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package acme

import (
	"crypto"
	"crypto/ecdsa"
	"crypto/rsa"
	"encoding/base64"
	"errors"
	"io"
	"net/http"
	"strings"

	"github.com/square/go-jose"
)

// KeySize is a default RSA key size
const KeySize = 2048

var errNoNonces = errors.New("out of nonces")

// Signer ...
type Signer struct {
	signer jose.Signer
	thumb  string
	nonces chan string
}

func NewSigner(privKey crypto.PrivateKey) (*Signer, error) {
	thumb := func(pubKey crypto.PublicKey, alg string) (string, error) {
		wk := &jose.JsonWebKey{Key: pubKey, Algorithm: alg}
		t, err := wk.Thumbprint(crypto.SHA256)
		return base64.RawURLEncoding.EncodeToString(t), err
	}
	switch k := privKey.(type) {
	case *rsa.PrivateKey:
		s, err := jose.NewSigner(jose.RS256, k)
		if err != nil {
			return nil, err
		}
		t, err := thumb(k.Public(), "RSA")
		if err != nil {
			return nil, err
		}
		sig := &Signer{signer: s, thumb: t, nonces: make(chan string, 100)}
		sig.signer.SetNonceSource(sig)
		return sig, nil
	case *ecdsa.PrivateKey:
		s, err := jose.NewSigner(jose.ES384, k)
		if err != nil {
			return nil, err
		}
		t, err := thumb(k.Public(), "EC")
		if err != nil {
			return nil, err
		}
		sig := &Signer{signer: s, thumb: t, nonces: make(chan string, 100)}
		sig.signer.SetNonceSource(sig)
		return sig, nil
	default:
		return nil, ErrKeyType
	}
}

// Nonce implements jose nonce provider
func (s Signer) Nonce() (string, error) {
	select {
	case nonce := <-s.nonces:
		return nonce, nil
	default:
		return "", errNoNonces
	}
}

// RoundTrip extracts nonces from HTTP response
func (s Signer) RoundTrip(req *http.Request) (*http.Response, error) {
	resp, err := http.DefaultTransport.RoundTrip(req)
	if err != nil {
		return nil, err
	}
	nonce := resp.Header.Get("Replay-Nonce")
	if nonce == "" {
		return nil, errNoNonces
	}
	if len(s.nonces) == cap(s.nonces) {
		<-s.nonces // drop oldest
	}
	s.nonces <- nonce
	return resp, nil
}

// Sign implements Signer interface
func (s Signer) Sign(msg []byte) (io.Reader, error) {
	obj, err := s.signer.Sign(msg)
	if err != nil {
		return nil, err
	}
	return strings.NewReader(obj.FullSerialize()), nil
}

func (s Signer) KeyAuth(token string) string {
	return token + "." + s.thumb
}