/*
 * Function to drop child tables from a time-based partition set.
 * Options to move table to different schema, drop only indexes or actually drop the table from the database.
 */
CREATE FUNCTION drop_partition_time(p_parent_table text, p_retention interval DEFAULT NULL, p_keep_table boolean DEFAULT NULL, p_keep_index boolean DEFAULT NULL, p_retention_schema text DEFAULT NULL) RETURNS int
    LANGUAGE plpgsql SECURITY DEFINER
    AS $$
DECLARE

ex_context                  text;
ex_detail                   text;
ex_hint                     text;
ex_message                  text;
v_adv_lock                  boolean;
v_child_table               text;
v_datetime_string           text;
v_drop_count                int := 0;
v_index                     record;
v_job_id                    bigint;
v_jobmon                    boolean;
v_jobmon_schema             text;
v_old_search_path           text;
v_partition_interval             interval;
v_partition_timestamp       timestamp;
v_quarter                   text;
v_retention                 interval;
v_retention_keep_index      boolean;
v_retention_keep_table      boolean;
v_retention_schema          text;
v_step_id                   bigint;
v_time_position             int;
v_type                      text;
v_year                      text;

BEGIN

v_adv_lock := pg_try_advisory_xact_lock(hashtext('pg_partman drop_partition_time'));
IF v_adv_lock = 'false' THEN
    RAISE NOTICE 'drop_partition_time already running.';
    RETURN 0;
END IF;

-- Allow override of configuration options
IF p_retention IS NULL THEN
    SELECT  
        partition_type
        , partition_interval::interval
        , retention::interval
        , retention_keep_table
        , retention_keep_index
        , datetime_string
        , retention_schema
        , jobmon
    INTO
        v_type
        , v_partition_interval
        , v_retention
        , v_retention_keep_table
        , v_retention_keep_index
        , v_datetime_string
        , v_retention_schema
        , v_jobmon
    FROM @extschema@.part_config 
    WHERE parent_table = p_parent_table 
    AND (partition_type = 'time' OR partition_type = 'time-custom')
    AND retention IS NOT NULL;

    IF v_partition_interval IS NULL THEN
        RAISE EXCEPTION 'Configuration for given parent table with a retention period not found: %', p_parent_table;
    END IF;
ELSE
    SELECT  
        partition_type
        , partition_interval::interval
        , retention_keep_table
        , retention_keep_index
        , datetime_string
        , retention_schema
        , jobmon
    INTO
        v_type
        , v_partition_interval
        , v_retention_keep_table
        , v_retention_keep_index
        , v_datetime_string
        , v_retention_schema
        , v_jobmon
    FROM @extschema@.part_config 
    WHERE parent_table = p_parent_table 
    AND (partition_type = 'time' OR partition_type = 'time-custom'); 
    v_retention := p_retention;

    IF v_partition_interval IS NULL THEN
        RAISE EXCEPTION 'Configuration for given parent table not found: %', p_parent_table;
    END IF;
END IF;

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

IF p_keep_table IS NOT NULL THEN
    v_retention_keep_table = p_keep_table;
END IF;
IF p_keep_index IS NOT NULL THEN
    v_retention_keep_index = p_keep_index;
END IF;
IF p_retention_schema IS NOT NULL THEN
    v_retention_schema = p_retention_schema;
END IF;

-- Loop through child tables of the given parent
FOR v_child_table IN 
    SELECT n.nspname||'.'||c.relname FROM pg_inherits i join pg_class c ON i.inhrelid = c.oid join pg_namespace n ON c.relnamespace = n.oid WHERE i.inhparent::regclass = p_parent_table::regclass ORDER BY i.inhrelid ASC
LOOP
    -- pull out datetime portion of partition's tablename to make the next one
    v_time_position := (length(v_child_table) - position('p_' in reverse(v_child_table))) + 2;
    IF v_partition_interval <> '3 months' OR (v_partition_interval = '3 months' AND v_type = 'time-custom') THEN
        v_partition_timestamp := to_timestamp(substring(v_child_table from v_time_position), v_datetime_string);
    ELSE
        -- to_timestamp doesn't recognize 'Q' date string formater. Handle it
        v_year := split_part(substring(v_child_table from v_time_position), 'q', 1);
        v_quarter := split_part(substring(v_child_table from v_time_position), 'q', 2);
        CASE
            WHEN v_quarter = '1' THEN
                v_partition_timestamp := to_timestamp(v_year || '-01-01', 'YYYY-MM-DD');
            WHEN v_quarter = '2' THEN
                v_partition_timestamp := to_timestamp(v_year || '-04-01', 'YYYY-MM-DD');
            WHEN v_quarter = '3' THEN
                v_partition_timestamp := to_timestamp(v_year || '-07-01', 'YYYY-MM-DD');
            WHEN v_quarter = '4' THEN
                v_partition_timestamp := to_timestamp(v_year || '-10-01', 'YYYY-MM-DD');
        END CASE;
    END IF;

