init domain

crates/domain/src/services/mod.rs

@@ -0,0 +1 @@
+pub mod review_history;

crates/domain/src/services/review_history.rs

@@ -0,0 +1,53 @@
+use crate::{errors::DomainError, models::ReviewHistory, value_objects::Rating};
+
+pub struct ReviewHistoryAnalyzer;
+
+#[derive(Debug, PartialEq)]
+pub enum Trend {
+    Improved,
+    Declined,
+    Neutral,
+}
+
+impl ReviewHistoryAnalyzer {
+    pub fn sort_chronologically(history: &mut ReviewHistory) {
+        history
+            .viewings
+            .sort_by(|a, b| a.watched_at().cmp(&b.watched_at()));
+    }
+
+    pub fn get_latest_rating(history: &ReviewHistory) -> Option<&Rating> {
+        history
+            .viewings
+            .iter()
+            .max_by_key(|r| r.watched_at())
+            .map(|r| r.rating())
+    }
+
+    pub fn rating_trend(history: &ReviewHistory) -> Result<Trend, DomainError> {
+        if history.viewings.len() < 2 {
+            return Ok(Trend::Neutral);
+        }
+
+        let mut sorted_history = history.clone();
+        Self::sort_chronologically(&mut sorted_history);
+
+        let latest_review = sorted_history.viewings.pop().unwrap();
+        let latest_rating = latest_review.rating().value() as f32;
+
+        let previous_sum: u32 = sorted_history
+            .viewings
+            .iter()
+            .map(|r| r.rating().value() as u32)
+            .sum();
+        let historical_average = previous_sum as f32 / sorted_history.viewings.len() as f32;
+
+        if latest_rating > historical_average {
+            Ok(Trend::Improved)
+        } else if latest_rating < historical_average {
+            Ok(Trend::Declined)
+        } else {
+            Ok(Trend::Neutral)
+        }
+    }
+}