libtokamap 0.2.2

A library for flexible data mapping and transformation using TokaMap compatible mappings

LibTokaMap

A C++20 library for flexible data mapping and transformation with support for multiple data sources and mapping types.

Overview

LibTokaMap is a flexible mapping library designed to handle complex data transformations through configurable JSON-based mapping definitions. It provides a plugin-based architecture for data sources and supports various mapping types including value mappings, data source mappings, expression mappings, and custom mappings.

Features

• Multiple Mapping Types: Support for value, data source, expression, dimension, and custom mappings
• Pluggable Data Sources: Extensible architecture for custom data source implementations
• JSON Configuration: Human-readable JSON-based mapping definitions
• Caching Support: Built-in RAM caching for improved performance
• Type Safety: Strong typing with C++20 features
• Subset Operations: Advanced data slicing and subsetting capabilities
• Scale/Offset Transformations: Built-in support for linear data transformations

Building

Requirements

• C++20 compatible compiler
• CMake 3.15+
• nlohmann/json library
• Pantor/Inja templating engine
• GSL-lite (Guidelines Support Library)
• ExprTk expression parsing library

Build Instructions

mkdir build
cd build
cmake .. -DENABLE_TESTING=ON -DENABLE_EXAMPLES=ON
make

CMake Options

• ENABLE_TESTING: Build unit tests (default: OFF)
• ENABLE_EXAMPLES: Build example applications (default: OFF)

Usage

Basic Example

#include <libtokamap.hpp>

int main() {
    libtokamap::MappingHandler mapping_handler;

    // Initialize with configuration
    nlohmann::json config = {
        {"mapping_directory", "/path/to/mappings"}
    };
    mapping_handler.init(config);

    // Perform mapping
    std::type_index data_type = std::type_index{typeid(double)};
    int rank = 1;
    nlohmann::json extra_attributes = {{"shot", 12345}};

    auto result = mapping_handler.map(
        "my_mapping",
        "path/to/data",
        data_type,
        rank,
        extra_attributes
    );

    return 0;
}

Custom Data Source

class MyDataSource : public libtokamap::DataSource {
public:
    TypedDataArray get(const DataSourceArgs& map_args,
                      const MapArguments& arguments,
                      RamCache* ram_cache) override {
        // Implement your data retrieval logic
        // Return TypedDataArray with your data
    }
};

// Register the data source
auto data_source = std::make_unique<MyDataSource>();
libtokamap::DataSourceMapping::register_data_source("MY_SOURCE", std::move(data_source));

Mapping Types

Value Mapping

Direct value assignment from JSON configuration.

{
    "map_type": "VALUE",
    "value": 42
}

Data Source Mapping

Retrieves data from registered data sources.

{
    "map_type": "DATA_SOURCE",
    "data_source": "JSON",
    "args": {
        "file": "data.json",
        "path": "measurements.temperature"
    },
    "scale": 1.0,
    "offset": 0.0,
    "slice": "[0:10]"
}

Expression Mapping

Evaluates mathematical expressions.

{
    "map_type": "EXPR",
    "expr": "x * 2 + y",
    "parameters": {
        "x": "path/to/x",
        "y": "path/to/y"
    }
}

Dimension Mapping

Handles array dimension information.

{
    "map_type": "DIMENSION",
    "dim_probe": "array/path"
}

Custom Mapping

User-defined mapping logic.

{
    "map_type": "CUSTOM",
    "custom_type": "my_custom_mapping"
}

Configuration

Mapping Directory Structure

mappings/
├── experiment1/
│   ├── mappings.cfg.json
│   ├── globals.json
│   └── group_name1/
│       └── partition1_0/
│           ├── globals.json
│           └── mappings.json
│       └── partition1_100/
│           ├── globals.json
│           └── mappings.json
│       └── ...
│   └── group_name2/
│       └── ...
└── experiment2/
    └── ...

Configuration File Format

{
    "mapping_directory": "/path/to/mappings",
    "cache_enabled": true,
    "cache_size": 100
}

API Reference

MappingHandler

Main class for handling mapping operations.

Methods

• void init(const nlohmann::json& config): Initialize with configuration
• TypedDataArray map(...): Perform mapping operation
• void reset(): Reset handler state

DataSource

Base class for implementing custom data sources.

Virtual Methods

• TypedDataArray get(...): Retrieve data from source

Mapping Types

Base classes for different mapping implementations:

• Mapping: Base mapping interface
• ValueMapping: Direct value mappings
• DataSourceMapping: Data source mappings
• ExprMapping: Expression-based mappings
• DimMapping: Dimension mappings
• CustomMapping: User-defined mappings

Utilities

Subset Operations

• Slice parsing: "[0:10]", "[::2]", "[1:5:2]"
• Multi-dimensional slicing support
• Range validation and boundary checking

Scale/Offset Transformations

• Linear transformations: output = input * scale + offset
• Applied after data retrieval and slicing

Caching

• RAM-based caching for frequently accessed data
• Configurable cache policies
• Automatic cache invalidation

Examples

See the examples/ directory for complete working examples:

• simple_mapper/: Basic mapping example with JSON data source

Testing

Run the test suite:

cd build
make test

Version Information

Current version: 0.1.0

Contributing

Code Style

• Follow C++20 best practices
• Use clang-format for code formatting
• Enable all compiler warnings (-Wall -Werror -Wpedantic)

TODO Items

• Make mapping values case insensitive
• Remove references to IDSs
• Replace reinterpret_cast with bit_cast (still exist in map_arguments.hpp)
• Replace boost::split with std::views::split
• Switch from using std::type_index to DataType enum?
• Add exception types
• Add README and docs for library
• Tidy up DataSource get(...) arguments
• Adding system packaging to CMake
• Make mapping directory nesting configurable
• Remove SignalType logic
• Add C++20 template constraints
• Replace std::string{} with string_literals
• Fix logging
• Add tests for parse_slices
• Replace gsl::span with std::span
• Handle mismatch of request data type and returned data type, i.e. type conversions?
• Check returned data against expected rank
• Add JSON schema files into repo (from IMAS MASTU mapping)
• Validate JSON mappings on read
• Use std::format instead of string concatenation

License

See the main project LICENSE file for license information.

Dependencies

• nlohmann/json: JSON parsing and manipulation
• Pantor/Inja: Template engine for dynamic content generation
• ExprTk: Mathematical expression parsing and evaluation