day9 done

lib/oasis/src/lib.rs

@@ -1,8 +1,13 @@
 use std::{num::ParseIntError, str::FromStr};
 
+/// Errors than can occur during an Oasis report
 #[derive(Debug)]
 pub enum OasisError {
+    /// Failed to parse History
     ParseHistory(ParseIntError),
+
+    /// No histories found when parsing
+    NoHistories,
 }
 
 impl From<ParseIntError> for OasisError {
@@ -11,58 +16,58 @@ impl From<ParseIntError> for OasisError {
     }
 }
 
+/// A value from an Oasis report
 pub type Value = i64;
 
+/// A Layer in a History
 #[derive(Debug, Clone)]
 pub struct Layer(Vec<Value>);
 
 impl Layer {
-    #[inline(always)]
+    /// Checks if all values in the layer is `0`
     fn is_all_zero(&self) -> bool {
         self.0.iter().all(|n| *n == 0)
     }
 
-    #[inline(always)]
+    /// Calculates the differences between values in the layer, to create the layer below it.
     pub fn get_next_layer(&self) -> Option<Self> {
         if self.is_all_zero() {
             return None;
         }
 
+        // Get differences
         let next = self.0.windows(2).map(|a| a[1] - a[0]).collect();
 
         Some(Self(next))
     }
 
-    #[inline(always)]
+    /// Returns the last value of the layer, if any
     pub fn last_value(&self) -> Option<&Value> {
         self.0.last()
     }
 
-    #[inline(always)]
+    /// Returns the first value of the layer, if any
     pub fn first_value(&self) -> Option<&Value> {
         self.0.first()
     }
 }
 
+/// A History
 #[derive(Debug)]
-pub struct History(Layer);
+pub struct History(Vec<Layer>);
 
 impl FromStr for History {
     type Err = OasisError;
 
     fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Ok(Self(Layer(
+        // Create a vector, containing the first layer
+        let mut layers = vec![Layer(
             s.split_whitespace()
                 .map(|x| x.parse::<Value>())
                 .collect::<Result<_, _>>()?,
-        )))
-    }
-}
-
-impl History {
-    fn get_layers(&self) -> Vec<Layer> {
-        let mut layers = vec![self.0.clone()];
+        )];
 
+        // Calculate the rest of the layers
         loop {
             let Some(current) = layers.last() else {
                 unreachable!("Always at least one layer!")
@@ -75,42 +80,59 @@ impl History {
             }
         }
 
-        layers
+        Ok(Self(layers))
     }
+}
 
+impl History {
+    /// Calculates the next value in the history
     pub fn calculate_next_value(&self) -> Value {
-        self.get_layers()
+        self.0
             .iter()
             .rev()
             .fold(0, |acc, layer| layer.last_value().map_or(acc, |value| acc + value))
     }
 
+    /// Calculates the previous value in the history
     pub fn calculate_prev_value(&self) -> Value {
-        self.get_layers()
-            .iter()
-            .rev()
-            .fold(0, |acc, layer| layer.first_value().map_or(acc, |value| acc + value))
+        self.0.iter().rev().fold(0, |below, layer| {
+            layer.first_value().map_or(below, |value| value - below)
+        })
     }
 }
 
+/// An Oasis-Report
 #[derive(Debug)]
 pub struct Report(Vec<History>);
 
 impl Report {
+    /// Returns the sum of all the next values in the Reports Histories
     pub fn get_next_values_sum(&self) -> Value {
         self.0.iter().map(|history| history.calculate_next_value()).sum()
     }
 
+    /// Returns the sum of all the previous values in the Reports Histories
     pub fn get_prev_values_sum(&self) -> Value {
         self.0.iter().map(|history| history.calculate_prev_value()).sum()
     }
+
+    /// Checks if the report is empty (No histories)
+    fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
 }
 
 impl FromStr for Report {
     type Err = OasisError;
 
     fn from_str(s: &str) -> Result<Self, Self::Err> {
-        Ok(Self(s.lines().map(History::from_str).collect::<Result<_, _>>()?))
+        let report = Self(s.lines().map(History::from_str).collect::<Result<_, _>>()?);
+
+        if report.is_empty() {
+            return Err(OasisError::NoHistories);
+        }
+
+        Ok(report)
     }
 }
 
@@ -139,6 +161,12 @@ mod tests {
         assert_eq!(sum, -2);
     }
 
+    #[test]
+    #[should_panic]
+    fn empty_test() {
+        Report::from_str("").expect("Failed to parse");
+    }
+
     #[test]
     fn solution_1() {
         let report = Report::from_str(EXAMPLE_1).expect("Failed to parse");