package main

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"math"
	"time"
)

var ErrInvalidSession = fmt.Errorf("session not found")

type Sess struct {
	User User
	expr time.Time
}

type Sessions struct {
	sessions map[string]Sess
}

func (s *Sessions) Create(user User, expr time.Duration) (string, error) {
	if s.sessions == nil {
		s.sessions = map[string]Sess{}
	}
	key := randomStr(24)
	s.sessions[key] = Sess{
		User: user,
		expr: time.Now().Add(expr),
	}
	return key, nil
}

func (s *Sessions) Get(key string) (User, error) {
	if s.sessions == nil {
		s.sessions = map[string]Sess{}
		return User{}, ErrInvalidSession
	}
	sess, ok := s.sessions[key]
	if !ok {
		return User{}, ErrInvalidSession
	}
	if sess.expr.Before(time.Now()) {
		delete(s.sessions, key)
		return User{}, ErrInvalidSession
	}
	return sess.User, nil
}

func (s *Sessions) Refresh(key string, user User, expr time.Duration) error {
	if s.sessions == nil {
		s.sessions = map[string]Sess{}
		return ErrInvalidSession
	}
	sess, ok := s.sessions[key]
	if !ok {
		return ErrInvalidSession
	}
	if sess.expr.Before(time.Now()) {
		delete(s.sessions, key)
		return ErrInvalidSession
	}
	s.sessions[key] = Sess{
		User: user,
		expr: time.Now().Add(expr),
	}
	return nil
}

func (s *Sessions) Destroy(key string) {
	if s.sessions == nil {
		s.sessions = map[string]Sess{}
		return
	}
	delete(s.sessions, key)
}

// taken from https://stackoverflow.com/a/55860599
func randomStr(l int) string {
	buff := make([]byte, int(math.Ceil(float64(l)/float64(1.33333333333))))
	rand.Read(buff)
	str := base64.RawURLEncoding.EncodeToString(buff)
	return str[:l] // strip 1 extra character we get from odd length results
}