package session

import (
	"context"
	"encoding/base64"
	"fmt"
	"log/slog"
	"net/http"

	"github.com/gorilla/sessions"
	"go.uber.org/fx"
	"sneak.berlin/go/webhooker/internal/config"
	"sneak.berlin/go/webhooker/internal/database"
	"sneak.berlin/go/webhooker/internal/logger"
)

const (
	// SessionName is the name of the session cookie
	SessionName = "webhooker_session"

	// UserIDKey is the session key for user ID
	UserIDKey = "user_id"

	// UsernameKey is the session key for username
	UsernameKey = "username"

	// AuthenticatedKey is the session key for authentication status
	AuthenticatedKey = "authenticated"
)

// nolint:revive // SessionParams is a standard fx naming convention
type SessionParams struct {
	fx.In
	Config   *config.Config
	Database *database.Database
	Logger   *logger.Logger
}

// Session manages encrypted session storage
type Session struct {
	store  *sessions.CookieStore
	log    *slog.Logger
	config *config.Config
}

// New creates a new session manager. The cookie store is initialized
// during the fx OnStart phase after the database is connected, using
// a session key that is auto-generated and stored in the database.
func New(lc fx.Lifecycle, params SessionParams) (*Session, error) {
	s := &Session{
		log:    params.Logger.Get(),
		config: params.Config,
	}

	lc.Append(fx.Hook{
		OnStart: func(_ context.Context) error { // nolint:revive // ctx unused but required by fx
			sessionKey, err := params.Database.GetOrCreateSessionKey()
			if err != nil {
				return fmt.Errorf("failed to get session key: %w", err)
			}

			keyBytes, err := base64.StdEncoding.DecodeString(sessionKey)
			if err != nil {
				return fmt.Errorf("invalid session key format: %w", err)
			}

			if len(keyBytes) != 32 {
				return fmt.Errorf("session key must be 32 bytes (got %d)", len(keyBytes))
			}

			store := sessions.NewCookieStore(keyBytes)

			// Configure cookie options for security
			store.Options = &sessions.Options{
				Path:     "/",
				MaxAge:   86400 * 7, // 7 days
				HttpOnly: true,
				Secure:   !params.Config.IsDev(), // HTTPS in production
				SameSite: http.SameSiteLaxMode,
			}

			s.store = store
			s.log.Info("session manager initialized")
			return nil
		},
	})

	return s, nil
}

// Get retrieves a session for the request
func (s *Session) Get(r *http.Request) (*sessions.Session, error) {
	return s.store.Get(r, SessionName)
}

// Save saves the session
func (s *Session) Save(r *http.Request, w http.ResponseWriter, sess *sessions.Session) error {
	return sess.Save(r, w)
}

// SetUser sets the user information in the session
func (s *Session) SetUser(sess *sessions.Session, userID, username string) {
	sess.Values[UserIDKey] = userID
	sess.Values[UsernameKey] = username
	sess.Values[AuthenticatedKey] = true
}

// ClearUser removes user information from the session
func (s *Session) ClearUser(sess *sessions.Session) {
	delete(sess.Values, UserIDKey)
	delete(sess.Values, UsernameKey)
	delete(sess.Values, AuthenticatedKey)
}

// IsAuthenticated checks if the session has an authenticated user
func (s *Session) IsAuthenticated(sess *sessions.Session) bool {
	auth, ok := sess.Values[AuthenticatedKey].(bool)
	return ok && auth
}

// GetUserID retrieves the user ID from the session
func (s *Session) GetUserID(sess *sessions.Session) (string, bool) {
	userID, ok := sess.Values[UserIDKey].(string)
	return userID, ok
}

// GetUsername retrieves the username from the session
func (s *Session) GetUsername(sess *sessions.Session) (string, bool) {
	username, ok := sess.Values[UsernameKey].(string)
	return username, ok
}

// Destroy invalidates the session
func (s *Session) Destroy(sess *sessions.Session) {
	sess.Options.MaxAge = -1
	s.ClearUser(sess)
}

// Regenerate creates a new session with the same values but a fresh ID.
// The old session is destroyed (MaxAge = -1) and saved, then a new session
// is created. This prevents session fixation attacks by ensuring the
// session ID changes after privilege escalation (e.g. login).
func (s *Session) Regenerate(r *http.Request, w http.ResponseWriter, oldSess *sessions.Session) (*sessions.Session, error) {
	// Copy the values from the old session
	oldValues := make(map[interface{}]interface{})
	for k, v := range oldSess.Values {
		oldValues[k] = v
	}

	// Destroy the old session
	oldSess.Options.MaxAge = -1
	s.ClearUser(oldSess)
	if err := oldSess.Save(r, w); err != nil {
		return nil, fmt.Errorf("failed to destroy old session: %w", err)
	}

	// Create a new session (gorilla/sessions generates a new ID)
	newSess, err := s.store.New(r, SessionName)
	if err != nil {
		// store.New may return an error alongside a new empty session
		// if the old cookie is now invalid. That is expected after we
		// destroyed it above. Only fail on a nil session.
		if newSess == nil {
			return nil, fmt.Errorf("failed to create new session: %w", err)
		}
	}

	// Restore the copied values into the new session
	for k, v := range oldValues {
		newSess.Values[k] = v
	}

	// Apply the standard session options (the destroyed old session had
	// MaxAge = -1, which store.New might inherit from the cookie).
	newSess.Options = &sessions.Options{
		Path:     "/",
		MaxAge:   86400 * 7,
		HttpOnly: true,
		Secure:   !s.config.IsDev(),
		SameSite: http.SameSiteLaxMode,
	}

	return newSess, nil
}