52 lines
1.4 KiB
C#
52 lines
1.4 KiB
C#
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namespace Books.Api.Tests.Helpers;
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/// <summary>
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/// Generates valid Danish CVR numbers for testing.
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/// </summary>
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public static class CvrGenerator
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{
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private static readonly int[] Weights = [2, 7, 6, 5, 4, 3, 2, 1];
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private static readonly Random Random = new();
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/// <summary>
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/// Generates a random valid CVR number with correct modulus 11 checksum.
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/// </summary>
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public static string Generate()
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{
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// Generate 7 random digits
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var digits = new int[8];
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for (var i = 0; i < 7; i++)
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{
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digits[i] = Random.Next(0, 10);
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}
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// Ensure first digit is not 0 (CVR numbers don't start with 0)
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if (digits[0] == 0) digits[0] = Random.Next(1, 10);
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// Calculate checksum digit using modulus 11
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// Sum of (digit * weight) for first 7 digits
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var sum = 0;
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for (var i = 0; i < 7; i++)
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{
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sum += digits[i] * Weights[i];
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}
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// Find the last digit that makes sum % 11 == 0
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// We need: (sum + digit * 1) % 11 == 0
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// So: digit = (11 - (sum % 11)) % 11
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var remainder = sum % 11;
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var checkDigit = (11 - remainder) % 11;
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// If checkDigit is 10, we can't use it (single digit only)
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// So regenerate
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if (checkDigit == 10)
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{
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return Generate();
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}
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digits[7] = checkDigit;
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return string.Join("", digits);
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}
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}
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