using System.Collections.Generic;
using System.Linq;
using Prefab.Catalog.Domain.Entities;

namespace Prefab.Web.Pricing;

public sealed record FromPriceResult(decimal? Amount, string? Currency, bool IsPriced);

/// <summary>
/// Computes a display-friendly "from price" for catalog products by examining model and variant pricing.
/// </summary>
public sealed class FromPriceCalculator
{
    private const string DefaultCurrency = "USD";
    private readonly string _currencyCode;

    public FromPriceCalculator(string? currencyCode = null)
    {
        _currencyCode = string.IsNullOrWhiteSpace(currencyCode) ? DefaultCurrency : currencyCode.Trim();
    }

    public FromPriceResult Compute(Product product)
    {
        ArgumentNullException.ThrowIfNull(product);

        if (product.Price.HasValue)
        {
            return new FromPriceResult(product.Price.Value, _currencyCode, true);
        }

        var variantPrices = ExtractVariantPrices(product.Variants);
        if (variantPrices.Count > 0)
        {
            var minimum = variantPrices.Min();
            return new FromPriceResult(minimum, _currencyCode, true);
        }

        return new FromPriceResult(null, null, false);
    }

    private static List<decimal> ExtractVariantPrices(IEnumerable<Product> variants) =>
        variants
            .Where(variant => variant is { Kind: ProductKind.Variant, Price: not null })
            .Select(variant => variant.Price!.Value)
            .ToList();
}