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use num_traits::ToPrimitive;
use std::{cmp::min, fmt};
pub struct LongestCommonSubstring<'a> {
pub text: &'a [u8],
pub start: usize,
pub len: usize,
}
impl<'a> fmt::Debug for LongestCommonSubstring<'a> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "T[{}..{}]", self.start, self.start + self.len)
}
}
impl<'a> LongestCommonSubstring<'a> {
#[inline(always)]
pub fn as_bytes(&self) -> &[u8] {
&self.text[self.start..self.start + self.len]
}
}
#[inline(always)]
pub fn common_prefix_len(a: &[u8], b: &[u8]) -> usize {
let n = min(a.len(), b.len());
for i in 0..n {
if a[i] != b[i] {
return i;
}
}
n
}
pub fn longest_substring_match<'a, Index>(
text: &'a [u8],
mut sa: &[Index],
needle: &[u8],
) -> LongestCommonSubstring<'a>
where
Index: ToPrimitive,
{
macro_rules! sa {
($x: expr) => {
sa[$x].to_usize().unwrap()
};
}
macro_rules! suff {
($x: expr) => {
&text[sa!($x)..]
};
}
macro_rules! len {
($x: expr) => {
common_prefix_len(suff!($x), needle)
};
}
macro_rules! lcs {
($start: expr, $len: expr) => {
LongestCommonSubstring {
text: text,
start: $start,
len: $len,
}
};
}
loop {
match sa.len() {
1 => {
return lcs!(sa!(0), len!(0));
}
2 => {
let x = len!(0);
let y = len!(1);
return if x > y {
lcs!(sa!(0), x)
} else {
lcs!(sa!(1), y)
};
}
_ => {
let mid = sa.len() / 2;
if needle > suff!(mid) {
sa = &sa[mid..];
} else {
sa = &sa[..=mid];
}
}
}
}
}
pub struct NotSorted {
i: usize,
j: usize,
}
impl fmt::Debug for NotSorted {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(
f,
"invariant doesn't hold: suf(SA({})) < suf(SA({}))",
self.i, self.j
)
}
}
impl fmt::Display for NotSorted {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Debug::fmt(self, f)
}
}
impl std::error::Error for NotSorted {}
pub fn verify<Index>(input: &[u8], sa: &[Index]) -> Result<(), NotSorted>
where
Index: ToPrimitive,
{
macro_rules! sa {
($x: expr) => {
sa[$x].to_usize().unwrap()
};
}
macro_rules! suff {
($x: expr) => {
&input[sa!($x)..]
};
}
for i in 0..(input.len() - 1) {
if !(suff!(i) < suff!(i + 1)) {
return Err(NotSorted { i: i, j: i + 1 });
}
}
Ok(())
}
pub struct SuffixArray<'a, Index>
where
Index: ToPrimitive,
{
sa: Vec<Index>,
text: &'a [u8],
}
pub trait StringIndex<'a> {
fn longest_substring_match(&self, needle: &[u8]) -> LongestCommonSubstring<'a>;
}
impl<'a, Index> SuffixArray<'a, Index>
where
Index: ToPrimitive,
{
pub fn new(text: &'a [u8], sa: Vec<Index>) -> Self {
Self { sa, text }
}
pub fn into_parts(self) -> (&'a [u8], Vec<Index>) {
(self.text, self.sa)
}
pub fn verify(&self) -> Result<(), NotSorted> {
verify(self.text, &self.sa[..])
}
pub fn text(&self) -> &[u8] {
return self.text;
}
}
impl<'a, Index> StringIndex<'a> for SuffixArray<'a, Index>
where
Index: ToPrimitive,
{
fn longest_substring_match(&self, needle: &[u8]) -> LongestCommonSubstring<'a> {
longest_substring_match(self.text, &self.sa[..], needle)
}
}
#[cfg(test)]
mod tests {
#[test]
fn it_works() {
assert_eq!(2 + 2, 4);
}
}