using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using NUnit.Framework;

namespace TableParser
{
    [TestFixture]
    public class QuotedFieldTaskTests
    {
        [TestCase("''", 0, "", 2)]
        [TestCase("'a'", 0, "a", 3)]
        [TestCase("\'\'", 0, "", 2)]
        [TestCase("\'a\'", 0, "a", 3)]
        [TestCase(@"some text ""QF \"""" other text", 10, "QF \"", 7)]
        [TestCase("\"a", 0, "a", 2)]
        public void Test(string line, int startIndex, string expectedValue, int expectedLength)
        {
            var actualToken = QuotedFieldTask.ReadQuotedField(line, startIndex);
            Assert.AreEqual(new Token(expectedValue, startIndex, expectedLength), actualToken);
        }
    }

    class QuotedFieldTask
    {
        public static Token ReadQuotedField(string line, int startIndex)
        {
            var result = new StringBuilder();
            var whatQuote = line[startIndex];
            var lastQuote = line.LastIndexOf(whatQuote);
            var endIndex = lastQuote;
            if (lastQuote == 0 || lastQuote == startIndex)
            {
                lastQuote = line.Length - 1;
                endIndex = lastQuote + 1;
            }
            var deltaIndex = lastQuote - startIndex;
            line = DeleteSlashes(line, startIndex, endIndex);
            return new Token(line, startIndex, deltaIndex + 1);
        }

        public static string DeleteSlashes(string line, int startIndex, int endIndex)
        {
            var result = new StringBuilder();
            for (var i = startIndex + 1; i < endIndex; i++)
            {
                if (line[i] == '\\')
                {
                    if (line[i + 1] == '\"' || line[i + 1] == '\'' || line[i + 1] == '\\')
                    {
                        result.Append(line[i + 1]);
                        i++;
                    }
                }
                else result.Append(line[i]);
            }

            return result.ToString();
        }
    }
}