feat: #26107 uplink discounts for traitors (no nukies for now) (#26297)

* feat: #26107 uplink discounts for traitors and nukies

* refactor: #26107 extracted discount label from price of StoreListingControl

* refactor: minor renaming

* refactor: parametrized adding discounts to uplink store

* fix: #26107 prevent exception on empty discountOptions

* feat: uplink now have 'Discounted' category which contains all discounted items on this session.

* after merge fixups

* rename discount categories according to common sense

* refactor: DiscountOptions is now optional (nullable) on ListingData

* add nullability check ignore for already checked listingData.DiscountOptions

* fix after merge store menu ui

* remove unused using

* final fix after merge conflicts

* [refactor]: #26107 fix variables naming in UplinkSystem

* fix: #26107 fix after merge

* refactor: #26107 now supports discountDownUntil on ListingItem, instead of % of discount

* feat: #26107 support multiple currency discount in store on side of discount message label

* refactor: #26107 extracted discounts initialization to separate system. StoreDiscountData are spread as array and not list now

* refactor: #26107 move more code from storesystem to StoreDiscountComponent

* refactor: #26107 separated StoreSystem and StoreDiscountSystem using events

* fix: #26107 placed not-nullable variable initialization in ListingData for tests

* refactor: #26107 minor renaming, xml-docs

* fix: #26107 changed most of discounts to be down to half price for balance purposes

* ids used in with discounts are now ProtoIds, dicountCategories are now prototypes, code with weights simplified

* decoupled storesystem and store discount system

* xml-docs

* refactor:  #26107 xml-doc for StoreDiscountSystem

* is now a thing (tmp)

* fix: compilation errors + StoreDiscountData.DiscountCategoryId

* refactor: rename ListingDataWithCostModifiers, fix all cost related code, enpittyfy performance, uglify uplink_catalog

* refactor: removed unused code, more StoreDiscountSystem docs, simplify code

* refactor: moved discount category logic to respective system, now creating ListingData c-tor clones all mutable fields as expected

* refactor: rename back (its not prototype)

* refactor: move ListingItemsInitializingEvent to file with handling logic

* refactor: comments for StoreBuyFinishedEvent handling, more logging

* refactor: moved StoreInitializedEvent, xml-doc

* refactor: simplify StoreDiscountSystem code  (reduce nesting) + xml-doc

* refactor: restore old listing data cost field name

* refactor: fix linter in uplink_catalog.yml

* refactor: xml-doc for ListingDataWithCostModifiers

* refactor: limit usage of ListingData in favour of ListingDataWithCostModifiers

* refactor: purged linq, removed custom datafield names, minor cleanup

* refactor: removed double-allocation on getting available listings

* refactor: StoreSystem.OnBuyRequest now uses component.FullListingsCatalog as reference point (as it was in original code)

* fix: minor discount categories on uplink items changes following design overview

* refactor: StoreBuyListingMessage now uses protoId and not whole object

* refactor: store refund and discount integration test, RefreshAllListings now translates previous cost modifiers to refreshed list, if state previous to refresh had any listing items

---------

Co-authored-by: pa.pecherskij <pa.pecherskij@interfax.ru>

Content.Shared/StoreDiscount/Components/StoreDiscountComponent.cs

@@ -0,0 +1,51 @@
+using Content.Shared.FixedPoint;
+using Content.Shared.Store;
+using Robust.Shared.GameStates;
+using Robust.Shared.Prototypes;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.StoreDiscount.Components;
+
+/// <summary>
+/// Partner-component for adding discounts functionality to StoreSystem using StoreDiscountSystem.
+/// </summary>
+[RegisterComponent, NetworkedComponent]
+public sealed partial class StoreDiscountComponent : Component
+{
+    /// <summary>
+    /// Discounts for items in <see cref="ListingData"/>.
+    /// </summary>
+    [ViewVariables, DataField]
+    public IReadOnlyList<StoreDiscountData> Discounts = Array.Empty<StoreDiscountData>();
+}
+
+/// <summary>
+/// Container for listing item discount state.
+/// </summary>
+[Serializable, NetSerializable, DataDefinition]
+public sealed partial class StoreDiscountData
+{
+    /// <summary>
+    /// Id of listing item to be discounted.
+    /// </summary>
+    [DataField(required: true)]
+    public ProtoId<ListingPrototype> ListingId;
+
+    /// <summary>
+    /// Amount of discounted items. Each buy will decrement this counter.
+    /// </summary>
+    [DataField]
+    public int Count;
+
+    /// <summary>
+    /// Discount category that provided this discount.
+    /// </summary>
+    [DataField(required: true)]
+    public ProtoId<DiscountCategoryPrototype> DiscountCategory;
+
+    /// <summary>
+    /// Map of currencies to flat amount of discount.
+    /// </summary>
+    [DataField]
+    public Dictionary<ProtoId<CurrencyPrototype>, FixedPoint2> DiscountAmountByCurrency = new();
+}