Chris Chen
76 lines
2.4 KiB
C#
76 lines
2.4 KiB
C#
namespace ROLAC.API.Services.Disbursement;
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/// <summary>
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/// Converts a monetary amount to the English words used on a check, e.g.
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/// 1234.56 → "One Thousand Two Hundred Thirty-Four and 56/100 Dollars".
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/// Pure and dependency-free so it is easily unit-tested.
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/// </summary>
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public static class AmountToWords
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{
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private static readonly string[] Ones =
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[
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"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine",
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"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen",
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"Seventeen", "Eighteen", "Nineteen",
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];
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private static readonly string[] Tens =
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[
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"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety",
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];
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// index 1.. → 10^(3*index)
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private static readonly string[] Scales = ["", "Thousand", "Million", "Billion", "Trillion"];
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public static string Convert(decimal amount)
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{
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if (amount < 0) amount = 0m;
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// Round half-up to cents.
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amount = Math.Round(amount, 2, MidpointRounding.AwayFromZero);
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var dollars = (long)Math.Floor(amount);
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var cents = (int)Math.Round((amount - dollars) * 100m, MidpointRounding.AwayFromZero);
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var words = dollars == 0 ? "Zero" : ThreeDigitGroupsToWords(dollars);
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return $"{words} and {cents:00}/100 Dollars";
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}
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private static string ThreeDigitGroupsToWords(long n)
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{
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// Split into groups of three digits, low to high.
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var groups = new List<int>();
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while (n > 0) { groups.Add((int)(n % 1000)); n /= 1000; }
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var parts = new List<string>();
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for (var i = groups.Count - 1; i >= 0; i--)
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{
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if (groups[i] == 0) continue;
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var group = HundredsToWords(groups[i]);
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var scale = Scales[i];
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parts.Add(string.IsNullOrEmpty(scale) ? group : $"{group} {scale}");
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}
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return string.Join(" ", parts);
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}
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private static string HundredsToWords(int n)
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{
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var parts = new List<string>();
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if (n >= 100)
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{
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parts.Add($"{Ones[n / 100]} Hundred");
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n %= 100;
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}
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if (n >= 20)
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{
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var t = Tens[n / 10];
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var o = n % 10;
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parts.Add(o == 0 ? t : $"{t}-{Ones[o]}");
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}
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else if (n > 0)
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{
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parts.Add(Ones[n]);
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}
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return string.Join(" ", parts);
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}
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}
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