//go:generate go run internal/cmd/genheader/main.go

// Package jwk implements JWK as described in https://tools.ietf.org/html/rfc7517
package jwk

import (
	"bytes"
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/ed25519"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"io"
	"io/ioutil"
	"math/big"
	"net/http"

	"github.com/lestrrat-go/backoff/v2"
	"github.com/lestrrat-go/jwx/internal/base64"
	"github.com/lestrrat-go/jwx/internal/json"
	"github.com/lestrrat-go/jwx/jwa"
	"github.com/lestrrat-go/jwx/x25519"
	"github.com/pkg/errors"
)

var registry = json.NewRegistry()

func bigIntToBytes(n *big.Int) ([]byte, error) {
	if n == nil {
		return nil, errors.New(`invalid *big.Int value`)
	}
	return n.Bytes(), nil
}

// New creates a jwk.Key from the given key (RSA/ECDSA/symmetric keys).
//
// The constructor auto-detects the type of key to be instantiated
// based on the input type:
//
//   * "crypto/rsa".PrivateKey and "crypto/rsa".PublicKey creates an RSA based key
//   * "crypto/ecdsa".PrivateKey and "crypto/ecdsa".PublicKey creates an EC based key
//   * "crypto/ed25519".PrivateKey and "crypto/ed25519".PublicKey creates an OKP based key
//   * []byte creates a symmetric key
func New(key interface{}) (Key, error) {
	if key == nil {
		return nil, errors.New(`jwk.New requires a non-nil key`)
	}

	var ptr interface{}
	switch v := key.(type) {
	case rsa.PrivateKey:
		ptr = &v
	case rsa.PublicKey:
		ptr = &v
	case ecdsa.PrivateKey:
		ptr = &v
	case ecdsa.PublicKey:
		ptr = &v
	default:
		ptr = v
	}

	switch rawKey := ptr.(type) {
	case *rsa.PrivateKey:
		k := NewRSAPrivateKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case *rsa.PublicKey:
		k := NewRSAPublicKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case *ecdsa.PrivateKey:
		k := NewECDSAPrivateKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case *ecdsa.PublicKey:
		k := NewECDSAPublicKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case ed25519.PrivateKey:
		k := NewOKPPrivateKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case ed25519.PublicKey:
		k := NewOKPPublicKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case x25519.PrivateKey:
		k := NewOKPPrivateKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case x25519.PublicKey:
		k := NewOKPPublicKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	case []byte:
		k := NewSymmetricKey()
		if err := k.FromRaw(rawKey); err != nil {
			return nil, errors.Wrapf(err, `failed to initialize %T from %T`, k, rawKey)
		}
		return k, nil
	default:
		return nil, errors.Errorf(`invalid key type '%T' for jwk.New`, key)
	}
}

// PublicSetOf returns a new jwk.Set consisting of
// public keys of the keys contained in the set.
//
// This is useful when you are generating a set of private keys, and
// you want to generate the corresponding public versions for the
// users to verify with.
//
// Be aware that all fields will be copied onto the new public key. It is the caller's
// responsibility to remove any fields, if necessary.
func PublicSetOf(v Set) (Set, error) {
	newSet := NewSet()

	for iter := v.Iterate(context.TODO()); iter.Next(context.TODO()); {
		pair := iter.Pair()
		pubKey, err := PublicKeyOf(pair.Value.(Key))
		if err != nil {
			return nil, errors.Wrapf(err, `failed to get public key of %T`, pair.Value)
		}
		newSet.Add(pubKey)
	}

	return newSet, nil
}

// PublicKeyOf returns the corresponding public version of the jwk.Key.
// If `v` is a SymmetricKey, then the same value is returned.
// If `v` is already a public key, the key itself is returned.
//
// If `v` is a private key type that has a `PublicKey()` method, be aware
// that all fields will be copied onto the new public key. It is the caller's
// responsibility to remove any fields, if necessary
func PublicKeyOf(v Key) (Key, error) {
	switch v := v.(type) {
	case PublicKeyer:
		return v.PublicKey()
	default:
		return nil, errors.Errorf(`unknown jwk.Key type %T`, v)
	}
}

