class Aws::S3::EncryptionV2::KmsCipherProvider

def build_encryption_context(cek_alg, options = {})
  kms_context = (options[:kms_encryption_context] || {})
    .each_with_object({}) { |(k, v), h| h[k.to_s] = v }
  if kms_context.include? 'aws:x-amz-cek-alg'
    raise ArgumentError, 'Conflict in reserved KMS Encryption Context ' \
      'key aws:x-amz-cek-alg. This value is reserved for the S3 ' \
      'Encryption Client and cannot be set by the user.'
  end
  {
    'aws:x-amz-cek-alg' => cek_alg
  }.merge(kms_context)
end

def decode64(str)
  Base64.decode64(str)
end

def decryption_cipher(envelope, options = {})
  encryption_context = Json.load(envelope['x-amz-matdesc'])
  cek_alg = envelope['x-amz-cek-alg']
  case envelope['x-amz-wrap-alg']
  when 'kms'
    unless options[:security_profile] == :v2_and_legacy
      raise Errors::LegacyDecryptionError
    end
  when 'kms+context'
    if cek_alg != encryption_context['aws:x-amz-cek-alg']
      raise Errors::CEKAlgMismatchError
    end
    if encryption_context != build_encryption_context(cek_alg, options)
      raise Errors::DecryptionError, 'Value of encryption context from'\
        ' envelope does not match the provided encryption context'
    end
  when 'AES/GCM'
    raise ArgumentError, 'Key mismatch - Client is configured' \
            ' with a KMS key and the x-amz-wrap-alg is AES/GCM.'
  when 'RSA-OAEP-SHA1'
    raise ArgumentError, 'Key mismatch - Client is configured' \
            ' with a KMS key and the x-amz-wrap-alg is RSA-OAEP-SHA1.'
  else
    raise ArgumentError, 'Unsupported wrap-alg: ' \
        "#{envelope['x-amz-wrap-alg']}"
  end
  any_cmk_mode = false || options[:kms_allow_decrypt_with_any_cmk]
  decrypt_options = {
    ciphertext_blob: decode64(envelope['x-amz-key-v2']),
    encryption_context: encryption_context
  }
  unless any_cmk_mode
    decrypt_options[:key_id] = @kms_key_id
  end
  key = Aws::Plugins::UserAgent.metric('S3_CRYPTO_V2') do
    @kms_client.decrypt(decrypt_options).plaintext
  end
  iv = decode64(envelope['x-amz-iv'])
  block_mode =
    case cek_alg
    when 'AES/CBC/PKCS5Padding'
      :CBC
    when 'AES/CBC/PKCS7Padding'
      :CBC
    when 'AES/GCM/NoPadding'
      :GCM
    else
      type = envelope['x-amz-cek-alg'].inspect
      msg = "unsupported content encrypting key (cek) format: #{type}"
      raise Errors::DecryptionError, msg
    end
  Utils.aes_decryption_cipher(block_mode, key, iv)
end

def encode64(str)
  Base64.encode64(str).split("\n") * ""
end

def encryption_cipher(options = {})
  validate_key_for_encryption
  encryption_context = build_encryption_context(@content_encryption_schema, options)
  key_data = Aws::Plugins::UserAgent.metric('S3_CRYPTO_V2') do
    @kms_client.generate_data_key(
      key_id: @kms_key_id,
      encryption_context: encryption_context,
      key_spec: 'AES_256'
    )
  end
  cipher = Utils.aes_encryption_cipher(:GCM)
  cipher.key = key_data.plaintext
  envelope = {
    'x-amz-key-v2' => encode64(key_data.ciphertext_blob),
    'x-amz-iv' => encode64(cipher.iv = cipher.random_iv),
    'x-amz-cek-alg' => @content_encryption_schema,
    'x-amz-tag-len' => (AES_GCM_TAG_LEN_BYTES * 8).to_s,
    'x-amz-wrap-alg' => @key_wrap_schema,
    'x-amz-matdesc' => Json.dump(encryption_context)
  }
  cipher.auth_data = '' # auth_data must be set after key and iv
  [envelope, cipher]
end

def initialize(options = {})
  @kms_key_id = validate_kms_key(options[:kms_key_id])
  @kms_client = options[:kms_client]
  @key_wrap_schema = validate_key_wrap(
    options[:key_wrap_schema]
  )
  @content_encryption_schema = validate_cek(
    options[:content_encryption_schema]
  )
end

def validate_cek(content_encryption_schema)
  case content_encryption_schema
  when :aes_gcm_no_padding
    "AES/GCM/NoPadding"
  else
    raise ArgumentError, "Unsupported content_encryption_schema: #{content_encryption_schema}"
  end
end

def validate_key_for_encryption
  if @kms_key_id == :kms_allow_decrypt_with_any_cmk
    raise ArgumentError, 'Unable to encrypt/write objects with '\
      'kms_key_id = :kms_allow_decrypt_with_any_cmk.  Provide ' \
      'a valid kms_key_id on client construction.'
  end
end

def validate_key_wrap(key_wrap_schema)
  case key_wrap_schema
  when :kms_context then 'kms+context'
  else
    raise ArgumentError, "Unsupported key_wrap_schema: #{key_wrap_schema}"
  end
end

def validate_kms_key(kms_key_id)
  if kms_key_id.nil? || kms_key_id.length.zero?
    raise ArgumentError, 'KMS CMK ID was not specified. ' \
      'Please specify a CMK ID, ' \
      'or set kms_key_id: :kms_allow_decrypt_with_any_cmk to use ' \
      'any valid CMK from the object.'
  end
  if kms_key_id.is_a?(Symbol) && kms_key_id != :kms_allow_decrypt_with_any_cmk
    raise ArgumentError, 'kms_key_id must be a valid KMS CMK or be ' \
      'set to :kms_allow_decrypt_with_any_cmk'
  end
  kms_key_id
end