package service

import (
	"context"
	"crypto/subtle"
	"errors"
	"log/slog"
	"net/mail"
	"spend-sparrow/internal/db"
	mailTemplate "spend-sparrow/internal/template/mail"
	"spend-sparrow/internal/types"
	"strings"
	"time"

	"github.com/google/uuid"
	"golang.org/x/crypto/argon2"
)

var (
	ErrInvalidCredentials = errors.New("invalid email or password")
	ErrInvalidPassword    = errors.New("the password needs to be 8 characters long, contain at least one number, one special, one uppercase and one lowercase character")
	ErrInvalidEmail       = errors.New("invalid email")
	ErrAccountExists      = errors.New("account already exists")
	ErrSessionIdInvalid   = errors.New("session ID is invalid")
	ErrTokenInvalid       = errors.New("token is invalid")
)

type Auth interface {
	SignUp(ctx context.Context, email string, password string) (*types.User, error)
	SendVerificationMail(ctx context.Context, userId uuid.UUID, email string)
	VerifyUserEmail(ctx context.Context, token string) error

	SignIn(ctx context.Context, session *types.Session, email string, password string) (*types.Session, *types.User, error)
	SignInSession(ctx context.Context, sessionId string) (*types.Session, *types.User, error)
	SignInAnonymous(ctx context.Context) (*types.Session, error)
	SignOut(ctx context.Context, sessionId string) error

	DeleteAccount(ctx context.Context, user *types.User, currPass string) error

	ChangePassword(ctx context.Context, user *types.User, sessionId string, currPass, newPass string) error

	SendForgotPasswordMail(ctx context.Context, email string) error
	ForgotPassword(ctx context.Context, token string, newPass string) error

	IsCsrfTokenValid(ctx context.Context, tokenStr string, sessionId string) bool
	GetCsrfToken(ctx context.Context, session *types.Session) (string, error)

	CleanupSessionsAndTokens(ctx context.Context) error
}

type AuthImpl struct {
	db             db.Auth
	random         Random
	clock          Clock
	mail           Mail
	serverSettings *types.Settings
}

func NewAuth(db db.Auth, random Random, clock Clock, mail Mail, serverSettings *types.Settings) *AuthImpl {
	return &AuthImpl{
		db:             db,
		random:         random,
		clock:          clock,
		mail:           mail,
		serverSettings: serverSettings,
	}
}

func (service AuthImpl) SignIn(ctx context.Context, session *types.Session, email string, password string) (*types.Session, *types.User, error) {
	user, err := service.db.GetUserByEmail(ctx, email)
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil, nil, ErrInvalidCredentials
		} else {
			return nil, nil, types.ErrInternal
		}
	}

	hash := GetHashPassword(password, user.Salt)

	if subtle.ConstantTimeCompare(hash, user.Password) == 0 {
		return nil, nil, ErrInvalidCredentials
	}

	newSession, err := service.createSession(ctx, user.Id)
	if err != nil {
		return nil, nil, types.ErrInternal
	}

	err = service.db.DeleteSession(ctx, session.Id)
	if err != nil {
		return nil, nil, types.ErrInternal
	}

	tokens, err := service.db.GetTokensBySessionIdAndType(ctx, session.Id, types.TokenTypeCsrf)
	if err != nil {
		return nil, nil, types.ErrInternal
	}
	for _, token := range tokens {
		err = service.db.DeleteToken(ctx, token.Token)
		if err != nil {
			return nil, nil, types.ErrInternal
		}
	}

	return newSession, user, nil
}

func (service AuthImpl) SignInSession(ctx context.Context, sessionId string) (*types.Session, *types.User, error) {
	if sessionId == "" {
		return nil, nil, ErrSessionIdInvalid
	}

	session, err := service.db.GetSession(ctx, sessionId)
	if err != nil {
		return nil, nil, types.ErrInternal
	}
	if session.ExpiresAt.Before(service.clock.Now()) {
		_ = service.db.DeleteSession(ctx, sessionId)
		return nil, nil, nil
	}

	if session.UserId == uuid.Nil {
		return session, nil, nil
	}

	user, err := service.db.GetUser(ctx, session.UserId)
	if err != nil {
		return nil, nil, types.ErrInternal
	}

	return session, user, nil
}

func (service AuthImpl) SignInAnonymous(ctx context.Context) (*types.Session, error) {
	session, err := service.createSession(ctx, uuid.Nil)
	if err != nil {
		return nil, types.ErrInternal
	}

	slog.Info("anonymous session created", "session-id", session.Id)

	return session, nil
}

func (service AuthImpl) SignUp(ctx context.Context, email string, password string) (*types.User, error) {
	_, err := mail.ParseAddress(email)
	if err != nil {
		return nil, ErrInvalidEmail
	}

