Armor price calculations (#11417)

Co-authored-by: CommieFlowers <rasmus.cedergren@hotmail.com>
fixes https://github.com/space-wizards/space-station-14/issues/11299

Content.Server/Armor/ArmorSystem.cs

@@ -2,14 +2,20 @@ using Content.Shared.Damage;
 using Content.Server.Examine;
 using Content.Shared.Verbs;
 using Robust.Shared.Utility;
+using Content.Server.Cargo.Systems;
+using Robust.Shared.Prototypes;
+using Content.Shared.Damage.Prototypes;
 using Content.Shared.Inventory;
 
 namespace Content.Server.Armor
 {
     public sealed class ArmorSystem : EntitySystem
     {
+        const double CoefDefaultPrice = 2; // default price of 1% protection against any type of damage
+        const double FlatDefaultPrice = 10; //default price of 1 damage protection against a certain type of damage
 
         [Dependency] private readonly ExamineSystem _examine = default!;
+        [Dependency] private readonly IPrototypeManager _protoManager = default!;
 
         public override void Initialize()
         {
@@ -17,6 +23,43 @@ namespace Content.Server.Armor
 
             SubscribeLocalEvent<ArmorComponent, InventoryRelayedEvent<DamageModifyEvent>>(OnDamageModify);
             SubscribeLocalEvent<ArmorComponent, GetVerbsEvent<ExamineVerb>>(OnArmorVerbExamine);
+            SubscribeLocalEvent<ArmorComponent, PriceCalculationEvent>(GetArmorPrice);
+        }
+
+        private void GetArmorPrice(EntityUid uid, ArmorComponent component, ref PriceCalculationEvent args)
+        {
+            if (component.Modifiers == null)
+                return;
+
+            double price = 0;
+
+            foreach (var modifier in component.Modifiers.Coefficients)
+            {
+                _protoManager.TryIndex(modifier.Key, out DamageTypePrototype? damageType);
+
+                if (damageType != null)
+                {
+                    price += damageType.ArmorPriceCoefficient * 100 * (1 - modifier.Value);
+                }
+                else
+                {
+                    price += CoefDefaultPrice * 100 * (1 - modifier.Value);
+                }
+            }
+            foreach (var modifier in component.Modifiers.FlatReduction)
+            {
+                _protoManager.TryIndex(modifier.Key, out DamageTypePrototype? damageType);
+
+                if (damageType != null)
+                {
+                    price += damageType.ArmorPriceFlat * modifier.Value;
+                }
+                else
+                {
+                    price += FlatDefaultPrice * modifier.Value;
+                }
+            }
+            args.Price += price;
         }
 
         private void OnDamageModify(EntityUid uid, ArmorComponent component, InventoryRelayedEvent<DamageModifyEvent> args)