// Utilities for HTML manipulation.

HTMLEncode[line] :=
{
   line =~ %s/&/&/g;
   line =~ %s/</&lt;/g;
   line =~ %s/>/&gt;/g;
   return line
}


// Decodes the hex-encoded parts of an argument.
URLDecode[arg] :=
{
   return arg =~ %s/%([0-9a-fA-F]{2})/char[parseInt[$1, 16]]/ge
}


// Helper function to return a zero-padded hexadecimal number.
hexpad[c] :=
{
   cc = hex[char[c]]
   if (length[cc] == 1)
      cc = "0$cc"
   return "%$cc"
}

// URL encode a part of a string to be used in a URL.  The specification for
// URLs (RFC 1738, Dec. '94) states "...Only alphanumerics [0-9a-zA-Z], the
// special characters "$-_.+!*'()," and reserved characters used for
// their reserved purposes may be used unencoded within a URL."
URLEncode[str] :=
{
   return str =~ %s/([^0-9a-zA-Z\$\-\_\.\+\!\*\'\(\)\,])/hexpad[$1]/ge
}

// Make the <OPTIONS> tags for an HTML <SELECT> list, with the specified
// item selected.
// makeselect[list, selected]
makeSelect[list, selected] :=
{
   for [name, val] list
   {
      if (val != undef)         // Has value
      {
         vs = "$val"               // Coerce to string
         valStr = (val != undef) ? " VALUE=\"" + HTMLEncode[vs] + "\"" : ""
         sel = (vs == selected ? " SELECTED" : "")
      } else
         sel = (name == selected ? " SELECTED" : "")
      println["    <OPTION$valStr$sel>" + HTMLEncode["$name"]]
   }
}


// Format a Frink expression into a prettier HTML equivalent.
formatExpression[expr] :=
{
   expr =~ %s/\^([\/\d\w\.\-]+)/<SUP>$1<\/SUP>/g  // Draw superscripts
   expr =~ %s/\+(\s*)-\s*1\s+/-$1/g;  // "+ -1"   goes to "-"
   expr =~ %s/\+(\s*)-/-$1/g;         // "+ -" goes to "-"
   return expr
}