Price oracle (#11)

* update services

aqua-examples/price-oracle/mean_service/src/main.rs

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2021 Fluence Labs Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+use marine_rs_sdk::{marine, module_manifest};
+
+module_manifest!();
+
+fn main() {}
+
+#[marine]
+pub struct Result {
+    pub result: f64,
+    pub success: bool,
+    pub error_msg: String,
+}
+
+#[marine]
+pub fn mean(data: Vec<f64>) -> Result {
+    match calc_mean(data.iter()) {
+        Some(res) => Result {
+            result: res,
+            success: true,
+            error_msg: "".to_string(),
+        },
+        None => Result {
+            result: -1f64,
+            success: false,
+            error_msg: "Failure to calculate mean. Check your inputs.".to_string(),
+        },
+    }
+}
+
+fn calc_mean<'a>(data: impl ExactSizeIterator<Item = &'a f64>) -> Option<f64> {
+    let n = data.len() as u64;
+    if n < 1 {
+        return None;
+    }
+    let res = (data.sum::<f64>() / n as f64) as f64;
+    let res = format!("{:.2}", res).parse::<f64>().unwrap();
+    Some(res)
+}