using System;

//abc
static void Match_ABC(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    const string pattern = @"abc";
    if(input[0..3].SequenceEqual(pattern))
    {
        ptr += 3;
        region_end = ptr;
    }
}

//a[abc]d
static void Match_A_charset_ABC_C(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    if(input[0] == 'a' && (input[1] == 'a' || input[1] == 'b' || input[1] == 'c') && input[2] == 'd')
    {
        ptr += 3;
        region_end = ptr;
    }
}

//[abc]
static void Match_charset_ABC(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    if(input[0] == 'a' || input[0] == 'b' || input[0] == 'c')
    {
        ptr += 1;
        region_end = ptr;
    }
}

//.
static void Match_Dot(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    ptr += 1;
    region_end = ptr;
}

//a{3,5}

static void Match_A_3_5(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    do
    {
        if(input[ptr..].StartsWith("aaa"))
        {
            ptr += 3;
            region_end = ptr;
        }
        else
        {
            break;
        }
        for(int i = 0; i < 2; i++)
        {
            if(input[ptr] == 'a')
            {
                ptr += 1;
                region_end = ptr;
            }
            else
            {
                break;
            }
        }

    } while(false);
}

//(ab){2,3}
static void Match_AB_2_3(ReadOnlySpan<char> input)
{
    int ptr = 0;
    int region_start = ptr;
    int region_end = region_start;

    do
    {
        if(input[ptr..].StartsWith("abab"))
        {
            ptr += 4;
            region_end = ptr;
        }
        else
        {
            break;
        }
        for(int i = 0; i < 1; i++)
        {
            if(input[ptr..].StartsWith("ab"))
            {
                ptr += 2;
                region_end = ptr;
            }
            else
            {
                break;
            }
        }

    } while(false);
}