ParadoxSaveParser/ParadoxSaveParser.Lib/SearchExpression.cs

using System.Diagnostics;
using System.Linq;

namespace ParadoxSaveParser.Lib;

public record SearchArgs(string key, int currentDepth, int localIndex);

public interface ISearchExpression
{
    bool DoesMatch(SearchArgs args);
}

public class SearchExpression : ISearchExpression
{
    private List<ISearchExpression> _compiledExpression;
    private int _expressionDepth;

    private SearchExpression(List<ISearchExpression> compiledExpression, int expressionDepth)
    {
        _compiledExpression = compiledExpression;
        _expressionDepth = expressionDepth;
    }

    
    public bool DoesMatch(SearchArgs args)
    {
        int index = args.currentDepth - _expressionDepth;
        if (index < 0 || index >= _compiledExpression.Count)
            return true;

        return _compiledExpression[index].DoesMatch(args);
    }

    
    private static bool CharEqualsAndNotEscaped(char c, ReadOnlySpan<char> chars, int i) => 
        chars[i] == c && (i < 1 || chars[i - 1] != '\\') && (i < 2 || chars[i - 2] != '\\');

    public static SearchExpression Parse(string query) => ParseInternal(query, 0);
    
    private static SearchExpression ParseInternal(ReadOnlySpan<char> query, int expressionDepth)
    {
        var compiledExpression = new List<ISearchExpression>();
        ISearchExpression exprPart;
        int partBegin = 0;
        int bracketBalance = 0;
        int expressionDepthIncrement = 0;
        
        for (int i = 0; i < query.Length; i++)
        {
            if (CharEqualsAndNotEscaped('(', query, i))
                bracketBalance++;
            else if (CharEqualsAndNotEscaped(')', query, i))
                bracketBalance--;
            else if (bracketBalance == 0 && CharEqualsAndNotEscaped('.', query, i))
            {
                var part = query.Slice(partBegin, i - partBegin);
                expressionDepthIncrement++;
                exprPart = ParsePart(part, query, partBegin, 
                    expressionDepth + expressionDepthIncrement);
                compiledExpression.Add(exprPart);
                partBegin = i + 1;
            }
        }

        exprPart = ParsePart(query.Slice(partBegin), query, partBegin, 
            expressionDepth + expressionDepthIncrement);
        compiledExpression.Add(exprPart);
        
        return new SearchExpression(compiledExpression, expressionDepth);
    }

    private static ISearchExpression ParsePart(ReadOnlySpan<char> part, 
        ReadOnlySpan<char> query, int partBegin, int expressionDepth)
    {
        if (part is "*")
        {
            return new AnyMatchExpression();
        }
        
        if (CharEqualsAndNotEscaped('[', query, partBegin))
        {
            part = part.Slice(1, part.Length - 2);
            return new IndexMatchExpression(int.Parse(part));
        }
        
        if(part[0] is '(')
        {
            var subExprs = new List<ISearchExpression>();
            ISearchExpression subExpr;
            part = part.Slice(1, part.Length - 2);
            int supExprBegin = 0;
            for (int j = 0; j < part.Length; j++)
            {
                if (CharEqualsAndNotEscaped('|', part, j))
                {
                    subExpr = ParseInternal(part.Slice(supExprBegin, j - supExprBegin), 
                        expressionDepth);
                    subExprs.Add(subExpr);
                    supExprBegin = j + 1;
                }
            }
                
            subExpr = ParseInternal(part.Slice(supExprBegin), expressionDepth);
            subExprs.Add(subExpr);
            return new MultipleMatchExpression(subExprs);
        }
        
        return new ExactMatchExpression(part.ToString());
    }
    
    private record AnyMatchExpression : ISearchExpression
    {
        public bool DoesMatch(SearchArgs args) => true;
    }
    
    private record MultipleMatchExpression(List<ISearchExpression> subExprs) : ISearchExpression
    {
        public bool DoesMatch(SearchArgs args)
        {
            foreach (var e in subExprs)
            {
                if(e.DoesMatch(args))
                    return true;
            }
            return false;
        }
    }

    private record IndexMatchExpression(int index) : ISearchExpression
    {
        public bool DoesMatch(SearchArgs args) => args.localIndex == index;
    }
    
    private record ExactMatchExpression(string key) : ISearchExpression
    {
        public bool DoesMatch(SearchArgs args) => args.key == key;
    }

}