LudosData/backend/tests/LudosData.Api.Tests/PricingTests.cs

using System.Text.Json;
using LudosData.Api.Domain;
using LudosData.Api.Services.Pricing;

namespace LudosData.Api.Tests;

/// <summary>
/// The pricing logic, tested without touching eBay.
///
/// Everything that decides what a number means — which listings count, which
/// tier they land in, and how they aggregate — is pure and lives here. Only the
/// HTTP call itself needs credentials, and it is the least interesting part.
/// </summary>
public class ListingClassificationTests
{
    [Theory]
    [InlineData("Chrono Trigger SNES Cartridge Only", GameCondition.Loose)]
    [InlineData("Super Metroid - loose cart, tested", GameCondition.Loose)]
    [InlineData("Banjo-Kazooie N64 game only", GameCondition.Loose)]
    [InlineData("Earthbound SNES CIB", GameCondition.Cib)]
    [InlineData("Ocarina of Time complete in box", GameCondition.Cib)]
    [InlineData("Mario Kart 64 with box and manual", GameCondition.Cib)]
    [InlineData("Boxed Pokemon Yellow Game Boy", GameCondition.Cib)]
    [InlineData("Metroid Prime FACTORY SEALED", GameCondition.Sealed)]
    [InlineData("Halo 3 Xbox 360 Brand New Sealed", GameCondition.Sealed)]
    [InlineData("Final Fantasy VII WATA 9.4 graded", GameCondition.Sealed)]
    public void Titles_are_sorted_into_the_right_tier(string title, GameCondition expected)
    {
        Assert.Equal(expected, ListingCondition.Classify(title, "Used"));
    }

    [Theory]
    // These are the dangerous ones: cheap, plentiful, and not the game.
    [InlineData("Chrono Trigger SNES BOX ONLY no game")]
    [InlineData("Super Mario World manual only")]
    [InlineData("Zelda Ocarina of Time REPRODUCTION cartridge")]
    [InlineData("N64 game case replacement")]
    [InlineData("Custom art label for Earthbound")]
    [InlineData("Lot of 12 SNES games")]
    [InlineData("Nintendo 64 bundle 5 games")]
    public void Accessories_reproductions_and_lots_are_discarded(string title)
    {
        // Counting a $6 "box only" listing as a copy of the game would drag a
        // loose median to nonsense.
        Assert.Null(ListingCondition.Classify(title, "Used"));
    }

    [Fact]
    public void An_unqualified_listing_falls_back_to_the_sellers_flag()
    {
        Assert.Equal(GameCondition.Sealed, ListingCondition.Classify("Chrono Trigger", "New"));
        // Unqualified and used reads as loose, the conservative assumption.
        Assert.Equal(GameCondition.Loose, ListingCondition.Classify("Chrono Trigger", "Used"));
    }
}

public class PriceMathTests
{
    [Fact]
    public void Median_of_an_odd_sample_is_the_middle_value()
    {
        // Sorted first: [10, 20, 30].
        Assert.Equal(20m, PriceMath.Median([10m, 30m, 20m]));
    }

    [Fact]
    public void Median_of_an_even_sample_averages_the_middle_pair()
    {
        Assert.Equal(25m, PriceMath.Median([10m, 20m, 30m, 40m]));
    }

    [Fact]
    public void Median_of_nothing_is_null_rather_than_zero()
    {
        // A game with no listings is unpriced, which is not the same as free.
        Assert.Null(PriceMath.Median([]));
    }

    [Fact]
    public void A_wildly_optimistic_listing_does_not_move_the_estimate()
    {
        var withOutlier = new List<decimal> { 40m, 42m, 45m, 44m, 43m, 41m, 5000m };

        var kept = PriceMath.RemoveOutliers(withOutlier);

        Assert.DoesNotContain(5000m, kept);
        // A mean would have been dragged past 750; the median holds.
        Assert.InRange(PriceMath.Median(kept)!.Value, 40m, 45m);
    }

    [Fact]
    public void Small_samples_are_left_alone()
    {
        // With three points, quartiles are meaningless and trimming would throw
        // away most of the evidence.
        var values = new List<decimal> { 10m, 20m, 900m };
        Assert.Equal(3, PriceMath.RemoveOutliers(values).Count);
    }

    [Fact]
    public void Summarise_reports_a_price_and_a_sample_count_per_tier()
    {
        var listings = new List<PricedListing>
        {
            new(20m, GameCondition.Loose),
            new(24m, GameCondition.Loose),
            new(22m, GameCondition.Loose),
            new(80m, GameCondition.Cib),
            new(90m, GameCondition.Cib),
            new(400m, GameCondition.Sealed),
        };

        var estimate = PriceMath.Summarise(listings, discarded: 4);

