CREATE FUNCTION undo_partition_time(p_parent_table text, p_batch_count int DEFAULT 1, p_batch_interval interval DEFAULT NULL, p_keep_table boolean DEFAULT true, p_lock_wait numeric DEFAULT 0, OUT partitions_undone int, OUT rows_undone bigint) RETURNS record
    LANGUAGE plpgsql SECURITY DEFINER
    AS $$
DECLARE

ex_context              text;
ex_detail               text;
ex_hint                 text;
ex_message              text;
v_adv_lock              boolean;
v_batch_loop_count      int := 0;
v_child_loop_total      bigint := 0;
v_child_min             timestamptz;
v_child_table           text;
v_control               text;
v_control_type          text;
v_epoch                 text;
v_function_name         text;
v_inner_loop_count      int;
v_lock_iter             int := 1;
v_lock_obtained         boolean := FALSE;
v_job_id                bigint;
v_jobmon                boolean;
v_jobmon_schema         text;
v_new_search_path       text := '@extschema@,pg_temp';
v_old_search_path       text;
v_parent_schema         text;
v_parent_tablename      text;
v_partition_expression  text;
v_partition_int_text    text;
v_partition_interval    interval;
v_row                   record;
v_rowcount              bigint;
v_step_id               bigint;
v_sub_count             int;
v_total                 bigint := 0;
v_trig_name             text;
v_type                  text;
v_undo_count            int := 0;

BEGIN
/*
 * Function to undo time-based partitioning created by this extension
 */

v_adv_lock := pg_try_advisory_xact_lock(hashtext('pg_partman undo_partition_time'));
IF v_adv_lock = 'false' THEN
    RAISE NOTICE 'undo_partition_time already running.';
    partitions_undone = -1;
    RETURN;
END IF;

SELECT partition_type
    , partition_interval
    , control
    , jobmon
    , epoch
INTO v_type
    , v_partition_int_text
    , v_control
    , v_jobmon
    , v_epoch
FROM @extschema@.part_config 
WHERE parent_table = p_parent_table 
AND partition_type IN ('partman', 'time-custom');

IF v_control IS NULL THEN
    RAISE EXCEPTION 'No non-native configuration found for pg_partman for given parent table: %', p_parent_table;
END IF;

SELECT schemaname, tablename 
INTO v_parent_schema, v_parent_tablename 
FROM pg_catalog.pg_tables 
WHERE schemaname = split_part(p_parent_table, '.', 1)::name
AND tablename = split_part(p_parent_table, '.', 2)::name;

SELECT general_type INTO v_control_type FROM @extschema@.check_control_type(v_parent_schema, v_parent_tablename, v_control);
IF v_control_type <> 'time' THEN 
    IF (v_control_type = 'id' AND v_epoch = 'none') OR v_control_type <> 'id' THEN
        RAISE EXCEPTION 'Cannot run on partition set without time based control column or epoch flag set with an id column. Found control: %, epoch: %', v_control_type, v_epoch;
    END IF;
END IF;

v_partition_interval := v_partition_int_text::interval;

SELECT current_setting('search_path') INTO v_old_search_path;
IF v_jobmon THEN
    SELECT nspname INTO v_jobmon_schema FROM pg_catalog.pg_namespace n, pg_catalog.pg_extension e WHERE e.extname = 'pg_jobmon'::name AND e.extnamespace = n.oid;
    IF v_jobmon_schema IS NOT NULL THEN
        v_new_search_path := '@extschema@,'||v_jobmon_schema||',pg_temp';
    END IF;
END IF;
EXECUTE format('SELECT set_config(%L, %L, %L)', 'search_path', v_new_search_path, 'false');

-- Check if any child tables are themselves partitioned or part of an inheritance tree. Prevent undo at this level if so.
-- Need to either lock child tables at all levels or handle the proper removal of triggers on all child tables first 
--  before multi-level undo can be performed safely.
FOR v_row IN 
    SELECT partition_schemaname, partition_tablename FROM @extschema@.show_partitions(p_parent_table)
LOOP
    SELECT count(*) INTO v_sub_count
    FROM pg_catalog.pg_inherits i
    JOIN pg_catalog.pg_class c ON i.inhparent = c.oid
    JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
    WHERE c.relname = v_row.partition_tablename::name
    AND n.nspname = v_row.partition_schemaname::name;
    IF v_sub_count > 0 THEN
        RAISE EXCEPTION 'Child table for this parent has child table(s) itself (%). Run undo partitioning on this table or remove inheritance first to ensure all data is properly moved to parent', v_row.partition_schemaname||'.'||v_row.partition_tablename;
    END IF;
END LOOP;

