// 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 identityawareproxy

import (
	"fmt"
	"time"

	"code.vikunja.io/api/pkg/db"

	"code.vikunja.io/api/pkg/config"
	"code.vikunja.io/api/pkg/modules/auth"
	"code.vikunja.io/api/pkg/user"
	"github.com/dgrijalva/jwt-go"
	"github.com/labstack/echo/v4"
)

const IAPClaimsContextKey string = "iapClaims"

// IAPClaims represents the claims made by the authentication JWT
// passed in by the identity-aware proxy
type IAPClaims struct {
	Email             string `json:"email"`
	Name              string `json:"name,omitempty"`
	PreferredUsername string `json:"preferred_username,omitempty"`
	jwt.StandardClaims
}

// Auth provider used to allow auth to get a web.Auth from the IAP provided identity
type IAPAuthProvider struct{}

func Init() {
	auth.RegisterAuthProvider(auth.AuthTypeIAPUser, IAPAuthProvider{})
	auth.RegisterAuthMiddleware(auth.AuthTypeIAPUser, Middleware())
}

// NewIAPUserJWTAuthtoken generates and signes a new jwt token for a user
// These are intentionally short lived because they can be regenerated at
// any time from the IAP authn information. They are not related to
// session length and are only used to provide user info to the frontend
// and a hint to auth.go to retrieve auth data from the IAP.
func NewIAPUserJWTAuthtoken(u *user.User) (token string, err error) {
	// Set claims
	claims := newIAPUserJWTAuthClaims(u)
	t := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)

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

func newIAPUserJWTAuthClaims(u *user.User) (claims *auth.AuthClaims) {
	return &auth.AuthClaims{
		Type:         auth.AuthTypeIAPUser,
		UserID:       u.ID,
		UserUsername: u.Username,
		UserEmail:    u.Email,
		UserName:     u.Name,
		StandardClaims: jwt.StandardClaims{
			ExpiresAt: time.Now().Add(time.Minute * 5).Unix(),
		},
	}
}

func userForIAPClaims(cl *IAPClaims) (u *user.User, err error) {
	s := db.NewSession()
	defer s.Close()

	// Check if we have seen this user before
	u, err = auth.GetOrCreateUserFromExternalAuth(s, cl.Issuer, cl.Subject, cl.Email, cl.Name, cl.PreferredUsername)
	if err != nil {
		_ = s.Rollback()
		return nil, err
	}

	err = s.Commit()
	if err != nil {
		return nil, err
	}

	return u, nil
}

func (p IAPAuthProvider) RenewToken(c echo.Context, authClaims *auth.AuthClaims) (string, error) {
	// Get user
	u, err := p.GetUser(c, authClaims)
	if err != nil {
		return "", nil
	}

	// Create token
	return NewIAPUserJWTAuthtoken(u)
}

// Get a web.Auth object from the identity that the IAP provides
func (p IAPAuthProvider) GetUser(c echo.Context, authClaims *auth.AuthClaims) (*user.User, error) {
	s := db.NewSession()
	defer s.Close()

	// Get the user from the IAP identity
	cl := c.Get(IAPClaimsContextKey).(*IAPClaims)
	u, err := userForIAPClaims(cl)
	if err != nil {
		return nil, err
	}

	// Sanity check that the user the frontend thinks it has (the authClaims from the JWT it passed in)
	// is the same as the user provided by the IAP.
	if authClaims.UserID != u.ID {
		return nil, ErrIAPUserFrontendMismatch{}
	}

	return u, nil
}

// Validates the claims in the jwt
// Matches the jwt-go Claims interface
func (c *IAPClaims) Valid() error {
	// Validate that expiresAt and issuedAt are set and valid (with up to 1 minute of skew)
	now := TimeFunc()
	skew := time.Minute
	if !c.VerifyExpiresAt(now.Add(-skew).Unix(), true) {
		delta := now.Sub(time.Unix(c.ExpiresAt, 0))
		return fmt.Errorf("token is expired by %v", delta)
	}
	if !c.VerifyIssuedAt(now.Add(skew).Unix(), true) {
		return fmt.Errorf("token used before issued")

	}

	// Validate that subject, email, and issuer are all set
	if c.Subject == "" {
		return fmt.Errorf("token missing subject")
	}
	if c.Email == "" {
		return fmt.Errorf("token missing email")
	}
	if c.Issuer == "" {
		return fmt.Errorf("token missing issuer")
	}

	return nil
}