PdfPig/src/UglyToad.PdfPig.Tokenization/NumericTokenizer.cs

namespace UglyToad.PdfPig.Tokenization
{
    using System;
    using System.Globalization;
    using System.Text;
    using Core;
    using Tokens;

    internal sealed class NumericTokenizer : ITokenizer
    {
        private const byte Zero = 48;
        private const byte Nine = 57;

        public bool ReadsNextByte { get; } = true;

        public bool TryTokenize(byte currentByte, IInputBytes inputBytes, out IToken token)
        {
            token = null;

            using var characters = new ValueStringBuilder(stackalloc char[32]);

            var initialSymbol = currentByte is (byte)'-' or (byte)'+';

            if ((currentByte >= Zero && currentByte <= Nine) || currentByte == '.')
            {
                characters.Append((char)currentByte);
            }
            else if (initialSymbol)
            {
                characters.Append((char) currentByte);
            }
            else
            {
                return false;
            }

            var previousSymbol = initialSymbol;

            while (inputBytes.MoveNext())
            {
                var b = inputBytes.CurrentByte;

                if (b == '+' || b == '-')
                {
                    if (previousSymbol)
                    {
                        continue;
                    }

                    characters.Append((char) b);
                    previousSymbol = true;
                }
                else if ((b >= Zero && b <= Nine) ||
                         b == '.' ||
                         b == 'E' ||
                         b == 'e')
                {
                    previousSymbol = false;
                    characters.Append((char)b);
                }
                else
                {
                    break;
                }
            }

            var str = characters.ToString();

            switch (str)
            {
                case "-1":
                    token = NumericToken.MinusOne;
                    return true;
                case "-":
                case ".":
                case "0":
                case "0000":
                    token = NumericToken.Zero;
                    return true;
                case "1":
                    token = NumericToken.One;
                    return true;
                case "2":
                    token = NumericToken.Two;
                    return true;
                case "3":
                    token = NumericToken.Three;
                    return true;
                case "4":
                    token = NumericToken.Four;
                    return true;
                case "5":
                    token = NumericToken.Five;
                    return true;
                case "6":
                    token = NumericToken.Six;
                    return true;
                case "7":
                    token = NumericToken.Seven;
                    return true;
                case "8":
                    token = NumericToken.Eight;
                    return true;
                case "9":
                    token = NumericToken.Nine;
                    return true;
                case "10":
                    token = NumericToken.Ten;
                    return true;
                case "11":
                    token = NumericToken.Eleven;
                    return true;
                case "12":
                    token = NumericToken.Twelve;
                    return true;
                case "13":
                    token = NumericToken.Thirteen;
                    return true;
                case "14":
                    token = NumericToken.Fourteen;
                    return true;
                case "15":
                    token = NumericToken.Fifteen;
                    return true;
                case "16":
                    token = NumericToken.Sixteen;
                    return true;
                case "17":
                    token = NumericToken.Seventeen;
                    return true;
                case "18":
                    token = NumericToken.Eighteen;
                    return true;
                case "19":
                    token = NumericToken.Nineteen;
                    return true;
                case "20":
                    token = NumericToken.Twenty;
                    return true;
                case "100":
                    token = NumericToken.OneHundred;
                    return true;
                case "500":
                    token = NumericToken.FiveHundred;
                    return true;
                case "1000":
                    token = NumericToken.OneThousand;
                    return true;
                default:
                    if (!double.TryParse(str, NumberStyles.Any, CultureInfo.InvariantCulture, out var value))
                    {
                        if (TryParseInvalidNumber(str, out value))
                        {
                            token = new NumericToken(value);
                            return true;
                        }

                        return false;
                    }

                    token = new NumericToken(value);
                    return true;
            }           
        }

        private static bool TryParseInvalidNumber(string numeric, out double result)
        {
            result = 0;

            if (!numeric.Contains("-") && !numeric.Contains("+"))
            {
                return false;
            }

            var parts = numeric.Split(new string[] { "+", "-" }, StringSplitOptions.RemoveEmptyEntries);

            if (parts.Length == 0)
            {
                return false;
            }

            foreach (var part in parts)
            {
                if (!double.TryParse(part, NumberStyles.Any, CultureInfo.InvariantCulture, out var partNumber))
                {
                    return false;
                }

                result += partNumber;
            }

            return true;
        }
    }
}