	if !isPasswordValid(password) {
		return nil, ErrInvalidPassword
	}

	userId, err := service.random.UUID()
	if err != nil {
		return nil, types.ErrInternal
	}

	salt, err := service.random.Bytes(16)
	if err != nil {
		return nil, types.ErrInternal
	}

	hash := GetHashPassword(password, salt)

	user := types.NewUser(userId, email, false, nil, false, hash, salt, service.clock.Now())

	err = service.db.InsertUser(ctx, user)
	if err != nil {
		if errors.Is(err, db.ErrAlreadyExists) {
			return nil, ErrAccountExists
		} else {
			return nil, types.ErrInternal
		}
	}

	return user, nil
}

func (service AuthImpl) SendVerificationMail(ctx context.Context, userId uuid.UUID, email string) {
	tokens, err := service.db.GetTokensByUserIdAndType(ctx, userId, types.TokenTypeEmailVerify)
	if err != nil && !errors.Is(err, db.ErrNotFound) {
		return
	}

	var token *types.Token

	if len(tokens) > 0 {
		token = tokens[0]
	}

	if token == nil {
		newTokenStr, err := service.random.String(32)
		if err != nil {
			return
		}

		token = types.NewToken(
			userId,
			"",
			newTokenStr,
			types.TokenTypeEmailVerify,
			service.clock.Now(),
			service.clock.Now().Add(24*time.Hour))

		err = service.db.InsertToken(ctx, token)
		if err != nil {
			return
		}
	}

	var w strings.Builder
	err = mailTemplate.Register(service.serverSettings.BaseUrl, token.Token).Render(context.Background(), &w)
	if err != nil {
		slog.Error("Could not render welcome email", "err", err)
		return
	}

	service.mail.SendMail(email, "Welcome to spend-sparrow", w.String())
}

func (service AuthImpl) VerifyUserEmail(ctx context.Context, tokenStr string) error {
	if tokenStr == "" {
		return types.ErrInternal
	}

	token, err := service.db.GetToken(ctx, tokenStr)
	if err != nil {
		return types.ErrInternal
	}

	user, err := service.db.GetUser(ctx, token.UserId)
	if err != nil {
		return types.ErrInternal
	}

	if token.Type != types.TokenTypeEmailVerify {
		return types.ErrInternal
	}

	now := service.clock.Now()

	if token.ExpiresAt.Before(now) {
		return types.ErrInternal
	}

	user.EmailVerified = true
	user.EmailVerifiedAt = &now

	err = service.db.UpdateUser(ctx, user)
	if err != nil {
		return types.ErrInternal
	}

	_ = service.db.DeleteToken(ctx, token.Token)
	return nil
}

func (service AuthImpl) SignOut(ctx context.Context, sessionId string) error {
	return service.db.DeleteSession(ctx, sessionId)
}

func (service AuthImpl) DeleteAccount(ctx context.Context, user *types.User, currPass string) error {
	userDb, err := service.db.GetUser(ctx, user.Id)
	if err != nil {
		return types.ErrInternal
	}

	currHash := GetHashPassword(currPass, userDb.Salt)
	if subtle.ConstantTimeCompare(currHash, userDb.Password) == 0 {
		return ErrInvalidCredentials
	}

	err = service.db.DeleteUser(ctx, user.Id)
	if err != nil {
		return err
	}

	service.mail.SendMail(user.Email, "Account deleted", "Your account has been deleted")

	return nil
}

func (service AuthImpl) ChangePassword(ctx context.Context, user *types.User, sessionId string, currPass, newPass string) error {
	if !isPasswordValid(newPass) {
		return ErrInvalidPassword
	}

	if currPass == newPass {
		return ErrInvalidPassword
	}

	currHash := GetHashPassword(currPass, user.Salt)

	if subtle.ConstantTimeCompare(currHash, user.Password) == 0 {
		return ErrInvalidCredentials
	}

	newHash := GetHashPassword(newPass, user.Salt)
	user.Password = newHash

	err := service.db.UpdateUser(ctx, user)
	if err != nil {
		return err
	}

	sessions, err := service.db.GetSessions(ctx, user.Id)
	if err != nil {
		return types.ErrInternal
	}
	for _, s := range sessions {
		if s.Id != sessionId {
			err = service.db.DeleteSession(ctx, s.Id)
			if err != nil {
				return types.ErrInternal
			}
		}
	}

	return nil
}

func (service AuthImpl) SendForgotPasswordMail(ctx context.Context, email string) error {
	tokenStr, err := service.random.String(32)
	if err != nil {
		return err
	}

