"""media_assets.media_kind (E7 S5a: the video|audio|file discriminator for the media library)

Adds a stored media-kind to each asset so the library can gate its actions on it (play/edit for
media, download-only for a generic uploaded file) instead of re-deriving from codecs in prose. The
column is the single home of the invariant `downloads.mediakind.derive` computes at finalize.

Backfill for existing rows: a stored video codec -> 'video', an audio-only codec -> 'audio', an
editor derivative (source_kind='edit', which carries no codecs but is always a video clip) ->
'video'. Rows still pending/errored (no codecs, not an edit) stay NULL — kind is set when they
finalize. Empty `media_kind` never reaches the UI: only `ready`/`done` rows render actions, and
those are all backfilled here.
"""

from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op

revision: str = "0076_media_asset_kind"
down_revision: Union[str, None] = "0075_playlist_sync_baseline"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column("media_assets", sa.Column("media_kind", sa.String(length=16), nullable=True))
    op.execute(
        """
        UPDATE media_assets
           SET media_kind = CASE
               WHEN vcodec IS NOT NULL THEN 'video'
               WHEN acodec IS NOT NULL THEN 'audio'
               WHEN source_kind = 'edit' THEN 'video'
               ELSE NULL
           END
        """
    )


def downgrade() -> None:
    op.drop_column("media_assets", "media_kind")