"""Synthetic posts — FC authors a post for content that arrived as chat.

Milestone 388, step E2. Discord is a delivery channel, not a publisher: one
message is not one post, and today every message becomes its own `post` row
competing with authored work for the same surface. This adds the three columns
that let FC group a creator's variant drop into a post it wrote itself, while
keeping that fact visible and the grouping reversible.

## Why a flag and a back-pointer rather than a separate table

A synthetic post has to BE a post — same row, same columns — or every existing
surface (feed, provenance, translation, attachments, series) would need a
second code path for it. `synthesized_by` marks the ones FC authored;
`absorbed_by_post_id` points a member message-post at the post that replaced
it in the feed. The members are not deleted: they remain the images' true
origin, and destroying them would make the grouping un-auditable at exactly
the moment somebody wants to check it.

Reversal is one DELETE. `absorbed_by_post_id` is ON DELETE SET NULL, so
removing a synthetic post releases its members and they return to the feed
unaided.

Revision ID: 0092
Revises: 0091
Create Date: 2026-09-10

"""
from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op

revision: str = "0092"
down_revision: Union[str, None] = "0091"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    # No CHECK on synthesized_by (rule 36 considered and declined): there is one
    # grouper today and a second would be a new VALUE, not a new invariant —
    # matching source.error_type and service_seen.kind.
    op.add_column("post", sa.Column("synthesized_by", sa.String(length=32), nullable=True))
    op.add_column("post", sa.Column("synthesis_details", sa.JSON(), nullable=True))
    op.add_column(
        "post", sa.Column("absorbed_by_post_id", sa.Integer(), nullable=True),
    )
    op.create_index(
        op.f("ix_post_absorbed_by_post_id"), "post", ["absorbed_by_post_id"],
    )
    # SET NULL, not CASCADE: deleting the synthetic post must RELEASE its
    # members, never take them with it. The members are the real capture.
    op.create_foreign_key(
        "fk_post_absorbed_by_post_id_post", "post", "post",
        ["absorbed_by_post_id"], ["id"], ondelete="SET NULL",
    )

    # Grouping tunables. Every one of these is operator-facing (project rule
    # 25) because the quality bar here is a judgement call no test can settle:
    # too greedy merges distinct pieces, too shy leaves a drop scattered.
    op.add_column(
        "ml_settings",
        sa.Column(
            "discord_grouping_enabled", sa.Boolean(),
            server_default="true", nullable=False,
        ),
    )
    op.add_column(
        "ml_settings",
        sa.Column(
            "discord_group_max_distance", sa.Float(),
            server_default=sa.text("0.10"), nullable=False,
        ),
    )
    op.add_column(
        "ml_settings",
        sa.Column(
            "discord_group_window_minutes", sa.Float(),
            server_default=sa.text("60"), nullable=False,
        ),
    )


def downgrade() -> None:
    op.drop_column("ml_settings", "discord_group_window_minutes")
    op.drop_column("ml_settings", "discord_group_max_distance")
    op.drop_column("ml_settings", "discord_grouping_enabled")
    op.drop_constraint("fk_post_absorbed_by_post_id_post", "post", type_="foreignkey")
    op.drop_index(op.f("ix_post_absorbed_by_post_id"), table_name="post")
    op.drop_column("post", "absorbed_by_post_id")
    op.drop_column("post", "synthesis_details")
    op.drop_column("post", "synthesized_by")