using System.Diagnostics.CodeAnalysis;
using JetBrains.Annotations;

namespace AyCode.Utils.Extensions
{
    public static class StringExtensions
    {
        //[ContractAnnotation("str:null => true; str:notnull <= false")]
        [ContractAnnotation("str:null => true; str:notnull <= false")]
        public static bool IsNullOrEmpty([NotNullWhen(returnValue: false)] this string str) => str == null || str.Length == 0;

        [ContractAnnotation("str:null => true;")]
        public static bool IsNullOrWhiteSpace([NotNullWhen(returnValue: false)] this string str)
        {
            if (str == null || str.Length == 0) return true;
            if (!char.IsWhiteSpace(str[0])) return false;

            for (var i = 1; i < str.Length; i++)
            {
                if (!char.IsWhiteSpace(str[i]))
                    return false;
            }

            return true;
        }

        public static string FirstLetterToUpper(string str)
        {
            if (str.IsNullOrWhiteSpace())
                return str;

            if (str.Length == 1)
                return str.ToUpper();

            str = str.ToLower();

            return char.ToUpper(str[0]) + str[1..];
        }
    }
}