-- Return an array of table names scanned by a given query
--
-- Requires PostgreSQL 9.x+
--
CREATE OR REPLACE FUNCTION CDB_QueryTablesText(query text)
RETURNS text[]
AS $$
DECLARE
  exp XML;
  tables text[];
  rec RECORD;
  rec2 RECORD;
BEGIN
  
  tables := '{}';

  FOR rec IN SELECT CDB_QueryStatements(query) q LOOP

    IF NOT ( rec.q ilike 'select%' or rec.q ilike 'with%' ) THEN
        --RAISE WARNING 'Skipping %', rec.q;
        CONTINUE;
    END IF;

    BEGIN
      EXECUTE 'EXPLAIN (FORMAT XML, VERBOSE) ' || rec.q INTO STRICT exp;
    EXCEPTION WHEN others THEN
      -- TODO: if error is 'relation "xxxxxx" does not exist', take xxxxxx as
      --       the affected table ?
      RAISE WARNING 'CDB_QueryTables cannot explain query: % (%: %)', rec.q, SQLSTATE, SQLERRM;
      RAISE EXCEPTION '%', SQLERRM;
      CONTINUE;
    END;

    -- Now need to extract all values of <Relation-Name>

    -- RAISE DEBUG 'Explain: %', exp;

    FOR rec2 IN WITH
      inp AS (
        SELECT
          xpath('//x:Relation-Name/text()', exp, ARRAY[ARRAY['x', 'http://www.postgresql.org/2009/explain']]) as x,
          xpath('//x:Relation-Name/../x:Schema/text()', exp, ARRAY[ARRAY['x', 'http://www.postgresql.org/2009/explain']]) as s
      )
      SELECT unnest(x)::text as p, unnest(s)::text as sc from inp
    LOOP
      -- RAISE DEBUG 'tab: %', rec2.p;
      -- RAISE DEBUG 'sc: %', rec2.sc;
      tables := array_append(tables, format('%s.%s', quote_ident(rec2.sc), quote_ident(rec2.p)));
    END LOOP;

    -- RAISE DEBUG 'Tables: %', tables;

  END LOOP;

  -- RAISE DEBUG 'Tables: %', tables;

  -- Remove duplicates and sort by name
  IF array_upper(tables, 1) > 0 THEN
    WITH dist as ( SELECT DISTINCT unnest(tables)::text as p ORDER BY p )
       SELECT array_agg(p) from dist into tables;
  END IF;

  --RAISE DEBUG 'Tables: %', tables;

  return tables;
END
$$ LANGUAGE 'plpgsql' VOLATILE STRICT;


-- Keep CDB_QueryTables with same signature for backwards compatibility.
-- It should probably be removed in the future.
CREATE OR REPLACE FUNCTION CDB_QueryTables(query text)
RETURNS name[]
AS $$
BEGIN
  RETURN CDB_QueryTablesText(query)::name[];
END
$$ LANGUAGE 'plpgsql' VOLATILE STRICT;

--------------------------------------------------------------------------------

-- Return a set of (dbname, schema_name, table_name, updated_at)
-- This assumes the local (schema_name, table_name) maps to the remote one with the same name
CREATE OR REPLACE FUNCTION CDB_QueryTables_Updated_At(query text)
RETURNS TABLE(db_name text, schema_name text, table_name text, updated_at timestamptz)
AS $$
    WITH query_tables AS (
      SELECT unnest(CDB_QueryTablesText(query)) schema_table_name
    ), query_tables_oid AS (
      SELECT schema_table_name, schema_table_name::regclass::oid AS reloid
      FROM query_tables
    ),
    fqtn AS (
      SELECT
        (CASE WHEN c.relkind = 'f' THEN _cdb_dbname_of_foreign_table(query_tables_oid.reloid)
              ELSE current_database()
         END)::text AS dbname,
         n.nspname::text schema_name,
         c.relname::text table_name,
         c.relkind,
         query_tables_oid.reloid
      FROM query_tables_oid, pg_catalog.pg_class c
      LEFT JOIN pg_catalog.pg_namespace n ON c.relnamespace = n.oid
      WHERE c.oid = query_tables_oid.reloid
    )
    SELECT fqtn.dbname, fqtn.schema_name, fqtn.table_name,
      (CASE WHEN relkind = 'f' THEN CDB_Get_Foreign_Updated_At(reloid)
            ELSE (SELECT md.updated_at FROM CDB_TableMetadata md WHERE md.tabname = reloid)
      END) AS updated_at
    FROM fqtn;
$$ LANGUAGE SQL;


CREATE OR REPLACE FUNCTION _cdb_dbname_of_foreign_table(reloid oid)
RETURNS TEXT AS $$
    SELECT option_value FROM pg_options_to_table((

        SELECT fs.srvoptions
        FROM pg_foreign_table ft
        LEFT JOIN pg_foreign_server fs ON ft.ftserver = fs.oid
        WHERE ft.ftrelid = reloid

    )) WHERE option_name='dbname';
$$ LANGUAGE SQL;


-- TODO: move to the right place
-- Return the last updated time of a set of tables
CREATE OR REPLACE FUNCTION CDB_Last_Updated_Time(tables text[])
RETURNS timestamptz AS $$
    WITH t AS (
        SELECT unnest(tables) AS schema_table_name
    ), t_oid AS (
        SELECT (t.schema_table_name)::regclass::oid as reloid FROM t
    ), t_updated_at AS (
        SELECT
            (CASE WHEN relkind = 'f' THEN CDB_Get_Foreign_Updated_At(reloid)
                  ELSE (SELECT md.updated_at FROM CDB_TableMetadata md WHERE md.tabname = reloid)
             END) AS updated_at
        FROM t_oid
        LEFT JOIN pg_catalog.pg_class c ON c.oid = reloid
    ) SELECT max(updated_at) FROM t_updated_at;
$$ LANGUAGE SQL;