Revert chain command (#393)

* Revert chain command

* BLOCKS -> NUM

* Fixed warning

substrate/polkadot/cli/src/lib.rs

@@ -223,6 +223,10 @@ pub fn run<I, T, W>(args: I, worker: W) -> error::Result<()> where
 		return import_blocks(matches, worker.exit_only());
 	}
 
+	if let Some(matches) = matches.subcommand_matches("revert") {
+		return revert_chain(matches);
+	}
+
 	let (spec, is_global) = load_spec(&matches)?;
 	let mut config = service::Configuration::default_with_spec(spec);
 
@@ -248,7 +252,7 @@ pub fn run<I, T, W>(args: I, worker: W) -> error::Result<()> where
 
 	config.pruning = match matches.value_of("pruning") {
 		Some("archive") => PruningMode::ArchiveAll,
-		None => PruningMode::keep_blocks(256),
+		None => PruningMode::default(),
 		Some(s) => PruningMode::keep_blocks(s.parse()
 			.map_err(|_| error::ErrorKind::Input("Invalid pruning mode specified".to_owned()))?),
 	};
@@ -495,6 +499,25 @@ fn import_blocks<E>(matches: &clap::ArgMatches, exit: E) -> error::Result<()>
 	Ok(())
 }
 
+fn revert_chain(matches: &clap::ArgMatches) -> error::Result<()> {
+	let (spec, _) = load_spec(&matches)?;
+	let base_path = base_path(matches);
+	let mut config = service::Configuration::default_with_spec(spec);
+	config.database_path = db_path(&base_path, config.chain_spec.id()).to_string_lossy().into();
+
+	let client = service::new_client(config)?;
+
+	let blocks = match matches.value_of("NUM") {
+		Some(v) => v.parse().map_err(|_| "Invalid block count specified")?,
+		None => 256,
+	};
+
+	let reverted = client.revert(blocks)?;
+	let info = client.info()?.chain;
+	info!("Reverted {} blocks. Best: #{} ({})", reverted, info.best_number, info.best_hash);
+	Ok(())
+}
+
 fn run_until_exit<C, W>(
 	runtime: &mut Runtime,
 	service: service::Service<C>,