Extensions

public static class Extensions
{
    public static int Find(this string s, string match)
    {
        for (int i = 0; i <= s.Length - match.Length; i++)
        {
            string sub = s.Substring(i, match.Length);
            if (sub == match)
                return i;
        }
        return -1;
    }
    public static int Find(this string s, string match, int occurence)
    {
        int occurences = 0;
        for (int i = 0; i <= s.Length - match.Length; i++)
        {
            string sub = s.Substring(i, match.Length);
            if (sub == match)
            {
                occurences++;
                if (occurences == occurence)
                    return i;
            }
        }
        return -1;
    }
    public static int Find(this string s, string match, int start, int end)
    {
        for (int i = start; i <= end - match.Length; i++)
        {
            string sub = s.Substring(i, match.Length);
            if (sub == match)
                return i;
        }
        return -1;
    }
    public static int GetLastNumber(this string s)
    {
        int n = 0;
        bool isLastNumber = false;
        for (int i = 0; i < s.Length; i++)
        {
            isLastNumber = int.TryParse(s.Substring(i), out n);
            if (isLastNumber)
                return n;
        }
        throw new ArgumentException("The string has no number in the end.");
    }
    public static int[] FindAll(this string s, string match)
    {
        List<int> indices = new List<int>();
        for (int i = 0; i <= s.Length - match.Length; i++)
        {
            string sub = s.Substring(i, match.Length);
            if (sub == match)
                indices.Add(i);
        }
        return indices.ToArray();
    }
    public static int[] FindAll(this string s, string match, int start, int end)
    {
        List<int> indices = new List<int>();
        for (int i = start; i <= end - match.Length; i++)
        {
            string sub = s.Substring(i, match.Length);
            if (sub == match)
                indices.Add(i);
        }
        return indices.ToArray();
    }
    public static string Substring(this string s, string from, string to)
    {
        int startIndex = s.Find(from) + from.Length;
        int endIndex = s.Find(to);
        int length = endIndex - startIndex;
        return s.Substring(startIndex, length);
    }
    public static string RemoveLastNumber(this string s)
    {
        string l = s;
        for (int i = 0; i < s.Length; i++)
        {
            l = s.Substring(i);
            if (int.TryParse(l, out int shit))
                return s.Substring(0, i);
        }
        return s;
    }
    public static string Replace(this string originalString, string stringToReplaceWith, int startIndex, int length)
    {
        string result = originalString;
        result = result.Remove(startIndex, length);
        result = result.Insert(startIndex, stringToReplaceWith);
        return result;
    }
    public static string ReplaceWholeWord(this string originalString, string oldString, string newString)
    {
        for (int i = originalString.Length - oldString.Length; i >= 0; i--)
        {
            if (originalString.Substring(i, oldString.Length) == oldString)
                if ((i > 0 ? (!originalString[i - 1].IsLetterOrNumber()) : true) && (i < originalString.Length - oldString.Length ? (!originalString[i + oldString.Length].IsLetterOrNumber()) : true))
                {
                    originalString = originalString.Replace(newString, i, oldString.Length);
                    i -= oldString.Length;
                }
        }
        return originalString;
    }
    public static int[] FindOccurences(this string[] a, string match)
    {
        if (a != null)
        {
            List<int> occurences = new List<int>();
            for (int i = 0; i < a.Length; i++)
                if (a[i] == match)
                    occurences.Add(i);
            return occurences.ToArray();
        }
        else return new int[0];
    }
    public static bool ContainsWholeWord(this string s, string match)
    {
        for (int i = s.Length - match.Length; i >= 0; i--)
        {
            if (s.Substring(i, match.Length) == match)
                if ((i > 0 ? (!s[i - 1].IsLetterOrNumber()) : true) && (i < s.Length - match.Length ? (!s[i + match.Length].IsLetterOrNumber()) : true))
                    return true;
        }
        return false;
    }
    public static bool Contains(this string[] a, string match)
    {
        if (a != null)
        {
            for (int i = 0; i < a.Length; i++)
                if (a[i] == match)
                    return true;
            return false;
        }
        return false;
    }
    public static bool ContainsAtLeast(this string[] a, string match)
    {
        if (a != null)
        {
            for (int i = 0; i < a.Length; i++)
                if (a[i].Contains(match))
                    return true;
            return false;
        }
        return false;
    }
    public static bool ContainsAtLeastWholeWord(this string[] a, string match)
    {
        if (a != null)
        {
            for (int i = 0; i < a.Length; i++)
                if (a[i].ContainsWholeWord(match))
                    return true;
            return false;
        }
        return false;
    }
    public static string[] Replace(this string[] a, char oldChar, char newChar)
    {
        for (int i = 0; i < a.Length; i++)
            a[i] = a[i].Replace(oldChar, newChar);
        return a;
    }
    public static string[] Replace(this string[] a, string oldString, string newString)
    {
        for (int i = 0; i < a.Length; i++)
            a[i] = a[i].Replace(oldString, newString);
        return a;
    }
    public static string[] ReplaceWholeWord(this string[] a, string oldString, string newString)
    {
        for (int i = 0; i < a.Length; i++)
            a[i] = a[i].ReplaceWholeWord(oldString, newString);
        return a;
    }
    public static string Combine(this string[] s)
    {
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < s.Length; i++)
            str = str.Append(s[i]);
        return str.ToString();
    }
    public static string Combine(this string[] s, string separator)
    {
        StringBuilder str = new StringBuilder();
        for (int i = 0; i < s.Length; i++)
            str = str.Append(s[i] + separator);
        return str.ToString();
    }
    public static bool IsNumber(this char c)
    {
        if (c >= 48 && c <= 57)
            return true;
        return false;
    }
    public static bool IsLetter(this char c)
    {
        if (c >= 65 && c <= 90 || c >= 97 && c <= 122)
            return true;
        return false;
    }
    public static bool IsLetterOrNumber(this char c) => IsLetter(c) || IsNumber(c) ;
}