initial commit

src/caesar.rs

@@ -0,0 +1,56 @@
+use crate::util;
+
+pub struct CaesarCipher {
+    alphabet: Vec<char>,
+    offset: i64,
+}
+
+impl CaesarCipher {
+    pub fn new(alphabet: impl Into<Vec<char>>, offset: i64) -> anyhow::Result<Self> {
+        let alphabet = alphabet.into();
+        let offset = offset % alphabet.len() as i64;
+
+        util::verify_alphabet(&alphabet)?;
+
+        Ok(Self { alphabet, offset })
+    }
+
+    pub fn encode(&self, input: &str) -> anyhow::Result<String> {
+        let mut output = String::with_capacity(input.len());
+
+        for c in input.chars() {
+            let index = self.get_index(c, self.offset)?;
+            output.push(self.alphabet[index])
+        }
+
+        Ok(output)
+    }
+
+    pub fn decode(&self, input: &str) -> anyhow::Result<String> {
+        let mut output = String::with_capacity(input.len());
+
+        for c in input.chars() {
+            let index = self.get_index(c, -self.offset)?;
+            output.push(self.alphabet[index])
+        }
+
+        Ok(output)
+    }
+
+    fn get_index(&self, c: char, offset: i64) -> anyhow::Result<usize> {
+        let mut index =
+            self.alphabet
+                .iter()
+                .position(|&x| x == c)
+                .ok_or(anyhow::anyhow!("cannot encode character {:?}", c))? as i64
+                + offset;
+
+        while index < 0 {
+            index += self.alphabet.len() as i64;
+        }
+
+        index %= self.alphabet.len() as i64;
+
+        Ok(index as usize)
+    }
+}