using System;
using System.Collections.Generic;
using System.Linq;
using EvoCalculator.Core.Models.Common;

namespace EvoCalculator.Core.FinanceFormulas;

public class XNPV
{
    private readonly IEnumerable<Flow> _flows;
    private double _rate;

    public XNPV(IEnumerable<Flow> flows, double rate)
    {
        _flows = flows;
        _rate = rate;
    }

    public double GetResult()
    {
        if (_rate <= -1)
            _rate = -1 + 1E-10; // Very funky ... Better check what an IRR <= -100% means

        var startDate = _flows.OrderBy(i => i.Date).First().Date;
        return
            (from item in _flows
                let days = -(item.Date - startDate).Days
                select (double) item.Value * Math.Pow(1 + _rate, (double) days / 365)).Sum();
    }

    public double GetResultPrime()
    {
        var startDate = _flows.OrderBy(i => i.Date).First().Date;
        return (from item in _flows
            let daysRatio = -(item.Date - startDate).Days / 365
            select (double) item.Value * daysRatio * Math.Pow(1.0 + _rate, daysRatio - 1)).Sum();
    }
}