using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using GameOfLife.Entities;

namespace GameOfLife.IO
{
    // https://conwaylife.com/wiki/Apgcode
    public class ApgcodeDecoder
    {
        private static readonly Regex PrefixRegex = new Regex(@"(?<header>.+(?=_))?_?(?<code>.+)");
        private static readonly Regex ExpansionRegex = new Regex(@"y(\w+)");
        public Pattern Pattern { get; }
        public PatternMetadata Metadata { get; }

        public ApgcodeDecoder(string apgcode, string name = null)
        {
            var match = PrefixRegex.Match(apgcode);
            if (!match.Success)
                throw new ArgumentException("Invalid apgcode");
            var header = match.Groups["header"].Value;
            var code = match.Groups["code"].Value;
            if (!string.IsNullOrEmpty(header))
                Metadata = new ApgcodePatternMetaData(header,name);

            var expanded = ExpandAbbreviations(code);
            Pattern = DecodeCells(expanded).ToPattern();
        }

        private IEnumerable<Cell> DecodeCells(string expanded)
        {
            var rowNum = 0;
            foreach (var strip in expanded.Split('z'))
            {
                var colBits = strip.Select(ConvertToUint).ToArray();
                for (var i = 0; i < 5; i++)
                {
                    var colNum = 0;
                    foreach (var colBit in colBits)
                    {
                        if ((colBit >> i & 0b_1) == 1)
                            yield return new Cell(colNum, rowNum);
                        colNum++;
                    }

                    rowNum++;
                }
            }
        }

        public static string ExpandAbbreviations(string apgcode)
        {
            apgcode = apgcode.Replace("w", "00");
            apgcode = apgcode.Replace("x", "000");
            apgcode = ExpansionRegex.Replace(apgcode, m =>
                new string('0', 4 + Convert.ToInt32(ConvertToUint(m.Groups[1].Value[0]))));
            return apgcode;
        }

        public static uint ConvertToUint(char c)
        {
            if (c >= '0' && c <= '9')
                return (uint)(c - '0');
            if (c >= 'a' && c <= 'z')
                return (uint)(c - 'a' + 10);
            throw new Exception("Cannot convert char " + c.ToString());
        }
    }
}