class ActionDispatch::ParamBuilder

def self.make_default(param_depth_limit)
  new param_depth_limit
end

def from_hash(hash, encoding_template: nil)
  # Force encodings from encoding template
  hash = Request::Utils::CustomParamEncoder.encode_for_template(hash, encoding_template)
  # Assert valid encoding
  Request::Utils.check_param_encoding(hash)
  # Convert hashes to HWIA (or UploadedFile), and deep-munge nils
  # out of arrays
  hash = Request::Utils.normalize_encode_params(hash)
  hash
end

def from_pairs(pairs, encoding_template: nil)
  params = make_params
  pairs.each do |k, v|
    if Hash === v
      v = ActionDispatch::Http::UploadedFile.new(v)
    end
    store_nested_param(params, k, v, 0, encoding_template)
  end
  params
rescue ArgumentError => e
  raise InvalidParameterError, e.message, e.backtrace
end

def from_query_string(qs, separator: nil, encoding_template: nil)
  from_pairs QueryParser.each_pair(qs, separator), encoding_template: encoding_template
end

def initialize(param_depth_limit)
  @param_depth_limit = param_depth_limit
end

def make_params
  ActiveSupport::HashWithIndifferentAccess.new
end

def new_depth_limit(param_depth_limit)
  self.class.new @params_class, param_depth_limit
end

def params_hash_has_key?(hash, key)
  return false if key.include?("[]")
  key.split(/[\[\]]+/).inject(hash) do |h, part|
    next h if part == ""
    return false unless params_hash_type?(h) && h.key?(part)
    h[part]
  end
  true
end

def params_hash_type?(obj)
  Hash === obj
end

def store_nested_param(params, name, v, depth, encoding_template = nil)
  raise ParamsTooDeepError if depth >= param_depth_limit
  if !name
    # nil name, treat same as empty string (required by tests)
    k = after = ""
  elsif depth == 0
    if ignore_leading_brackets || (ignore_leading_brackets.nil? && LEADING_BRACKETS_COMPAT)
      # Rack 2 compatible behavior, ignore leading brackets
      if name =~ /\A[\[\]]*([^\[\]]+)\]*/
        k = $1
        after = $' || ""
        if !ignore_leading_brackets && (k != $& || !after.empty? && !after.start_with?("["))
          ActionDispatch.deprecator.warn("Skipping over leading brackets in parameter name #{name.inspect} is deprecated and will parse differently in Rails 8.1 or Rack 3.0.")
        end
      else
        k = name
        after = ""
      end
    else
      # Start of parsing, don't treat [] or [ at start of string specially
      if start = name.index("[", 1)
        # Start of parameter nesting, use part before brackets as key
        k = name[0, start]
        after = name[start, name.length]
      else
        # Plain parameter with no nesting
        k = name
        after = ""
      end
    end
  elsif name.start_with?("[]")
    # Array nesting
    k = "[]"
    after = name[2, name.length]
  elsif name.start_with?("[") && (start = name.index("]", 1))
    # Hash nesting, use the part inside brackets as the key
    k = name[1, start - 1]
    after = name[start + 1, name.length]
  else
    # Probably malformed input, nested but not starting with [
    # treat full name as key for backwards compatibility.
    k = name
    after = ""
  end
  return if k.empty?
  if depth == 0 && String === v
    # We have to wait until we've found the top part of the name,
    # because that's what the encoding template is configured with
    if encoding_template && (designated_encoding = encoding_template[k]) && !v.frozen?
      v.force_encoding(designated_encoding)
    end
    # ... and we can't validate the encoding until after we've
    # applied any template override
    unless v.valid_encoding?
      raise InvalidParameterError, "Invalid encoding for parameter: #{v.scrub}"
    end
  end
  if after == ""
    if k == "[]" && depth != 0
      return (v || !ActionDispatch::Request::Utils.perform_deep_munge) ? [v] : []
    else
      params[k] = v
    end
  elsif after == "["
    params[name] = v
  elsif after == "[]"
    params[k] ||= []
    raise ParameterTypeError, "expected Array (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(Array)
    params[k] << v if v || !ActionDispatch::Request::Utils.perform_deep_munge
  elsif after.start_with?("[]")
    # Recognize x[][y] (hash inside array) parameters
    unless after[2] == "[" && after.end_with?("]") && (child_key = after[3, after.length - 4]) && !child_key.empty? && !child_key.index("[") && !child_key.index("]")
      # Handle other nested array parameters
      child_key = after[2, after.length]
    end
    params[k] ||= []
    raise ParameterTypeError, "expected Array (got #{params[k].class.name}) for param `#{k}'" unless params[k].is_a?(Array)
    if params_hash_type?(params[k].last) && !params_hash_has_key?(params[k].last, child_key)
      store_nested_param(params[k].last, child_key, v, depth + 1)
    else
      params[k] << store_nested_param(make_params, child_key, v, depth + 1)
    end
  else
    params[k] ||= make_params
    raise ParameterTypeError, "expected Hash (got #{params[k].class.name}) for param `#{k}'" unless params_hash_type?(params[k])
    params[k] = store_nested_param(params[k], after, v, depth + 1)
  end
  params
end