// Copyright (C) 2018 Marius Schellenberger

// Package jwt provides a easy to use JSON Web Token and blacklisting library
package jwt

import (
	"crypto/hmac"
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"errors"
	"io"
	"strings"
	"time"
)

const (
	// Header is the default HTTP Authorization header name
	Header = "Authorization"
	// DefaultExpiry is the default token expiration time
	DefaultExpiry = time.Hour * 12
	// KeySize is the secret key size
	KeySize = 64

	typ = "JWT"
)

// DefaultSecretReader is the default secret key generator
var DefaultSecretReader = rand.Reader

var (
	ErrNoJWT               = errors.New("not a json web token")
	ErrEmptyToken          = errors.New("token is empty")
	ErrUnsupportedAlg      = errors.New("unsupported algorithm")
	ErrInvalid             = errors.New("token validation failed")
	ErrBlacklisted         = errors.New("token blacklisted")
	ErrBlacklistNotEnabled = errors.New("blacklisting is not enabled")
	ErrNBF                 = errors.New("token not valid yet")
	ErrEXP                 = errors.New("token expired")
	ErrMissingEXP          = errors.New("missing exp claim")
	ErrMissingTokenParts   = errors.New("missing token parts")
	ErrEmptySignature      = errors.New("token signature is empty")
	ErrTokenIsNil          = errors.New("token is nil")
	ErrInvalidKeySize      = errors.New("invalid secret key size")
)

// JWT represents the JSON Web Token signing and blacklisting infrastructure
type JWT struct {
	key    []byte
	expiry time.Duration

	blacklist Blacklist
	done      chan struct{}
}

// New returns a new JWT object with the given expiry timeout.
// If the timeout is less or equal to zero the default expiry (12 hours) is used.
// If blacklisting is enabled, the JWT object leaks a goroutine to garbage-collect expired blacklisted tokens.
// Call the Stop() method to exit the goroutine.
func New(expiry time.Duration, blacklist Blacklist, secret io.Reader) (*JWT, error) {
	if expiry <= 0 {
		expiry = DefaultExpiry
	}
	if secret == nil {
		secret = DefaultSecretReader
	}
	secret = io.LimitReader(secret, KeySize)
	key := make([]byte, KeySize)
	i, err := secret.Read(key)
	if err != nil {
		return nil, errors.New("secret reader error: " + err.Error())
	}
	if i < KeySize {
		return nil, ErrInvalidKeySize
	}
	jwt := &JWT{
		key:       key,
		expiry:    expiry,
		blacklist: blacklist,
	}
	if blacklist != nil {
		jwt.done = make(chan struct{})
		go jwt.clean()
	}
	return jwt, nil
}

func (jwt *JWT) sum(token string, h Hash) []byte {
	mac := hmac.New(h.Hash, jwt.key)
	mac.Write([]byte(token))
	return mac.Sum(nil)
}

// Invalidate checks if a token is already blacklisted
// If the token is not blacklisted, it will get blacklisted
func (jwt *JWT) Invalidate(t *Token) error {
	if jwt.blacklist == nil {
		return ErrBlacklistNotEnabled
	}
	if t == nil {
		return ErrTokenIsNil
	}
	var (
		expOK bool
		exp   int64
	)
	switch n := t.Claims["exp"].(type) {
	case json.Number:
		if i, err := n.Int64(); err == nil {
			exp = i
			expOK = true
		}
	case float64:
		exp = int64(n)
		expOK = true
	}
	if !expOK {
		return ErrMissingEXP
	}
	if err := jwt.blacklisted(t.Sig()); err != nil {
		return err
	}
	jwt.blacklist.Add(t.Sig(), exp)
	return nil
}

// blacklisted checks if a token is blacklisted
func (jwt *JWT) blacklisted(sig string) error {
	if sig == "" {
		return ErrEmptySignature
	}
	if jwt.blacklist.Check(sig) {
		return ErrBlacklisted
	}
	return nil
}

// clean looks for expired blacklisted tokens and removes them
func (jwt *JWT) clean() {
	for {
		t := time.NewTimer(time.Hour)
		select {
		case <-t.C:
		case <-jwt.done:
			t.Stop()
			return
		}
		now := time.Now().UTC().Unix()
		for k, v := range jwt.blacklist.Map() {
			if now > v {
				jwt.blacklist.Remove(k)
			}
		}
	}
}

