[#809] Thin Edge JSON events support for Cumulocity mapper (#831)

* [#809] Thin Edge JSON events support for Cumulocity mapper

2 files changed, 163 insertions, 0 deletions

diff --git a/crates/core/thin_edge_json/src/event.rs b/crates/core/thin_edge_json/src/event.rs
new file mode 100644
index 00000000..fa58fdbc
--- /dev/null
+++ b/crates/core/thin_edge_json/src/event.rs
@@ -0,0 +1,162 @@
+use serde::Deserialize;
+use time::OffsetDateTime;
+
+use self::error::ThinEdgeJsonDeserializerError;
+
+/// In-memory representation of ThinEdge JSON event.
+#[derive(Debug, Deserialize, PartialEq)]
+pub struct ThinEdgeEvent {
+    pub name: String,
+    pub data: Option<ThinEdgeEventData>,
+}
+
+/// In-memory representation of ThinEdge JSON event payload
+#[derive(Debug, Deserialize, PartialEq)]
+pub struct ThinEdgeEventData {
+    pub message: Option<String>,
+    #[serde(default)]
+    #[serde(deserialize_with = "clock::deserialize_iso8601_timestamp")]
+    pub time: Option<OffsetDateTime>,
+}
+
+pub mod error {
+    #[derive(thiserror::Error, Debug)]
+    pub enum ThinEdgeJsonDeserializerError {
+        #[error("Unsupported topic: {0}")]
+        UnsupportedTopic(String),
+
+        #[error("Event name can not be empty")]
+        EmptyEventName,
+
+        #[error(transparent)]
+        SerdeJsonError(#[from] serde_json::error::Error),
+    }
+}
+
+impl ThinEdgeEvent {
+    pub fn try_from(
+        mqtt_topic: &str,
+        mqtt_payload: &str,
+    ) -> Result<Self, ThinEdgeJsonDeserializerError> {
+        let topic_split: Vec<&str> = mqtt_topic.split('/').collect();
+        if topic_split.len() == 3 {
+            let event_name = topic_split[2];
+            if event_name.is_empty() {
+                return Err(ThinEdgeJsonDeserializerError::EmptyEventName);
+            }
+
+            let event_data = if mqtt_payload.is_empty() {
+                None
+            } else {
+                Some(serde_json::from_str(mqtt_payload)?)
+            };
+
+            Ok(Self {
+                name: event_name.into(),
+                data: event_data,
+            })
+        } else {
+            Err(ThinEdgeJsonDeserializerError::UnsupportedTopic(
+                mqtt_topic.into(),
+            ))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use assert_matches::assert_matches;
+    use serde_json::{json, Value};
+    use test_case::test_case;
+    use time::macros::datetime;
+
+    #[test_case(
+        "tedge/events/click_event",
+        json!({
+            "message": "Someone clicked",
+            "time": "2021-04-23T19:00:00+05:00",
+        }),
+        ThinEdgeEvent {
+            name: "click_event".into(),
+            data: Some(ThinEdgeEventData {
+                message: Some("Someone clicked".into()),
+                time: Some(datetime!(2021-04-23 19:00:00 +05:00)),
+            }),
+        };
+        "event parsing"
+    )]
+    #[test_case(
+        "tedge/events/click_event",
+        json!({
+            "message": "Someone clicked",
+        }),
+        ThinEdgeEvent {
+            name: "click_event".into(),
+            data: Some(ThinEdgeEventData {
+                message: Some("Someone clicked".into()),
+                time: None,
+            }),
+        };
+        "event parsing without timestamp"
+    )]
+    #[test_case(
+        "tedge/events/click_event",
+        json!({
+            "time": "2021-04-23T19:00:00+05:00",
+        }),
+        ThinEdgeEvent {
+            name: "click_event".into(),
+            data: Some(ThinEdgeEventData {
+                message: None,
+                time: Some(datetime!(2021-04-23 19:00:00 +05:00)),
+            }),
+        };
+        "event parsing without message"
+    )]
+    #[test_case(
+        "tedge/events/click_event",
+        json!({}),
+        ThinEdgeEvent {
+            name: "click_event".into(),
+            data: Some(ThinEdgeEventData {
+                message: None,
+                time: None,
+            }),
+        };
+        "event parsing without message or timestamp"
+    )]
+    fn parse_thin_edge_event_json(
+        event_topic: &str,
+        event_payload: Value,
+        expected_event: ThinEdgeEvent,
+    ) {
+        let event =
+            ThinEdgeEvent::try_from(event_topic, event_payload.to_string().as_str()).unwrap();
+
+        assert_eq!(event, expected_event);
+    }
+
+    #[test]
+    fn event_translation_empty_event_name() {
+        let result = ThinEdgeEvent::try_from("tedge/events/", "{}");
+
+        assert_matches!(result, Err(ThinEdgeJsonDeserializerError::EmptyEventName));
+    }
+
+    #[test]
+    fn event_translation_more_than_three_topic_levels() {
+        let result = ThinEdgeEvent::try_from("tedge/events/page/click", "{}");
+
+        assert_matches!(
+            result,
+            Err(ThinEdgeJsonDeserializerError::UnsupportedTopic(_))
+        );
+    }
+
+    #[test]
+    fn event_translation_empty_payload() {
+        let result = ThinEdgeEvent::try_from("tedge/events/click_event", "");
+        assert_matches!(result.unwrap().data, None);
+    }
+}
diff --git a/crates/core/thin_edge_json/src/lib.rs b/crates/core/thin_edge_json/src/lib.rs
index 441b5441..8915bf14 100644
--- a/crates/core/thin_edge_json/src/lib.rs
+++ b/crates/core/thin_edge_json/src/lib.rs
@@ -4,6 +4,7 @@
 pub mod alarm;
 pub mod builder;
 pub mod data;
+pub mod event;
 pub mod group;
 pub mod measurement;
 pub mod parser;