"""phase31 — add ios_version and last_seen_at to api_device_tokens

Extends the existing api_device_tokens table (phase7) so the admin
Devices page can show iOS version and time of last app launch.
Drops the unused device_registrations table created by phase30 if it exists.
"""

from alembic import op

revision      = 'phase31_device_registry'
down_revision = 'phase30_device_registry'
branch_labels = None
depends_on    = None


def upgrade():
    # Add ios_version column if it doesn't exist
    op.execute("""
        ALTER TABLE api_device_tokens
        ADD COLUMN IF NOT EXISTS ios_version VARCHAR(20) NULL
    """)

    # Add last_seen_at column if it doesn't exist
    op.execute("""
        ALTER TABLE api_device_tokens
        ADD COLUMN IF NOT EXISTS last_seen_at DATETIME NULL
    """)

    # Backfill last_seen_at from registered_at for existing rows
    op.execute("""
        UPDATE api_device_tokens
        SET last_seen_at = registered_at
        WHERE last_seen_at IS NULL
    """)

    # Drop the incorrectly created device_registrations table from phase30 if present
    op.execute("DROP TABLE IF EXISTS device_registrations")


def downgrade():
    op.execute("ALTER TABLE api_device_tokens DROP COLUMN IF EXISTS ios_version")
    op.execute("ALTER TABLE api_device_tokens DROP COLUMN IF EXISTS last_seen_at")