package keypairs

import (
	"crypto"
	"crypto/dsa"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"io"
	"log"
	"math/big"
	"time"
)

var EInvalidPrivateKey = errors.New("PrivateKey must be of type *rsa.PrivateKey or *ecdsa.PrivateKey")
var EInvalidPublicKey = errors.New("PublicKey must be of type *rsa.PublicKey or *ecdsa.PublicKey")
var EParsePrivateKey = errors.New("PrivateKey bytes could not be parsed as PEM or DER (PKCS8, SEC1, or PKCS1) or JWK")
var EParseJWK = errors.New("JWK is missing required base64-encoded JSON fields")
var EInvalidKeyType = errors.New("The JWK's 'kty' must be either 'RSA' or 'EC'")
var EInvalidCurve = errors.New("The JWK's 'crv' must be either of the NIST standards 'P-256' or 'P-384'")

const EDevSwapPrivatePublic = "[Developer Error] You passed either crypto.PrivateKey or crypto.PublicKey where the other was expected."

const EDevBadKeyType = "[Developer Error] crypto.PublicKey and crypto.PrivateKey are somewhat deceptive. They're actually empty interfaces that accept any object, even non-crypto objects. You passed an object of type '%T' by mistake."

// PrivateKey is a zero-cost typesafe substitue for crypto.PrivateKey
type PrivateKey interface {
	Public() crypto.PublicKey
}

// PublicKey thinly veils crypto.PublicKey for type safety
type PublicKey interface {
	crypto.PublicKey
	Thumbprint() string
	Key() crypto.PublicKey
}

type ECPublicKey struct {
	PublicKey *ecdsa.PublicKey // empty interface
	KID       string
	Expiry    time.Time
}

type RSAPublicKey struct {
	PublicKey *rsa.PublicKey // empty interface
	KID       string
	Expiry    time.Time
}

func (p *ECPublicKey) Thumbprint() string {
	return ThumbprintUntypedPublicKey(p.PublicKey)
}
func (p *ECPublicKey) Key() crypto.PublicKey {
	return p.PublicKey
}
func (p *ECPublicKey) ExpireAt(t time.Time) {
	p.Expiry = t
}

func (p *RSAPublicKey) Thumbprint() string {
	return ThumbprintUntypedPublicKey(p.PublicKey)
}
func (p *RSAPublicKey) Key() crypto.PublicKey {
	return p.PublicKey
}
func (p *RSAPublicKey) ExpireAt(t time.Time) {
	p.Expiry = t
}

// TypesafePublicKey wraps a crypto.PublicKey to make it typesafe.
func NewPublicKey(pub crypto.PublicKey, kid ...string) PublicKey {
	var k PublicKey
	switch p := pub.(type) {
	case *ecdsa.PublicKey:
		eckey := &ECPublicKey{
			PublicKey: p,
		}
		if 0 != len(kid) {
			eckey.KID = kid[0]
		} else {
			eckey.KID = ThumbprintECPublicKey(p)
		}
		k = eckey
	case *rsa.PublicKey:
		rsakey := &RSAPublicKey{
			PublicKey: p,
		}
		if 0 != len(kid) {
			rsakey.KID = kid[0]
		} else {
			rsakey.KID = ThumbprintRSAPublicKey(p)
		}
		k = rsakey
	case *ecdsa.PrivateKey:
		panic(errors.New(EDevSwapPrivatePublic))
	case *rsa.PrivateKey:
		panic(errors.New(EDevSwapPrivatePublic))
	case *dsa.PublicKey:
		panic(EInvalidPublicKey)
	case *dsa.PrivateKey:
		panic(EInvalidPublicKey)
	default:
		panic(errors.New(fmt.Sprintf(EDevBadKeyType, pub)))
	}

	return k
}

func MarshalJWKPublicKey(key PublicKey, exp ...time.Time) []byte {
	// thumbprint keys are alphabetically sorted and only include the necessary public parts
	switch k := key.Key().(type) {
	case *rsa.PublicKey:
		return MarshalRSAPublicKey(k, exp...)
	case *ecdsa.PublicKey:
		return MarshalECPublicKey(k, exp...)
	case *dsa.PublicKey:
		panic(EInvalidPublicKey)
	default:
		// this is unreachable because we know the types that we pass in
		log.Printf("keytype: %t, %+v\n", key, key)
		panic(EInvalidPublicKey)
	}
}

func ThumbprintPublicKey(pub *PublicKey) string {
	return ThumbprintUntypedPublicKey(pub)
}

func ThumbprintUntypedPublicKey(pub crypto.PublicKey) string {
	switch p := pub.(type) {
	case *ecdsa.PublicKey:
		return ThumbprintECPublicKey(p)
	case *rsa.PublicKey:
		return ThumbprintRSAPublicKey(p)
	default:
		panic(EInvalidPublicKey)
	}
}

