// Package xmlenc is a partial implementation of the xmlenc standard
// as described in https://www.w3.org/TR/2002/REC-xmlenc-core-20021210/Overview.html.
// The purpose of this implementation is to support encrypted SAML assertions.
package xmlenc

import (
	"crypto/rand"
	"hash"

	"github.com/beevik/etree"
)

// RandReader is a thunk that allows test to replace the source of randomness used by
// this package. By default it is Reader from crypto/rand.
var RandReader = rand.Reader

// Encrypter is an interface that encrypts things. Given a plaintext it returns an
// XML EncryptedData or EncryptedKey element. The required type of `key` varies
// depending on the implementation.
type Encrypter interface {
	Encrypt(key interface{}, plaintext []byte, nonce []byte) (*etree.Element, error)
}

// Decrypter is an interface that decrypts things. The Decrypt() method returns the
// plaintext version of the EncryptedData or EncryptedKey element passed.
//
// You probably don't have to use this interface directly, instead you may call
// Decrypt() and it will examine the element to determine which Decrypter to use.
type Decrypter interface {
	Algorithm() string
	Decrypt(key interface{}, ciphertextEl *etree.Element) ([]byte, error)
}

// DigestMethod represents a digest method such as SHA1, etc.
type DigestMethod interface {
	Algorithm() string
	Hash() hash.Hash
}

var (
	decrypters    = map[string]Decrypter{}
	digestMethods = map[string]DigestMethod{}
)

// RegisterDecrypter registers the specified decrypter to that it can be
// used with Decrypt().
func RegisterDecrypter(d Decrypter) {
	decrypters[d.Algorithm()] = d
}

// RegisterDigestMethod registers the specified digest method to that it can be
// used with Decrypt().
func RegisterDigestMethod(dm DigestMethod) {
	digestMethods[dm.Algorithm()] = dm
}

// BlockCipher implements a cipher with a fixed size key like AES or 3DES.
type BlockCipher interface {
	Encrypter
	Decrypter
	KeySize() int
}