class JWT::JWK::EC

def []=(key, value)
  raise ArgumentError, 'cannot overwrite cryptographic key attributes' if EC_KEY_ELEMENTS.include?(key.to_sym)
  super
end

def check_jwk_params!(key_params, params)
  raise ArgumentError, 'cannot overwrite cryptographic key attributes' unless (EC_KEY_ELEMENTS & params.keys).empty?
  raise JWT::JWKError, "Incorrect 'kty' value: #{key_params[:kty]}, expected #{KTY}" unless key_params[:kty] == KTY
  raise JWT::JWKError, 'Key format is invalid for EC' unless key_params[:crv] && key_params[:x] && key_params[:y]
end

def create_ec_key(jwk_crv, jwk_x, jwk_y, jwk_d)
  point = create_point(jwk_crv, jwk_x, jwk_y)
  return ::JWT::JWA::Ecdsa.create_public_key_from_point(point) unless jwk_d
  # https://datatracker.ietf.org/doc/html/rfc5915.html
  # ECPrivateKey ::= SEQUENCE {
  #   version        INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
  #   privateKey     OCTET STRING,
  #   parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
  #   publicKey  [1] BIT STRING OPTIONAL
  # }
  sequence = OpenSSL::ASN1::Sequence([
                                       OpenSSL::ASN1::Integer(1),
                                       OpenSSL::ASN1::OctetString(OpenSSL::BN.new(decode_octets(jwk_d), 2).to_s(2)),
                                       OpenSSL::ASN1::ObjectId(point.group.curve_name, 0, :EXPLICIT),
                                       OpenSSL::ASN1::BitString(point.to_octet_string(:uncompressed), 1, :EXPLICIT)
                                     ])
  OpenSSL::PKey::EC.new(sequence.to_der)
end

def create_ec_key(jwk_crv, jwk_x, jwk_y, jwk_d)
  point = create_point(jwk_crv, jwk_x, jwk_y)
  ::JWT::JWA::Ecdsa.create_public_key_from_point(point).tap do |key|
    key.private_key = OpenSSL::BN.new(decode_octets(jwk_d), 2) if jwk_d
  end
end

def create_point(jwk_crv, jwk_x, jwk_y)
  curve = EC.to_openssl_curve(jwk_crv)
  x_octets = decode_octets(jwk_x)
  y_octets = decode_octets(jwk_y)
  # The details of the `Point` instantiation are covered in:
  # - https://docs.ruby-lang.org/en/2.4.0/OpenSSL/PKey/EC.html
  # - https://www.openssl.org/docs/manmaster/man3/EC_POINT_new.html
  # - https://tools.ietf.org/html/rfc5480#section-2.2
  # - https://www.secg.org/SEC1-Ver-1.0.pdf
  # Section 2.3.3 of the last of these references specifies that the
  # encoding of an uncompressed point consists of the byte `0x04` followed
  # by the x value then the y value.
  OpenSSL::PKey::EC::Point.new(
    OpenSSL::PKey::EC::Group.new(curve),
    OpenSSL::BN.new([0x04, x_octets, y_octets].pack('Ca*a*'), 2)
  )
end

def decode_octets(base64_encoded_coordinate)
  bytes = ::JWT::Base64.url_decode(base64_encoded_coordinate)
  # Some base64 encoders on some platform omit a single 0-byte at
  # the start of either Y or X coordinate of the elliptic curve point.
  # This leads to an encoding error when data is passed to OpenSSL BN.
  # It is know to have happened to exported JWKs on a Java application and
  # on a Flutter/Dart application (both iOS and Android). All that is
  # needed to fix the problem is adding a leading 0-byte. We know the
  # required byte is 0 because with any other byte the point is no longer
  # on the curve - and OpenSSL will actually communicate this via another
  # exception. The indication of a stripped byte will be the fact that the
  # coordinates - once decoded into bytes - should always be an even
  # bytesize. For example, with a P-521 curve, both x and y must be 66 bytes.
  # With a P-256 curve, both x and y must be 32 and so on. The simplest way
  # to check for this truncation is thus to check whether the number of bytes
  # is odd, and restore the leading 0-byte if it is.
  if bytes.bytesize.odd?
    ZERO_BYTE + bytes
  else
    bytes
  end
end

