Common crate for substrate-relay (#1082)

* lib-substrate-relay

* pass to build

* remove unused file

* clippy && tests

* Changed follow suggestions

* License

* Make changes follow suggested

* docs

* fix fmt

bridges/relays/lib-substrate-relay/src/helpers.rs

@@ -0,0 +1,41 @@
+// Copyright 2019-2021 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity Bridges Common is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Substrate relay helpers
+
+use relay_utils::metrics::{FloatJsonValueMetric, PrometheusError, Registry};
+
+/// Creates standalone token price metric.
+pub fn token_price_metric(
+	registry: &Registry,
+	prefix: Option<&str>,
+	token_id: &str,
+) -> Result<FloatJsonValueMetric, PrometheusError> {
+	FloatJsonValueMetric::new(
+		registry,
+		prefix,
+		format!(
+			"https://api.coingecko.com/api/v3/simple/price?ids={}&vs_currencies=btc",
+			token_id
+		),
+		format!("$.{}.btc", token_id),
+		format!("{}_to_base_conversion_rate", token_id.replace("-", "_")),
+		format!(
+			"Rate used to convert from {} to some BASE tokens",
+			token_id.to_uppercase()
+		),
+	)
+}