/**
* <summary>Generates a deterministic RNG seed based on the game date and ID.</summary>
* <remarks>
* In order to keep the seeds as deterministic as possible, each type
* has a separately generated RNG seed. Each seed is created by left
* shifting the year number by a small amount, bitwise ORing another
* number (A), and then bitwise XORing the entire result by the player's
* game ID, giving a unique seed for each month/biweek/week on each
* playthrough.
*
* For monthly events, the number (A) is a number 0-3 representing
* the season number. For biweekly events, the number (A) is a number
* 0-8 representing which half of which month we're in. For weekly events,
* the number (A) is a number 0-16 representing which week of which month
* we're in.
*
* Note that while the seed for monthly events does not include the week
* number, the seed for weekly events includes the month. The first is
* to ensure that the monthly seed remains consistent throughout the
* month. The second is to prevent the same four weekly events from
* occuring throughout the entire year. The biweekly seed includes the
* month for the same reason.
*
* The game ID is retrieved via the expression
* <code>StardewValley.Game1.uniqueIDForThisGame</code>
* </remarks>
*
* <param name="type">The type of event being generated.</param>
* <param name="date">The date of generation.</param>
* <returns>A deterministicly generated RNG seed.</returns>
*/
private int GetRNGSeed(EventType type, SDate date)
{
int year = date.Year;
int gameID = (int)StardewValley.Game1.uniqueIDForThisGame;
int month = date.SeasonAsInt(); // range: 0-3 (2 bits)
int biweek = date.Week() / 2; // range: 0-1 (1 bit)
int week = date.Week(); // range: 0-3 (2 bits)
switch (type)
{
case EventType.Monthly:
return(((year << 2) | month) ^ gameID);
case EventType.Biweekly:
return(((year << 3) | (month << 1) | biweek) ^ gameID);
case EventType.Weekly:
return(((year << 4) | (month << 2) | week) ^ gameID);
default:
return(0); // TODO: Some kind of error?
}
}