/*
    * Copyright 2012-2025 CodeLibs Project and the Others.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *     http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied. See the License for the specific language
   * governing permissions and limitations under the License.
   */
  package org.codelibs.fess.entity;
  
  import java.time.LocalDateTime;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.UUID;
  import java.util.concurrent.CopyOnWriteArrayList;
  
  /**
   * Represents a chat session containing conversation history.
   *
   * @author FessProject
   */
  public class ChatSession {
  
      /** The unique session identifier. */
      private String sessionId;
  
      /** The user ID associated with this session. */
      private String userId;
  
      /** The timestamp when the session was created. */
      private LocalDateTime createdAt;
  
      /** The timestamp when the session was last accessed. */
      private volatile LocalDateTime lastAccessedAt;
  
      /** The list of messages in this session. */
      private List<ChatMessage> messages;
  
      /** Lock object for thread-safe message operations. */
      private final Object messagesLock = new Object();
  
      /**
       * Default constructor.
       */
      public ChatSession() {
          this.sessionId = UUID.randomUUID().toString();
          this.createdAt = LocalDateTime.now();
          this.lastAccessedAt = this.createdAt;
          this.messages = new CopyOnWriteArrayList<>();
      }
  
      /**
       * Creates a new chat session for the specified user.
       *
       * @param userId the user ID
       */
      public ChatSession(final String userId) {
          this();
          this.userId = userId;
      }
  
      /**
       * Gets the session ID.
       *
       * @return the session ID
       */
      public String getSessionId() {
          return sessionId;
      }
  
      /**
       * Sets the session ID.
       *
       * @param sessionId the session ID
       */
      public void setSessionId(final String sessionId) {
          this.sessionId = sessionId;
      }
  
      /**
       * Gets the user ID.
       *
       * @return the user ID
       */
      public String getUserId() {
          return userId;
      }
  
      /**
       * Sets the user ID.
       *
       * @param userId the user ID
      */
     public void setUserId(final String userId) {
         this.userId = userId;
     }
 
     /**
      * Gets the creation timestamp.
      *
      * @return the creation timestamp
      */
     public LocalDateTime getCreatedAt() {
         return createdAt;
     }
 
     /**
      * Sets the creation timestamp.
      *
      * @param createdAt the creation timestamp
      */
     public void setCreatedAt(final LocalDateTime createdAt) {
         this.createdAt = createdAt;
     }
 
     /**
      * Gets the last accessed timestamp.
      *
      * @return the last accessed timestamp
      */
     public LocalDateTime getLastAccessedAt() {
         return lastAccessedAt;
     }
 
     /**
      * Sets the last accessed timestamp.
      *
      * @param lastAccessedAt the last accessed timestamp
      */
     public void setLastAccessedAt(final LocalDateTime lastAccessedAt) {
         this.lastAccessedAt = lastAccessedAt;
     }
 
     /**
      * Returns a copy of the message list in this session.
      *
      * @return a new list containing all messages
      */
     public List<ChatMessage> getMessages() {
         synchronized (messagesLock) {
             if (messages == null) {
                 return new ArrayList<>();
             }
             return new ArrayList<>(messages);
         }
     }
 
     /**
      * Sets the message list for this session.
      *
      * @param messages the messages to set
      */
     public void setMessages(final List<ChatMessage> messages) {
         synchronized (messagesLock) {
             if (messages == null) {
                 this.messages = null;
             } else if (messages instanceof CopyOnWriteArrayList) {
                 this.messages = messages;
             } else {
                 this.messages = new CopyOnWriteArrayList<>(messages);
             }
         }
     }
 
     /**
      * Adds a message to this session and updates the last accessed timestamp.
      *
      * @param message the message to add
      */
     public void addMessage(final ChatMessage message) {
         synchronized (messagesLock) {
             if (messages == null) {
                 messages = new CopyOnWriteArrayList<>();
             }
             messages.add(message);
         }
         this.lastAccessedAt = LocalDateTime.now();
     }
 
     /**
      * Adds a user message to this session.
      *
      * @param content the message content
      */
     public void addUserMessage(final String content) {
         addMessage(ChatMessage.userMessage(content));
     }
 
     /**
      * Adds an assistant message to this session.
      *
      * @param content the message content
      */
     public void addAssistantMessage(final String content) {
         addMessage(ChatMessage.assistantMessage(content));
     }
 
     /**
      * Updates the last accessed timestamp to the current time.
      */
     public void touch() {
         this.lastAccessedAt = LocalDateTime.now();
     }
 
     /**
      * Returns the number of messages in this session.
      *
      * @return the message count
      */
     public int getMessageCount() {
         synchronized (messagesLock) {
             return messages != null ? messages.size() : 0;
         }
     }
 
     /**
      * Clears all messages in this session and updates the last accessed timestamp.
      */
     public void clearMessages() {
         synchronized (messagesLock) {
             if (messages != null) {
                 messages.clear();
             }
         }
         this.lastAccessedAt = LocalDateTime.now();
     }
 
     /**
      * Trims the message history to keep only the most recent messages.
      *
      * @param maxMessages the maximum number of messages to retain
      */
     public void trimHistory(final int maxMessages) {
         synchronized (messagesLock) {
             if (messages != null && messages.size() > maxMessages) {
                 int start = messages.size() - maxMessages;
                 // Ensure trimmed history starts with a user message, not an assistant message
                 if (start < messages.size() && ChatMessage.ROLE_ASSISTANT.equals(messages.get(start).getRole())) {
                     start = Math.max(0, start - 1);
                 }
                 final List<ChatMessage> trimmed = new ArrayList<>(messages.subList(start, messages.size()));
                 messages.clear();
                 messages.addAll(trimmed);
             }
         }
     }
 }