package service

import (
	"context"
	"crypto/rand"
	"crypto/subtle"
	"database/sql"
	"encoding/base64"
	"errors"
	"log/slog"
	"net/http"
	"net/mail"
	"strings"
	"time"

	"me-fit/db"
	"me-fit/template/auth"
	tempMail "me-fit/template/mail"
	"me-fit/types"
	"me-fit/utils"

	"github.com/a-h/templ"
	"github.com/google/uuid"
	"golang.org/x/crypto/argon2"
)

// TESTED

var (
	ErrInternalServer            = errors.New("Internal Server Error")
	ErrInvalidUsernameOrPassword = errors.New("Invalid username or password")
)

// NOT TESTED

type AuthService struct {
	db    *sql.DB
	dbSer *db.AuthDb
}

func NewAuthService(db *sql.DB) *AuthService {
	return &AuthService{
		db: db,
	}
}

func (a *AuthService) SignUp(email string, password string) (*types.SessionId, error) {
	_, err := mail.ParseAddress(email)
	if err != nil {
		return nil, errors.Join(errors.New("Invalid email"))
	}

	err = checkPassword(password)
	if err != nil {
		return nil, err
	}

	userId, err := uuid.NewRandom()
	if err != nil {
		utils.LogError("Could not generate UUID for new user", err)
		return nil, ErrInternalServer
	}

	salt := make([]byte, 16)
	_, err = rand.Read(salt)
	if err != nil {
		utils.LogError("Could not generate salt for new user", err)
		return nil, ErrInternalServer
	}

	hash := getHashPassword(password, salt)

	err := a.dbSer.InsertUser(a.db, userId, email, hash, salt)
	_, err = a.db.Exec("INSERT INTO user (user_uuid, email, email_verified, is_admin, password, salt, created_at) VALUES (?, ?, FALSE, FALSE, ?, ?, datetime())", userId, email, hash, salt)
	if err != nil {
		// This does leak information about the email being in use, though not specifically stated
		// It needs to be refacoteres to "If the email is not already in use, an email has been send to your address", or something
		// The happy path, currently a redirect, needs to send the same message!
		// Then it is also important to have the same compute time in both paths
		// Otherwise an attacker could guess emails when comparing the response time
		if strings.Contains(err.Error(), "email") {
			return nil, errors.New("Bad Request")
		}

		utils.LogError("Could not insert user", err)
		return nil, ErrInternalServer
	}

	sessionId, err := createSession(a.db, userId)
	if err != nil {
		return nil, err
	}

	// Send verification email as a goroutine
	go SendVerificationEmail(a.db, userId.String(), email)
	return sessionId, nil
}

func (a *AuthService) SignIn(email string, password string) (*types.SessionId, error) {
	start := time.Now()

	sessionId, err := a.internalSignIn(email, password)

	duration := time.Since(start)
	timeToWait := 100 - duration.Milliseconds()
	// It is important to sleep for a while to prevent timing attacks
	// If the email is correct, the server will calculate the hash, which will take some time
	// This way an attacker could guess emails when comparing the response time
	// Because of that, we cant use WriteHeader in the middle of the function. We have to wait until the end
	// Unfortunatly this makes the code harder to read
	time.Sleep(time.Duration(timeToWait) * time.Millisecond)

	return sessionId, err
}

func (a *AuthService) internalSignIn(email string, password string) (*types.SessionId, error) {
	var (
		userId    uuid.UUID
		savedHash []byte
		salt      []byte
	)

	err := a.db.QueryRow("SELECT user_uuid, password, salt FROM user WHERE email = ?", email).Scan(&userId, &savedHash, &salt)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil, ErrInvalidUsernameOrPassword
		}
		utils.LogError("Could not query user on sign in", err)
		return nil, ErrInternalServer
	}

	new_hash := getHashPassword(password, salt)

	if subtle.ConstantTimeCompare(new_hash, savedHash) == 0 {
		return nil, errors.Join(ErrInvalidUsernameOrPassword)
	}

	sessionId, err := createSession(a.db, userId)
	if err != nil {
		return nil, err
	}

	return sessionId, nil
}

func GetUserFromSessionId(db *sql.DB, sessionId types.SessionId) *types.User {
	if sessionId == "" {
		return nil
	}

	var (
		createdAt     time.Time
		userId        uuid.UUID
		email         string
		emailVerified bool
	)

	err := db.QueryRow(`
			SELECT u.user_uuid, u.email, u.email_verified, s.created_at
			FROM session s
			INNER JOIN user u ON s.user_uuid = u.user_uuid
			WHERE session_id = ?`, sessionId).Scan(&userId, &email, &emailVerified, &createdAt)
	if err != nil {
		slog.Warn("Could not verify session: " + err.Error())
		return nil
	}

