Função em FirebirdSQL para converter BLOB/RTF em Texto Puro

create or alter function STR_UNRTF (
    P_SOURCE_RTF blob sub_type text)
returns blob sub_type text
AS
declare variable tagstart integer;
declare variable tagfinish integer;
declare variable i integer;
declare variable tagfound blob sub_type text;
declare variable result_text blob sub_type text;
declare variable tag_open varchar(255)='';
declare variable tag_close varchar(255)='';
declare variable char_test varchar(255);
declare variable char_hex varchar(255);
declare variable char_hex_to_str varchar(255);
declare variable lquote varchar(1);
declare variable hexa_len integer=2;
BEGIN
  -- essa procedure/função retorna um texto (blob) sem a porção de tags rtf, ex:
  -- ret=STR_UNRTF(string_rtf);   // resultado: texto sem as tags rtf
  -- Util para tornar um texto RTF texto pesquisável.
  result_text='';
  lquote='''';
  p_source_rtf=trim(:p_source_rtf);
  tag_open='{';
  tag_close='}';

  -- porém o primeiro caractere se começar com {  ou o ultimo caracter terminar com }
  -- deverá ser removido
  char_test=left(:p_source_rtf,char_length(:tag_open));
  if (char_test=:tag_open) then
  begin
    p_source_rtf=substring(:p_source_rtf from 2 for char_length(:p_source_rtf));
    p_source_rtf=trim(:p_source_rtf);
  end
  char_test=right(:p_source_rtf,char_length(:tag_close));
  if (char_test=:tag_close) then
  begin
    p_source_rtf=substring(:p_source_rtf from 1 for char_length(:p_source_rtf)-char_length(:tag_close));
    p_source_rtf=trim(:p_source_rtf);
  end

  -- Remove tudo que estiver em {tag}
  tagstart = position (:tag_open, :p_source_rtf);
  while (:tagstart > 0) do
  begin
    tagfinish = position (:tag_close, :p_source_rtf, :tagstart);
    if (:tagfinish<:tagstart) then
      tagfinish=char_length(:p_source_rtf);
    tagfound = substring (:p_source_rtf from :tagstart for ((:tagfinish - :tagstart) + 1));
    p_source_rtf = replace (:p_source_rtf, :tagfound, '');
    tagstart = position (:tag_open, :p_source_rtf);
  end

  -- RTF tem \escape para caracteres especiais, ex: fabrica\'e7\'e3o = fabricação
  -- È preciso localizar todos os escapes e trocá-los pelas suas referencias Hexa->Ascii
  tag_open='\'||:lquote;
  tag_close=' ';
  tagstart = position (:tag_open, :p_source_rtf);
  char_hex='';
  hexa_len=2+(char_length(:tag_open));
  while (:tagstart > 0) do
  begin
    char_hex=substring(:p_source_rtf from :tagstart for :hexa_len);
    char_hex_to_str='0x'||substring(:char_hex from char_length(:tag_open)+1);
    i=cast(:char_hex_to_str as int);
    if (i>0) then
    begin
      char_hex_to_str=ascii_char(i);
    end
    else
    begin
      char_hex_to_str='{'||:char_hex_to_str||'}';
    end
    p_source_rtf = replace (:p_source_rtf, :char_hex, :char_hex_to_str);
    tagstart = position (:tag_open, :p_source_rtf);
  end
  p_source_rtf=trim(:p_source_rtf);

  -- RTF tem tags assim:
  -- \viewkind4\uc1\pard\sa200\sl276\slmult1\lang1046\fs20 blabla bla bla
  -- É preciso localizar essas tags e trocar por vazios

  tag_open='\';
  tag_close=' ';
  tagstart = position (:tag_open, :p_source_rtf);
  while (:tagstart > 0) do
  begin
    tagfinish = position (:tag_close, :p_source_rtf, :tagstart);
    if (:tagfinish<:tagstart) then
      tagfinish=char_length(:p_source_rtf);
    tagfound = substring (:p_source_rtf from :tagstart for ((:tagfinish - :tagstart) + 1));
    p_source_rtf = replace (:p_source_rtf, :tagfound, '');
    tagstart = position (:tag_open, :p_source_rtf);
  end

  -- finaliza
  result_text = trim(:p_source_rtf);

  return :result_text;
END