// Copyright 2012-2018 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package server

import (
	"crypto/tls"
	"encoding/base64"
	"strings"

	"github.com/nats-io/nkeys"
	"golang.org/x/crypto/bcrypt"
)

// Authentication is an interface for implementing authentication
type Authentication interface {
	// Check if a client is authorized to connect
	Check(c ClientAuthentication) bool
}

// ClientAuthentication is an interface for client authentication
type ClientAuthentication interface {
	// Get options associated with a client
	GetOpts() *clientOpts
	// If TLS is enabled, TLS ConnectionState, nil otherwise
	GetTLSConnectionState() *tls.ConnectionState
	// Optionally map a user after auth.
	RegisterUser(*User)
}

// NkeyUser is for multiple nkey based users
type NkeyUser struct {
	Nkey        string       `json:"user"`
	Permissions *Permissions `json:"permissions,omitempty"`
	Account     *Account     `json:"account,omitempty"`
}

// User is for multiple accounts/users.
type User struct {
	Username    string       `json:"user"`
	Password    string       `json:"password"`
	Permissions *Permissions `json:"permissions,omitempty"`
	Account     *Account     `json:"account,omitempty"`
}

// clone performs a deep copy of the User struct, returning a new clone with
// all values copied.
func (u *User) clone() *User {
	if u == nil {
		return nil
	}
	clone := &User{}
	*clone = *u
	clone.Permissions = u.Permissions.clone()
	return clone
}

// clone performs a deep copy of the NkeyUser struct, returning a new clone with
// all values copied.
func (n *NkeyUser) clone() *NkeyUser {
	if n == nil {
		return nil
	}
	clone := &NkeyUser{}
	*clone = *n
	clone.Permissions = n.Permissions.clone()
	return clone
}

// SubjectPermission is an individual allow and deny struct for publish
// and subscribe authorizations.
type SubjectPermission struct {
	Allow []string `json:"allow,omitempty"`
	Deny  []string `json:"deny,omitempty"`
}

// Permissions are the allowed subjects on a per
// publish or subscribe basis.
type Permissions struct {
	Publish   *SubjectPermission `json:"publish"`
	Subscribe *SubjectPermission `json:"subscribe"`
}

// RoutePermissions are similar to user permissions
// but describe what a server can import/export from and to
// another server.
type RoutePermissions struct {
	Import *SubjectPermission `json:"import"`
	Export *SubjectPermission `json:"export"`
}

// clone will clone an individual subject permission.
func (p *SubjectPermission) clone() *SubjectPermission {
	if p == nil {
		return nil
	}
	clone := &SubjectPermission{}
	if p.Allow != nil {
		clone.Allow = make([]string, len(p.Allow))
		copy(clone.Allow, p.Allow)
	}
	if p.Deny != nil {
		clone.Deny = make([]string, len(p.Deny))
		copy(clone.Deny, p.Deny)
	}
	return clone
}

// clone performs a deep copy of the Permissions struct, returning a new clone
// with all values copied.
func (p *Permissions) clone() *Permissions {
	if p == nil {
		return nil
	}
	clone := &Permissions{}
	if p.Publish != nil {
		clone.Publish = p.Publish.clone()
	}
	if p.Subscribe != nil {
		clone.Subscribe = p.Subscribe.clone()
	}
	return clone
}

// checkAuthforWarnings will look for insecure settings and log concerns.
// Lock is assumed held.
func (s *Server) checkAuthforWarnings() {
	warn := false
	if s.opts.Password != "" && !isBcrypt(s.opts.Password) {
		warn = true
	}
	for _, u := range s.users {
		if !isBcrypt(u.Password) {
			warn = true
			break
		}
	}
	if warn {
		// Warning about using plaintext passwords.
		s.Warnf("Plaintext passwords detected, use nkeys or bcrypt.")
	}
}

// If opts.Users or opts.Nkeys have definitions without an account
// defined assign them to the default global account.
// Lock should be held.
func (s *Server) assignGlobalAccountToOrphanUsers() {
	for _, u := range s.users {
		if u.Account == nil {
			u.Account = s.gacc
		}
	}
	for _, u := range s.nkeys {
		if u.Account == nil {
			u.Account = s.gacc
		}
	}
}

// configureAuthorization will do any setup needed for authorization.
// Lock is assumed held.
func (s *Server) configureAuthorization() {
	if s.opts == nil {
		return
	}

	// Snapshot server options.
	opts := s.getOpts()

