PkmnLib_rs/src/utils/string_key.rs

use arcstr::ArcStr;
use hashbrown::HashMap;
use parking_lot::RwLock;
use std::borrow::Borrow;
use std::ffi::CStr;
use std::fmt::{Display, Formatter};
use std::hash::{Hash, Hasher};
use std::ops::Deref;
use std::sync::LazyLock;

/// StringKey is an immutable string that is used for indexing of hashmaps or equality a lot.
/// By reference counting the string instead of copying, and caching the hash, we can get some
/// free speed out of it. Note that StringKeys also compare case insensitive, so that for example
/// `charmander` == `Charmander`.
#[derive(Clone, Debug)]
#[cfg_attr(feature = "wasm", derive(unique_type_id_derive::UniqueTypeId))]
pub struct StringKey {
    /// The underlying reference counted string.
    str: ArcStr,
    /// The unique hash of the string.
    hash: u32,
}

/// A cache of all allocated strings. This allows us to re-use strings that are often used without
/// allocation.
static STRING_CACHE: LazyLock<RwLock<HashMap<u32, ArcStr>>> = LazyLock::new(|| RwLock::new(HashMap::new()));
/// An empty StringKey
static EMPTY: LazyLock<StringKey> = LazyLock::new(|| StringKey::new(""));

impl StringKey {
    /// Gets the hash of a string.
    pub const fn get_hash(s: &str) -> u32 {
        let mut crc: u32 = 0xffffffff;
        let mut i: usize = 0;
        while i < s.len() {
            crc = (crc >> 8) ^ CRC_TABLE[((crc ^ (to_lower(s.as_bytes()[i]) as u32)) & 0xff) as usize];
            i += 1;
        }
        crc ^ 0xffffffff
    }

    /// Creates a new StringKey. If we can find a value for this StringKey in the cache, we re-use
    /// that value.
    pub fn new(s: &str) -> Self {
        let hash = Self::get_hash(s);
        {
            let cache_read = STRING_CACHE.read();
            let cached_value = cache_read.get(&hash);
            if let Some(cached_value) = cached_value {
                return Self {
                    str: cached_value.clone(),
                    hash,
                };
            }
        }
        {
            let mut cache_write = STRING_CACHE.write();
            if let Some(cached_value) = cache_write.get(&hash) {
                return Self {
                    str: cached_value.clone(),
                    hash,
                };
            }
            let s: ArcStr = s.into();
            let v = Self { str: s.clone(), hash };
            cache_write.insert(hash, s);
            v
        }
    }

    /// Gets the empty StringKey.
    pub fn empty() -> Self {
        EMPTY.clone()
    }

    /// Gets the underlying string for the StringKey.
    pub fn str(&self) -> &str {
        &self.str
    }

    /// Gets the hash of the string value.
    pub fn hash(&self) -> u32 {
        self.hash
    }
}

impl PartialEq<Self> for StringKey {
    fn eq(&self, other: &Self) -> bool {
        self.hash == other.hash
    }
}

impl Eq for StringKey {}

impl Hash for StringKey {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.hash.hash(state);
    }
}

impl From<&str> for StringKey {
    fn from(s: &str) -> Self {
        StringKey::new(s)
    }
}

impl Borrow<u32> for StringKey {
    fn borrow(&self) -> &u32 {
        &self.hash
    }
}

impl Display for StringKey {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.write_str(self.str.deref())
    }
}

impl Into<StringKey> for &CStr {
    fn into(self) -> StringKey {
        StringKey::new(self.to_str().unwrap())
    }
}
/// Converts a character to lowercased in a const safe way.
const fn to_lower(c: u8) -> u8 {
    if c >= b'A' && c <= b'Z' {
        return c + (b'a' - b'A');
    }
    c
}

/// A lookup table for use in CRC32 hash.
const CRC_TABLE: &[u32] = &[
    0, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4,
    0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2, 0xF3B97148,
    0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, 0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,
    0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1,
    0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75,
    0xDCD60DCF, 0xABD13D59, 0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599,
    0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
    0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433, 0x7807C9A2,
    0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162,
    0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA,
    0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65, 0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,
    0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73,
    0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3,
    0xB966D409, 0xCE61E49F, 0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B,
    0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
    0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, 0xF00F9344,
    0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0,
    0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4,
    0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B, 0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,
    0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795,
    0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31,
    0x2CD99E8B, 0x5BDEAE1D, 0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785,
    0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
    0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777, 0x88085AE6,
    0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE,
    0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, 0x40DF0B66,
    0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9, 0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,
    0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37,
    0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D,
];

#[cfg(test)]
mod tests {
    extern crate test;

    use crate::StringKey;

    #[test]
    fn create_empty_stringkey() {
        let sk = StringKey::new("".into());
        assert_eq!(sk.str(), "");
        assert_eq!(sk.hash(), 0);
        assert_eq!(sk.hash(), StringKey::get_hash(""));
    }

    #[test]
    fn create_stringkey_foo() {
        let sk = StringKey::new("foo".into());
        assert_eq!(sk.str(), "foo");
        assert_eq!(sk.hash(), 2356372769);
        assert_eq!(sk.hash(), StringKey::get_hash("foo"));
        assert_eq!(sk.hash(), StringKey::get_hash("FOo"));
    }

    #[test]
    fn create_stringkey_bar() {
        let sk = StringKey::new("bar".into());
        assert_eq!(sk.str(), "bar");
        assert_eq!(sk.hash(), 1996459178);
        assert_eq!(sk.hash(), StringKey::get_hash("bar"));
        assert_eq!(sk.hash(), StringKey::get_hash("baR"));
    }
}