Fix flashblocks index (#36)

* Use different approach

* fmt

Author: SozinM

src/publish.rs

@@ -120,8 +120,10 @@ impl Step<Flashblocks> for PublishFlashblock {
 				.expect("withdrawals_root is present"),
 		};
 
+		// Get 0-index to use in flashblock
+		let index = self.flashblock_number.index();
 		// Increment flashblock number since we've built the flashblock
-		let index = self.flashblock_number.advance();
+		self.flashblock_number.advance();
 
 		// Push the contents of the payload
 		if let Err(e) = self.sink.publish(&FlashblocksPayloadV1 {

src/state.rs

@@ -27,6 +27,14 @@ impl FlashblockNumber {
 		self.target_flashblocks.load(Ordering::Relaxed)
 	}
 
+	/// Returns current flashblock in 0-index format
+	pub fn index(&self) -> u64 {
+		self
+			.current_flashblock
+			.load(Ordering::Relaxed)
+			.saturating_sub(1)
+	}
+
 	pub fn advance(&self) -> u64 {
 		self.current_flashblock.fetch_add(1, Ordering::Relaxed)
 	}