Declarative Shops

[BasicallyIAmFox]

What is the new feature?

Modernizes NPC shops. #3067.
Replaces ModNPC.SetupShop hook with ModNPC.AddShops (see Porting Notes)
ModNPC.ModifyActiveShop allows manual shop creation in old style.

Why should this be part of tModLoader?

It could allow checking what items NPC can sell or not, better mod compatibility, and also allows easily insert item before/after X item, as well as adding some conditions to already existing items. Also avoids possible IndexOutOfRangeException, if too many items were added in single shop. Info mods can show how to obtain X item because conditions for them are localized.

Are there alternative designs?

This PR offers a good compromise between flexibility (via AbstractNPCShop) and standardisation. Some aspects are not ideal like the implementation of the 'fixed layout' bartender, but work pretty well overall.

Sample usage for the new feature

public override void AddShops()
{
    var shop = new NPCShop(Type, "Shop"); // You can have different internal names for your shop
    shop.Add<ExampleItem>(); // Adds Example Item in the shop.

    shop.InsertBefore(ModContent.ItemType<ExampleItem>(), ModContent.ItemType<ExampleLifeFruit>()); // Puts Example Life Fruit right before Example Item.

    shop.GetEntry(ModContent.ItemType<ExampleBuffPotion>()).Disable(); // Hides Example Buff Potion from the shop. Will throw an exception if item not found.
    // Safely hides Example Buff Potion from the shop.
    if (shop.TryGetEntry(ModContent.ItemType<ExampleBuffPotion>(), out var entry)) {
        entry.Disable();
    }

    shop.Add(ModContent.ItemType<ExampleSoul>(), NPCShop.Condition.BloodMoon); // Puts an item if its Blood Moon.

    shop.Register();
}

ExampleMod updates

ExampleNPCShop, WeaponWithGrowingDamage, ExampleGlobalNPC were updated.
And of course all town npcs. (ExamplePerson, ExampleTravelingMerchant and ExampleBoneMerchant)

Porting Notes

ModPylon.IsPylonForSale(int npcType, Player player, bool isNPCHappyEnough) -> ModPylon.GetNPCShopEntry()
ModNPC.SetupShop(Chest shop, ref int nextSlot) -> ModNPC.ModifyActiveShop()
ModNPC.OnChatButtonClicked(bool firstButton, ref bool shop) -> ModNPC.OnChatButtonClicked(bool firstButton, ref string shopName)
GlobalNPC.SetupShop(int type, Chest shop, ref int nextSlot) -> GlobalNPC.ModifyActiveShop(NPC npc, string shopName, Item[] items)

FAQ

• Does this remove the 40 item per shop limit?
  • No, but it should be compatible with a future PR that does.
  • In the mean time, a warning message will be displayed to the user when the shop has too many items to fit.
• How can I randomize my shop items?
  • True randomization would mean contents change every time the shop is opened, and is probably not desirable. Better to use something like moon phases, or a static variable which you change periodically.
  • Several moon phase related conditions have been added, mostly to support skeleton merchant, but you can make your own conditions with a localization like "Randomly, with 10% chance depending on moon phase" or similar.
• How can I explicitly lay out my shop like DD2 bartender?
  • The only way to do that would be through adding entries and to call Entry.ReserveSlot() method afterwards. If conditions are not met, then it will put 'air' item instead of simply not doing anything. Example:

  shop.Add(
    new NPCShop.Entry(
      ModContent.ItemType<ExampleItem>(),
      Condition.IsMoonFull)
    .ReserveSlot()
  )
  

• Can I use this to add items to travelling merchant's shop?
  • Not at this stage. no.
  • Please continue to use ModifyActiveShop
    • You can use TravellingMerchantShop.AddInfoEntry to add entries to the 'informational' list of the shop, so mods like recipe browser can show how to obtain the item.

[Solxanich]

Internal note: previously #3072

[Solxanich]

Initial Pass Through.

Great job getting this going, I want to say we are more than half way there.