	// Check for multiple users first
	// This just checks and sets up the user map if we have multiple users.
	if opts.CustomClientAuthentication != nil {
		s.info.AuthRequired = true
	} else if opts.Nkeys != nil || opts.Users != nil {
		// Support both at the same time.
		if opts.Nkeys != nil {
			s.nkeys = make(map[string]*NkeyUser)
			for _, u := range opts.Nkeys {
				s.nkeys[u.Nkey] = u
			}
		}
		if opts.Users != nil {
			s.users = make(map[string]*User)
			for _, u := range opts.Users {
				s.users[u.Username] = u
			}
		}
		s.assignGlobalAccountToOrphanUsers()
		s.info.AuthRequired = true
	} else if opts.Username != "" || opts.Authorization != "" {
		s.info.AuthRequired = true
	} else {
		s.users = nil
		s.info.AuthRequired = false
	}
}

// checkAuthorization will check authorization based on client type and
// return boolean indicating if client is authorized.
func (s *Server) checkAuthorization(c *client) bool {
	switch c.typ {
	case CLIENT:
		return s.isClientAuthorized(c)
	case ROUTER:
		return s.isRouterAuthorized(c)
	default:
		return false
	}
}

// isClientAuthorized will check the client against the proper authorization method and data.
// This could be nkey, token, or username/password based.
func (s *Server) isClientAuthorized(c *client) bool {
	// Snapshot server options by hand and only grab what we really need.
	s.optsMu.RLock()
	customClientAuthentication := s.opts.CustomClientAuthentication
	authorization := s.opts.Authorization
	username := s.opts.Username
	password := s.opts.Password
	s.optsMu.RUnlock()

	// Check custom auth first, then nkeys, then multiple users, then token, then single user/pass.
	if customClientAuthentication != nil {
		return customClientAuthentication.Check(c)
	}

	var nkey *NkeyUser
	var user *User
	var ok bool

	s.mu.Lock()
	authRequired := s.info.AuthRequired
	if !authRequired {
		// TODO(dlc) - If they send us credentials should we fail?
		s.mu.Unlock()
		return true
	}

	// Check if we have nkeys or users for client.
	hasNkeys := s.nkeys != nil
	hasUsers := s.users != nil
	if hasNkeys && c.opts.Nkey != "" {
		nkey, ok = s.nkeys[c.opts.Nkey]
		if !ok {
			s.mu.Unlock()
			return false
		}
	} else if hasUsers && c.opts.Username != "" {
		user, ok = s.users[c.opts.Username]
		if !ok {
			s.mu.Unlock()
			return false
		}
	}
	s.mu.Unlock()

	// Verify the signature against the nonce.
	if nkey != nil {
		if c.opts.Sig == "" {
			return false
		}
		sig, err := base64.StdEncoding.DecodeString(c.opts.Sig)
		if err != nil {
			return false
		}
		pub, err := nkeys.FromPublicKey(c.opts.Nkey)
		if err != nil {
			return false
		}
		if err := pub.Verify(c.nonce, sig); err != nil {
			return false
		}
		c.RegisterNkeyUser(nkey)
		return true
	}

	if user != nil {
		ok = comparePasswords(user.Password, c.opts.Password)
		// If we are authorized, register the user which will properly setup any permissions
		// for pub/sub authorizations.
		if ok {
			c.RegisterUser(user)
		}
		return ok
	}

	if authorization != "" {
		return comparePasswords(authorization, c.opts.Authorization)
	} else if username != "" {
		if username != c.opts.Username {
			return false
		}
		return comparePasswords(password, c.opts.Password)
	}

	return false
}

// checkRouterAuth checks optional router authorization which can be nil or username/password.
func (s *Server) isRouterAuthorized(c *client) bool {
	// Snapshot server options.
	opts := s.getOpts()

	if s.opts.CustomRouterAuthentication != nil {
		return s.opts.CustomRouterAuthentication.Check(c)
	}

	if opts.Cluster.Username == "" {
		return true
	}

	if opts.Cluster.Username != c.opts.Username {
		return false
	}
	if !comparePasswords(opts.Cluster.Password, c.opts.Password) {
		return false
	}
	return true
}

// Support for bcrypt stored passwords and tokens.
const bcryptPrefix = "$2a$"

// isBcrypt checks whether the given password or token is bcrypted.
func isBcrypt(password string) bool {
	return strings.HasPrefix(password, bcryptPrefix)
}

func comparePasswords(serverPassword, clientPassword string) bool {
	// Check to see if the server password is a bcrypt hash
	if isBcrypt(serverPassword) {
		if err := bcrypt.CompareHashAndPassword([]byte(serverPassword), []byte(clientPassword)); err != nil {
			return false
		}
	} else if serverPassword != clientPassword {
		return false
	}
	return true
}