// Vikunja is a to-do list application to facilitate your life.
// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public Licensee as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public Licensee for more details.
//
// You should have received a copy of the GNU Affero General Public Licensee
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package auth

import (
	"net/http"
	"time"

	"xorm.io/xorm"

	"code.vikunja.io/api/pkg/config"
	"code.vikunja.io/api/pkg/models"
	"code.vikunja.io/api/pkg/user"
	"code.vikunja.io/web"
	"github.com/dgrijalva/jwt-go"
	petname "github.com/dustinkirkland/golang-petname"
	"github.com/labstack/echo/v4"
)

// These are all valid auth types
type AuthType int

const (
	AuthTypeUnknown AuthType = iota
	AuthTypeUser
	AuthTypeLinkShare
	AuthTypeIAPUser
)

// Key used to store authClaims
const AuthClaimsContextKey string = "authClaims"

// Token represents an authentification token in signed string form
type Token struct {
	Token string `json:"token"`
}

// Claims made in the JWT token for various auth types
// Only the auth module should introspect and handle claims
type AuthClaims struct {
	// Common to all claims
	Type AuthType `json:"type"`

	// AuthTypeUser and AuthTypeIAPUser claims
	UserID       int64  `json:"user_id,omitempty"`
	UserUsername string `json:"user_username,omitempty"`
	UserEmail    string `json:"user_email,omitempty"`
	UserName     string `json:"user_name,omitempty"`

	UserEmailRemindersEnabled bool `json:"user_email_reminders_enabled"`

	// AuthTypeLinkShare claims
	ShareID         int64        `json:"share_id,omitempty"`
	ShareHash       string       `json:"share_hash,omitempty"`
	ShareListID     int64        `json:"share_list_id,omitempty"`
	ShareRight      models.Right `json:"share_right,omitempty"`
	ShareSharedByID int64        `json:"share_shared_by_id,omitempty"`

	// Common claims
	jwt.StandardClaims
}

// An AuthProvider provides alternative methods of authentication
// In these cases, AuthClaims may contain hints to the user identity,
// but an outside source is the final source-of-truth for auth (e.g. Identity-Aware Proxy auth)
type AuthProvider interface {
	GetUser(echo.Context, *AuthClaims) (*user.User, error)
	RenewToken(echo.Context, *AuthClaims) (string, error)
}

var authProviders = map[AuthType]AuthProvider{}

func RegisterAuthProvider(t AuthType, provider AuthProvider) {
	authProviders[t] = provider
}

// NewTokenResponse creates a new token response from a token
func NewTokenResponse(t string, c echo.Context) error {
	return c.JSON(http.StatusOK, Token{Token: t})
}

// NewUserAuthTokenResponse creates a new user auth token response from a user object.
func NewUserAuthTokenResponse(u *user.User, c echo.Context) error {
	t, err := NewUserJWTAuthtoken(u)
	if err != nil {
		return err
	}

	return NewTokenResponse(t, c)
}

// NewUserJWTAuthtoken generates and signes a new jwt token for a user. This is a global function to be able to call it from integration tests.
func NewUserJWTAuthtoken(u *user.User) (token string, err error) {
	// Set claims
	claims := &AuthClaims{
		Type:                      AuthTypeUser,
		UserID:                    u.ID,
		UserUsername:              u.Username,
		UserEmail:                 u.Email,
		UserName:                  u.Name,
		UserEmailRemindersEnabled: u.EmailRemindersEnabled,
		StandardClaims: jwt.StandardClaims{
			ExpiresAt: time.Now().Add(time.Hour * 72).Unix(),
		},
	}

	t := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)

	// Generate encoded token and send it as response.
	return t.SignedString([]byte(config.ServiceJWTSecret.GetString()))
}

// NewLinkShareJWTAuthtoken creates a new jwt token from a link share
func NewLinkShareJWTAuthtoken(share *models.LinkSharing) (token string, err error) {
	// Set claims
	claims := &AuthClaims{
		Type:            AuthTypeLinkShare,
		ShareID:         share.ID,
		ShareHash:       share.Hash,
		ShareListID:     share.ListID,
		ShareRight:      share.Right,
		ShareSharedByID: share.SharedByID,
		StandardClaims: jwt.StandardClaims{
			ExpiresAt: time.Now().Add(time.Hour * 72).Unix(),
		},
	}

	t := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)

	// Generate encoded token and send it as response.
	return t.SignedString([]byte(config.ServiceJWTSecret.GetString()))
}

// GetAuthFromClaims returns a web.Auth object from jwt claims or from an
// alternative authProvider
func GetAuthFromClaims(c echo.Context) (a web.Auth, err error) {
	claims := c.Get(AuthClaimsContextKey).(*AuthClaims)
	if claims.Type == AuthTypeLinkShare && config.ServiceEnableLinkSharing.GetBool() {
		return getLinkShareFromClaims(claims)
	}
	if claims.Type == AuthTypeUser {
		return getUserFromClaims(claims), nil
	}
	if authProvider, ok := authProviders[claims.Type]; ok {
		return authProvider.GetUser(c, claims)
	}
	return nil, echo.NewHTTPError(http.StatusBadRequest, models.Message{Message: "Invalid JWT token."})
}

