// 2024-03-14  Rachel Lydia Rand
// Population Reduction Projector
// A C# console app


Console.WriteLine("Hello, World!");

string numberFormat = "#,##0";

decimal averageLifespan = 80;
decimal currentPopulation = 8000000000;
decimal startingPopulationByYear = currentPopulation / averageLifespan;

Console.WriteLine("currentPopulation = " + currentPopulation.ToString(numberFormat));
Console.WriteLine("startingPopulationByYear = " + startingPopulationByYear.ToString(numberFormat));

decimal currentReplacementRate = 1M;
decimal newReplacementRate = currentReplacementRate / 4;

Console.WriteLine("");
Console.WriteLine("newReplacementRate = " + newReplacementRate.ToString());

int numOfYearsToProject = 300;
int yearsOfLowerBirthrate = 40;
int averageAgeOfChildbirth = 30;
decimal runningPopulation = currentPopulation;
int startingYear = 2025;
List<int> NumberOfBirthsInYearYear = new List<int>();
List<decimal> NumberOfBirthsInYear = new List<decimal>();

for(int a = startingYear; a < startingYear + numOfYearsToProject; a++)
{
    decimal decreaseAmount = 0;
    decimal increaseAmount = 0;

    // deaths
    if (a < startingYear + averageLifespan)
    {        
        decreaseAmount = startingPopulationByYear;
    }
    else
    { 
        for(int b = 0; b < NumberOfBirthsInYearYear.Count; b++)
        {
            if (NumberOfBirthsInYearYear[b] == a - averageLifespan)
            {
                decreaseAmount = NumberOfBirthsInYear[b];
            }
        }
    }

    // births
    if(a <  startingYear + averageAgeOfChildbirth)
    {
        increaseAmount = startingPopulationByYear * newReplacementRate;
    }
    else
    {
        
        for (int b = 0; b < NumberOfBirthsInYearYear.Count; b++)
        {
            if (NumberOfBirthsInYearYear[b] == a - averageAgeOfChildbirth)
            {
                if (a < startingYear + yearsOfLowerBirthrate)
                {
                    // still having less births
                    increaseAmount = NumberOfBirthsInYear[b] * newReplacementRate;
                }
                else
                {
                    // back to normal replacement rate
                    increaseAmount = NumberOfBirthsInYear[b] * currentReplacementRate;
                }                    
            }            
        }
    }

    runningPopulation -= decreaseAmount;//deaths this year
    runningPopulation += increaseAmount;//births this year
    Console.WriteLine("Year = " + a.ToString() + " | totalPopulation = " + runningPopulation.ToString(numberFormat) + " | decreaseAmount = " + decreaseAmount.ToString(numberFormat) + " | increaseAmount = " + increaseAmount.ToString(numberFormat) + "<br />");

    NumberOfBirthsInYearYear.Add(a);
    NumberOfBirthsInYear.Add(increaseAmount);
}





Console.ReadLine();