func MarshalECPublicKey(k *ecdsa.PublicKey, exp ...time.Time) []byte {
	thumb := ThumbprintECPublicKey(k)
	crv := k.Curve.Params().Name
	x := base64.RawURLEncoding.EncodeToString(k.X.Bytes())
	y := base64.RawURLEncoding.EncodeToString(k.Y.Bytes())
	expstr := ""
	if 0 != len(exp) {
		expstr = fmt.Sprintf(`"exp":%q,`, exp[0].Format(time.RFC3339))
	}
	return []byte(fmt.Sprintf(`{"kid":%q,%s"crv":%q,"kty":"EC","x":%q,"y":%q}`, expstr, thumb, crv, x, y))
}

func MarshalECPublicKeyWithoutKeyID(k *ecdsa.PublicKey) []byte {
	crv := k.Curve.Params().Name
	x := base64.RawURLEncoding.EncodeToString(k.X.Bytes())
	y := base64.RawURLEncoding.EncodeToString(k.Y.Bytes())
	return []byte(fmt.Sprintf(`{"crv":%q,"kty":"EC","x":%q,"y":%q}`, crv, x, y))
}

func ThumbprintECPublicKey(k *ecdsa.PublicKey) string {
	thumbprintable := MarshalECPublicKeyWithoutKeyID(k)
	sha := sha256.Sum256(thumbprintable)
	return base64.RawURLEncoding.EncodeToString(sha[:])
}

func MarshalRSAPublicKey(p *rsa.PublicKey, exp ...time.Time) []byte {
	thumb := ThumbprintRSAPublicKey(p)
	e := base64.RawURLEncoding.EncodeToString(big.NewInt(int64(p.E)).Bytes())
	n := base64.RawURLEncoding.EncodeToString(p.N.Bytes())
	expstr := ""
	if 0 != len(exp) {
		expstr = fmt.Sprintf(`"exp":%q,`, exp[0].Format(time.RFC3339))
	}
	return []byte(fmt.Sprintf(`{"kid":%q,%s"e":%q,"kty":"RSA","n":%q}`, expstr, thumb, e, n))
}

func MarshalRSAPublicKeyWithoutKeyID(p *rsa.PublicKey) []byte {
	e := base64.RawURLEncoding.EncodeToString(big.NewInt(int64(p.E)).Bytes())
	n := base64.RawURLEncoding.EncodeToString(p.N.Bytes())
	return []byte(fmt.Sprintf(`{"e":%q,"kty":"RSA","n":%q}`, e, n))
}

func ThumbprintRSAPublicKey(p *rsa.PublicKey) string {
	thumbprintable := MarshalRSAPublicKeyWithoutKeyID(p)
	sha := sha256.Sum256([]byte(thumbprintable))
	return base64.RawURLEncoding.EncodeToString(sha[:])
}

func ParsePrivateKey(block []byte) (PrivateKey, error) {
	var pemblock *pem.Block
	var blocks = make([][]byte, 0, 1)

	// Parse the PEM, if it's a pem
	for {
		pemblock, block = pem.Decode(block)
		if nil != pemblock {
			// got one block, there may be more
			blocks = append(blocks, pemblock.Bytes)
		} else {
			// the last block was not a PEM block
			// therefore the next isn't either
			if 0 != len(block) {
				blocks = append(blocks, block)
			}
			break
		}
	}

	// Parse PEM blocks (openssl generates junk metadata blocks for ECs)
	// or the original DER, or the JWK
	for i, _ := range blocks {
		block = blocks[i]
		if key, err := parsePrivateKey(block); nil == err {
			return key, nil
		}
	}

	// If we didn't parse a key arleady, we failed
	return nil, EParsePrivateKey
}

func ParsePrivateKeyString(block string) (PrivateKey, error) {
	return ParsePrivateKey([]byte(block))
}

func parsePrivateKey(der []byte) (PrivateKey, error) {
	var key PrivateKey

	//fmt.Println("1. ParsePKCS8PrivateKey")
	xkey, err := x509.ParsePKCS8PrivateKey(der)
	if nil == err {
		switch k := xkey.(type) {
		case *rsa.PrivateKey:
			key = k
		case *ecdsa.PrivateKey:
			key = k
		default:
			// ignore nil and unknown key types
		}
	}

	if nil != err {
		//fmt.Println("2. ParseECPrivateKey")
		key, err = x509.ParseECPrivateKey(der)
		if nil != err {
			//fmt.Println("3. ParsePKCS1PrivateKey")
			key, err = x509.ParsePKCS1PrivateKey(der)
			if nil != err {
				//fmt.Println("4. ParseJWKPrivateKey")
				key, err = ParseJWKPrivateKey(der)
			}
		}
	}