	user, err := service.db.GetUserByEmail(ctx, email)
	if err != nil {
		if errors.Is(err, db.ErrNotFound) {
			return nil
		} else {
			return types.ErrInternal
		}
	}

	token := types.NewToken(
		user.Id,
		"",
		tokenStr,
		types.TokenTypePasswordReset,
		service.clock.Now(),
		service.clock.Now().Add(15*time.Minute))

	err = service.db.InsertToken(ctx, token)
	if err != nil {
		return types.ErrInternal
	}

	var mail strings.Builder
	err = mailTemplate.ResetPassword(service.serverSettings.BaseUrl, token.Token).Render(context.Background(), &mail)
	if err != nil {
		slog.Error("Could not render reset password email", "err", err)
		return types.ErrInternal
	}
	service.mail.SendMail(email, "Reset Password", mail.String())

	return nil
}

func (service AuthImpl) ForgotPassword(ctx context.Context, tokenStr string, newPass string) error {
	if !isPasswordValid(newPass) {
		return ErrInvalidPassword
	}

	token, err := service.db.GetToken(ctx, tokenStr)
	if err != nil {
		return ErrTokenInvalid
	}

	err = service.db.DeleteToken(ctx, tokenStr)
	if err != nil {
		return err
	}

	if token.Type != types.TokenTypePasswordReset ||
		token.ExpiresAt.Before(service.clock.Now()) {
		return ErrTokenInvalid
	}

	user, err := service.db.GetUser(ctx, token.UserId)
	if err != nil {
		slog.Error("Could not get user from token", "err", err)
		return types.ErrInternal
	}

	passHash := GetHashPassword(newPass, user.Salt)

	user.Password = passHash
	err = service.db.UpdateUser(ctx, user)
	if err != nil {
		return err
	}

	sessions, err := service.db.GetSessions(ctx, user.Id)
	if err != nil {
		return types.ErrInternal
	}

	for _, session := range sessions {
		err = service.db.DeleteSession(ctx, session.Id)
		if err != nil {
			return types.ErrInternal
		}
	}

	return nil
}

func (service AuthImpl) IsCsrfTokenValid(ctx context.Context, tokenStr string, sessionId string) bool {
	token, err := service.db.GetToken(ctx, tokenStr)
	if err != nil {
		return false
	}

	if token.Type != types.TokenTypeCsrf ||
		token.SessionId != sessionId ||
		token.ExpiresAt.Before(service.clock.Now()) {
		return false
	}

	return true
}

func (service AuthImpl) GetCsrfToken(ctx context.Context, session *types.Session) (string, error) {
	if session == nil {
		return "", types.ErrInternal
	}

	tokens, _ := service.db.GetTokensBySessionIdAndType(ctx, session.Id, types.TokenTypeCsrf)

	if len(tokens) > 0 {
		return tokens[0].Token, nil
	}

	tokenStr, err := service.random.String(32)
	if err != nil {
		return "", types.ErrInternal
	}

	token := types.NewToken(
		session.UserId,
		session.Id,
		tokenStr,
		types.TokenTypeCsrf,
		service.clock.Now(),
		service.clock.Now().Add(8*time.Hour))
	err = service.db.InsertToken(ctx, token)
	if err != nil {
		return "", types.ErrInternal
	}

	slog.Info("CSRF-Token created", "token", tokenStr)

	return tokenStr, nil
}

func (service AuthImpl) CleanupSessionsAndTokens(ctx context.Context) error {
	err := service.db.DeleteOldSessions(ctx)
	if err != nil {
		return types.ErrInternal
	}

	err = service.db.DeleteOldTokens(ctx)
	if err != nil {
		return types.ErrInternal
	}

	return nil
}

func (service AuthImpl) createSession(ctx context.Context, userId uuid.UUID) (*types.Session, error) {
	sessionId, err := service.random.String(32)
	if err != nil {
		return nil, types.ErrInternal
	}

	createAt := service.clock.Now()
	expiresAt := createAt.Add(24 * time.Hour)

	session := types.NewSession(sessionId, userId, createAt, expiresAt)

	err = service.db.InsertSession(ctx, session)
	if err != nil {
		return nil, types.ErrInternal
	}

	return session, nil
}

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

func isPasswordValid(password string) bool {
	if len(password) < 8 ||
		!strings.ContainsAny(password, "0123456789") ||
		!strings.ContainsAny(password, "ABCDEFGHIJKLMNOPQRSTUVWXYZ") ||
		!strings.ContainsAny(password, "abcdefghijklmnopqrstuvwxyz") ||
		!strings.ContainsAny(password, "!@#$%^&*()_+-=[]{}\\|;:'\",.<>/?") {
		return false
	} else {
		return true
	}
}