	if createdAt.Add(time.Duration(8 * time.Hour)).Before(time.Now()) {
		return nil
	} else {
		return types.NewUser(userId, email, sessionId, emailVerified)
	}
}
func ValidateEmail(db *sql.DB, token string) error {
	result, err := db.Exec(`
		UPDATE user
		SET email_verified = true, email_verified_at = datetime()
		WHERE user_uuid = (
			SELECT user_uuid
			FROM user_token
			WHERE type = "email_verify"
			AND token = ?
		);`, token)

	if err != nil {
		return errors.Join(errors.New("Could not update user on verify response"), err)
	}

	i, err := result.RowsAffected()
	if err != nil {
		return errors.Join(errors.New("Could not get rows affected on verify response"), err)
	}

	if i == 0 {
		return errors.New("Token is invalid")
	}

	return nil
}

func UserInfoComp(user *types.User) templ.Component {

	if user != nil {
		return auth.UserComp(user.Email)
	} else {
		return auth.UserComp("")
	}
}

func SignOut(db *sql.DB, user *types.User) error {
	if user == nil {
		return nil
	}

	_, err := db.Exec("DELETE FROM session WHERE session_id = ?", user.SessionId)
	if err != nil {
		return errors.Join(errors.New("Could not delete session"), err)
	}

	return nil
}

func DeleteAccount(db *sql.DB, user *types.User, password string) error {

	if password == "" {
		return errors.New("Please enter your password")
	}

	var (
		storedHash []byte
		salt       []byte
	)

	err := db.QueryRow("SELECT password, salt FROM user WHERE user_uuid = ?", user.Id).Scan(&storedHash, &salt)
	if err != nil {
		return errors.Join(errors.New("Could not get password"), err)
	}

	currHash := getHashPassword(password, salt)
	if subtle.ConstantTimeCompare(currHash, storedHash) == 0 {
		return errors.New("Password is not correct")
	}

	_, err = db.Exec("DELETE FROM workout WHERE user_id = ?", user.Id)
	if err != nil {
		return errors.Join(errors.New("Could not delete workouts"), err)
	}

	_, err = db.Exec("DELETE FROM user_token WHERE user_uuid = ?", user.Id)
	if err != nil {
		return errors.Join(errors.New("Could not delete tokens"), err)
	}

	_, err = db.Exec("DELETE FROM session WHERE user_uuid = ?", user.Id)
	if err != nil {
		return errors.Join(errors.New("Could not delete sessions"), err)
	}

	_, err = db.Exec("DELETE FROM user WHERE user_uuid = ?", user.Id)
	if err != nil {
		return errors.Join(errors.New("Could not delete user"), err)
	}

	go utils.SendMail(user.Email, "Account deleted", "Your account has been deleted")
	return nil
}

func ChangePassword(db *sql.DB, user *types.User, currPass string, newPass string) error {

	err := checkPassword(newPass)
	if err != nil {
		return err
	}

	if currPass == newPass {
		return errors.New("New password can not be the same as the current password")
	}

	var (
		storedHash []byte
		salt       []byte
	)

	err = db.QueryRow("SELECT password, salt FROM user WHERE user_uuid = ?", user.Id).Scan(&storedHash, &salt)
	if err != nil {
		return errors.Join(errors.New("Could not get password"), err)
	}

	currHash := getHashPassword(currPass, salt)
	if subtle.ConstantTimeCompare(currHash, storedHash) == 0 {
		return errors.New("Current password is not correct")
	}

	newHash := getHashPassword(newPass, salt)

	_, err = db.Exec("UPDATE user SET password = ? WHERE user_uuid = ?", newHash, user.Id)
	if err != nil {
		return errors.Join(errors.New("Could not update password"), err)
	}

	return nil
}

func ActualResetPassword(db *sql.DB, token string, newPass string) error {

	err := checkPassword(newPass)
	if err != nil {
		return err
	}

	var (
		userId uuid.UUID
		salt   []byte
	)

	err = db.QueryRow(`
			SELECT u.user_uuid, salt
			FROM user_token t
			INNER JOIN user u ON t.user_uuid = u.user_uuid
			WHERE t.token = ? 
			AND t.type = 'password_reset'
			AND t.expires_at > datetime()
			`, token).Scan(&userId, &salt)
	if err != nil {
		return errors.Join(errors.New("Could not get user from token"), err)
	}

	_, err = db.Exec("DELETE FROM user_token WHERE token = ? AND type = 'password_reset'", token)
	if err != nil {
		return errors.Join(errors.New("Could not delete token"), err)
	}

	passHash := getHashPassword(newPass, salt)

