--[[nef_20221122 PARSER 
The function log.bb_iterate returns the three values used for iteration.  The arguments:
1. The string to be parsed.
2. First index into the string. Typically 0 (or nil). Default nil.
Returning values for the iteration function:
1. The next index into the string.  Will be nil if the string is exhausted.
2. The preamble text (the text before the bbcode). Null string if there is none.
3. The bbcode in table form.  This will be nil if the string is terminating with text.

The bbcode table contains the following fields:
bb:      bbcode - see the table bb_alias for valid codes
open:    bb is the first (or only) part of a bbcode sequence (boolean)
close:   bb is the second (or only) part of a bbcode sequence (boolean)
options: table containing fields in the form (key, value): (option identifier, option value)
         the valid identifiers are listed in the table keywords; the value will be a string
         or number depending on the identifier.
         
The table log.bb_alias is also included for convenience.
-]]
do            -- PARSER
   local function get_string(arg_text, current)
     local Start, End, arg = arg_text: find('(%b"")%s*', current)
     if arg then return arg: gsub('"',''), End end end
   local function get_num   (arg_text, current)
     local Start, End, arg = arg_text: find('(%d+)%s*',  current)
     if arg then return tonumber(arg), End end end
  
   local keywords = setmetatable( {
      name        = get_string;
      foreground  = get_string;
      background  = get_string;
      target      = get_string;
      fg  = get_string;
      bg  = get_string;
      tgt = get_string;
      id  = get_num;
      x   = get_num;
      y   = get_num;
                                      }, {
        __index =  function () return function () end end;
                                         })
  
   local bb_forms = {
            "%[%s*%/%s*(%a%w*)%s*(.-)%s*%]";  -- 1 close
            "%[%s*(%a%w*)%s*(.-)%s*%/%s*%]";  -- 2 both
            "%[%s*(%a%w*)%s*(.-)%s*%]";       -- 3 open
                    }
                   
   local function get_arg (arg_text) -- upvalue keywords
     local P1, args = 0, {}  
     while P1 and P1 < #arg_text do 
       local S, P2, key = arg_text: find("(%a%w*)%s*=%s*", P1 +1)
       if    P2 and P2 < #arg_text
       then  args [key], P2 = keywords [key] (arg_text, P2 +1)
       else  P2 = nil
       end
       if    P2 then P1 = P2
       else  S, P1 = arg_text: find("^%s+%s*", P1 +1)
       end
     end; return  P1 or #arg_text, args
   end
           --    get_arg end
           
   local _ENV
      =  _ENV
      
   _ENV = log
   bb_alias = {
   bold = 'b';underline = 'u';italic = 'i'; strike = 's';color ='c';link = 'l';
   b    = 'b';u         = 'u';i      = 'i'; s      = 's';c     ='c';l    = 'l';
              }
   function bb_iterate(text, P0) return          
     function (text, P0) -- upvalue alias, bb_forms, get_arg
       if P0 < #text then local current = P0 +1
          local Start, End, bb_text = text: find(".-(%b[])", current)
          if Start then 
             for form = 1,3 do 
               local S, E, bbcode, arg_text =  bb_text: find(bb_forms [form])
               if   bbcode and bb_alias [bbcode] 
               then local P1, args = get_arg (arg_text)
                    return End, text: sub(current, current + P1),
       {bb = bbcode, open = form > 1, close = form < 3, options = args}
               end
             end 
          end
          return #text, text: sub(current) -- , nil (no bbcode at end)
       end
     end, text, P0 or 0
   end
  
end
 ----------- end PARSER