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use std::collections::HashMap;
#[cfg(test)]
mod tests;
pub struct FastrieBuilderNode<V> {
built: bool,
value: Option<V>,
children: HashMap<u8, FastrieBuilderNode<V>>,
}
const IDX_BYTES: usize = 3;
const RESERVED_BYTE: u8 = 0xFF;
const MAX_CLUSTER_GAP_LEN: i16 = 3;
fn reserve_idx(vec: &mut Vec<u8>) -> usize {
let pos = vec.len();
for _ in 0..IDX_BYTES {
vec.push(RESERVED_BYTE);
};
pos
}
fn encode_idx(idx: usize) -> [u8; IDX_BYTES] {
assert!(idx <= 2usize.pow((8 * IDX_BYTES) as u32) - 1);
[(idx >> 16) as u8, (idx >> 8) as u8, idx as u8]
}
fn decode_idx(encoded: &[u8]) -> usize {
assert_eq!(encoded.len(), IDX_BYTES);
((encoded[0] as usize) << 16) | ((encoded[1] as usize) << 8) | (encoded[2] as usize)
}
fn write_idx(vec: &mut Vec<u8>, pos: usize, idx: usize) -> () {
vec[pos..pos + IDX_BYTES].copy_from_slice(&encode_idx(idx))
}
fn push_idx(vec: &mut Vec<u8>, idx: usize) -> () {
vec.extend_from_slice(&encode_idx(idx))
}
fn read_idx(data: &[u8], pos: usize) -> usize {
decode_idx(&data[pos..pos + IDX_BYTES])
}
pub struct FastrieBuild<V> {
pub values: Vec<V>,
pub data: Vec<u8>,
}
impl<V> FastrieBuilderNode<V> {
pub fn new() -> FastrieBuilderNode<V> {
FastrieBuilderNode { built: false, value: None, children: HashMap::new() }
}
pub fn add(&mut self, pattern: &[u8], value: V) -> () {
let mut current: &mut FastrieBuilderNode<V> = self;
for c in pattern {
if !current.children.contains_key(c) {
current.children.insert(*c, FastrieBuilderNode::new());
};
current = current.children.get_mut(c).unwrap();
};
current.value = Some(value);
}
fn _build(&mut self, data: &mut Vec<u8>, values: &mut Vec<V>) -> () {
assert!(!self.built);
self.built = true;
let value_idx: usize = if self.value.is_some() {
let idx = values.len() + 1;
values.push(self.value.take().unwrap());
idx
} else { 0 };
push_idx(data, value_idx);
let mut child_chars = self.children.keys().map(|k| *k).collect::<Vec<u8>>();
child_chars.sort();
let mut child_char_clusters: Vec<Vec<Option<u8>>> = vec![];
let mut last_char: i16 = std::i16::MIN;
for c in child_chars {
let p = c as i16;
if last_char + MAX_CLUSTER_GAP_LEN < p {
child_char_clusters.push(Vec::new());
} else {
for _ in last_char..p - 1 {
child_char_clusters.last_mut().unwrap().push(None);
};
};
child_char_clusters.last_mut().unwrap().push(Some(c));
last_char = p;
};
child_char_clusters.sort_by(|a, b| b.len().cmp(&a.len()));
let mut replace_with_child_indices: HashMap<u8, usize> = HashMap::new();
data.push(!self.children.is_empty() as u8);
let mut last_cluster_next_cluster_dist_pos: Option<usize> = None;
for cluster in &child_char_clusters {
let cluster_pos = data.len();
if let Some(out_pos) = last_cluster_next_cluster_dist_pos {
write_idx(data, out_pos, cluster_pos);
};
last_cluster_next_cluster_dist_pos = Some(reserve_idx(data));
let min = cluster.first().unwrap().unwrap();
let max = cluster.last().unwrap().unwrap();
data.push(min);
data.push(max);
for c in cluster {
match c {
Some(c) => {
debug_assert!(!replace_with_child_indices.contains_key(c));
replace_with_child_indices.insert(*c, reserve_idx(data));
}
None => { push_idx(data, 0); }
};
};
};
if let Some(out_pos) = last_cluster_next_cluster_dist_pos {
write_idx(data, out_pos, 0);
};
for cluster in &child_char_clusters {
for c in cluster {
if let Some(c) = c {
write_idx(data, *replace_with_child_indices.get(c).unwrap(), data.len());
let child_node = self.children.get_mut(c).unwrap();
child_node._build(data, values);
};
};
};
}
pub fn prebuild(&mut self) -> FastrieBuild<V> {
let mut data: Vec<u8> = Vec::new();
let mut values: Vec<V> = Vec::new();
self._build(&mut data, &mut values);
FastrieBuild { values, data }
}
}
pub struct Fastrie<'v, 'd, V> {
values: Option<&'v [V]>,
data: &'d [u8],
}
pub struct FastrieMatch<'v, V> {
pub end: usize,
pub value: &'v V,
}
pub const fn from_prebuilt_without_values<'d>(data: &'d [u8]) -> Fastrie<'_, 'd, ()> {
Fastrie { values: None, data }
}
impl<V> Fastrie<'_, '_, V> {
pub const fn from_prebuilt<'v, 'd>(values: &'v [V], data: &'d [u8]) -> Fastrie<'v, 'd, V> {
Fastrie { values: Some(values), data }
}
pub fn memory_size(&self) -> usize {
self.data.len()
}
fn _longest_matching_prefix(&self, text: &[u8]) -> Option<(usize, usize)> {
let mut node_pos: usize = 0;
let mut match_opt: Option<(usize, usize)> = None;
'outer: for (i, &c) in text.iter().enumerate() {
if self.data[node_pos + IDX_BYTES] == 0 {
break;
};
let mut cluster_pos: usize = node_pos + IDX_BYTES + 1;
loop {
let next_cluster_pos = read_idx(&self.data, cluster_pos);
let cluster_min: u8 = self.data[cluster_pos + IDX_BYTES];
let cluster_max: u8 = self.data[cluster_pos + IDX_BYTES + 1];
if c >= cluster_min && c <= cluster_max {
node_pos = read_idx(&self.data, cluster_pos + IDX_BYTES + 2 + ((c - cluster_min) as usize) * IDX_BYTES);
if node_pos == 0 {
break 'outer;
} else {
break;
};
};
if next_cluster_pos == 0 {
break 'outer;
};
cluster_pos = next_cluster_pos;
};
let node_value_idx: usize = read_idx(&self.data, node_pos);
if node_value_idx != 0 {
match_opt = Some((i, node_value_idx - 1));
};
};
match_opt
}
pub fn contains_key(&self, key: &[u8]) -> bool {
self._longest_matching_prefix(key).filter(|(i, _)| *i == key.len() - 1).is_some()
}
pub fn longest_matching_prefix(&self, text: &[u8]) -> Option<FastrieMatch<V>> {
self._longest_matching_prefix(text).map(|(end, value_idx)| FastrieMatch {
end,
value: &self.values.unwrap()[value_idx],
})
}
}