    -- Add one interval since partition names contain the start of the constraint period
    IF v_retention < (CURRENT_TIMESTAMP - (v_partition_timestamp + v_partition_interval)) THEN
        -- Only create a jobmon entry if there's actual retention work done
        IF v_jobmon_schema IS NOT NULL AND v_job_id IS NULL THEN
            v_job_id := add_job('PARTMAN DROP TIME PARTITION: '|| p_parent_table);
        END IF;

        IF v_jobmon_schema IS NOT NULL THEN
            v_step_id := add_step(v_job_id, 'Uninherit table '||v_child_table||' from '||p_parent_table);
        END IF;
        EXECUTE 'ALTER TABLE '||v_child_table||' NO INHERIT ' || p_parent_table;
        IF v_type = 'time-custom' THEN
            DELETE FROM @extschema@.custom_time_partitions WHERE parent_table = p_parent_table AND child_table = v_child_table;
        END IF;
        IF v_jobmon_schema IS NOT NULL THEN
            PERFORM update_step(v_step_id, 'OK', 'Done');
        END IF;
        IF v_retention_schema IS NULL THEN
            IF v_retention_keep_table = false THEN
                IF v_jobmon_schema IS NOT NULL THEN
                    v_step_id := add_step(v_job_id, 'Drop table '||v_child_table);
                END IF;
                EXECUTE 'DROP TABLE '||v_child_table||' CASCADE';
                IF v_jobmon_schema IS NOT NULL THEN
                    PERFORM update_step(v_step_id, 'OK', 'Done');
                END IF;
            ELSIF v_retention_keep_index = false THEN
                FOR v_index IN 
                    SELECT i.indexrelid::regclass AS name
                    , c.conname
                    FROM pg_catalog.pg_index i
                    LEFT JOIN pg_catalog.pg_constraint c ON i.indexrelid = c.conindid 
                    WHERE i.indrelid = v_child_table::regclass
                LOOP
                    IF v_jobmon_schema IS NOT NULL THEN
                        v_step_id := add_step(v_job_id, 'Drop index '||v_index.name||' from '||v_child_table);
                    END IF;
                    IF v_index.conname IS NOT NULL THEN
                        EXECUTE 'ALTER TABLE '||v_child_table||' DROP CONSTRAINT '||v_index.conname;
                    ELSE
                        EXECUTE 'DROP INDEX '||v_index.name;
                    END IF;
                    IF v_jobmon_schema IS NOT NULL THEN
                        PERFORM update_step(v_step_id, 'OK', 'Done');
                    END IF;
                END LOOP;
            END IF;
        ELSE -- Move to new schema
            IF v_jobmon_schema IS NOT NULL THEN
                v_step_id := add_step(v_job_id, 'Moving table '||v_child_table||' to schema '||v_retention_schema);
            END IF;

            EXECUTE 'ALTER TABLE '||v_child_table||' SET SCHEMA '||v_retention_schema; 

            IF v_jobmon_schema IS NOT NULL THEN
                PERFORM update_step(v_step_id, 'OK', 'Done');
            END IF;
        END IF; -- End retention schema if

        -- If child table is a subpartition, remove it from part_config & part_config_sub (should cascade due to FK)
        DELETE FROM @extschema@.part_config WHERE parent_table = v_child_table;

        v_drop_count := v_drop_count + 1;
    END IF; -- End retention check IF

END LOOP; -- End child table loop

IF v_jobmon_schema IS NOT NULL THEN
    IF v_job_id IS NOT NULL THEN
        v_step_id := add_step(v_job_id, 'Finished partition drop maintenance');
        PERFORM update_step(v_step_id, 'OK', v_drop_count||' partitions dropped.');
        PERFORM close_job(v_job_id);
    END IF;
    EXECUTE 'SELECT set_config(''search_path'','''||v_old_search_path||''',''false'')';
END IF;

RETURN v_drop_count;

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 DROP TIME PARTITION: %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
$$;