1 files changed, 119 insertions, 0 deletions
diff --git a/crates/rule-executor/src/processor/rule/determine_outcome.rs b/crates/rule-executor/src/processor/rule/determine_outcome.rs
new file mode 100644
index 0000000..727846d
--- /dev/null
+++ b/crates/rule-executor/src/processor/rule/determine_outcome.rs
@@ -0,0 +1,119 @@
+use tracing::trace;
+use warden_core::{configuration::rule::Band, message::RuleResult};
+
+pub(super) fn determine_outcome(value: i64, bands: &[Band], rule_result: &mut RuleResult) {
+    trace!("calculating outcome");
+    for band in bands {
+        let value_f64 = value as f64;
+
+        if band.lower_limit.is_none_or(|lower| value_f64 >= lower)
+            && band.upper_limit.is_none_or(|upper| value_f64 < upper)
+        {
+            rule_result.sub_rule_ref = band.sub_rule_ref.to_owned();
+            rule_result.reason = band.reason.to_owned();
+            break;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn make_band(lower: Option<f64>, upper: Option<f64>, sub_ref: &str, reason: &str) -> Band {
+        Band {
+            lower_limit: lower,
+            upper_limit: upper,
+            sub_rule_ref: sub_ref.to_string(),
+            reason: reason.to_string(),
+        }
+    }
+
+    #[test]
+    fn matches_band_within_limits() {
+        let bands = vec![
+            make_band(Some(0.0), Some(10.0), "A", "Between 0 and 10"),
+            make_band(Some(10.0), Some(20.0), "B", "Between 10 and 20"),
+        ];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(5, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "A");
+        assert_eq!(rule_result.reason, "Between 0 and 10");
+    }
+
+    #[test]
+    fn matches_band_lower_inclusive_upper_exclusive() {
+        let bands = vec![
+            make_band(Some(0.0), Some(10.0), "A", "Between 0 and 10"),
+            make_band(Some(10.0), Some(20.0), "B", "Between 10 and 20"),
+        ];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(10, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "B");
+        assert_eq!(rule_result.reason, "Between 10 and 20");
+    }
+
+    #[test]
+    fn no_match_when_above_all_bands() {
+        let bands = vec![
+            make_band(Some(0.0), Some(10.0), "A", "Between 0 and 10"),
+            make_band(Some(10.0), Some(20.0), "B", "Between 10 and 20"),
+        ];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(30, &bands, &mut rule_result);
+
+        assert_eq!(rule_result, RuleResult::default());
+    }
+
+    #[test]
+    fn match_when_no_upper_limit() {
+        let bands = vec![make_band(Some(0.0), None, "A", "Above 0")];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(100, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "A");
+        assert_eq!(rule_result.reason, "Above 0");
+    }
+
+    #[test]
+    fn match_when_no_lower_limit() {
+        let bands = vec![make_band(None, Some(50.0), "A", "Below 50")];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(-10, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "A");
+        assert_eq!(rule_result.reason, "Below 50");
+    }
+
+    #[test]
+    fn match_when_no_limits() {
+        let bands = vec![make_band(None, None, "A", "Any value")];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(9999, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "A");
+        assert_eq!(rule_result.reason, "Any value");
+    }
+
+    #[test]
+    fn stops_after_first_match() {
+        let bands = vec![
+            make_band(None, None, "A", "Any value"),
+            make_band(None, None, "B", "Second band"),
+        ];
+        let mut rule_result = RuleResult::default();
+
+        determine_outcome(5, &bands, &mut rule_result);
+
+        assert_eq!(rule_result.sub_rule_ref, "A");
+        assert_eq!(rule_result.reason, "Any value");
+    }
+}