// PublicRawKeyOf returns the corresponding public key of the given
// value `v` (e.g. given *rsa.PrivateKey, *rsa.PublicKey is returned)
// If `v` is already a public key, the key itself is returned.
// The returned value will always be a pointer to the public key,
// except when a []byte (e.g. symmetric key, ed25519 key) is passed to `v`.
// In this case, the same []byte value is returned.
func PublicRawKeyOf(v interface{}) (interface{}, error) {
	// This may be a silly idea, but if the user gave us a non-pointer value...
	var ptr interface{}
	switch v := v.(type) {
	case rsa.PrivateKey:
		ptr = &v
	case rsa.PublicKey:
		ptr = &v
	case ecdsa.PrivateKey:
		ptr = &v
	case ecdsa.PublicKey:
		ptr = &v
	default:
		ptr = v
	}

	switch x := ptr.(type) {
	case *rsa.PrivateKey:
		return &x.PublicKey, nil
	case *rsa.PublicKey:
		return x, nil
	case *ecdsa.PrivateKey:
		return &x.PublicKey, nil
	case *ecdsa.PublicKey:
		return x, nil
	case ed25519.PrivateKey:
		return x.Public(), nil
	case ed25519.PublicKey:
		return x, nil
	case x25519.PrivateKey:
		return x.Public(), nil
	case x25519.PublicKey:
		return x, nil
	case []byte:
		return x, nil
	default:
		return nil, errors.Errorf(`invalid key type passed to PublicKeyOf (%T)`, v)
	}
}

// Fetch fetches a JWK resource specified by a URL. The url must be
// pointing to a resource that is supported by `net/http`.
//
// If you are using the same `jwk.Set` for long periods of time during
// the lifecycle of your program, and would like to periodically refresh the
// contents of the object with the data at the remote resource,
// consider using `jwk.AutoRefresh`, which automatically refreshes
// jwk.Set objects asynchronously.
func Fetch(ctx context.Context, urlstring string, options ...FetchOption) (Set, error) {
	res, err := fetch(ctx, urlstring, options...)
	if err != nil {
		return nil, err
	}

	defer res.Body.Close()
	keyset, err := ParseReader(res.Body)
	if err != nil {
		return nil, errors.Wrap(err, `failed to parse JWK set`)
	}
	return keyset, nil
}

func fetch(ctx context.Context, urlstring string, options ...FetchOption) (*http.Response, error) {
	var httpcl HTTPClient = http.DefaultClient
	bo := backoff.Null()
	for _, option := range options {
		//nolint:forcetypeassert
		switch option.Ident() {
		case identHTTPClient{}:
			httpcl = option.Value().(HTTPClient)
		case identFetchBackoff{}:
			bo = option.Value().(backoff.Policy)
		}
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, urlstring, nil)
	if err != nil {
		return nil, errors.Wrap(err, "failed to new request to remote JWK")
	}

	b := bo.Start(ctx)
	var lastError error
	for backoff.Continue(b) {
		res, err := httpcl.Do(req)
		if err != nil {
			lastError = errors.Wrap(err, "failed to fetch remote JWK")
			continue
		}

		if res.StatusCode != http.StatusOK {
			lastError = errors.Errorf("failed to fetch remote JWK (status = %d)", res.StatusCode)
			continue
		}
		return res, nil
	}

	// It's possible for us to get here without populating lastError.
	// e.g. what if we bailed out of `for backoff.Contineu(b)` without making
	// a single request? or, <-ctx.Done() returned?
	if lastError == nil {
		lastError = errors.New(`fetching remote JWK did not complete`)
	}
	return nil, lastError
}