def ec_key
  @ec_key ||= create_ec_key(self[:crv], self[:x], self[:y], self[:d])
end

def encode_octets(octets)
  return unless octets
  ::JWT::Base64.url_encode(octets)
end

def export(options = {})
  exported = parameters.clone
  exported.reject! { |k, _| EC_PRIVATE_KEY_ELEMENTS.include? k } unless private? && options[:include_private] == true
  exported
end

def extract_key_params(key)
  case key
  when JWT::JWK::EC
    key.export(include_private: true)
  when OpenSSL::PKey::EC # Accept OpenSSL key as input
    @ec_key = key # Preserve the object to avoid recreation
    parse_ec_key(key)
  when Hash
    key.transform_keys(&:to_sym)
  else
    raise ArgumentError, 'key must be of type OpenSSL::PKey::EC or Hash with key parameters'
  end
end

def import(jwk_data)
  new(jwk_data)
end

def initialize(key, params = nil, options = {})
  params ||= {}
  # For backwards compatibility when kid was a String
  params = { kid: params } if params.is_a?(String)
  key_params = extract_key_params(key)
  params = params.transform_keys(&:to_sym)
  check_jwk_params!(key_params, params)
  super(options, key_params.merge(params))
end

def jwa
  return super if self[:alg]
  curve_name = self.class.to_openssl_curve(self[:crv])
  JWA.resolve(JWA::Ecdsa.curve_by_name(curve_name)[:algorithm])
end

def key_digest
  _crv, x_octets, y_octets = keypair_components(ec_key)
  sequence = OpenSSL::ASN1::Sequence([OpenSSL::ASN1::Integer.new(OpenSSL::BN.new(x_octets, BINARY)),
                                      OpenSSL::ASN1::Integer.new(OpenSSL::BN.new(y_octets, BINARY))])
  OpenSSL::Digest::SHA256.hexdigest(sequence.to_der)
end

def keypair
  ec_key
end

def keypair_components(ec_keypair)
  encoded_point = ec_keypair.public_key.to_bn.to_s(BINARY)
  case ec_keypair.group.curve_name
  when 'prime256v1'
    crv = 'P-256'
    x_octets, y_octets = encoded_point.unpack('xa32a32')
  when 'secp256k1'
    crv = 'P-256K'
    x_octets, y_octets = encoded_point.unpack('xa32a32')
  when 'secp384r1'
    crv = 'P-384'
    x_octets, y_octets = encoded_point.unpack('xa48a48')
  when 'secp521r1'
    crv = 'P-521'
    x_octets, y_octets = encoded_point.unpack('xa66a66')
  else
    raise JWT::JWKError, "Unsupported curve '#{ec_keypair.group.curve_name}'"
  end
  [crv, x_octets, y_octets]
end

def members
  EC_PUBLIC_KEY_ELEMENTS.each_with_object({}) { |i, h| h[i] = self[i] }
end

def parse_ec_key(key)
  crv, x_octets, y_octets = keypair_components(key)
  octets = key.private_key&.to_bn&.to_s(BINARY)
  {
    kty: KTY,
    crv: crv,
    x: encode_octets(x_octets),
    y: encode_octets(y_octets),
    d: encode_octets(octets)
  }.compact
end

def private?
  ec_key.private_key?
end

def public_key
  ec_key
end

def signing_key
  ec_key
end

def to_openssl_curve(crv)
  # The JWK specs and OpenSSL use different names for the same curves.
  # See https://tools.ietf.org/html/rfc5480#section-2.1.1.1 for some
  # pointers on different names for common curves.
  case crv
  when 'P-256' then 'prime256v1'
  when 'P-384' then 'secp384r1'
  when 'P-521' then 'secp521r1'
  when 'P-256K' then 'secp256k1'
  else raise JWT::JWKError, 'Invalid curve provided'
  end
end

def verify_key
  ec_key
end