namespace EvoCalculator.Core.FinanceFormulas;

public class Interpolation
{
    private int[] values1 = { 7, 12, 18, 24, 36, 60 };
    private int[] percentages1 = { 60, 50, 40, 29, 25, 25 };
    private int[] percentages2 = { 45, 35, 30, 26, 25, 25 };
    private int[] percentages3 = { 35, 30, 27, 25, 25, 25 };

    private int[] values;
    private int[] percentages;

    public Interpolation(decimal PI)
    {
        switch (PI)
        {
            case >= 0.06m:
                values = values1;
                percentages = percentages1;
                break;
            case >= 0.03m and < 0.06m:
                values = values1;
                percentages = percentages2;
                break;
            default:
                values = values1;
                percentages = percentages3;
                break;
        }
    }

    public decimal Interpolate(decimal targetValue)
    {
        var lowerValue = values[0];
        var lowerPercentage = percentages[0];
        var higherValue = values[0];
        var higherPercentage = percentages[0];

        for (var i = 1; i < values.Length; i++)
        {
            if (values1[i] <= targetValue)
            {
                lowerValue = values[i];
                lowerPercentage = percentages[i];
            }
            else
            {
                higherValue = values[i];
                higherPercentage = percentages[i];
                break;
            }
        }

        var percentage = lowerPercentage + (higherPercentage - lowerPercentage) * (targetValue - lowerValue) /
            (higherValue - lowerValue);
        return percentage;
    }
}