// ParseRawKey is a combination of ParseKey and Raw. It parses a single JWK key,
// and assigns the "raw" key to the given parameter. The key must either be
// a pointer to an empty interface, or a pointer to the actual raw key type
// such as *rsa.PrivateKey, *ecdsa.PublicKey, *[]byte, etc.
func ParseRawKey(data []byte, rawkey interface{}) error {
	key, err := ParseKey(data)
	if err != nil {
		return errors.Wrap(err, `failed to parse key`)
	}

	if err := key.Raw(rawkey); err != nil {
		return errors.Wrap(err, `failed to assign to raw key variable`)
	}

	return nil
}

// parsePEMEncodedRawKey parses a key in PEM encoded ASN.1 DER format. It tires its
// best to determine the key type, but when it just can't, it will return
// an error
func parsePEMEncodedRawKey(src []byte) (interface{}, []byte, error) {
	block, rest := pem.Decode(src)
	if block == nil {
		return nil, nil, errors.New(`failed to decode PEM data`)
	}

	switch block.Type {
	// Handle the semi-obvious cases
	case "RSA PRIVATE KEY":
		key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse PKCS1 private key`)
		}
		return key, rest, nil
	case "RSA PUBLIC KEY":
		key, err := x509.ParsePKCS1PublicKey(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse PKCS1 public key`)
		}
		return key, rest, nil
	case "EC PRIVATE KEY":
		key, err := x509.ParseECPrivateKey(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse EC private key`)
		}
		return key, rest, nil
	case "PUBLIC KEY":
		// XXX *could* return dsa.PublicKey
		key, err := x509.ParsePKIXPublicKey(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse PKIX public key`)
		}
		return key, rest, nil
	case "PRIVATE KEY":
		key, err := x509.ParsePKCS8PrivateKey(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse PKCS8 private key`)
		}
		return key, rest, nil
	case "CERTIFICATE":
		cert, err := x509.ParseCertificate(block.Bytes)
		if err != nil {
			return nil, nil, errors.Wrap(err, `failed to parse certificate`)
		}
		return cert.PublicKey, rest, nil
	default:
		return nil, nil, errors.Errorf(`invalid PEM block type %s`, block.Type)
	}
}

// ParseKey parses a single key JWK. Unlike `jwk.Parse` this method will
// report failure if you attempt to pass a JWK set. Only use this function
// when you know that the data is a single JWK.
//
// Given a WithPEM(true) option, this function assumes that the given input
// is PEM encoded ASN.1 DER format key.
//
// Note that a successful parsing of any type of key does NOT necessarily
// guarantee a valid key. For example, no checks against expiration dates
// are performed for certificate expiration, no checks against missing
// parameters are performed, etc.
func ParseKey(data []byte, options ...ParseOption) (Key, error) {
	var parsePEM bool
	var localReg *json.Registry
	for _, option := range options {
		//nolint:forcetypeassert
		switch option.Ident() {
		case identPEM{}:
			parsePEM = option.Value().(bool)
		case identLocalRegistry{}:
			// in reality you can only pass either withLocalRegistry or
			// WithTypedField, but since withLocalRegistry is used only by us,
			// we skip checking
			localReg = option.Value().(*json.Registry)
		case identTypedField{}:
			pair := option.Value().(typedFieldPair)
			if localReg == nil {
				localReg = json.NewRegistry()
			}
			localReg.Register(pair.Name, pair.Value)
		}
	}

	if parsePEM {
		raw, _, err := parsePEMEncodedRawKey(data)
		if err != nil {
			return nil, errors.Wrap(err, `failed to parse PEM encoded key`)
		}
		return New(raw)
	}

	var hint struct {
		Kty string          `json:"kty"`
		D   json.RawMessage `json:"d"`
	}

	if err := json.Unmarshal(data, &hint); err != nil {
		return nil, errors.Wrap(err, `failed to unmarshal JSON into key hint`)
	}

	var key Key
	switch jwa.KeyType(hint.Kty) {
	case jwa.RSA:
		if len(hint.D) > 0 {
			key = newRSAPrivateKey()
		} else {
			key = newRSAPublicKey()
		}
	case jwa.EC:
		if len(hint.D) > 0 {
			key = newECDSAPrivateKey()
		} else {
			key = newECDSAPublicKey()
		}
	case jwa.OctetSeq:
		key = newSymmetricKey()
	case jwa.OKP:
		if len(hint.D) > 0 {
			key = newOKPPrivateKey()
		} else {
			key = newOKPPublicKey()
		}
	default:
		return nil, errors.Errorf(`invalid key type from JSON (%s)`, hint.Kty)
	}

