package main

import (
	"bytes"
	"container/heap"
	"crypto/rand"
	"crypto/sha1"
	"database/sql"
	"encoding/base64"
	"errors"
	_ "github.com/lib/pq"
	"golang.org/x/crypto/pbkdf2"
	"log"
	"net/http"
	"strings"
	"time"
)

type SessionData struct {
	sid      string
	username string
	priority time.Time
	index    int
}

type SessionQueue []*SessionData

func (pq SessionQueue) Len() int {
	return len(pq)
}

func (pq SessionQueue) Less(i, j int) bool {
	return pq[i].priority.Before(pq[j].priority)
}

func (pq SessionQueue) Swap(i, j int) {
	pq[i], pq[j] = pq[j], pq[i]
	pq[i].index = i
	pq[j].index = j
}

func (pq *SessionQueue) Push(x interface{}) {
	n := len(*pq)
	item := x.(*SessionData)
	item.index = n
	*pq = append(*pq, item)
}

func (pq *SessionQueue) Pop() interface{} {
	old := *pq
	n := len(old)
	item := old[n-1]
	item.index = -1 // for safety
	*pq = old[0 : n-1]
	return item
}

var (
	sessions     = make(map[string]*SessionData)
	sessionQueue = make(SessionQueue, 0)
	db           *sql.DB
)

func sessionExpirer() {
	for {
		for len(sessionQueue) > 0 && time.Now().After(sessionQueue[0].priority) {
			session := heap.Pop(&sessionQueue).(*SessionData)
			delete(sessions, session.sid)
		}
		time.Sleep(time.Second * 5)
	}
}

func init() {
	go sessionExpirer()

	connStr := "user=levyraati dbname=levyraati sslmode=disable"
	var err error
	db, err = sql.Open("postgres", connStr)
	if err != nil {
		log.Fatal(err)
	}
	_, err = db.Query("SELECT 1")
	if err != nil {
		log.Fatal(err)
	}
}

func addSession(data *SessionData) {
	sessions[data.sid] = data
	heap.Push(&sessionQueue, data)
}

func generateHash(password string) (string, error) {
	salt := make([]byte, 11)

	if _, err := rand.Read(salt); err != nil {
		log.Println(err)
		return "", errors.New("Couldn't generate random string")
	}

	passwordBytes := []byte(password)
	key := hashPasswordSalt(passwordBytes, salt)

	saltStr := base64.StdEncoding.EncodeToString(salt)
	keyStr := base64.StdEncoding.EncodeToString(key)
	return saltStr + "$" + keyStr, nil
}

func hashOk(password, hashed string) (bool, error) {
	parts := strings.Split(hashed, "$")
	if len(parts) != 2 {
		return false, errors.New("Invalid data stored in database for password")
	}
	salt, err := base64.StdEncoding.DecodeString(parts[0])
	if err != nil {
		return false, err
	}
	passwordHash, err := base64.StdEncoding.DecodeString(parts[1])
	if err != nil {
		return false, err
	}
	if len(passwordHash) != 32 {
		return false, errors.New("Password hash was not 32 bytes long")
	}

	key := hashPasswordSalt([]byte(password), salt)
	return bytes.Equal(key, passwordHash), nil
}

func hashPasswordSalt(password, salt []byte) []byte {
	return pbkdf2.Key(password, salt, 4096, 32, sha1.New)
}

func userOk(username, password string) (bool, error) {
	var hash string
	err := db.QueryRow("SELECT u.password FROM public.user u WHERE lower(u.username) = lower($1)", username).Scan(&hash)
	if err != nil {
		if err.Error() == "sql: no rows in result set" {
			return false, nil
		} else {
			return false, err
		}
	}

	ok, err := hashOk(password, hash)
	if err != nil {
		return false, err
	}
	return ok, nil
}

func tryLogin(username, password string, longerTime bool) (http.Cookie, error) {
	if exists, err := userOk(username, password); !exists {
		if err != nil {
			return http.Cookie{}, err
		}
		return http.Cookie{},
			errors.New("The username or password you entered isn't correct.")
	}

	sid, err := randString(32)
	if err != nil {
		return http.Cookie{}, err
	}

	duration := time.Hour * 1
	if longerTime {
		duration = time.Hour * 24 * 14
	}

	loginCookie := http.Cookie{
		Name:     "id",
		Value:    sid,
		MaxAge:   int(duration.Seconds()),
		HttpOnly: true,
	}

	expiration := time.Now().Add(duration)
	addSession(&SessionData{sid, username, expiration, 0})

	return loginCookie, nil
}

func getSession(req *http.Request) (*SessionData, error) {
	cookie, err := req.Cookie("id")
	if err != nil {
		return nil, err
	}

	session, exists := sessions[cookie.Value]
	if !exists {
		return nil, errors.New("Session expired from server")
	}
	return session, nil
}

func randString(size int) (string, error) {
	buf := make([]byte, size)

	if _, err := rand.Read(buf); err != nil {
		log.Println(err)
		return "", errors.New("Couldn't generate random string")
	}

	return base64.URLEncoding.EncodeToString(buf)[:size], nil
}