func capitalise(_ value: Any?) -> Any? {
  if let array = value as? [Any?] {
    return array.map { stringify($0).capitalized }
  } else {
    return stringify(value).capitalized
  }
}

func uppercase(_ value: Any?) -> Any? {
  if let array = value as? [Any?] {
    return array.map { stringify($0).uppercased() }
  } else {
    return stringify(value).uppercased()
  }
}

func lowercase(_ value: Any?) -> Any? {
  if let array = value as? [Any?] {
    return array.map { stringify($0).lowercased() }
  } else {
    return stringify(value).lowercased()
  }
}

func defaultFilter(value: Any?, arguments: [Any?]) -> Any? {
  // value can be optional wrapping nil, so this way we check for underlying value
  if let value = value, String(describing: value) != "nil" {
    return value
  }

  for argument in arguments {
    if let argument = argument {
      return argument
    }
  }

  return nil
}

func joinFilter(value: Any?, arguments: [Any?]) throws -> Any? {
  guard arguments.count < 2 else {
    throw TemplateSyntaxError("'join' filter takes a single argument")
  }

  let separator = stringify(arguments.first ?? "")

  if let value = value as? [Any] {
    return value
      .map(stringify)
      .joined(separator: separator)
  }

  return value
}

func splitFilter(value: Any?, arguments: [Any?]) throws -> Any? {
  guard arguments.count < 2 else {
    throw TemplateSyntaxError("'split' filter takes a single argument")
  }

  let separator = stringify(arguments.first ?? " ")
  if let value = value as? String {
    return value.components(separatedBy: separator)
  }

  return value
}