Add diffing algorithm

src/diff.rs

@@ -0,0 +1,68 @@
+use crate::items::ShopItem;
+
+pub fn diff_items(old: ShopItem, new: ShopItem) -> Option<String> {
+    if old == new {
+        // The items are the exact same
+        return None;
+    }
+
+    let mut result = Vec::new();
+    result.push("*Item updated*".into());
+
+    if old.full_name != new.full_name {
+        result.push(format!("*Name:* {} → {}", old.full_name, new.full_name));
+    } else {
+        result.push(format!("*Name:* {}", new.full_name));
+    }
+
+    if old.description != new.description {
+        result.push(format!(
+            "*Description:* {} → {}",
+            old.description.unwrap_or("_not set_".into()),
+            new.description.unwrap_or("_not set_".into())
+        ));
+    }
+
+    if old.price != new.price {
+        result.push(format!("*Price:* {} → {}", old.price, new.price));
+    }
+
+    if old.stock != new.stock {
+        result.push(format!(
+            "*Stock:* {} → {}",
+            old.stock
+                .map(|stock| stock.to_string())
+                .unwrap_or("Unlimited".into()),
+            new.stock
+                .map(|stock| stock.to_string())
+                .unwrap_or("Unlimited".into())
+        ));
+    }
+
+    Some(result.join("\n"))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn price_diff() {
+        let old = ShopItem {
+            full_name: "Test".into(),
+            price: 1,
+            ..Default::default()
+        };
+
+        let new = ShopItem {
+            full_name: "Test".into(),
+            price: 2,
+            ..Default::default()
+        };
+
+        assert_eq!(
+            diff_items(old, new),
+            Some("*Item updated*\n*Name:* Test\n*Price:* 1 → 2".into())
+        );
+    }
+}

src/items.rs

@@ -2,7 +2,7 @@ use scraper::{Html, Selector};
 use serde::{Deserialize, Serialize};
 use worker::*;
 
-#[derive(Serialize, Deserialize)]
+#[derive(Serialize, Deserialize, PartialEq, Eq, Default)]
 pub struct ShopItem {
     #[serde(rename = "Full Name")]
     pub full_name: String,

src/lib.rs

@@ -1,5 +1,6 @@
 use worker::*;
 
+mod diff;
 mod items;
 
 #[event(fetch, respond_with_errors)]