The Search Engine Project is a web crawling application crafted in C++, intended to scan internet websites and archive the collected data into a MySQL database. It empowers users with the ability to input search queries, and the application provides search results consisting of links containing the specified keywords. The links are sorted using the Pagerank algorithm, which ranks internet pages to prioritize the most relevant search results. Additionally, the project supports receiving queries from remote users through the TCP protocol. The project utilizes multithreading to enhance efficiency and enable concurrent searching and crawling, allowing users to search for information even while the crawling process is ongoing. It offers flexibility in its configuration options, allowing users to customize its behavior through a configuration file. Parameters such as scanning type (BFS or DFS), sorting method, and client interface (local or remote) can be defined to tailor the application to specific preferences and requirements.

The Crawler class is responsible for traversing web pages by retrieving URLs and parsing HTML content. It utilizes the Html_parser object to extract links and text from the retrieved pages. The extracted data is then passed to the Updater class, which handles the insertion of data into the database. The Updater class holds instances of classes that implement the Graph interface, representing the relationship between links, and the WordLinks interface, representing links that contain words. The Crawler also interacts with instances of the Scanner interface, which can be configured for BFS or DFS strategies. Thread_safe_set are employed to ensure the uniqueness of URLs. Additionally, the crawling process is controlled by the Limit_counter object, which stops the crawler when a specified limit of links is reached. The Limit_counter object is thread-safe, allowing for concurrent access and increases.

The Search_engine class is the application responsible for handling user queries, providing results, and sorting outcomes. The Search_engine class achieves its tasks by holding three objects:

• Client Interface: This object enables the Search_engine to receive queries from users. Whether the queries are entered locally via the console or remotely through sockets, the Search_engine efficiently manages user interactions.
• Searcher Instance: The Search_engine utilizes an instance of the Searcher interface to retrieve relevant search results from a specific database.
• Sorter Instance: Additionally, the Search_engine holds an instance of the Sorter interface to organize search results effectively. It can sort results either by word instances, the Pagerank algorithm, or any other custom sorting method specified.

The Singleton pattern is implemented for the Configuration class because many classes interact with it, and it holds important configuration settings such as the length of result links, number of threads, scanning type (BFS or DFS), sorting method, and whether the application is used locally or remotely. By making Configuration a Singleton, we ensure that there is only one instance of it throughout the application, and all classes can access its settings consistently.

During the crawling process, whenever the Updater class finishes inserting a buffer of links into the database, it notifies the Pagerank class. The Pagerank class then calculates the Pagerank scores for the newly inserted links. This ensures that Pagerank scores are updated in real-time as new data is added to the database.

The Crawler and Search_engine classes interact with various components and rely heavily on different parameters, such as sorting method, scanning type, number of threads, and other important settings provided by the Configuration class. These dependencies are injected during object creation, allowing for easier testing and modification. This approach enables greater flexibility and maintainability by decoupling the classes from specific implementations and allowing them to be customized based on configuration settings.

• Gumbo Parser : Used for parsing HTML content and extracting links from web pages.
  Install it using the command: sudo apt install -y libgumbo-dev

• Curlpp: Used for downloading pages from URLs.
  Install it using the command: sudo apt install -y libcurlpp-dev

• MySQL Connector/C++: Required for database interaction.
  Install it using the command: sudo apt-get install libmysqlcppconn-dev

• GCC Compiler: Project requires g++ compiler (version 7.3+) with C++17 support.