"""Add mobile_local_id to inspections and issues for mobile sync idempotency.

Phase B — iPad offline inspection submission.

Each inspection or issue submitted from the iPad app carries a UUID generated
on the device (mobile_local_id).  The server checks this field before creating
a new record so that network retries never produce duplicate rows.

Revision ID:  phase_b_mobile_local_id
Revises:      phase12_performance_indexes
"""

from alembic import op
import sqlalchemy as sa

revision      = 'phase_b_mobile_local_id'
down_revision = 'phase12_performance_indexes'
branch_labels = None
depends_on    = None


def _column_exists(conn, table, column):
    result = conn.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 _index_exists(conn, table, index):
    result = conn.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.STATISTICS "
        "WHERE TABLE_SCHEMA = DATABASE() "
        "AND TABLE_NAME = :table AND INDEX_NAME = :index"
    ), {"table": table, "index": index})
    return result.scalar() > 0


def upgrade():
    conn = op.get_bind()

    # ── inspections.mobile_local_id ───────────────────────────────────────
    if not _column_exists(conn, 'inspections', 'mobile_local_id'):
        op.execute(sa.text(
            "ALTER TABLE inspections ADD COLUMN mobile_local_id VARCHAR(64) NULL"
        ))

    if not _index_exists(conn, 'inspections', 'idx_inspections_mobile_local_id'):
        op.execute(sa.text(
            "CREATE INDEX idx_inspections_mobile_local_id ON inspections(mobile_local_id)"
        ))

    # ── issues.mobile_local_id ────────────────────────────────────────────
    if not _column_exists(conn, 'issues', 'mobile_local_id'):
        op.execute(sa.text(
            "ALTER TABLE issues ADD COLUMN mobile_local_id VARCHAR(64) NULL"
        ))

    if not _index_exists(conn, 'issues', 'idx_issues_mobile_local_id'):
        op.execute(sa.text(
            "CREATE INDEX idx_issues_mobile_local_id ON issues(mobile_local_id)"
        ))


def downgrade():
    conn = op.get_bind()

    if _index_exists(conn, 'inspections', 'idx_inspections_mobile_local_id'):
        op.execute(sa.text("DROP INDEX idx_inspections_mobile_local_id ON inspections"))

    if _column_exists(conn, 'inspections', 'mobile_local_id'):
        op.execute(sa.text("ALTER TABLE inspections DROP COLUMN mobile_local_id"))

    if _index_exists(conn, 'issues', 'idx_issues_mobile_local_id'):
        op.execute(sa.text("DROP INDEX idx_issues_mobile_local_id ON issues"))

    if _column_exists(conn, 'issues', 'mobile_local_id'):
        op.execute(sa.text("ALTER TABLE issues DROP COLUMN mobile_local_id"))