DROP FUNCTION IF EXISTS public.get_query_partitioning_of_an_existing_table_by_date_unix_time(text, text, integer, integer, text);

CREATE OR REPLACE FUNCTION public.get_query_partitioning_of_an_existing_table_by_date_unix_time(
	old_tablename text,
	new_tablename text,
	start_year integer,
	end_year integer,
	step text)
    RETURNS character varying
    LANGUAGE 'plpgsql'
    
    VOLATILE PARALLEL UNSAFE
AS $BODY$
DECLARE partition_tablename  TEXT;
		start_interval    	 TEXT;
	    end_interval         TEXT;
		i					 INTEGER;
		sql_str				 TEXT;
		start_unix_time    	 TEXT;
	    end_unix_time        TEXT;
	
BEGIN

	IF start_year > end_year THEN
		RAISE NOTICE '%', 'start_year > end_year';
		RETURN '';
	END IF;

	
	WHILE  start_year <= end_year  LOOP				-- loop through years
	
		-- set the initial month
		CASE  step 
			 WHEN 'monthly' THEN  i:= 1;
			 WHEN 'quaterly' THEN  i:= 3;
			 WHEN 'half-yearly' THEN  i:= 6;
			 WHEN 'yearly' THEN  i:= 12;
			 ELSE 
			 	RAISE NOTICE '%', 'Invalid step parameter. Valid values are : monthly, quaterly, half-yearly, yearly';
				EXIT;
		END CASE;	 
		
		
		WHILE i <= 12 LOOP							-- loop through month
		
			partition_tablename := '';
			
			CASE  step 
			 WHEN 'monthly' THEN 
			
					partition_tablename := old_tablename || '_' || lpad(i::text, 2, '0') || '_' || start_year::text;
					start_interval = start_year::text || '-' || lpad(i::text, 2, '0') || '-01';
					end_interval   = (date_trunc('month', start_interval::date)  + interval '1 months')::date;
					i := i + 1;
					
					start_unix_time = extract(epoch from (start_interval)::timestamp);
					end_unix_time = extract(epoch from (end_interval::date - Interval'1 sec')::timestamp);
					
					
			 WHEN 'quaterly' THEN

				IF (i % 3 = 0) THEN
					partition_tablename := old_tablename || '_Q' || i/3 || '_' || start_year::text;
					start_interval = start_year::text ||  '-' ||	case i/3
																when 1 then '01-01'
																when 2 then '04-01'
																when 3 then '07-01'
																when 4 then '10-01'
															end; 

					end_interval = (date_trunc('quarter', start_interval::date)  + interval '3 months')::date;
					i := i + 3;
					
					start_unix_time = extract(epoch from (start_interval)::timestamp);
					end_unix_time = extract(epoch from (end_interval::date - Interval'1 sec')::timestamp);
				END IF;
				
			
			WHEN 'half-yearly' THEN
				
				IF (i % 6 = 0) THEN
					partition_tablename := old_tablename || '_S' || i/6 || '_' ||  start_year::text;
					start_interval = start_year::text || case i/6  when 1 then '-01-01' else '-07-01' end ;
					end_interval =  (start_interval::date  + interval '6 months')::date;
					
					i := i + 6;
					
					start_unix_time = extract(epoch from (start_interval)::timestamp);
					end_unix_time = extract(epoch from (end_interval::date - Interval'1 sec')::timestamp);
				END IF;
				
			WHEN 'yearly' THEN
				
				IF (i % 12 = 0) THEN
					partition_tablename := old_tablename || '_' || start_year::text;
					start_interval =  start_year::text || '-01-01';
					end_interval = (date_trunc('year', start_interval::date)  + interval '1 year')::date;
					
					i := i + 12;
					
					start_unix_time = extract(epoch from (start_interval)::timestamp);
					end_unix_time = extract(epoch from (end_interval::date - Interval'1 sec')::timestamp);
				END IF;
			ELSE
				RAISE NOTICE '%', 'Invalid step parameter. Valid values are : monthly, quaterly, half-yearly, yearly';
				EXIT;
			END CASE;
			
			
			
			IF ( partition_tablename <> '') THEN
			 sql_str := COALESCE(sql_str, '') || CHR(13) || 'CREATE TABLE ' || partition_tablename || ' PARTITION OF ' || new_tablename || 
	 							   				' FOR VALUES FROM (' || start_unix_time || ') TO (' || end_unix_time || ');'; 
			END IF;
			
		END LOOP; 

		start_year := start_year + 1;
    	sql_str := COALESCE(sql_str, '') || CHR(13);
							
		
	END LOOP;

	--RAISE NOTICE '%', sql_str;

	RETURN  COALESCE(sql_str, '');

END;
$BODY$;