Add low balance check in claim token api

Author: sudo-shashank

docs/api-documentation.md

@@ -140,3 +140,14 @@ curl "https://forest-explorer.chainsafe.dev/api/claim_token?faucet_info=MainnetF
 ```bash
 ServerError|I'm a teapot - mainnet tokens are not available.
 ```
+
+---
+
+## Faucet Top-Up Requests
+
+If you encounter a server error indicating that faucet is exhausted (e.g.,
+"ServerError|Faucet is empty, Request top-up"), you can request a refill here:
+
+- [Request Faucet Top-Up](https://github.com/ChainSafe/forest-explorer/discussions/134)
+
+This discussion thread is monitored for top-up requests.

src/faucet/server_api.rs

@@ -219,6 +219,15 @@ pub async fn claim_token(
         .map_err(ServerFnError::new)?;
 
     SendWrapper::new(async move {
+        let faucet_balance = rpc
+            .wallet_balance(from, &faucet_info.token_type())
+            .await
+            .map_err(ServerFnError::new)?;
+        if faucet_balance < *faucet_info.drip_amount() {
+            return Err(ServerFnError::ServerError(
+                "Faucet is empty, Request top-up".to_string(),
+            ));
+        }
         match faucet_info {
             FaucetInfo::MainnetFIL => {
                 set_response_status(StatusCode::IM_A_TEAPOT);