"""phase22 — add is_customer_visible to issue_comments

Staff comments default to hidden from customers (is_customer_visible=FALSE).
Staff can tick a checkbox to share a comment with the customer.
Customer comments are always visible (is_customer_visible=TRUE, set at write time).
"""

import sqlalchemy as sa
from alembic import op

revision      = 'phase22_comment_visibility'
down_revision = 'phase21_performance_indexes'
branch_labels = None
depends_on    = None


def _column_exists(bind, table: str, column: str) -> bool:
    result = bind.execute(sa.text(
        "SELECT COUNT(*) FROM information_schema.columns "
        "WHERE table_schema = DATABASE() "
        "  AND table_name   = :table "
        "  AND column_name  = :column"
    ), {'table': table, 'column': column})
    return result.scalar() > 0


def upgrade():
    bind = op.get_bind()
    if not _column_exists(bind, 'issue_comments', 'is_customer_visible'):
        op.execute(sa.text(
            'ALTER TABLE issue_comments '
            'ADD COLUMN is_customer_visible BOOLEAN NOT NULL DEFAULT FALSE'
        ))


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