#nullable  enable
using System;
using System.Collections.Generic;
using System.Linq;

namespace BTCPayServer.Plugins.PointOfSale;

public class PoSOrder
{
    private readonly int _decimals;
    decimal _discount;
    decimal _tip;
    decimal? _tipTaxRate;
    public List<ItemLine> ItemLines = new();

    public PoSOrder(int decimals)
    {
        _decimals = decimals;
    }

    public record ItemLine(string ItemId, int Count, decimal UnitPrice, decimal TaxRate, bool TaxIncluded = false);
    public void AddLine(ItemLine line)
    {
        ItemLines.Add(line);
    }

    public class OrderSummary
    {
        public decimal Discount { get; set; }
        public decimal Tax { get; set; }
        public decimal TaxOnTip { get; set; }
        public decimal ItemsTotal { get; set; }
        public decimal PriceTaxExcluded { get; set; }
        public decimal Tip { get; set; }
        public decimal PriceTaxIncluded { get; set; }
        public decimal PriceTaxIncludedWithTips { get; set; }
    }

    public OrderSummary Calculate()
    {
        var ctx = new OrderSummary();
        foreach (var item in ItemLines)
        {
            var linePrice = item.UnitPrice * item.Count;
            var discount = linePrice * _discount / 100.0m;
            discount = Round(discount);
            ctx.Discount += discount;
            linePrice -= discount;

            decimal tax;
            decimal lineExcluded;
            if (item.TaxIncluded && item.TaxRate > 0)
            {
                tax = Round(linePrice * item.TaxRate / (100.0m + item.TaxRate));
                lineExcluded = linePrice - tax;
            }
            else
            {
                tax = Round(linePrice * item.TaxRate / 100.0m);
                lineExcluded = linePrice;
            }
            ctx.Tax += tax;
            ctx.PriceTaxExcluded += lineExcluded;
        }
        ctx.PriceTaxExcluded = Round(ctx.PriceTaxExcluded);
        ctx.PriceTaxIncluded = ctx.PriceTaxExcluded + ctx.Tax;
        ctx.Tip = Round(_tip);
        if (_tipTaxRate is { } rate && rate > 0 && ctx.Tip > 0)
        {
            ctx.TaxOnTip = Round(ctx.Tip * rate / 100.0m);
            ctx.Tax += ctx.TaxOnTip;
        }
        ctx.PriceTaxIncludedWithTips = ctx.PriceTaxIncluded + ctx.Tip + ctx.TaxOnTip;
        ctx.PriceTaxIncludedWithTips = Round(ctx.PriceTaxIncludedWithTips);
        ctx.ItemsTotal = ctx.PriceTaxExcluded + ctx.Discount;
        return ctx;
    }

    decimal Round(decimal value) => Math.Round(value, _decimals, MidpointRounding.AwayFromZero);

    public void AddTip(decimal tip)
    {
        _tip = Round(tip);
    }

    public void SetTipTaxRate(decimal? tipTaxRate)
    {
        if (tipTaxRate is < 0m)
            throw new ArgumentOutOfRangeException(nameof(tipTaxRate), "Tip tax rate cannot be negative.");

        _tipTaxRate = tipTaxRate;
    }
    public decimal? GetTipTaxRate()
    {
        return _tipTaxRate;
    }

    /// <summary>
    /// Returns the tax rate of the items in the cart.
    /// If the tax rates are not all the same, returns null.
    /// If the cart is empty, returns null.
    /// Else, returns the tax rate shared by all items
    /// </summary>
    /// <returns></returns>
    public decimal? GetTaxRate()
    {
        if (!ItemLines.Any())
            return null;
        return ItemLines.GroupBy(i => i.TaxRate).Count() == 1 ? ItemLines[0].TaxRate : null;
    }

    /// <summary>
    ///
    /// </summary>
    /// <param name="discount">From 0 to 100</param>
    public void AddDiscountRate(decimal discount)
    {
        _discount = discount;
    }
}