AppsheetEpplus/FormulaParsing/Excel/Functions/FunctionRepository.cs

/* Copyright (C) 2011  Jan Källman
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.

 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * The GNU Lesser General Public License can be viewed at http://www.opensource.org/licenses/lgpl-license.php
 * If you unfamiliar with this license or have questions about it, here is an http://www.gnu.org/licenses/gpl-faq.html
 *
 * All code and executables are provided "as is" with no warranty either express or implied.
 * The author accepts no liability for any damage or loss of business that this product may cause.
 *
 * Code change notes:
 *
 * Author							Change						Date
 *******************************************************************************
 * Mats Alm   		                Added		                2013-12-03
 *******************************************************************************/

using System;
using System.Collections.Generic;
using System.Globalization;

namespace AppsheetEpplus;

// Used to report the names of Excel functions that are not supported by EPPlus
public class FunctionException : SystemException {
  // Summary:
  //     Initializes a new instance of the System.FunctionException class.
  public FunctionException() {}

  //
  // Summary:
  //     Initializes a new instance of the System.FunctionException class with a specified
  //     error message.
  //
  // Parameters:
  //   message:
  //     The message that describes the error.
  public FunctionException(string message)
      : base(message) {}
}

/// <summary>
/// This class provides methods for accessing/modifying VBA Functions.
/// </summary>
public class FunctionRepository : IFunctionNameProvider {
  private readonly Dictionary<string, ExcelFunction> _functions = new(
      StringComparer.InvariantCulture);

  private FunctionRepository() {}

  public static FunctionRepository Create() {
    var repo = new FunctionRepository();
    repo.LoadModule(new BuiltInFunctions());
    return repo;
  }

  /// <summary>
  /// Loads a module of <see cref="ExcelFunction"/>s to the function repository.
  /// </summary>
  /// <param name="module">A <see cref="IFunctionModule"/> that can be used for adding functions</param>
  public virtual void LoadModule(IFunctionModule module) {
    foreach (var key in module.Functions.Keys) {
      var lowerKey = key.ToLower(CultureInfo.InvariantCulture);
      _functions[lowerKey] = module.Functions[key];
    }
  }

  public virtual ExcelFunction GetFunction(string name) {
    if (!_functions.ContainsKey(name.ToLower(CultureInfo.InvariantCulture))) {
      // Report that Excel function is not supported by EPPlus
      throw new FunctionException(
          string.Format("Excel function '{0}' is not supported in formulas.", name));
    }
    return _functions[name.ToLower(CultureInfo.InvariantCulture)];
  }

  /// <summary>
  /// Removes all functions from the repository
  /// </summary>
  public virtual void Clear() {
    _functions.Clear();
  }

  /// <summary>
  /// Returns true if the the supplied <paramref name="name"/> exists in the repository.
  /// </summary>
  /// <param name="name"></param>
  /// <returns></returns>
  public bool IsFunctionName(string name) {
    return _functions.ContainsKey(name.ToLower(CultureInfo.InvariantCulture));
  }

  /// <summary>
  /// Returns the names of all implemented functions.
  /// </summary>
  public IEnumerable<string> FunctionNames => _functions.Keys;

  /// <summary>
  /// Adds or replaces a function.
  /// </summary>
  /// <param name="functionName"> Case-insensitive name of the function that should be added or replaced.</param>
  /// <param name="functionImpl">An implementation of an <see cref="ExcelFunction"/>.</param>
  public void AddOrReplaceFunction(string functionName, ExcelFunction functionImpl) {
    Require.That(functionName).Named("functionName").IsNotNullOrEmpty();
    Require.That(functionImpl).Named("functionImpl").IsNotNull();
    var fName = functionName.ToLower(CultureInfo.InvariantCulture);
    if (_functions.ContainsKey(fName)) {
      _functions.Remove(fName);
    }
    _functions[fName] = functionImpl;
  }
}