// Sign will sign the provided token using the secret key
// This will overwrite existing 'exp' and 'nbf' claims
func (jwt *JWT) Sign(t *Token) (err error) {
	if t == nil {
		return ErrTokenIsNil
	}
	header := t.Header()
	switch t := header["typ"].(type) {
	case string:
		if t != typ {
			return ErrNoJWT
		}
	default:
		return ErrNoJWT
	}
	var h Hash
	switch a := header["alg"].(type) {
	case string:
		h = ParseHash(a)
		if h == nil {
			return ErrUnsupportedAlg
		}
	default:
		return ErrUnsupportedAlg
	}
	now := time.Now().UTC()
	t.Claims["exp"] = now.Add(jwt.expiry).Unix()
	t.Claims["nbf"] = now.Unix()
	head, err := json.Marshal(header)
	if err != nil {
		return
	}
	claims, err := json.Marshal(t.Claims)
	if err != nil {
		return
	}
	t.data = strings.Join([]string{base64.URLEncoding.EncodeToString(head), base64.URLEncoding.EncodeToString(claims)}, ".")
	t.raw = strings.Join([]string{t.data, base64.URLEncoding.EncodeToString(jwt.sum(t.data, h))}, ".")
	return
}

// Verify will verify the provided token using the secret key
func (jwt *JWT) Verify(t *Token) error {
	if t == nil {
		return ErrTokenIsNil
	}
	now := time.Now().UTC().Unix()
	var (
		exp   int64
		nbf   int64
		expOK bool
		nbfOK bool
		h     Hash
	)
	header := t.Header()
	switch t := header["typ"].(type) {
	case string:
		if t != typ {
			return ErrNoJWT
		}
	default:
		return ErrNoJWT
	}
	switch a := header["alg"].(type) {
	case string:
		h = ParseHash(a)
		if h == nil {
			return ErrUnsupportedAlg
		}
	default:
		return ErrUnsupportedAlg
	}

	switch n := t.Claims["exp"].(type) {
	case json.Number:
		if i, err := n.Int64(); err == nil {
			exp = i
			expOK = true
		}
	case float64:
		exp = int64(n)
		expOK = true
	}
	switch n := t.Claims["nbf"].(type) {
	case json.Number:
		if i, err := n.Int64(); err == nil {
			nbf = i
			nbfOK = true
		}
	case float64:
		nbf = int64(n)
		nbfOK = true
	}
	if jwt.blacklist != nil {
		err := jwt.blacklisted(t.Sig())
		if err != nil {
			return err
		}
	}
	if expOK && now > exp {
		return ErrEXP
	}
	if nbfOK && now < nbf {
		return ErrNBF
	}
	if !hmac.Equal(jwt.sum(t.Data(), h), t.RawSig()) {
		return ErrInvalid
	}
	return nil
}

// Stop will end the cleaner goroutinge execution
// Calling Stop twice or more will panic
func (jwt *JWT) Stop() error {
	if jwt.blacklist == nil {
		return ErrBlacklistNotEnabled
	}
	close(jwt.done)
	return nil
}

// DecodeToken decodes a raw string token into a *Token object
func DecodeToken(token string) (t *Token, err error) {
	if token == "" {
		return nil, ErrEmptyToken
	}
	parts := strings.Split(token, ".")
	if len(parts) < 3 {
		return nil, ErrMissingTokenParts
	}
	if len(parts) > 3 {
		return nil, ErrNoJWT
	}
	for _, v := range parts {
		if v == "" {
			return nil, ErrNoJWT
		}
	}
	t = new(Token)
	header, err := base64.URLEncoding.DecodeString(parts[0])
	if err != nil {
		return
	}
	err = json.Unmarshal(header, &t.header)
	if err != nil {
		return
	}
	claims, err := base64.URLEncoding.DecodeString(parts[1])
	if err != nil {
		return
	}
	err = json.Unmarshal(claims, &t.Claims)
	if err != nil {
		return
	}
	t.rawSignature, err = base64.URLEncoding.DecodeString(parts[2])
	t.signature = parts[2]
	t.data = strings.Join(parts[:2], ".")
	t.raw = token
	return
}

// Token is the JWT token representation
type Token struct {
	raw          string
	data         string
	signature    string
	rawSignature []byte
	header       map[string]interface{}
	Claims       map[string]interface{}
}

// String returns the tokens encoded string
func (t *Token) String() string {
	return t.raw
}

// Sig returns the Tokens URLEncoded signature
func (t *Token) Sig() string {
	return t.signature
}

// RawSig returns the Tokens raw signature
func (t *Token) RawSig() []byte {
	return t.rawSignature
}

// Header returns the Tokens header
func (t *Token) Header() map[string]interface{} {
	return t.header
}

// Data returns the first two token fields
func (t *Token) Data() string {
	return t.data
}

// NewToken returns a new *Token using the provided hash algorithm and claims
// If h is nil HS256 will be used
func NewToken(claims map[string]interface{}, h Hash) *Token {
	if h == nil {
		h = NewHS256()
	}
	return &Token{
		header: map[string]interface{}{
			"alg": h.Alg(),
			"typ": typ,
		},
		Claims: claims,
	}
}