"""phase19 — add mobile_photo_paths column to issues table

Background
----------
Issues created on the iPad can have multiple evidence photos.  The first photo
is stored in `photo_path` (existing single-string column).  Additional photos
were previously stored in `result_photos` (intended for resolution photos),
causing them to appear under "Resolution Details" on the web instead of
"Photo Evidence".

This migration adds `mobile_photo_paths JSON NULL` to store the extra
evidence photos from the iPad separately from resolution photos.

Safe to re-run — uses INFORMATION_SCHEMA existence check.
"""

import sqlalchemy as sa
from alembic import op

revision      = 'phase19_issue_mobile_photos'
down_revision = 'phase18_issue_reported_by'
branch_labels = None
depends_on    = None


def _column_exists(bind, table, column):
    result = bind.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS "
        "WHERE TABLE_SCHEMA = DATABASE() "
        "AND TABLE_NAME = :t AND COLUMN_NAME = :c"
    ), {"t": table, "c": column})
    return result.scalar() > 0


def upgrade():
    bind = op.get_bind()
    if not _column_exists(bind, 'issues', 'mobile_photo_paths'):
        op.add_column('issues', sa.Column(
            'mobile_photo_paths', sa.JSON(), nullable=True
        ))


def downgrade():
    bind = op.get_bind()
    if _column_exists(bind, 'issues', 'mobile_photo_paths'):
        op.execute(sa.text("ALTER TABLE issues DROP COLUMN mobile_photo_paths"))