	// But did you know?
	// You must return nil explicitly for interfaces
	// https://golang.org/doc/faq#nil_error
	if nil != err {
		return nil, err
	}

	return key, nil
}

func NewJWKPublicKey(m map[string]string) (PublicKey, error) {
	switch m["kty"] {
	case "RSA":
		return parseRSAPublicKey(m)
	case "EC":
		return parseECPublicKey(m)
	default:
		return nil, EInvalidKeyType
	}
}

func ParseJWKPublicKey(b []byte) (PublicKey, error) {
	return newJWKPublicKey(b)
}

func ParseJWKPublicKeyString(s string) (PublicKey, error) {
	return newJWKPublicKey(s)
}

func DecodeJWKPublicKey(r io.Reader) (PublicKey, error) {
	return newJWKPublicKey(r)
}

func newJWKPublicKey(data interface{}) (PublicKey, error) {
	var m map[string]string

	switch d := data.(type) {
	case map[string]string:
		m = d
	case io.Reader:
		m = make(map[string]string)
		if err := json.NewDecoder(d).Decode(&m); nil != err {
			return nil, err
		}
	case string:
		if err := json.Unmarshal([]byte(d), &m); nil != err {
			return nil, err
		}
	case []byte:
		if err := json.Unmarshal(d, &m); nil != err {
			return nil, err
		}
	default:
		panic("Developer Error: unsupported interface type")
	}

	return NewJWKPublicKey(m)
}

func ParseJWKPrivateKey(b []byte) (PrivateKey, error) {
	var m map[string]string
	if err := json.Unmarshal(b, &m); nil != err {
		return nil, err
	}

	switch m["kty"] {
	case "RSA":
		return parseRSAPrivateKey(m)
	case "EC":
		return parseECPrivateKey(m)
	default:
		return nil, EInvalidKeyType
	}
}

func parseRSAPublicKey(m map[string]string) (*RSAPublicKey, error) {
	// TODO grab expiry?
	kid, _ := m["kid"]
	n, _ := base64.RawURLEncoding.DecodeString(m["n"])
	e, _ := base64.RawURLEncoding.DecodeString(m["e"])
	if 0 == len(n) || 0 == len(e) {
		return nil, EParseJWK
	}
	ni := &big.Int{}
	ni.SetBytes(n)
	ei := &big.Int{}
	ei.SetBytes(e)

	pub := &rsa.PublicKey{
		N: ni,
		E: int(ei.Int64()),
	}

	return &RSAPublicKey{
		PublicKey: pub,
		KID:       kid,
	}, nil
}

func parseRSAPrivateKey(m map[string]string) (key *rsa.PrivateKey, err error) {
	pub, err := parseRSAPublicKey(m)
	if nil != err {
		return
	}

	d, _ := base64.RawURLEncoding.DecodeString(m["d"])
	p, _ := base64.RawURLEncoding.DecodeString(m["p"])
	q, _ := base64.RawURLEncoding.DecodeString(m["q"])
	dp, _ := base64.RawURLEncoding.DecodeString(m["dp"])
	dq, _ := base64.RawURLEncoding.DecodeString(m["dq"])
	qinv, _ := base64.RawURLEncoding.DecodeString(m["qi"])
	if 0 == len(d) || 0 == len(p) || 0 == len(dp) || 0 == len(dq) || 0 == len(qinv) {
		return nil, EParseJWK
	}

	di := &big.Int{}
	di.SetBytes(d)
	pi := &big.Int{}
	pi.SetBytes(p)
	qi := &big.Int{}
	qi.SetBytes(q)
	dpi := &big.Int{}
	dpi.SetBytes(dp)
	dqi := &big.Int{}
	dqi.SetBytes(dq)
	qinvi := &big.Int{}
	qinvi.SetBytes(qinv)

	key = &rsa.PrivateKey{
		PublicKey: *pub.PublicKey,
		D:         di,
		Primes:    []*big.Int{pi, qi},
		Precomputed: rsa.PrecomputedValues{
			Dp:   dpi,
			Dq:   dqi,
			Qinv: qinvi,
		},
	}

	return
}

func parseECPublicKey(m map[string]string) (*ECPublicKey, error) {
	// TODO grab expiry?
	kid, _ := m["kid"]
	x, _ := base64.RawURLEncoding.DecodeString(m["x"])
	y, _ := base64.RawURLEncoding.DecodeString(m["y"])
	if 0 == len(x) || 0 == len(y) || 0 == len(m["crv"]) {
		return nil, EParseJWK
	}

	xi := &big.Int{}
	xi.SetBytes(x)

	yi := &big.Int{}
	yi.SetBytes(y)

	var crv elliptic.Curve
	switch m["crv"] {
	case "P-256":
		crv = elliptic.P256()
	case "P-384":
		crv = elliptic.P384()
	case "P-521":
		crv = elliptic.P521()
	default:
		return nil, EInvalidCurve
	}

	pub := &ecdsa.PublicKey{
		Curve: crv,
		X:     xi,
		Y:     yi,
	}

	return &ECPublicKey{
		PublicKey: pub,
		KID:       kid,
	}, nil
}

func parseECPrivateKey(m map[string]string) (*ecdsa.PrivateKey, error) {
	pub, err := parseECPublicKey(m)
	if nil != err {
		return nil, err
	}

	d, _ := base64.RawURLEncoding.DecodeString(m["d"])
	if 0 == len(d) {
		return nil, EParseJWK
	}
	di := &big.Int{}
	di.SetBytes(d)

	return &ecdsa.PrivateKey{
		PublicKey: *pub.PublicKey,
		D:         di,
	}, nil
}