using Base62;
using Domain.AggregateModel.LinkAggregate;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace QRCodeService.Services
{
    public class ShortCodeService : IShortCodeService
    {
        private readonly ILinkRepository linkRepository;

        public ShortCodeService(ILinkRepository linkRepository)
        {
            this.linkRepository = linkRepository;
        }

        public async Task<string> GenShortCode(string url)
        {
            var full = 16;
            var length = 4;
            var idx = 0;

            while (true)
            {
                var code = CalculateShortCode(url, length, idx);
                var link = await linkRepository.GetAsync(code);
                if (link == null || link.FullUrl == url)
                {
                    return code;
                }
                idx++;
                if (idx * length == full)
                {
                    idx = 0;
                    length = 2 * length;
                }
            }
            
        }
        /// <summary>
        /// 计算短链接
        /// </summary>
        /// <param name="url"></param>
        /// <param name="length">4(四分之一) 8(半) 16(全长)</param>
        /// <param name="index"></param>
        /// <returns></returns>
        private string CalculateShortCode(string url,int length,int index)
        {
            using (var md5 = MD5.Create())
            {
                var result = md5.ComputeHash(Encoding.UTF8.GetBytes(url));
                if (length == 4)
                {
                    return BitConverter.ToInt32(result, 4 * index).ToBase62();
                }
                if(length == 8)
                {
                    return BitConverter.ToInt64(result, 8 * index).ToBase62();
                }
                if(length == 16)
                {
                    return BitConverter.ToInt64(result, 0).ToBase62() + BitConverter.ToInt64(result, 8).ToBase62();
                }
                if(length > 16)
                {
                    return BitConverter.ToInt64(result, 0).ToBase62() + BitConverter.ToInt64(result, 8).ToBase62() + length.ToBase62();
                }
                throw (new ArgumentOutOfRangeException());
            }
        }
    }
}