Move nick hue functions to their own module

src/nick.rs

@@ -0,0 +1,51 @@
+//! Nick-related utility functions.
+
+use crate::emoji::Emoji;
+
+/// Does not remove emoji.
+fn hue_normalize(text: &str) -> String {
+    text.chars()
+        .filter(|&c| c.is_ascii_alphanumeric() || c == '_' || c == '-')
+        .map(|c| c.to_ascii_lowercase())
+        .collect()
+}
+
+/// A re-implementation of [euphoria's nick hue hashing algorithm][0].
+///
+/// [0]: https://github.com/euphoria-io/heim/blob/master/client/lib/hueHash.js
+fn hue_hash(text: &str, offset: i64) -> u8 {
+    let mut val = 0_i32;
+    for bibyte in text.encode_utf16() {
+        let char_val = (bibyte as i32).wrapping_mul(439) % 256;
+        val = val.wrapping_mul(33).wrapping_add(char_val);
+    }
+
+    let val: i64 = val as i64 + 2_i64.pow(31);
+    ((val + offset) % 255) as u8
+}
+
+const GREENIE_OFFSET: i64 = 148 - 192; // 148 - hue_hash("greenie", 0)
+
+/// Calculate a nick's hue like [`hue`] but without removing colon-delimited
+/// emoji as part of normalization.
+///
+/// This should be slightly faster than [`hue`] but produces incorrect results
+/// if any colon-delimited emoji are present.
+pub fn hue_without_removing_emoji(nick: &str) -> u8 {
+    let normalized = hue_normalize(nick);
+    if normalized.is_empty() {
+        hue_hash(nick, GREENIE_OFFSET)
+    } else {
+        hue_hash(&normalized, GREENIE_OFFSET)
+    }
+}
+
+/// Calculate a nick's hue.
+///
+/// This is a reimplementation of [euphoria's nick hue hashing algorithm][0]. It
+/// should always return the same value as the official client's implementation.
+///
+/// [0]: https://github.com/euphoria-io/heim/blob/master/client/lib/hueHash.js
+pub fn hue(emoji: &Emoji, nick: &str) -> u8 {
+    hue_without_removing_emoji(&emoji.remove(nick))
+}