"""SeriesChapter — an ordered chapter/part within a series.

A series IS a Tag(kind='series'); a chapter groups ordered SeriesPages under it.
Reading order is (chapter.chapter_number, series_page.page_number): chapter_number
sets the order of chapters, page_number orders pages within a chapter.

chapter_number is an ordering key only (not unique) — reorder rewrites 1..N
wholesale, mirroring series_page.page_number, so a reorder can't transiently
collide on a unique index.

A chapter may be a placeholder (is_placeholder=True) — a reserved empty slot for
a section the operator doesn't have yet; it holds no pages and shows as a gap in
the reader. stated_page_start/end carry the page range parsed from the source
post (FC-6.2), used to flag missing-page gaps; both are nullable when unknown.

stated_part is the operator-facing "Part N" label (FC-6.4), separate from the
positional chapter_number: chapter_number is auto-managed ordering (rewritten
1..N on reorder/delete), while stated_part is the real installment number the
operator types — e.g. a series authored from a post that is Part 2 of a story.
Nullable when unset (the UI then falls back to showing chapter_number).
"""

from datetime import datetime

from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, Text, func
from sqlalchemy.orm import Mapped, mapped_column

from .base import Base


class SeriesChapter(Base):
    __tablename__ = "series_chapter"

    id: Mapped[int] = mapped_column(Integer, primary_key=True)
    series_tag_id: Mapped[int] = mapped_column(
        ForeignKey("tag.id", ondelete="CASCADE"), nullable=False, index=True
    )
    chapter_number: Mapped[int] = mapped_column(Integer, nullable=False)
    stated_part: Mapped[int | None] = mapped_column(Integer, nullable=True)
    title: Mapped[str | None] = mapped_column(Text, nullable=True)
    is_placeholder: Mapped[bool] = mapped_column(
        Boolean, nullable=False, server_default="false"
    )
    stated_page_start: Mapped[int | None] = mapped_column(Integer, nullable=True)
    stated_page_end: Mapped[int | None] = mapped_column(Integer, nullable=True)
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), nullable=False, server_default=func.now()
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True),
        nullable=False,
        server_default=func.now(),
        onupdate=func.now(),
    )