	if localReg != nil {
		dcKey, ok := key.(KeyWithDecodeCtx)
		if !ok {
			return nil, errors.Errorf(`typed field was requested, but the key (%T) does not support DecodeCtx`, key)
		}
		dc := json.NewDecodeCtx(localReg)
		dcKey.SetDecodeCtx(dc)
		defer func() { dcKey.SetDecodeCtx(nil) }()
	}

	if err := json.Unmarshal(data, key); err != nil {
		return nil, errors.Wrapf(err, `failed to unmarshal JSON into key (%T)`, key)
	}

	return key, nil
}

// Parse parses JWK from the incoming []byte.
//
// For JWK sets, this is a convenience function. You could just as well
// call `json.Unmarshal` against an empty set created by `jwk.NewSet()`
// to parse a JSON buffer into a `jwk.Set`.
//
// This method exists because many times the user does not know before hand
// if a JWK(s) resource at a remote location contains a single JWK key or
// a JWK set, and `jwk.Parse()` can handle either case, returning a JWK Set
// even if the data only contains a single JWK key
//
// If you are looking for more information on how JWKs are parsed, or if
// you know for sure that you have a single key, please see the documentation
// for `jwk.ParseKey()`.
func Parse(src []byte, options ...ParseOption) (Set, error) {
	var parsePEM bool
	var localReg *json.Registry
	for _, option := range options {
		//nolint:forcetypeassert
		switch option.Ident() {
		case identPEM{}:
			parsePEM = option.Value().(bool)
		case identTypedField{}:
			pair := option.Value().(typedFieldPair)
			if localReg == nil {
				localReg = json.NewRegistry()
			}
			localReg.Register(pair.Name, pair.Value)
		}
	}

	s := NewSet()

	if parsePEM {
		src = bytes.TrimSpace(src)
		for len(src) > 0 {
			raw, rest, err := parsePEMEncodedRawKey(src)
			if err != nil {
				return nil, errors.Wrap(err, `failed to parse PEM encoded key`)
			}
			key, err := New(raw)
			if err != nil {
				return nil, errors.Wrapf(err, `failed to create jwk.Key from %T`, raw)
			}
			s.Add(key)
			src = bytes.TrimSpace(rest)
		}
		return s, nil
	}

	if localReg != nil {
		dcKs, ok := s.(KeyWithDecodeCtx)
		if !ok {
			return nil, errors.Errorf(`typed field was requested, but the key set (%T) does not support DecodeCtx`, s)
		}
		dc := json.NewDecodeCtx(localReg)
		dcKs.SetDecodeCtx(dc)
		defer func() { dcKs.SetDecodeCtx(nil) }()
	}

	if err := json.Unmarshal(src, s); err != nil {
		return nil, errors.Wrap(err, "failed to unmarshal JWK set")
	}
	return s, nil
}

// ParseReader parses a JWK set from the incoming byte buffer.
func ParseReader(src io.Reader, options ...ParseOption) (Set, error) {
	// meh, there's no way to tell if a stream has "ended" a single
	// JWKs except when we encounter an EOF, so just... ReadAll
	buf, err := ioutil.ReadAll(src)
	if err != nil {
		return nil, errors.Wrap(err, `failed to read from io.Reader`)
	}

	return Parse(buf, options...)
}

// ParseString parses a JWK set from the incoming string.
func ParseString(s string, options ...ParseOption) (Set, error) {
	return Parse([]byte(s), options...)
}

// AssignKeyID is a convenience function to automatically assign the "kid"
// section of the key, if it already doesn't have one. It uses Key.Thumbprint
// method with crypto.SHA256 as the default hashing algorithm
func AssignKeyID(key Key, options ...Option) error {
	if _, ok := key.Get(KeyIDKey); ok {
		return nil
	}

	hash := crypto.SHA256
	for _, option := range options {
		//nolint:forcetypeassert
		switch option.Ident() {
		case identThumbprintHash{}:
			hash = option.Value().(crypto.Hash)
		}
	}

	h, err := key.Thumbprint(hash)
	if err != nil {
		return errors.Wrap(err, `failed to generate thumbprint`)
	}

