package models

import (
	"crypto/rand"
	"encoding/binary"
	"strconv"
	"time"
)

// The Session model represents a user being logged in.
type Session struct {
	ID      string
	UserID  int
	Expires time.Time
}

// GenerateID generates a unique ID for the session that's 64 base36 digits long.
func (session *Session) GenerateID() error {
	result := ""
	offset := 0
	data := make([]byte, 128)

	_, err := rand.Read(data)
	if err != nil {
		return err
	}

	for len(result) < 64 {
		result += strconv.FormatUint(binary.LittleEndian.Uint64(data[offset:]), 36)
		offset += 8

		if offset >= 128 {
			_, err = rand.Read(data)
			if err != nil {
				return err
			}

			offset = 0
		}
	}

	session.ID = result[:64]

	return nil
}

// SessionRepository is an interface for all database operations
// the user model makes.
type SessionRepository interface {
	// FindSessionByID finds a non-expired session by ID.
	FindSessionByID(id int) (Session, error)
	InsertSession(session Session) error
	RemoveSession(session Session) error
	ClearUserSessions(user User) error
	RemoveExpiredSessions() error
}