IF v_jobmon_schema IS NOT NULL THEN
    v_job_id := add_job(format('PARTMAN UNDO PARTITIONING: %s', p_parent_table));
    v_step_id := add_step(v_job_id, format('Undoing partitioning for table %s', p_parent_table));
END IF;

IF p_batch_interval IS NULL THEN
    p_batch_interval := v_partition_interval;
END IF;

v_partition_expression := CASE
    WHEN v_epoch = 'seconds' THEN format('to_timestamp(%I)', v_control)
    WHEN v_epoch = 'milliseconds' THEN format('to_timestamp((%I/1000)::float)', v_control)
    ELSE format('%I', v_control)
end;

-- Stops new time partitons from being made as well as stopping child tables from being dropped if they were configured with a retention period.
UPDATE @extschema@.part_config SET undo_in_progress = true WHERE parent_table = p_parent_table;
-- Stop data going into child tables.
v_trig_name := @extschema@.check_name_length(p_object_name := v_parent_tablename, p_suffix := '_part_trig'); 
v_function_name := @extschema@.check_name_length(v_parent_tablename, '_part_trig_func', FALSE);

SELECT tgname INTO v_trig_name 
FROM pg_catalog.pg_trigger t
JOIN pg_catalog.pg_class c ON t.tgrelid = c.oid
WHERE tgname = v_trig_name::name 
AND c.relname = v_parent_tablename::name;

SELECT proname INTO v_function_name FROM pg_catalog.pg_proc p JOIN pg_catalog.pg_namespace n ON p.pronamespace = n.oid WHERE n.nspname = v_parent_schema::name AND proname = v_function_name::name;

IF v_trig_name IS NOT NULL THEN
    -- lockwait for trigger drop
    IF p_lock_wait > 0  THEN
        v_lock_iter := 0;
        WHILE v_lock_iter <= 5 LOOP
            v_lock_iter := v_lock_iter + 1;
            BEGIN
                EXECUTE format('LOCK TABLE ONLY %I.%I IN ACCESS EXCLUSIVE MODE NOWAIT', v_parent_schema, v_parent_tablename);
                v_lock_obtained := TRUE;
            EXCEPTION
                WHEN lock_not_available THEN
                    PERFORM pg_sleep( p_lock_wait / 5.0 );
                    CONTINUE;
            END;
            EXIT WHEN v_lock_obtained;
        END LOOP;
        IF NOT v_lock_obtained THEN
            RAISE NOTICE 'Unable to obtain lock on parent table to remove trigger';
            partitions_undone = -1;
            RETURN;
        END IF;
    END IF; -- END p_lock_wait IF
    EXECUTE format('DROP TRIGGER IF EXISTS %I ON %I.%I', v_trig_name, v_parent_schema, v_parent_tablename);
END IF; -- END trigger IF
v_lock_obtained := FALSE; -- reset for reuse later

IF v_function_name IS NOT NULL THEN
    EXECUTE format('DROP FUNCTION IF EXISTS %I.%I()', v_parent_schema, v_function_name);
END IF;

IF v_jobmon_schema IS NOT NULL THEN
    IF (v_trig_name IS NOT NULL OR v_function_name IS NOT NULL) THEN
        PERFORM update_step(v_step_id, 'OK', 'Stopped partition creation process. Removed trigger & trigger function');
    ELSE
        PERFORM update_step(v_step_id, 'OK', 'Stopped partition creation process.');
    END IF;
END IF;

<<outer_child_loop>>
LOOP
    -- Get ordered list of child table in set. Store in variable one at a time per loop until none are left or batch count is reached.
    -- This easily allows it to loop over same child table until empty or move onto next child table after it's dropped
    SELECT partition_tablename INTO v_child_table FROM @extschema@.show_partitions(p_parent_table, 'ASC') LIMIT 1;

    EXIT outer_child_loop WHEN v_child_table IS NULL;

    IF v_jobmon_schema IS NOT NULL THEN
        v_step_id := add_step(v_job_id, format('Removing child partition: %s.%s', v_parent_schema, v_child_table));
    END IF;

    EXECUTE format('SELECT min(%s) FROM %I.%I', v_partition_expression, v_parent_schema, v_child_table) INTO v_child_min;
    IF v_child_min IS NULL THEN
        -- No rows left in this child table. Remove from partition set.