	if err := key.Set(KeyIDKey, base64.EncodeToString(h)); err != nil {
		return errors.Wrap(err, `failed to set "kid"`)
	}

	return nil
}

func cloneKey(src Key) (Key, error) {
	var dst Key
	switch src.(type) {
	case RSAPrivateKey:
		dst = NewRSAPrivateKey()
	case RSAPublicKey:
		dst = NewRSAPublicKey()
	case ECDSAPrivateKey:
		dst = NewECDSAPrivateKey()
	case ECDSAPublicKey:
		dst = NewECDSAPublicKey()
	case OKPPrivateKey:
		dst = NewOKPPrivateKey()
	case OKPPublicKey:
		dst = NewOKPPublicKey()
	case SymmetricKey:
		dst = NewSymmetricKey()
	default:
		return nil, errors.Errorf(`unknown key type %T`, src)
	}

	ctx := context.Background()
	for iter := src.Iterate(ctx); iter.Next(ctx); {
		pair := iter.Pair()
		if err := dst.Set(pair.Key.(string), pair.Value); err != nil {
			return nil, errors.Wrapf(err, `failed to set %s`, pair.Key.(string))
		}
	}
	return dst, nil
}

// Pem serializes the given jwk.Key in PEM encoded ASN.1 DER format,
// using either PKCS8 for private keys and PKIX for public keys.
// If you need to encode using PKCS1 or SEC1, you must do it yourself.
//
// Argument must be of type jwk.Key or jwk.Set
//
// Currently only EC (including Ed25519) and RSA keys (and jwk.Set
// comprised of these key types) are supported.
func Pem(v interface{}) ([]byte, error) {
	var set Set
	switch v := v.(type) {
	case Key:
		set = NewSet()
		set.Add(v)
	case Set:
		set = v
	default:
		return nil, errors.Errorf(`argument to Pem must be either jwk.Key or jwk.Set: %T`, v)
	}

	var ret []byte
	for i := 0; i < set.Len(); i++ {
		key, _ := set.Get(i)
		typ, buf, err := asnEncode(key)
		if err != nil {
			return nil, errors.Wrapf(err, `failed to encode content for key #%d`, i)
		}

		var block pem.Block
		block.Type = typ
		block.Bytes = buf
		ret = append(ret, pem.EncodeToMemory(&block)...)
	}
	return ret, nil
}

func asnEncode(key Key) (string, []byte, error) {
	switch key := key.(type) {
	case RSAPrivateKey, ECDSAPrivateKey, OKPPrivateKey:
		var rawkey interface{}
		if err := key.Raw(&rawkey); err != nil {
			return "", nil, errors.Wrap(err, `failed to get raw key from jwk.Key`)
		}
		buf, err := x509.MarshalPKCS8PrivateKey(rawkey)
		if err != nil {
			return "", nil, errors.Wrap(err, `failed to marshal PKCS8`)
		}
		return "PRIVATE KEY", buf, nil
	case RSAPublicKey, ECDSAPublicKey, OKPPublicKey:
		var rawkey interface{}
		if err := key.Raw(&rawkey); err != nil {
			return "", nil, errors.Wrap(err, `failed to get raw key from jwk.Key`)
		}
		buf, err := x509.MarshalPKIXPublicKey(rawkey)
		if err != nil {
			return "", nil, errors.Wrap(err, `failed to marshal PKIX`)
		}
		return "PUBLIC KEY", buf, nil
	default:
		return "", nil, errors.Errorf(`unsupported key type %T`, key)
	}
}

// RegisterCustomField allows users to specify that a private field
// be decoded as an instance of the specified type. This option has
// a global effect.
//
// For example, suppose you have a custom field `x-birthday`, which
// you want to represent as a string formatted in RFC3339 in JSON,
// but want it back as `time.Time`.
//
// In that case you would register a custom field as follows
//
//   jwk.RegisterCustomField(`x-birthday`, timeT)
//
// Then `key.Get("x-birthday")` will still return an `interface{}`,
// but you can convert its type to `time.Time`
//
//   bdayif, _ := key.Get(`x-birthday`)
//   bday := bdayif.(time.Time)
//
func RegisterCustomField(name string, object interface{}) {
	registry.Register(name, object)
}