Calculating bet profit using custom postgresql function

bet_profit.sql

CREATE OR REPLACE FUNCTION bet_profit(state character varying, stake float, odds float) RETURNS float AS $$
DECLARE
  result float := 0;
  half_stake float :=0;
BEGIN
  CASE state
    WHEN 'in_process' THEN
      result := 0;
    WHEN 'guessed' THEN
      result := (stake * odds);
    WHEN 'losed' THEN
      result := 0;
    WHEN 'half_losed' THEN
      result := (stake / 2.0);
    WHEN 'half_winnered' THEN
      half_stake := stake / 2.0;
      result := (half_stake * odds) + half_stake;
  END CASE;
  RETURN result - stake;
END;
$$ LANGUAGE plpgsql;

SELECT bet_profit(state, (details->'stake')::float, (details->'odds')::float) AS profit, id FROM bets LIMIT 1;