Only allow one flat fee per session (#72)

* only allow one flat fee per session

* add test

* update changelog and ammend readme

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to this project will be documented in this file.
 
+## Unreleased
+
+- Fixed bug where multiple flat fees are generated during the session. Instead
+  we now only use the first time a flat fee becomes active.
+
 ## 0.6.0 2024-06-04
 
 - Upgrade dependencies.

README.md

@@ -92,6 +92,24 @@ classDiagram
     TariffElement "1" --o "0..1" TariffRestriction
 ```
 
+## Interpretation
+
+This implementation aims to follow the OCPI specification as closely as 
+possible. However, as with any specification, details might be left open to 
+interpretation. The following is a list of assumptions that have been made in 
+this implementation:
+
+- We assume that a `FLAT` price component can only be active once in a session.
+  The first time a `FLAT` price component becomes active it will be used and 
+  subsequent active `FLAT` components will be ignored. Although this is not 
+  explicitly mentioned in the OCPI 2.*.* specs, we feel it is the correct 
+  interpretation.
+
+- We assume that the charging periods provided as input are well-formed. 
+  Meaning, each period in the session that has a different price must be 
+  provided as a separate charging period in the CDR. No attempt will be made
+  to subdivide or interpolate data inside a single provided period.
+
 ## Contributing
 
 We welcome community contributions to this project.

ocpi-tariffs/src/pricer.rs

@@ -115,8 +115,18 @@ impl<'a> Pricer<'a> {
         let mut total_charging_time = HoursDecimal::zero();
         let mut total_parking_time = HoursDecimal::zero();
 
+        let mut has_flat_fee = false;
+
         for (index, period) in cdr.periods.iter().enumerate() {
-            let components = tariff.active_components(period);
+            let mut components = tariff.active_components(period);
+
+            if components.flat.is_some() {
+                if has_flat_fee {
+                    components.flat = None;
+                } else {
+                    has_flat_fee = true;
+                }
+            }
 
             step_size.update(index, &components, period);
 

ocpi-tariffs/test_data/multiple_flat_fees/cdr.json

@@ -0,0 +1,45 @@
+{
+    "country_code": "BE",
+    "start_date_time": "2015-06-29T15:00:00Z",
+    "end_date_time": "2015-06-29T16:30:00Z",
+    "currency": "EUR",
+    "tariffs": [],
+    "cdr_location": { 
+        "country": "NLD"
+    },    
+    "charging_periods": [
+        {
+            "start_date_time": "2015-06-29T15:00:00Z",
+            "dimensions": [{
+                "type": "TIME",
+                "volume": 0.5
+            }]
+        }, 
+        {
+            "start_date_time": "2015-06-29T15:30:00Z",
+            "dimensions": [{
+                "type": "TIME",
+                "volume": 0.5
+            }]
+        },
+        {
+            "start_date_time": "2015-06-29T16:00:00Z",
+            "dimensions": [{
+                "type": "TIME",
+                "volume": 0.5
+            }]
+        }
+    ],
+    "total_fixed_cost": {
+        "excl_vat": 1.0,
+        "incl_vat": 1.0
+    },
+    "total_cost": {
+        "excl_vat": 1.0,
+        "incl_vat": 1.0
+    },
+    "total_energy": 0,
+    "total_time": 1.5,
+    "total_parking_time": 0,
+    "last_updated": "2015-06-29T22:01:13Z"
+}

ocpi-tariffs/test_data/multiple_flat_fees/tariff.json

@@ -0,0 +1,15 @@
+{
+  "country_code": "DE",
+  "party_id": "ALL",
+  "id": "12",
+  "currency": "EUR",
+  "elements": [{
+    "price_components": [{
+      "type": "FLAT",
+      "price": 1.00,
+      "vat": 0.0,
+      "step_size": 0
+    }]
+  }],
+  "last_updated": "2015-06-29T20:39:09Z"
+}