Requirements

We're building a bar graph library, and it's time to level up! We need to make it more flexible, powerful, and robust. Imagine users wanting to visualize various datasets with different styling needs – from simple sales figures to complex scientific data. The core challenge lies in designing a system that can handle diverse data sources, customizable bar styles, and real-time updates while remaining performant and thread-safe. Let's think through the data structures that can hold the data and how can we make the library work in a multi-threaded environment. # Requirements ## Functional Requirements 1. **Data Input:** * Support multiple data sources: * In-memory lists of numerical data. * CSV files (with configurable delimiters). * Ability to register a "DataProvider" interface implementation for custom data sources (e.g., a database query). * Handle missing or invalid data points gracefully (e.g., skip, replace with a default value, or throw an exception – configurable behavior). * Support for labeled data points (i.e., each numerical value is associated with a string label for the x-axis). 2. **Bar Styling:** * Allow customization of bar color (solid color or gradient). * Allow customization of bar width and spacing. * Support different bar shapes (rectangle, rounded rectangle, custom shapes via a "BarShape" interface). * Provide options for displaying labels above/below/inside the bars, with configurable font and color. * Ability to add tooltips that appear on mouse hover, displaying data value and label. 3. **Graph Layout & Scaling:** * Automatic scaling of the y-axis based on the data range. * Configurable y-axis label format (e.g., currency, percentage, scientific notation). * Options for displaying a grid (horizontal and/or vertical). * Support for logarithmic scaling on the y-axis. * Ability to zoom and pan the graph. 4. **Real-time Updates:** * Provide a mechanism for updating the data displayed on the graph dynamically. * Support for animations when data changes (e.g., bars smoothly growing/shrinking to new values). * The graph should be repaint itself whenever the data is changed. 5. **Exporting:** * Ability to export the graph as an image (PNG, JPG, SVG). * Ability to export the underlying data in CSV format. ## Non-Functional Requirements 1. **Thread Safety:** * The graph component must be thread-safe to allow updates from multiple threads (e.g., a background data feed). Protect shared data structures appropriately using locks or concurrent data structures. The updates should be atomic. 2. **Extensibility:** * The design should allow adding new data sources, bar styles, and graph layouts without modifying the core graph component. Favor interfaces and abstract classes over concrete implementations. Follow the Open/Closed Principle. 3. **Modularity:** * The library should be divided into well-defined modules with clear responsibilities. Strive for high cohesion and low coupling. 4. **Testability:** * The code should be easily testable using unit tests. Design classes with dependency injection in mind. Avoid static methods where possible. 5. **Performance:** * The graph should render efficiently, even with large datasets. Consider caching strategies for frequently accessed data. Avoid unnecessary object creation. 6. **Maintainability:** * The code should be well-documented and easy to understand. Use meaningful variable and method names. Follow coding conventions. 7. **Error Handling:** * The library should handle errors gracefully, providing informative error messages to the user. ## Core Entities 1. **`BarGraph`**: The main class representing the bar graph. It holds the data, styling information, and layout settings. It orchestrates the rendering process. 2. **`DataProvider`**: An interface for providing data to the graph. Implementations can read data from various sources (in-memory list, CSV file, database, etc.). 3. **`Bar`**: Represents a single bar in the graph. It holds the data value, label, and styling information for that bar. 4. **`BarStyle`**: An interface for defining the style of a bar. Implementations can specify the color, shape, width, spacing, and label format. 5. **`GraphLayout`**: An interface for defining the overall layout of the graph. Implementations can specify the scaling, grid, and axis labels. 6. **`Renderer`**: Responsible for the actual drawing of the graph. This decouples the rendering logic from the `BarGraph` class, making it easier to support different rendering technologies (e.g., Java Swing, HTML5 Canvas). 7. **`GraphData`**: Holds the raw data for the graph. Separates the data from the graph representation.

Design a Bar Graph Library.

Requirements

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