from fixtures.log_helper import log
from fixtures.neon_fixtures import NeonEnv, fork_at_current_lsn


#
# Test that the VM bit is cleared correctly at a HEAP_DELETE and
# HEAP_UPDATE record.
#
def test_vm_bit_clear(neon_simple_env: NeonEnv):
    env = neon_simple_env

    env.neon_cli.create_branch("test_vm_bit_clear", "empty")
    pg = env.postgres.create_start("test_vm_bit_clear")

    log.info("postgres is running on 'test_vm_bit_clear' branch")
    pg_conn = pg.connect()
    cur = pg_conn.cursor()

    # Install extension containing function needed for test
    cur.execute("CREATE EXTENSION neon_test_utils")

    # Create a test table and freeze it to set the VM bit.
    cur.execute("CREATE TABLE vmtest_delete (id integer PRIMARY KEY)")
    cur.execute("INSERT INTO vmtest_delete VALUES (1)")
    cur.execute("VACUUM FREEZE vmtest_delete")

    cur.execute("CREATE TABLE vmtest_update (id integer PRIMARY KEY)")
    cur.execute("INSERT INTO vmtest_update SELECT g FROM generate_series(1, 1000) g")
    cur.execute("VACUUM FREEZE vmtest_update")

    # DELETE and UPDATE the rows.
    cur.execute("DELETE FROM vmtest_delete WHERE id = 1")
    cur.execute("UPDATE vmtest_update SET id = 5000 WHERE id = 1")

    # Branch at this point, to test that later
    fork_at_current_lsn(env, pg, "test_vm_bit_clear_new", "test_vm_bit_clear")

    # Clear the buffer cache, to force the VM page to be re-fetched from
    # the page server
    cur.execute("SELECT clear_buffer_cache()")

    # Check that an index-only scan doesn't see the deleted row. If the
    # clearing of the VM bit was not replayed correctly, this would incorrectly
    # return deleted row.
    cur.execute(
        """
    set enable_seqscan=off;
    set enable_indexscan=on;
    set enable_bitmapscan=off;
    """
    )

    cur.execute("SELECT * FROM vmtest_delete WHERE id = 1")
    assert cur.fetchall() == []
    cur.execute("SELECT * FROM vmtest_update WHERE id = 1")
    assert cur.fetchall() == []

    cur.close()

    # Check the same thing on the branch that we created right after the DELETE
    #
    # As of this writing, the code in smgrwrite() creates a full-page image whenever
    # a dirty VM page is evicted. If the VM bit was not correctly cleared by the
    # earlier WAL record, the full-page image hides the problem. Starting a new
    # server at the right point-in-time avoids that full-page image.
    pg_new = env.postgres.create_start("test_vm_bit_clear_new")

    log.info("postgres is running on 'test_vm_bit_clear_new' branch")
    pg_new_conn = pg_new.connect()
    cur_new = pg_new_conn.cursor()

    cur_new.execute(
        """
    set enable_seqscan=off;
    set enable_indexscan=on;
    set enable_bitmapscan=off;
    """
    )

    cur_new.execute("SELECT * FROM vmtest_delete WHERE id = 1")
    assert cur_new.fetchall() == []
    cur_new.execute("SELECT * FROM vmtest_update WHERE id = 1")
    assert cur_new.fetchall() == []