Vendor Rating System

-- Delivery Score Calculation
DELIVERY_SCORE = (
    (on_time_deliveries / total_deliveries) * 50 +           -- OTD Rate (50%)
    (1 - ABS(actual_lead - quoted_lead) / quoted_lead) * 30 + -- Lead Accuracy (30%)
    (complete_orders / total_orders) * 20                     -- Fill Rate (20%)
) * 100

-- Quality Score Calculation
QUALITY_SCORE = (
    (1 - defects / total_units) * 40 +                       -- Defect-free Rate (40%)
    (1 - returns / total_shipments) * 30 +                   -- No-Return Rate (30%)
    (spec_compliant_items / total_items) * 30                -- Spec Compliance (30%)
) * 100

-- Overall Score (Weighted Sum)
OVERALL_SCORE = (
    delivery_score * category.delivery_weight +
    quality_score * category.quality_weight +
    price_score * category.price_weight +
    compliance_score * category.compliance_weight +
    responsiveness_score * category.responsiveness_weight
)

public class VendorRatingService : IVendorRatingService
{
    private readonly IVendorRepository _vendorRepo;
    private readonly IPerformanceRepository _performanceRepo;
    private readonly ICategoryRepository _categoryRepo;

    public async Task<VendorRating> CalculateVendorRating(
        Guid vendorId, DateRange period)
    {
        // 1. Get vendor and category weights
        var vendor = await _vendorRepo.GetByIdAsync(vendorId);
        var weights = await _categoryRepo.GetWeightsAsync(vendor.CategoryId);

        // 2. Collect raw performance metrics
        var metrics = await _performanceRepo
            .GetMetricsForPeriodAsync(vendorId, period);

        // 3. Calculate individual scores
        var deliveryScore = CalculateDeliveryScore(metrics);
        var qualityScore = CalculateQualityScore(metrics);
        var priceScore = CalculatePriceScore(metrics);
        var complianceScore = await CalculateComplianceScore(vendorId);
        var responsivenessScore = CalculateResponsivenessScore(metrics);

        // 4. Apply weights and sum
        var overallScore =
            deliveryScore * weights.DeliveryWeight +
            qualityScore * weights.QualityWeight +
            priceScore * weights.PriceWeight +
            complianceScore * weights.ComplianceWeight +
            responsivenessScore * weights.ResponsivenessWeight;

        // 5. Determine tier
        var tier = DetermineTier(overallScore);

        // 6. Save and return
        var rating = new VendorRating { ... };
        await _vendorRepo.SaveRatingAsync(rating);
        return rating;
    }

    private VendorTier DetermineTier(decimal score) => score switch
    {
        >= 90 => VendorTier.Platinum,
        >= 75 => VendorTier.Gold,
        >= 60 => VendorTier.Silver,
        >= 40 => VendorTier.Bronze,
        _ => VendorTier.UnderReview
    };
}