Custom Line Item Validator

AddonValidation.cs

using System;
using System.Linq;
using EPiServer;
using EPiServer.Commerce.Catalog.ContentTypes;
using EPiServer.Commerce.Order;
using EPiServer.Commerce.Validation;
using Mediachase.Commerce;
using Mediachase.Commerce.Catalog;
using Mediachase.Commerce.Catalog.Dto;

namespace CommerceExtensions.LineItem
{
    public class AddonValidation : ILineItemValidator
    {
        private readonly IContentLoader _contentLoader;
        private readonly ReferenceConverter _referenceConverter;
        private readonly ICatalogSystem _catalogSystem;
        private readonly IValidateAddOn _validateAddOn;

        public AddonValidation(IContentLoader contentLoader, ReferenceConverter referenceConverter, ICatalogSystem catalogSystem, IValidateAddOn validateAddOn)
        {
            _contentLoader = contentLoader;
            _referenceConverter = referenceConverter;
            _catalogSystem = catalogSystem;
            _validateAddOn = validateAddOn;
        }

        public bool Validate(ILineItem lineItem, IMarket market, Action<ILineItem, ValidationIssue> onValidationError)
        {
            ParameterValidator.ThrowIfNull<ILineItem>(() => lineItem, lineItem);
            ParameterValidator.ThrowIfNull<IMarket>(() => market, market);
            EntryContentBase entryContent = lineItem.GetEntryContent(this._referenceConverter, this._contentLoader);
            if (entryContent == null)
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToCodeMissing);
                return false;
            }

            // This item cannot be purchased alone as it is an AddOn
            if (!this._validateAddOn.Validate(lineItem))
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToUnavailableItem);
                return false;
            }

            if (!this.IsValidMarket(entryContent, market))
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToNotAvailableInMarket);
                return false;
            }

            if (!this.IsValidMarket(entryContent, market))
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToNotAvailableInMarket);
                return false;
            }
            DateTime utcNow = DateTime.UtcNow;
            if (!this.IsValidCatalog(entryContent, utcNow))
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToUnavailableCatalog);
                return false;
            }
            if (!this.IsValidEntry(entryContent, utcNow))
            {
                onValidationError(lineItem, ValidationIssue.RemovedDueToUnavailableItem);
                return false;
            }

            return true;
        }

        protected virtual bool IsValidMarket(EntryContentBase content, IMarket market)
        {
            return !content.MarketFilter.Any((string excludedMarket) => market.MarketId.Equals(new MarketId(excludedMarket)));
        }

        protected virtual bool IsValidCatalog(EntryContentBase entry, DateTime requestDate)
        {
            CatalogDto.CatalogRow catalogRow = this._catalogSystem.GetCatalogDto(entry.CatalogId).Catalog.FirstOrDefault<CatalogDto.CatalogRow>();
            return catalogRow != null && catalogRow.IsActive && requestDate >= catalogRow.StartDate && requestDate <= catalogRow.EndDate;
        }

        protected virtual bool IsValidEntry(EntryContentBase entry, DateTime requestDate)
        {
            DateTime t = (entry.StartPublish ?? DateTime.MinValue).ToUniversalTime();
            DateTime t2 = (entry.StopPublish ?? DateTime.MaxValue).ToUniversalTime();
            return !entry.IsPendingPublish && requestDate >= t && requestDate <= t2;
        }
    }
}

IValidateAddOn.cs

using EPiServer.Commerce.Order;

namespace CommerceExtensions.LineItem
{
    public interface IValidateAddOn
    {
        bool Validate(ILineItem lineItem);
    }
}

ValidateAddOn.cs

using EPiServer.Commerce.Order;

namespace CommerceExtensions.LineItem
{
    public class ValidateAddOn : IValidateAddOn
    {
        public bool Validate(ILineItem lineItem)
        {
            return true;
        }
    }
}