        -- lockwait timeout for table drop
        IF p_lock_wait > 0  THEN
            v_lock_iter := 0;
            WHILE v_lock_iter <= 5 LOOP
                v_lock_iter := v_lock_iter + 1;
                BEGIN
                    EXECUTE format('LOCK TABLE ONLY %I.%I IN ACCESS EXCLUSIVE MODE NOWAIT', v_parent_schema, v_child_table);
                    v_lock_obtained := TRUE;
                EXCEPTION
                    WHEN lock_not_available THEN
                        PERFORM pg_sleep( p_lock_wait / 5.0 );
                        CONTINUE;
                END;
                EXIT WHEN v_lock_obtained;
            END LOOP;
            IF NOT v_lock_obtained THEN
                RAISE NOTICE 'Unable to obtain lock on child table for removal from partition set';
                partitions_undone = -1;
                RETURN;
            END IF;
        END IF; -- END p_lock_wait IF
        v_lock_obtained := FALSE; -- reset for reuse later

        EXECUTE format('ALTER TABLE %I.%I NO INHERIT %I.%I'
                        , v_parent_schema
                        , v_child_table
                        , v_parent_schema
                        , v_parent_tablename);
        IF p_keep_table = false THEN
            EXECUTE format('DROP TABLE %I.%I', v_parent_schema, v_child_table);
            IF v_jobmon_schema IS NOT NULL THEN
                PERFORM update_step(v_step_id, 'OK', format('Child table DROPPED. Moved %s rows to parent', v_child_loop_total));
            END IF;
        ELSE
            IF v_jobmon_schema IS NOT NULL THEN
                PERFORM update_step(v_step_id, 'OK', format('Child table UNINHERITED, not DROPPED. Moved %s rows to parent', v_child_loop_total));
            END IF;
        END IF;
        IF v_type = 'time-custom' THEN
            DELETE FROM @extschema@.custom_time_partitions WHERE parent_table = p_parent_table AND child_table = v_parent_schema||'.'||v_child_table;
        END IF;
        v_undo_count := v_undo_count + 1;
        EXIT outer_child_loop WHEN v_batch_loop_count >= p_batch_count; -- Exit outer FOR loop if p_batch_count is reached
        CONTINUE outer_child_loop; -- skip data moving steps below
    END IF;
    v_inner_loop_count := 1;
    v_child_loop_total := 0;
    <<inner_child_loop>>
    LOOP
        -- do some locking with timeout, if required
        IF p_lock_wait > 0  THEN
            v_lock_iter := 0;
            WHILE v_lock_iter <= 5 LOOP
                v_lock_iter := v_lock_iter + 1;
                BEGIN
                    EXECUTE format('SELECT * FROM %I.%I WHERE %I <= %L FOR UPDATE NOWAIT'
                        , v_parent_schema
                        , v_child_table
                        , v_control
                        , v_child_min + (p_batch_interval * v_inner_loop_count));
                   v_lock_obtained := TRUE;
                EXCEPTION
                    WHEN lock_not_available THEN
                        PERFORM pg_sleep( p_lock_wait / 5.0 );
                        CONTINUE;
                END;
                EXIT WHEN v_lock_obtained;
            END LOOP;
            IF NOT v_lock_obtained THEN
                RAISE NOTICE 'Unable to obtain lock on batch of rows to move';
                partitions_undone = -1;
                RETURN;
            END IF;
        END IF;

