// parse http multipart form data body
// calls a callback for each part
// returns a count of parts
// multipart_fn
//
// Example:
//   ------geckoformboundary8a20292b9973036de6f4d2c70f63e1d8
//   Content-Disposition: form-data; name="file"; filename="genulid.c"
//   Content-Type: text/x-csrc
//
// The final marker has -- at the end.
//
//   ------geckoformboundary8a20292b9973036de6f4d2c70f63e1d8--

typedef void (*multipart_fn)(void *opaque, int index, str name, str mime_type, str filename, str databytes);

static str http_header_get_attr(str header, str attr_prefix){
  str_pair x = str_split_at_str(header, attr_prefix);
  if(str_eq(header, x.a)) return (str){0};
  str attr = x.b;
  x = str_split_at(attr, '"');
  if(str_eq(attr, x.a)) return (str){0};
  return x.a;
}

static int http_parse_multipart_formdata(str body, multipart_fn cb, void *cbdata){
  str const CR = kstr("\r");
  str const LF = kstr("\n");

  str const o = body;
  str_pair x = str_split_at(body, '\n');
  if(str_eq(body, x.a)){
    debug("boundary not found");
    return 0;
  }

  str boundary = x.a;
  bool has_crlf = (boundary.len && str_ends_with(boundary, kstr("\r")));
  if(has_crlf) boundary = str_drop_last(boundary, 1);
  debug("boundary [%.*s]\n", pstr(boundary));

  int nparts=0;
  body = x.b;

  str const content_disposition_prefix = kstr("content-disposition: form-data;");
  str const content_type_prefix = kstr("content-type: ");

  while(body.len){
    x = str_split_at_str(body, boundary);
    if(str_eq(body, x.a)){
      warn("multipart missing end boundary at offset:%ld\n", (body.data-o.data));
      return 0;
    }
    str part = x.a;
    unless(str_ends_with(part, LF)){
      warn("multipart part missing LF before boundary at offset:%ld\n", (body.data-o.data));
      return 0;
    }
    part = str_drop_last(part, 1);
    if(str_ends_with(part, CR)) part = str_drop_last(part, 1);
    body = x.b;

    str name = {0};
    str mime_type = {0};
    str filename = {0};

    str header = part;
    bool header_complete = false;
    while(header.len){
      x = str_split_at(header, '\n');
      if(str_eq(header, x.a)) return 0;
      str line = x.a;
      header = x.b;
      if(line.len && '\r'==line.data[line.len-1]) line=str_drop_last(line, 1);
      if(0==line.len){ header_complete=true; break; }
      if(str_starts_with_ci(line, content_disposition_prefix)){
        str rest = str_drop(line, content_disposition_prefix.len);
        name = http_header_get_attr(rest, kstr(" name=\""));
        filename = http_header_get_attr(rest, kstr(" filename=\""));
      }else if(str_starts_with_ci(line, content_type_prefix)){
        mime_type = str_drop(line, content_type_prefix.len);
      }
    }
    unless(header_complete){
      warn("multipart header not terminated\n");
      return 0;
    }
    part = header;
    cb(cbdata, nparts, name, mime_type, filename, part);

    ++nparts;

    bool const final_boundary = str_starts_with(body, kstr("--"));
    if(final_boundary) return nparts;

    if(body.len && '\r'==body.data[0]) body=str_drop(body, 1);
    unless(body.len && '\n'==body.data[0]){
      warn("multipart boundary missing newline\n");
      return 0;
    }
    body = str_drop(body, 1);
  }

  warn("http_parse_multipart_formdata failed to find final boundary\n");
  return 0;
}