	_, err = db.Exec("UPDATE user SET password = ? WHERE user_uuid = ?", passHash, userId)
	if err != nil {
		return errors.Join(errors.New("Could not update password"), err)
	}

	return nil
}

func ResetPassword(db *sql.DB, email string) (string, error) {

	if email == "" {
		return "", errors.New("Please enter an email")
	}

	token, err := randomToken()
	if err != nil {
		return "", errors.Join(errors.New("Could not generate token"), err)
	}

	res, err := db.Exec(`
			INSERT INTO user_token (user_uuid, type, token, created_at, expires_at)
			SELECT user_uuid, 'password_reset', ?, datetime(), datetime('now', '+15 minute')
			FROM user
			WHERE email = ?
			`, token, email)
	if err != nil {
		return "", errors.Join(errors.New("Could not insert token"), err)
	}

	i, err := res.RowsAffected()
	if err != nil {
		return "", errors.Join(errors.New("Could not get rows affected"), err)
	}

	if i == 0 {
		return "", nil
	} else {
		return token, nil
	}
}

func SendVerificationEmail(db *sql.DB, userId string, email string) {

	var token string
	err := db.QueryRow("SELECT token FROM user_token WHERE user_uuid = ? AND type = 'email_verify'", userId).Scan(&token)
	if err != nil && err != sql.ErrNoRows {
		utils.LogError("Could not get token", err)
		return
	}

	if token == "" {
		token, err := randomToken()
		if err != nil {
			utils.LogError("Could not generate token", err)
			return
		}

		_, err = db.Exec("INSERT INTO user_token (user_uuid, type, token, created_at) VALUES (?, 'email_verify', ?, datetime())", userId, token)
		if err != nil {
			utils.LogError("Could not insert token", err)
			return
		}
	}

	var w strings.Builder
	err = tempMail.Register(token).Render(context.Background(), &w)
	if err != nil {
		utils.LogError("Could not render welcome email", err)
		return
	}
	utils.SendMail(email, "Welcome to ME-FIT", w.String())
}

func createSession(db *sql.DB, user_uuid uuid.UUID) (*types.SessionId, error) {
	sessionId, err := randomToken()
	if err != nil {
		return nil, err
	}

	// Delete old inactive sessions
	_, err = db.Exec("DELETE FROM session WHERE created_at < datetime('now','-8 hours') AND user_uuid = ?", user_uuid)
	if err != nil {
		utils.LogError("Could not delete old sessions", err)
		return nil, ErrInternalServer
	}

	_, err = db.Exec("INSERT INTO session (session_id, user_uuid, created_at) VALUES (?, ?, datetime())", sessionId, user_uuid)
	if err != nil {
		utils.LogError("Could not insert new session", err)
		return nil, ErrInternalServer
	}

	sessionIdType := types.SessionId(sessionId)
	return &sessionIdType, nil
}

func tryCreateSessionAndSetCookie(r *http.Request, w http.ResponseWriter, db *sql.DB, user_uuid uuid.UUID) bool {
	sessionId, err := randomToken()
	if err != nil {
		utils.LogError("Could not generate session ID", err)
		auth.Error("Internal Server Error").Render(r.Context(), w)
		return false
	}

	// Delete old inactive sessions
	_, err = db.Exec("DELETE FROM session WHERE created_at < datetime('now','-8 hours') AND user_uuid = ?", user_uuid)
	if err != nil {
		utils.LogError("Could not delete old sessions", err)
	}

	_, err = db.Exec("INSERT INTO session (session_id, user_uuid, created_at) VALUES (?, ?, datetime())", sessionId, user_uuid)
	if err != nil {
		utils.LogError("Could not insert session", err)
		auth.Error("Internal Server Error").Render(r.Context(), w)
		return false
	}

	cookie := http.Cookie{
		Name:     "id",
		Value:    sessionId,
		MaxAge:   60 * 60 * 8, // 8 hours
		Secure:   true,
		HttpOnly: true,
		SameSite: http.SameSiteStrictMode,
		Path:     "/",
	}
	http.SetCookie(w, &cookie)

	return true
}

func getHashPassword(password string, salt []byte) []byte {
	return argon2.IDKey([]byte(password), salt, 1, 64*1024, 1, 16)
}

func checkPassword(password string) error {

	if len(password) < 8 ||
		!strings.ContainsAny(password, "0123456789") ||
		!strings.ContainsAny(password, "ABCDEFGHIJKLMNOPQRSTUVWXYZ") ||
		!strings.ContainsAny(password, "abcdefghijklmnopqrstuvwxyz") ||
		!strings.ContainsAny(password, "!@#$%^&*()_+-=[]{}\\|;:'\",.<>/?") {
		return errors.New("Password needs to be 8 characters long, contain at least one number, one special, one uppercase and one lowercase character")
	} else {
		return nil
	}
}

//TODO: delete

func getSessionID(r *http.Request) types.SessionId {
	for _, c := range r.Cookies() {
		if c.Name == "id" {
			return types.SessionId(c.Value)
		}
	}
	return ""
}

func GetUserFromRequest(db *sql.DB, r *http.Request) *types.User {
	sessionId := getSessionID(r)
	return GetUserFromSessionId(db, sessionId)
}

func randomToken() (string, error) {
	b := make([]byte, 32)
	_, err := rand.Read(b)
	if err != nil {
		utils.LogError("Could not generate random token", err)
		return "", ErrInternalServer
	}

	return base64.StdEncoding.EncodeToString(b), nil
}