// Package session (session manager) control process session lifetime create, update and destroy
package session

import (
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"time"
)

var milis int64 = 1000

// for provider fun
var provides = make(map[string]Provider)

// ProviderNames return slice of strings - registered Provider names
func ProviderNames() []string {
	var prdnames []string
	for pn := range provides {
		prdnames = append(prdnames, pn)
	}
	return prdnames
}

// MilisPerSec return time resolution (milliseconds / 1sec)
func MilisPerSec() int64 {
	return milis
}

// Session interface implement storage for one session and have maxLifetime and lastAccessTime
type Session interface {
	//set session value and update last access time
	Set(key, value interface{}) error
	//get session value and update last access time
	Get(key interface{}) (v any, err error)
	//delete session value
	Delete(key interface{}) error
	//get session id for session
	SessionID() string
}

// Provider interace implement lifecycle for one session
type Provider interface {
	//create new session using sid value
	Init(sid string) (Session, error)
	//read return existing session by id or if not exist create new session
	Read(sid string) (Session, error)
	//destroy remove session with sid from storage if exist
	Destroy(sid string) error
	//regenerate id change old sid to newsid and preserve existing session data
	RegenerateID(oldsid, newsid string) (err error)
	//gc remove all sessions with > maxLifetime
	GC(maxlifetime int64)
}

// Register makes a session provide available by the provided name.
// If Register is called twice with the same name or if driver is nil, it panics.
func Register(name string, provide Provider) {
	if provide == nil {
		panic("session: Register provide is nil, must be import any session storage implementation")
	}
	if _, dup := provides[name]; dup {
		panic("session: Already registered provider: " + name)
	}
	provides[name] = provide
}

// Manager controls all sessions with registered storage provider
type Manager struct {
	cookieName  string
	provider    Provider
	maxlifetime int64
	secure      bool
}

// NewManager create new *Manager for provideName, cookieName and maxlifetime in seconds
func NewManager(providerName, cookieName string, maxlifetime int64, ssl bool) (*Manager, error) {
	var provider Provider
	var ok bool
	if provider, ok = provides[providerName]; !ok {
		return nil, fmt.Errorf("session: Provider: %q not found (forgotten import?)", providerName)
	}
	m := &Manager{
		cookieName: cookieName, provider: provider,
		maxlifetime: maxlifetime, secure: ssl,
	}
	m.GC()
	return m, nil
}

// generate new secure 32 byte sessionID
func (manager *Manager) sessionID() (sid string, err error) {
	b := make([]byte, 32)
	if _, err = io.ReadFull(rand.Reader, b); err != nil {
		return "", fmt.Errorf("Session manager error: generate sessionID failed: %w", err)
	}
	return base64.URLEncoding.EncodeToString(b), nil
}

// SessionStart start session for next http response
func (manager *Manager) SessionStart(w http.ResponseWriter, r *http.Request) (session Session, err error) {
	var cookie *http.Cookie
	var sid string
	if cookie, err = r.Cookie(manager.cookieName); err != nil || cookie == nil {
		if sid, err = manager.sessionID(); err != nil {
			return nil, err
		}
		if session, err = manager.provider.Init(sid); err != nil {
			return nil, fmt.Errorf("Session init failed: %w", err)
		}
		cookie := http.Cookie{
			Name: manager.cookieName, Value: url.QueryEscape(sid), Path: "/",
			HttpOnly: true, MaxAge: int(manager.maxlifetime),
			Secure: manager.secure,
		}
		http.SetCookie(w, &cookie)
	} else {
		if sid, err = url.QueryUnescape(cookie.Value); err != nil {
			return nil, fmt.Errorf("Session cookie decode error: %v", err)
		}
		if session, err = manager.provider.Read(sid); err != nil {
			return nil, fmt.Errorf("Session provider read error: %w", err)
		}
	}
	return
}

// SessionDestroy end session and delete session data at the server
func (manager *Manager) SessionDestroy(w http.ResponseWriter, r *http.Request) (err error) {
	var cookie *http.Cookie
	if cookie, err = r.Cookie(manager.cookieName); err != nil || cookie.Value == "" {
		return
	}

	manager.provider.Destroy(cookie.Value)
	rmcookie := http.Cookie{
		Name: manager.cookieName, Path: "/", HttpOnly: true,
		Expires: time.Now(), MaxAge: -1,
	}
	http.SetCookie(w, &rmcookie)
	return nil
}

// RegenerateID vhange sid and preserve all session data
func (manager *Manager) RegenerateID(w http.ResponseWriter, r *http.Request) {
	if ck, err := r.Cookie(manager.cookieName); err == nil && ck.Value != "" {
		if newid, err := manager.sessionID(); err != nil {
			manager.provider.RegenerateID(ck.Value, newid)
		}
	}
}

// GC remove sessions which exceeded manager.maxLifetime
func (manager *Manager) GC() {
	manager.provider.GC(manager.maxlifetime)
	msec := milis * manager.maxlifetime
	time.AfterFunc(time.Duration(msec), func() { manager.GC() })
}