refactor: better alphabets

src/alphabets.rs

@@ -1,8 +1,7 @@
 use crate::error;
 
-const ALPHABETS: [(&'static str, &'static str); 22] = [
-    ("numeric", "1234567890"),
-    ("abcd", "abcd"),
+const ALPHABETS: [(&'static str, &'static str); 21] = [
+    // ("abcd", "abcd"),
     ("qwerty", "asdfqwerzxcvjklmiuopghtybn"),
     ("qwerty-homerow", "asdfjklgh"),
     ("qwerty-left-hand", "asdfqwerzcxv"),
@@ -23,14 +22,45 @@ const ALPHABETS: [(&'static str, &'static str); 22] = [
     ("colemak-homerow", "arstneiodh"),
     ("colemak-left-hand", "arstqwfpzxcv"),
     ("colemak-right-hand", "neioluymjhk"),
+    (
+        "longest",
+        "aoeuqjkxpyhtnsgcrlmwvzfidb;,~<>'@!#$%^&*~1234567890",
+    ),
 ];
 
+/// Parse a name string into `Alphabet`, used during CLI parsing.
+///
+/// # Note
+///
+/// Letters 'n' and 'N' are systematically removed to prevent conflict with
+/// navigation keys (arrows and 'n' 'N').
+pub fn parse_alphabet(src: &str) -> Result<Alphabet, error::ParseError> {
+    let alphabet_pair = ALPHABETS.iter().find(|&(name, _letters)| name == &src);
+
+    match alphabet_pair {
+        Some((_name, letters)) => {
+            let letters = letters.replace(&['n', 'N'][..], "");
+            Ok(Alphabet(letters.to_string()))
+        }
+        None => Err(error::ParseError::UnknownAlphabet),
+    }
+}
+
 /// Type-safe string alphabet (newtype).
 #[derive(Debug)]
 pub struct Alphabet(pub String);
 
 impl Alphabet {
-    /// Create `n` hints.
+    /// Create `n` hints from the Alphabet.
+    ///
+    /// An Alphabet of `m` letters can produce at most `m^2` hints. In case
+    /// this limit is exceeded, this function will generate the `n` hints from
+    /// an Alphabet which has more letters (50). This will ensure 2500 hints
+    /// can be generated, which should cover all use cases (I think even
+    /// easymotion has less).
+    ///
+    /// If more hints are needed, unfortunately, this will keep producing
+    /// empty (`""`) hints.
     ///
     /// ```
     /// // The algorithm works as follows:
@@ -46,7 +76,19 @@ impl Alphabet {
     /// // pick a, generate aa ab ac ad  | (a) (b) (c) (d) aa ab ac ad ba bb bc bd ca cb cc cd da db dc dd
     /// ```
     pub fn make_hints(&self, n: usize) -> Vec<String> {
-        let letters: Vec<String> = self.0.chars().map(|s| s.to_string()).collect();
+        // Shortcut if we have enough letters in the Alphabet.
+        if self.0.len() >= n {
+            return self.0.chars().take(n).map(|c| c.to_string()).collect();
+        }
+
+        // Use the "longest" alphabet if the current alphabet cannot produce as
+        // many hints as asked.
+        let letters: Vec<char> = if self.0.len().pow(2) >= n {
+            self.0.chars().collect()
+        } else {
+            let alt_alphabet = parse_alphabet("longest").unwrap();
+            alt_alphabet.0.chars().collect()
+        };
 
         let mut lead = letters.clone();
         let mut prev: Vec<String> = Vec::new();
@@ -65,34 +107,23 @@ impl Alphabet {
             let gen: Vec<String> = letters
                 .iter()
                 .take(n - lead.len() - prev.len())
-                .map(|s| prefix.clone() + s)
+                .map(|c| format!("{}{}", prefix, c))
                 .collect();
 
             // Insert gen in front of prev
-            prev.splice(0..0, gen);
+            prev.splice(..0, gen);
         }
 
-        lead = lead.iter().take(n - prev.len()).cloned().collect();
-        lead.append(&mut prev);
-        lead
-    }
-}
+        // Finalize by concatenating the lead and prev components, filling
+        // with "" as necessary.
+        let lead: Vec<String> = lead.iter().map(|c| c.to_string()).collect();
 
-/// Parse a name string into `Alphabet`, supporting the CLI.
-///
-/// # Note
-///
-/// Letters 'n' and 'N' are systematically removed to prevent conflict with
-/// navigation keys (arrows and 'n' 'N').
-pub fn parse_alphabet(src: &str) -> Result<Alphabet, error::ParseError> {
-    let alphabet_pair = ALPHABETS.iter().find(|&(name, _letters)| name == &src);
+        let filler: Vec<String> = std::iter::repeat("")
+            .take(n - lead.len() - prev.len())
+            .map(|s| s.to_string())
+            .collect();
 
-    match alphabet_pair {
-        Some((_name, letters)) => {
-            let letters = letters.replace(&['n', 'N'][..], "");
-            Ok(Alphabet(letters.to_string()))
-        }
-        None => Err(error::ParseError::UnknownAlphabet),
+        [lead, prev, filler].concat()
     }
 }
 
@@ -124,7 +155,7 @@ mod tests {
     #[test]
     fn composed_matches_max_2() {
         let alphabet = Alphabet("ab".to_string());
-        let hints = alphabet.make_hints(8);
+        let hints = alphabet.make_hints(4);
         assert_eq!(hints, ["aa", "ab", "ba", "bb"]);
     }
 
@@ -136,6 +167,24 @@ mod tests {
             hints,
             ["a", "ba", "bb", "bc", "bd", "ca", "cb", "cc", "cd", "da", "db", "dc", "dd"]
         );
-        // a (b) (c) (d) a ba bc bd ca cb cc cd da db dc dd
+    }
+
+    #[test]
+    fn matches_with_longest_alphabet() {
+        let alphabet = Alphabet("ab".to_string());
+        let hints = alphabet.make_hints(2500);
+        assert_eq!(hints.len(), 2500);
+        assert_eq!(&hints[..3], ["aa", "ao", "ae"]);
+        assert_eq!(&hints[2497..], ["08", "09", "00"]);
+    }
+
+    #[test]
+    fn matches_exceed_longest_alphabet() {
+        let alphabet = Alphabet("ab".to_string());
+        let hints = alphabet.make_hints(10000);
+        // 2500 unique hints are produced from the longest alphabet
+        // The 7500 last ones come from the filler ("" empty hints).
+        assert_eq!(hints.len(), 10000);
+        assert!(&hints[2500..].iter().all(|s| s == ""));
     }
 }

src/lib.rs

@@ -57,8 +57,12 @@ pub struct CliOpt {
     /// Alphabet to draw hints from.
     ///
     /// Possible values are "{A}", "{A}-homerow", "{A}-left-hand",
-    /// "{A}-right-hand", where "{A}" is one of "qwerty", "azerty", "qwertz",
-    /// "dvorak", "colemak". Examples: "qwerty", "dvorak-homerow".
+    /// "{A}-right-hand", where "{A}" is one of "qwerty", "azerty", "qwertz"
+    /// "dvorak", "colemak".
+    ///
+    /// # Examples
+    ///
+    /// "qwerty", "dvorak-homerow", "azerty-right-hand".
     #[clap(short = "k", long, default_value = "dvorak",
                 parse(try_from_str = alphabets::parse_alphabet))]
     alphabet: alphabets::Alphabet,