUID] = mapped_column(ForeignKey("users.id"), index=True)
    body: Mapped[str] = mapped_column(Text)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), default=lambda: datetime.now(timezone.utc), index=True
    )
    read_at: Mapped[datetime | None] = mapped_column(
        DateTime(timezone=True), nullable=True, default=None
    )