EpplusFormulaParser/ExpressionGraph/ExpressionGraphBuilder.cs

/*******************************************************************************
 * You may amend and distribute as you like, but don't remove this header!
 *
 * EPPlus provides server-side generation of Excel 2007/2010 spreadsheets.
 * See http://www.codeplex.com/EPPlus for details.
 *
 * 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       		        2013-03-01 (Prior file history on https://github.com/swmal/ExcelFormulaParser)
 *******************************************************************************/

using System.Collections.Generic;
using System.Linq;

namespace EpplusFormulaParser;

internal sealed class ExpressionGraphBuilder {
  private readonly ExpressionGraph _graph = new();
  private int _tokenIndex;
  private bool _negateNextExpression;

  public ExpressionGraph Build(List<Token> tokens) {
    _tokenIndex = 0;
    BuildUp(tokens, null);
    return _graph;
  }

  private void BuildUp(List<Token> tokens, Expression? parent) {
    while (_tokenIndex < tokens.Count) {
      var token = tokens[_tokenIndex];
      if (token.TokenType == TokenType.Operator && Operator.TryParse(token.Value, out var op)) {
        SetOperatorOnExpression(parent, op);
      } else if (token.TokenType == TokenType.Function) {
        BuildFunctionExpression(tokens, parent, token.Value);
      } else if (token.TokenType == TokenType.OpeningEnumerable) {
        _tokenIndex++;
        BuildEnumerableExpression(tokens, parent);
      } else if (token.TokenType == TokenType.OpeningParenthesis) {
        _tokenIndex++;
        BuildGroupExpression(tokens, parent);
      } else if (token.TokenType == TokenType.ClosingParenthesis
          || token.TokenType == TokenType.ClosingEnumerable) {
        break;
      } else if (token.TokenType == TokenType.Negator) {
        _negateNextExpression = true;
      } else if (token.TokenType == TokenType.Percent) {
        SetOperatorOnExpression(parent, Operator.Percent);
        if (parent == null) {
          _graph.Add(ConstantExpressions.Percent);
        } else {
          parent.AddChild(ConstantExpressions.Percent);
        }
      } else {
        CreateAndAppendExpression(ref parent, token);
      }
      _tokenIndex++;
    }
  }

  private void BuildEnumerableExpression(List<Token> tokens, Expression? parent) {
    if (parent == null) {
      _graph.Add(new EnumerableExpression());
      BuildUp(tokens, _graph.Current);
    } else {
      var enumerableExpression = new EnumerableExpression();
      parent.AddChild(enumerableExpression);
      BuildUp(tokens, enumerableExpression);
    }
  }

  private void CreateAndAppendExpression(ref Expression? parent, Token token) {
    if (IsWaste(token)) {
      return;
    }
    if (parent != null
        && (token.TokenType == TokenType.Comma || token.TokenType == TokenType.SemiColon)) {
      parent = parent.PrepareForNextChild();
      return;
    }
    if (_negateNextExpression) {
      token.Negate();
      _negateNextExpression = false;
    }
    var expression = ExpressionFactory.Create(token);
    if (parent == null) {
      _graph.Add(expression);
    } else {
      parent.AddChild(expression);
    }
  }

  private bool IsWaste(Token token) {
    if (token.TokenType == TokenType.String) {
      return true;
    }
    return false;
  }

  private void BuildFunctionExpression(List<Token> tokens, Expression? parent, string funcName) {
    if (parent == null) {
      _graph.Add(new FunctionExpression(funcName));
      _negateNextExpression = false;
      HandleFunctionArguments(tokens, _graph.Current!);
    } else {
      var func = new FunctionExpression(funcName);
      _negateNextExpression = false;
      parent.AddChild(func);
      HandleFunctionArguments(tokens, func);
    }
  }

  private void HandleFunctionArguments(List<Token> tokens, Expression function) {
    _tokenIndex++;
    var token = tokens.ElementAt(_tokenIndex);
    if (token.TokenType != TokenType.OpeningParenthesis) {
      throw new ExcelErrorValueException();
    }
    _tokenIndex++;
    BuildUp(tokens, function.Children.First());
  }

  private void BuildGroupExpression(List<Token> tokens, Expression? parent) {
    if (parent == null) {
      _graph.Add(new GroupExpression(_negateNextExpression));
      _negateNextExpression = false;
      BuildUp(tokens, _graph.Current);
    } else {
      if (parent.IsGroupedExpression || parent is FunctionArgumentExpression) {
        var newGroupExpression = new GroupExpression(_negateNextExpression);
        _negateNextExpression = false;
        parent.AddChild(newGroupExpression);
        BuildUp(tokens, newGroupExpression);
      }
      BuildUp(tokens, parent);
    }
  }

  private void SetOperatorOnExpression(Expression? parent, IOperator op) {
    if (parent == null) {
      _graph.Current!.Operator = op;
    } else {
      Expression candidate;
      if (parent is FunctionArgumentExpression) {
        candidate = parent.Children.Last();
      } else {
        candidate = parent.Children.Last();
        if (candidate is FunctionArgumentExpression) {
          candidate = candidate.Children.Last();
        }
      }
      candidate.Operator = op;
    }
  }
}