// getLinkShareFromClaims builds a link sharing object from jwt claims
func getLinkShareFromClaims(claims *AuthClaims) (share *models.LinkSharing, err error) {
	share = &models.LinkSharing{}
	share.ID = claims.ShareID
	share.Hash = claims.ShareHash
	share.ListID = claims.ShareListID
	share.Right = claims.ShareRight
	share.SharedByID = claims.ShareSharedByID

	if share.Hash == "" {
		return nil, echo.NewHTTPError(http.StatusBadRequest, models.Message{Message: "Invalid JWT token."})
	}

	return
}

// getUserFromClaims Returns a new user from jwt claims
func getUserFromClaims(claims *AuthClaims) (u *user.User) {
	u = &user.User{
		ID:       claims.UserID,
		Email:    claims.UserEmail,
		Username: claims.UserUsername,
		Name:     claims.UserName,
	}

	return
}

// GetCurrentUser returns the current user based on its jwt token
func GetCurrentUser(c echo.Context) (u *user.User, err error) {
	auth, err := GetAuthFromClaims(c)
	if err != nil {
		return nil, err
	}

	u, ok := auth.(*user.User)
	if !ok {
		return nil, user.ErrCouldNotGetUserID{}
	}

	return u, nil
}

// Generates a new jwt token for the types AuthTypeLinkShare and AuthTypeUser
func RenewToken(s *xorm.Session, c echo.Context) (token string, err error) {
	claims := c.Get(AuthClaimsContextKey).(*AuthClaims)

	if claims.Type == AuthTypeLinkShare {
		oldShare, err := getLinkShareFromClaims(claims)
		if err != nil {
			return "", err
		}
		share := &models.LinkSharing{}
		share.ID = oldShare.ID
		err = share.ReadOne(s, share)
		if err != nil {
			return "", err
		}
		return NewLinkShareJWTAuthtoken(share)
	}
	if claims.Type == AuthTypeUser {
		oldUser := getUserFromClaims(claims)
		u, err := user.GetUserWithEmail(s, &user.User{ID: oldUser.ID})
		if err != nil {
			return "", err
		}
		return NewUserJWTAuthtoken(u)
	}
	if authProvider, ok := authProviders[claims.Type]; ok {
		token, err := authProvider.RenewToken(c, claims)
		if err != nil {
			return "", err
		}
		return token, nil
	}
	return "", echo.NewHTTPError(http.StatusBadRequest, models.Message{Message: "Invalid JWT token."})
}

// GetOrCreateUserFromExternalAuth returns a user after finding or creating a matching user for the provided details
func GetOrCreateUserFromExternalAuth(s *xorm.Session, issuer, subject, email, name, preferredUsername string) (u *user.User, err error) {
	if issuer == "" || subject == "" || email == "" {
		return nil, echo.NewHTTPError(http.StatusBadRequest, models.Message{Message: "Missing required data."})
	}

	// Check if the user exists for that issuer and subject
	u, err = user.GetUserWithEmail(s, &user.User{
		Issuer:  issuer,
		Subject: subject,
	})
	if err != nil && !user.IsErrUserDoesNotExist(err) {
		return nil, err
	}

	// If no user exists, create one with the preferred username if it is not already taken
	if user.IsErrUserDoesNotExist(err) {
		uu := &user.User{
			Username: preferredUsername,
			Email:    email,
			IsActive: true,
			Issuer:   issuer,
			Subject:  subject,
		}

		// Check if we actually have a preferred username and generate a random one right away if we don't
		if uu.Username == "" {
			uu.Username = petname.Generate(3, "-")
		}

		u, err = user.CreateUser(s, uu)
		if err != nil && !user.IsErrUsernameExists(err) {
			return nil, err
		}

		// If their preferred username is already taken, create some random one from the email and subject
		if user.IsErrUsernameExists(err) {
			uu.Username = petname.Generate(3, "-")
			u, err = user.CreateUser(s, uu)
			if err != nil {
				return nil, err
			}
		}

		// And create its namespace
		err = models.CreateNewNamespaceForUser(s, u)
		if err != nil {
			return nil, err
		}

		return
	}

	// If it exists, check if the email address changed and change it if not
	if email != u.Email || (name != "" && name != u.Name) {
		if email != u.Email {
			u.Email = email
		}
		if name != "" && name != u.Name {
			u.Name = name
		}
		u, err = user.UpdateUser(s, &user.User{
			ID:      u.ID,
			Email:   u.Email,
			Name:    u.Name,
			Issuer:  issuer,
			Subject: subject,
		})
		if err != nil {
			return nil, err
		}
	}

	return
}