5dplomacy/MultiversalDiplomacy/Model/TimelineFactory.cs

51 lines
1.9 KiB
C#

namespace MultiversalDiplomacy.Model;
/// <summary>
/// A shared counter for handing out new timeline designations.
/// </summary>
internal class TimelineFactory
{
private static readonly char[] Letters = [
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
'u', 'v', 'w', 'x', 'y', 'z',
];
/// <summary>
/// Convert a string timeline identifier to its serial number.
/// </summary>
/// <param name="timeline">Timeline identifier.</param>
/// <returns>Integer.</returns>
public static int StringToInt(string timeline)
{
int result = Array.IndexOf(Letters, timeline[0]);
for (int i = 1; i < timeline.Length; i++) {
// The result is incremented by one because timeline designations are not a true base26 system.
// The "ones digit" maps a-z 0-25, but the "tens digit" maps a to 1, so "10" (26) is "aa" and not "a0"
result = (result + 1) * 26;
result += Array.IndexOf(Letters, timeline[i]);
}
return result;
}
/// <summary>
/// Convert a timeline serial number to its string identifier.
/// </summary>
/// <param name="designation">Integer.</param>
/// <returns>Timeline identifier.</returns>
public static string IntToString(int designation) {
static int downshift(int i ) => (i - (i % 26)) / 26;
IEnumerable<char> result = [Letters[designation % 26]];
for (int remainder = downshift(designation); remainder > 0; remainder = downshift(remainder) - 1) {
// We subtract 1 after downshifting for the same reason we add 1 above after upshifting.
//
result = result.Prepend(Letters[(remainder % 26 + 25) % 26]);
}
return new string(result.ToArray());
}
private int nextTimeline = 0;
public string NextTimeline() => IntToString(nextTimeline++);
}