        Assert.Equal(22m, estimate.Loose);
        Assert.Equal(85m, estimate.Cib);
        Assert.Equal(400m, estimate.New);
        Assert.Equal(3, estimate.LooseSamples);
        Assert.Equal(2, estimate.CibSamples);
        Assert.Equal(1, estimate.NewSamples);
        Assert.Equal(4, estimate.Discarded);
        Assert.True(estimate.HasAnyPrice);
    }

    [Fact]
    public void A_tier_with_no_listings_stays_null()
    {
        var estimate = PriceMath.Summarise([new PricedListing(20m, GameCondition.Loose)], 0);

        Assert.Equal(20m, estimate.Loose);
        Assert.Null(estimate.Cib);
        Assert.Null(estimate.New);
    }
}

public class EbayResponseParsingTests
{
    /// <summary>Shaped like a real Browse item_summary/search response.</summary>
    private const string SampleResponse = """
    {
      "total": 8,
      "itemSummaries": [
        { "title": "Chrono Trigger SNES Cartridge Only Authentic",
          "condition": "Used", "price": { "value": "120.00", "currency": "USD" } },
        { "title": "Chrono Trigger Super Nintendo loose cart tested",
          "condition": "Used", "price": { "value": "135.50", "currency": "USD" } },
        { "title": "Chrono Trigger SNES game only",
          "condition": "Used", "price": { "value": "128.00", "currency": "USD" } },
        { "title": "Chrono Trigger SNES CIB complete in box",
          "condition": "Used", "price": { "value": "650.00", "currency": "USD" } },
        { "title": "Chrono Trigger Super Nintendo with box and manual",
          "condition": "Used", "price": { "value": "700.00", "currency": "USD" } },
        { "title": "Chrono Trigger SNES FACTORY SEALED WATA",
          "condition": "New", "price": { "value": "12000.00", "currency": "USD" } },
        { "title": "Chrono Trigger SNES BOX ONLY no game",
          "condition": "Used", "price": { "value": "45.00", "currency": "USD" } },
        { "title": "Lot of 6 SNES RPG games including Chrono Trigger",
          "condition": "Used", "price": { "value": "300.00", "currency": "USD" } }
      ]
    }
    """;

    [Fact]
    public void A_search_response_is_split_into_tiers()
    {
        using var document = JsonDocument.Parse(SampleResponse);

        var estimate = EbayPriceProvider.Parse(document);

        Assert.Equal(128.00m, estimate.Loose);   // median of 120, 128, 135.50
        Assert.Equal(675.00m, estimate.Cib);     // mean of the middle pair
        Assert.Equal(12000.00m, estimate.New);

        // The box-only listing and the multi-game lot are both thrown out. Left
        // in, the $45 box would have halved the loose estimate.
        Assert.Equal(2, estimate.Discarded);
        Assert.Equal(3, estimate.LooseSamples);
    }

    [Fact]
    public void A_response_with_no_results_yields_no_prices()
    {
        using var document = JsonDocument.Parse("""{ "total": 0, "itemSummaries": [] }""");

        var estimate = EbayPriceProvider.Parse(document);

        Assert.False(estimate.HasAnyPrice);
    }

    [Fact]
    public void A_response_missing_the_results_array_does_not_throw()
    {
        using var document = JsonDocument.Parse("""{ "total": 0, "warnings": [] }""");

        Assert.False(EbayPriceProvider.Parse(document).HasAnyPrice);
    }

    [Fact]
    public void Listings_without_a_usable_price_are_discarded()
    {
        using var document = JsonDocument.Parse("""
        {
          "itemSummaries": [
            { "title": "Chrono Trigger SNES loose", "condition": "Used" },
            { "title": "Chrono Trigger SNES loose", "condition": "Used",
              "price": { "value": "0.00", "currency": "USD" } },
            { "title": "Chrono Trigger SNES loose", "condition": "Used",
              "price": { "value": "130.00", "currency": "USD" } }
          ]
        }
        """);

        var estimate = EbayPriceProvider.Parse(document);

        Assert.Equal(130.00m, estimate.Loose);
        Assert.Equal(1, estimate.LooseSamples);
        Assert.Equal(2, estimate.Discarded);
    }

    [Theory]
    [InlineData("SNES", "Super Nintendo SNES")]
    [InlineData("N64", "Nintendo 64")]
    [InlineData("360", "Xbox 360")]
    [InlineData("PS1", "PlayStation 1 PS1")]
    public void The_console_name_is_added_to_the_search(string system, string expected)
    {
        // Without it, "Chrono Trigger" returns SNES, PS1 and DS copies together
        // and the median lands between three different markets.
        Assert.Equal($"Chrono Trigger {expected}",
            EbayPriceProvider.BuildQuery("Chrono Trigger", system));
    }

    [Fact]
    public void A_game_with_no_system_searches_on_title_alone()
    {
        Assert.Equal("Chrono Trigger", EbayPriceProvider.BuildQuery("Chrono Trigger", null));
    }
}