"""migrate sections to canonical_markdown

将旧章节（有 sections 但 canonical_markdown 为空）从 sections 推导并写入 canonical_markdown。
同时创建 chapter_version 记录（source_type=migration）。

Revision ID: 0004_migrate_md
Revises: 0003_story_first
Create Date: 2026-03-19

"""

from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op
from sqlalchemy.orm import Session, selectinload

revision: str = "0004_migrate_md"
down_revision: Union[str, Sequence[str], None] = "0003_story_first"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def _sections_to_markdown(chapter) -> str:
    """从 sections 推导 markdown，与 helpers.sections_to_content_and_images 一致。"""
    sections = getattr(chapter, "sections", None) or []
    ordered = sorted(sections, key=lambda s: getattr(s, "order_index", 0))
    parts = []
    for s in ordered:
        text = (getattr(s, "content", None) or "").strip()
        if text:
            parts.append(text)
        img = _section_image_to_dict(s)
        if img:
            placeholder = (img.get("placeholder") or "").strip()
            if placeholder:
                parts.append(placeholder)
    return "\n\n".join(parts) if parts else ""


def _section_image_to_dict(section) -> dict | None:
    """与 helpers.section_image_to_dict 一致。"""
    from app.features.memoir.memoir_images.serializers import memoir_image_to_dict

    if getattr(section, "image_record", None):
        return memoir_image_to_dict(section.image_record)
    return None


def upgrade() -> None:
    from app.features.memoir.models import Chapter, ChapterSection, ChapterVersion

    conn = op.get_bind()
    session = Session(bind=conn)

    chapters = (
        session.query(Chapter)
        .options(
            selectinload(Chapter.sections).selectinload(ChapterSection.image_record),
        )
        .filter(
            sa.or_(
                Chapter.canonical_markdown.is_(None),
                Chapter.canonical_markdown == "",
            ),
        )
        .all()
    )

    for ch in chapters:
        md = _sections_to_markdown(ch)
        if not md.strip():
            continue

        # 创建 chapter_version（source_type=migration）
        import uuid

        from sqlalchemy import func

        count_stmt = sa.select(func.count(ChapterVersion.id)).where(
            ChapterVersion.chapter_id == ch.id
        )
        version_no = (session.execute(count_stmt).scalar() or 0) + 1

        version = ChapterVersion(
            id=str(uuid.uuid4()),
            chapter_id=ch.id,
            version_no=version_no,
            markdown_snapshot=md,
            actor_type="system",
            source_type="migration",
        )
        session.add(version)
        session.flush()

        ch.canonical_markdown = md
        ch.current_version_id = version.id

    # 由 alembic context 管理事务提交
    session.close()


def downgrade() -> None:
    # 数据迁移不可逆，downgrade 不清理 canonical_markdown
    pass