DutchNumberToWordsConverter.cs

namespace Humanizer;

/// <summary>
/// Dutch spelling of numbers is not really officially regulated.
/// There are a few different rules that can be applied.
/// Used the rules as stated here.
/// http://www.beterspellen.nl/website/?pag=110
/// </summary>
class DutchNumberToWordsConverter :
    GenderlessNumberToWordsConverter
{
    static readonly string[] UnitsMap = ["nul", "een", "twee", "drie", "vier", "vijf", "zes", "zeven", "acht", "negen", "tien", "elf", "twaalf", "dertien", "veertien", "vijftien", "zestien", "zeventien", "achttien", "negentien"];
    static readonly string[] TensMap = ["nul", "tien", "twintig", "dertig", "veertig", "vijftig", "zestig", "zeventig", "tachtig", "negentig"];

    class Fact
    {
        public long Value { get; set; }
        public required string Name { get; set; }
        public required string Prefix { get; set; }
        public required string Postfix { get; set; }
        public bool DisplayOneUnit { get; set; }
    }

    static readonly Fact[] Hunderds =
    [
        new()
        {
            Value = 1_000_000_000_000_000_000L,
            Name = "triljoen",
            Prefix = " ",
            Postfix = " ",
            DisplayOneUnit = true
        },
        new()
        {
            Value = 1_000_000_000_000_000L,
            Name = "biljard",
            Prefix = " ",
            Postfix = " ",
            DisplayOneUnit = true
        },
        new()
        {
            Value = 1_000_000_000_000L,
            Name = "biljoen",
            Prefix = " ",
            Postfix = " ",
            DisplayOneUnit = true
        },
        new()
        {
            Value = 1000000000,
            Name = "miljard",
            Prefix = " ",
            Postfix = " ",
            DisplayOneUnit = true
        },
        new()
        {
            Value = 1000000,
            Name = "miljoen",
            Prefix = " ",
            Postfix = " ",
            DisplayOneUnit = true
        },
        new()
        {
            Value = 1000,
            Name = "duizend",
            Prefix = "",
            Postfix = " ",
            DisplayOneUnit = false
        },
        new()
        {
            Value = 100,
            Name = "honderd",
            Prefix = "",
            Postfix = "",
            DisplayOneUnit = false
        }
    ];

    public override string Convert(long input)
    {
        var number = input;

        if (number == 0)
        {
            return UnitsMap[0];
        }

        if (number < 0)
        {
            return $"min {Convert(-number)}";
        }

        var word = "";

        foreach (var m in Hunderds)
        {
            var divided = number / m.Value;

            if (divided <= 0)
            {
                continue;
            }

            if (divided == 1 && !m.DisplayOneUnit)
            {
                word += m.Name;
            }
            else
            {
                word += Convert(divided) + m.Prefix + m.Name;
            }

            number %= m.Value;
            if (number > 0)
            {
                word += m.Postfix;
            }
        }

        if (number > 0)
        {
            if (number < 20)
            {
                word += UnitsMap[number];
            }
            else
            {
                var tens = TensMap[number / 10];
                var unit = number % 10;
                if (unit > 0)
                {
                    var units = UnitsMap[unit];
                    var trema = units.EndsWith("e");
                    word += units + (trema ? "ën" : "en") + tens;
                }
                else
                {
                    word += tens;
                }
            }
        }

        return word;
    }

    static readonly Dictionary<string, string> OrdinalExceptions = new()
    {
        {
            "een", "eerste"
        },
        {
            "drie", "derde"
        },
        {
            "miljoen", "miljoenste"
        },
    };

    static readonly char[] EndingCharForSte = ['t', 'g', 'd'];

    public override string ConvertToOrdinal(int number)
    {
        var word = Convert(number);

        foreach (var kv in OrdinalExceptions.Where(kv => word.EndsWith(kv.Key)))
        {
            // replace word with exception
            return StringHumanizeExtensions.Concat(word.AsSpan(0, word.Length - kv.Key.Length), kv.Value.AsSpan());
        }

        // achtste
        // twintigste, dertigste, veertigste, ...
        // honderdste, duizendste, ...
        if (word.LastIndexOfAny(EndingCharForSte) == word.Length - 1)
        {
            return word + "ste";
        }

        return word + "de";
    }
}