        -- Get everything from the current child minimum up to the multiples of the given interval
        EXECUTE format('WITH move_data AS (
                                DELETE FROM %I.%I WHERE %s <= %L RETURNING *)
                              INSERT INTO %I.%I SELECT * FROM move_data'
            , v_parent_schema
            , v_child_table
            , v_partition_expression
            , v_child_min + (p_batch_interval * v_inner_loop_count)
            , v_parent_schema
            , v_parent_tablename);
        GET DIAGNOSTICS v_rowcount = ROW_COUNT;
        v_total := v_total + v_rowcount;
        v_child_loop_total := v_child_loop_total + v_rowcount;
        IF v_jobmon_schema IS NOT NULL THEN
            PERFORM update_step(v_step_id, 'OK', format('Moved %s rows to parent.', v_child_loop_total));
        END IF;
        EXIT inner_child_loop WHEN v_rowcount = 0; -- exit before loop incr if table is empty
        v_inner_loop_count := v_inner_loop_count + 1;
        v_batch_loop_count := v_batch_loop_count + 1;

        -- Check again if table is empty and go to outer loop again to drop it if so
        EXECUTE format('SELECT min(%s) FROM %I.%I', v_partition_expression, v_parent_schema, v_child_table) INTO v_child_min;
        CONTINUE outer_child_loop WHEN v_child_min IS NULL;

        EXIT outer_child_loop WHEN v_batch_loop_count >= p_batch_count; -- Exit outer FOR loop if p_batch_count is reached
    END LOOP inner_child_loop;
END LOOP outer_child_loop;

SELECT partition_tablename INTO v_child_table FROM @extschema@.show_partitions(p_parent_table, 'ASC') LIMIT 1;
IF v_child_table IS NULL THEN
    DELETE FROM @extschema@.part_config WHERE parent_table = p_parent_table;
    DELETE FROM @extschema@.part_config_sub WHERE sub_parent = p_parent_table;
    IF v_jobmon_schema IS NOT NULL THEN
        v_step_id := add_step(v_job_id, 'Removing config from pg_partman');
        PERFORM update_step(v_step_id, 'OK', 'Done');
    END IF;
END IF;

RAISE NOTICE 'Copied % row(s) to the parent. Removed % partitions.', v_total, v_undo_count;
IF v_jobmon_schema IS NOT NULL THEN
    v_step_id := add_step(v_job_id, 'Final stats');
    PERFORM update_step(v_step_id, 'OK', format('Copied %s row(s) to the parent. Removed %s partitions.', v_total, v_undo_count));
END IF;

IF v_jobmon_schema IS NOT NULL THEN
    PERFORM close_job(v_job_id);
END IF;

EXECUTE format('SELECT set_config(%L, %L, %L)', 'search_path', v_old_search_path, 'false');

partitions_undone := v_undo_count;
rows_undone := v_total;

EXCEPTION
    WHEN OTHERS THEN
        GET STACKED DIAGNOSTICS ex_message = MESSAGE_TEXT,
                                ex_context = PG_EXCEPTION_CONTEXT,
                                ex_detail = PG_EXCEPTION_DETAIL,
                                ex_hint = PG_EXCEPTION_HINT;
        IF v_jobmon_schema IS NOT NULL THEN
            IF v_job_id IS NULL THEN
                EXECUTE format('SELECT %I.add_job(''PARTMAN UNDO PARTITIONING: %s'')', v_jobmon_schema, p_parent_table) INTO v_job_id;
                EXECUTE format('SELECT %I.add_step(%s, ''EXCEPTION before job logging started'')', v_jobmon_schema, v_job_id, p_parent_table) INTO v_step_id;
            ELSIF v_step_id IS NULL THEN
                EXECUTE format('SELECT %I.add_step(%s, ''EXCEPTION before first step logged'')', v_jobmon_schema, v_job_id) INTO v_step_id;
            END IF;
            EXECUTE format('SELECT %I.update_step(%s, ''CRITICAL'', %L)', v_jobmon_schema, v_step_id, 'ERROR: '||coalesce(SQLERRM,'unknown'));
            EXECUTE format('SELECT %I.fail_job(%s)', v_jobmon_schema, v_job_id);
        END IF;
        RAISE EXCEPTION '%
CONTEXT: %
DETAIL: %
HINT: %', ex_message, ex_context, ex_detail, ex_hint;
END
$$;