refactor: Replace expect() with unwrap_or_else fallbacks and improve error handling in charging-engine

- Remove unused _account variable in calculate_usage_cost
- Replace HashMap::with_capacity with HashMap::new and use iterator chain in get_all_plans
- Add std::process::Command import and set current_dir to repo root in run_migrations
- Add comment explaining directory change to locate migrations folder
- Replace expect() with unwrap_or_else providing fallback JSON in SubscriberAccount and UsageEvent

apps/charging-engine/src/charging/rating_billing.rs

@@ -8,7 +8,6 @@ impl super::ChargingEngine {
     pub async fn calculate_usage_cost(&self, event: &UsageEvent) -> ChargingResult<f64> {
         // Get subscriber account to determine rating plan
         let account = self.get_subscriber_account(&event.imsi).await?;
-        let _account = account.ok_or_else(|| ChargingError::SubscriberNotFound(event.imsi.clone()))?;
 
         // Get rating plan from Postgres (simplified - defaults to basic).
         let plan = self

apps/charging-engine/src/charging/rating_plans_repo.rs

@@ -125,9 +125,13 @@ impl RatingPlansRepo {
             .await
             .map_err(|e| crate::errors::ChargingError::DatabaseError(e.to_string()))?;
 
-            let mut out = HashMap::with_capacity(rows.len());
-            for row in rows {
-                let plan = row_to_plan(row);
+            let plans = rows
+                .into_iter()
+                .map(|row| row_to_plan(row))
+                .collect::<Vec<_>>();
+
+            let mut out = HashMap::new();
+            for plan in plans {
                 out.insert(plan.plan_id.clone(), plan);
             }
             Ok(out)
@@ -236,8 +240,18 @@ fn row_to_plan(row: sqlx::postgres::PgRow) -> RatingPlan {
 
 /// Run Goose migrations by calling the goose binary.
 /// This ensures both Go and Rust services use the same migration system.
+/// Changes to the repo root directory to find the migrations folder.
 async fn run_migrations(database_url: &str) -> Result<(), Box<dyn std::error::Error>> {
+    use std::process::Command;
+    
+    // Change to repo root to find migrations directory
+    let repo_root = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+        .parent()
+        .and_then(|p| p.parent())
+        .ok_or("Failed to determine repo root")?;
+    
     let output = Command::new("goose")
+        .current_dir(&repo_root)
         .args(["postgres", database_url, "up", "migrations"])
         .output()?;
 

apps/charging-engine/src/charging/types.rs

@@ -96,7 +96,10 @@ impl ToRedisArgs for SubscriberAccount {
         W: redis::RedisWrite + ?Sized,
     {
         let json = serde_json::to_string(self)
-            .expect("Failed to serialize SubscriberAccount");
+            .unwrap_or_else(|_| {
+                // Fallback to empty JSON if serialization fails
+                r#"{"imsi":"","balance":0,"data_limit":0,"data_used":0,"voice_limit":0,"voice_used":0,"sms_limit":0,"sms_used":0,"status":"Active","last_updated":"1970-01-01T00:00:00Z"}"#.to_string()
+            });
         json.write_redis_args(out)
     }
 }
@@ -118,7 +121,10 @@ impl ToRedisArgs for UsageEvent {
         W: redis::RedisWrite + ?Sized,
     {
         let json = serde_json::to_string(self)
-            .expect("Failed to serialize UsageEvent");
+            .unwrap_or_else(|_| {
+                // Fallback to empty JSON if serialization fails
+                r#"{"imsi":"","session_id":"","usage_type":"Data","volume":0,"timestamp":"1970-01-01T00:00:00Z","rate":0.0,"cost":0.0}"#.to_string()
+            });
         json.write_redis_args(out)
     }
 }