give the shop a typed error instead of string literals

ShopError variants are matchable; the message is the Display, rendered
at the log site, not baked into the error type.

crates/game-service/src/home_mode.rs

@@ -22,6 +22,28 @@ fn gold() -> LogicDataRef {
 fn diamonds() -> LogicDataRef {
     LogicDataRef::by_name(table::RESOURCES, RESOURCE_DIAMONDS)
 }
+#[derive(Debug, thiserror::Error)]
+pub enum ShopError {
+    #[error("not a card")]
+    NotACard,
+    #[error("not on sale")]
+    NotOnSale,
+    #[error("buy limit reached")]
+    BuyLimitReached,
+    #[error("nothing sells that")]
+    NotSold,
+    #[error("chest not sold")]
+    ChestNotSold,
+    #[error("no market price")]
+    NoMarketPrice,
+    #[error("price is not a resource")]
+    PriceNotResource,
+    #[error("not enough funds")]
+    CannotAfford,
+    #[error("unsupported currency")]
+    UnsupportedCurrency,
+}
+
 #[derive(Debug, Default)]
 pub struct TurnResult {
     pub claims: Vec<LogicClaimRewardCommand>,
@@ -92,11 +114,11 @@ impl HomeMode {
             _ => LogicDataRef::treasure_chest_for_arena(CHEST_FREE, arena),
         }
     }
-    fn market_cost(&self, give: &ShopEntry) -> Result<ShopEntry, &'static str> {
+    fn market_cost(&self, give: &ShopEntry) -> Result<ShopEntry, ShopError> {
         if let Some(chest) = give.data.as_treasure_chest() {
             let price = chest.shop_price();
             if price < 1 {
-                return Err("that chest is not sold in the shop");
+                return Err(ShopError::ChestNotSold);
             }
             return Ok(ShopEntry::new(diamonds(), price));
         }
@@ -106,27 +128,27 @@ impl HomeMode {
                 LogicGlobals::resource_diamond_cost(give.count),
             ));
         }
-        Err("that item has no market price")
+        Err(ShopError::NoMarketPrice)
     }
-    fn pay(&mut self, cost: &ShopEntry) -> Result<(), &'static str> {
+    fn pay(&mut self, cost: &ShopEntry) -> Result<(), ShopError> {
         if !cost.is_resource() {
-            return Err("the price must be a resource");
+            return Err(ShopError::PriceNotResource);
         }
         match cost.data.name() {
             RESOURCE_GOLD if self.logic.spend_gold(cost.count) => Ok(()),
             RESOURCE_DIAMONDS if self.logic.spend_diamonds(cost.count) => Ok(()),
-            RESOURCE_GOLD | RESOURCE_DIAMONDS => Err("the player cannot afford it"),
-            _ => Err("only gold and diamonds are accepted"),
+            RESOURCE_GOLD | RESOURCE_DIAMONDS => Err(ShopError::CannotAfford),
+            _ => Err(ShopError::UnsupportedCurrency),
         }
     }
-    fn buy_card(&mut self, card: &LogicDataRef) -> Result<Purchase, &'static str> {
-        let spell = card.as_spell().ok_or("that is not a card")?;
+    fn buy_card(&mut self, card: &LogicDataRef) -> Result<Purchase, ShopError> {
+        let spell = card.as_spell().ok_or(ShopError::NotACard)?;
         let buy_times = self
             .logic
             .shop_buy_times(card)
-            .ok_or("that card is not on sale right now")?;
+            .ok_or(ShopError::NotOnSale)?;
         if buy_times >= spell.shop_buy_limit() {
-            return Err("the buy limit for that card is reached");
+            return Err(ShopError::BuyLimitReached);
         }
         let cost = ShopEntry::new(gold(), spell.cost_in_shop(buy_times));
         self.pay(&cost)?;
@@ -143,14 +165,14 @@ impl HomeMode {
         data: &LogicDataRef,
         count: i32,
         shop: &ShopCatalog,
-    ) -> Result<Purchase, &'static str> {
+    ) -> Result<Purchase, ShopError> {
         if data.as_spell().is_some() {
             return self.buy_card(data);
         }
         let offer = shop
             .offer_for(data)
             .filter(|offer| offer.give.count == count)
-            .ok_or("nothing in the shop sells that")?
+            .ok_or(ShopError::NotSold)?
             .clone();
         let cost = match &offer.cost {
             Some(cost) => cost.clone(),
@@ -161,7 +183,7 @@ impl HomeMode {
             match offer.give.data.name() {
                 RESOURCE_GOLD => self.logic.add_gold(offer.give.count),
                 RESOURCE_DIAMONDS => self.logic.add_diamonds(offer.give.count),
-                _ => return Err("only gold and diamonds can be sold"),
+                _ => return Err(ShopError::UnsupportedCurrency),
             }
         }
         Ok(Purchase {
@@ -221,11 +243,11 @@ impl HomeMode {
                             result.changed = true;
                             result.purchases.push(purchase);
                         }
-                        Err(reason) => {
+                        Err(error) => {
                             tracing::warn!(
                                 command = command.command_type(),
                                 item = %data,
-                                reason,
+                                reason = %error,
                                 "shop purchase rejected"
                             );
                         }