// Copyright (c) 2026 Zeni Kim <zenik@smarteching.com>
// Use of this source code is governed by MIT-style
// license that can be found in the LICENSE file.

package core

import (
	"crypto/md5"
	"encoding/json"
	"fmt"
	"sync"
	"time"
)

// SessionUser handles user session data management with thread-safe operations.
// Sessions are stored in the cache (Redis) and are tied to an authenticated user
// via JWT tokens stored in cookies.
type SessionUser struct {
	mu               sync.RWMutex
	context          *Context
	userID           uint
	hashedSessionKey string
	authenticated    bool
	sessionStart     time.Time
	values           map[string]interface{}
}

// Init initializes the session by validating the user's JWT token from the cookie.
// It checks the cached token, verifies it matches, and loads any existing session data.
// Returns true if the session was successfully established.
func (s *SessionUser) Init(c *Context) bool {
	s.context = c

	// get cookie
	usercookie, err := c.GetCookie()
	if err != nil || usercookie.Token == "" {
		return false
	}

	payload, err := c.GetJWT().DecodeToken(usercookie.Token)
	if err != nil {
		return false
	}

	userID := uint(c.CastToInt(payload["userID"]))
	userAgent := c.GetUserAgent()

	// verify token against cached value
	hashedCacheKey := CreateAuthTokenHashedCacheKey(userID, userAgent)
	cachedToken, err := c.GetCache().Get(hashedCacheKey)
	if err != nil || cachedToken != usercookie.Token {
		return false
	}

	// session established - load session data from cache
	userAgent = c.GetUserAgent()
	sessionKey := fmt.Sprintf("sess_%v", userAgent)
	s.hashedSessionKey = CreateAuthTokenHashedCacheKey(userID, sessionKey)
	s.values = make(map[string]interface{})
	s.authenticated = true
	s.userID = userID

	value, _ := c.GetCache().Get(s.hashedSessionKey)
	if len(value) > 0 {
		_ = json.Unmarshal([]byte(value), &s.values)
	}

	return true
}

// Set stores a value in the session and persists it to the cache.
func (s *SessionUser) Set(key string, value interface{}) error {
	s.mu.Lock()
	s.values[key] = value
	s.mu.Unlock()
	return s.Save()
}

// Get retrieves a value from the session. Returns the value and a boolean indicating if the key exists.
func (s *SessionUser) Get(key string) (interface{}, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	val, ok := s.values[key]
	return val, ok
}

// Delete removes a specific key from the session and persists the change.
// Returns the deleted value if it existed.
func (s *SessionUser) Delete(key string) interface{} {
	s.mu.RLock()
	v, ok := s.values[key]
	s.mu.RUnlock()
	if ok {
		s.mu.Lock()
		delete(s.values, key)
		s.mu.Unlock()
	}
	s.Save()
	return v
}

// Flush deletes all session data from the cache.
func (s *SessionUser) Flush() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.hashedSessionKey != "" {
		_ = s.context.GetCache().Delete(s.hashedSessionKey)
	}
	s.values = make(map[string]interface{})
	s.authenticated = false
	return nil
}

// Save persists the current session values to the cache.
func (s *SessionUser) Save() error {
	s.mu.RLock()
	defer s.mu.RUnlock()

	if len(s.values) > 0 {
		buf, err := json.Marshal(&s.values)
		if err != nil {
			return err
		}
		return s.context.GetCache().Set(s.hashedSessionKey, string(buf))
	}

	_ = s.context.GetCache().Delete(s.hashedSessionKey)
	return nil
}

// GetUserID returns the user ID of the authenticated session user.
func (s *SessionUser) GetUserID() uint {
	return s.userID
}

// IsAuthenticated returns whether the session has been successfully authenticated.
func (s *SessionUser) IsAuthenticated() bool {
	return s.authenticated
}

// CreateAuthTokenHashedCacheKey generates a hashed cache key used to store JWT tokens and session data.
// The key is based on the user ID and user agent, hashed with MD5.
func CreateAuthTokenHashedCacheKey(userID uint, userAgent string) string {
	cacheKey := fmt.Sprintf("userid:_%v_useragent:_%v_jwt_token", userID, userAgent)
	return fmt.Sprintf("%x", md5.Sum([]byte(cacheKey)))
}