"""The reusable section-field library (字段表).

A *section field* is one heading a paper can contain — "1. Introduction",
"2.1 Dataset", "0 Abstract". Fields live in this one global library and are
never owned by a template.

Why there is no ``parent_id``
-----------------------------
A tree would make a field usable under exactly one parent, so a level-2 heading
such as "Background" could not sit under both "1. Introduction" and
"2. Related Work". Hierarchy is therefore expressed only by
:attr:`SectionField.level` (1, 2, 3 ...), which is a *rendering hint* — it
drives indentation and numbering semantics in the UI — while a field stays
free to be attached to any number of templates and any number of parents
within them.

The number that the reader sees is part of :attr:`name` and is written by the
user ("1. Introduction", "0 Abstract"). Nothing derives or rewrites it.

Ordering inside a template is *not* stored here: it lives in
``template_field.sort``. This table has no ``sort`` column on purpose, so that
one library field can occupy a different position in every template.
"""

from decimal import Decimal

from sqlalchemy import Integer, Numeric, String, text
from sqlalchemy.orm import Mapped, mapped_column

from app.db.base import Base
from app.models.mixins import TimestampMixin


class SectionField(TimestampMixin, Base):
    """A single reusable heading, with the typography it should render in."""

    __tablename__ = "section_field"

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

    #: Display name, numbering included. Stored and rendered verbatim.
    name: Mapped[str] = mapped_column(String(255), nullable=False)

    #: Heading depth: 1 for "1.", 2 for "1.1", 3 for "1.1.1". Rendering hint
    #: only — it does not link fields to each other.
    level: Mapped[int] = mapped_column(
        Integer,
        nullable=False,
        default=1,
        server_default=text("1"),
    )

    #: Font size in points. ``Numeric`` rather than ``Integer`` because the
    #: conventional Chinese sizes are fractional (五号 = 10.5pt,
    #: 小四 = 12pt).
    font_size: Mapped[Decimal] = mapped_column(
        Numeric(4, 1),
        nullable=False,
        default=Decimal("12.0"),
        server_default=text("12.0"),
    )

    #: Font colour as ``#RRGGBB`` — the canonical RGB encoding. The API
    #: normalises ``rgb(20, 30, 40)``, ``#abc`` and bare ``aabbcc`` to it on
    #: write, so the column always holds one comparable format.
    font_color: Mapped[str] = mapped_column(
        String(7),
        nullable=False,
        default="#000000",
        server_default=text("'#000000'"),
    )

    def __repr__(self) -> str:  # pragma: no cover - debugging aid
        return (
            f"<SectionField id={self.id} name={self.name!r} "
            f"level={self.level} color={self.font_color}>"
        )