Move crates under a sub folder to clean up the code

crates/milli/src/update/words_prefixes_fst.rs

@@ -0,0 +1,99 @@
+use std::iter::{repeat_with, FromIterator};
+use std::str;
+
+use fst::{SetBuilder, Streamer};
+use heed::RwTxn;
+
+use crate::{Index, Result, SmallString32};
+
+pub struct WordsPrefixesFst<'t, 'i> {
+    wtxn: &'t mut RwTxn<'i>,
+    index: &'i Index,
+    threshold: u32,
+    max_prefix_length: usize,
+}
+
+impl<'t, 'i> WordsPrefixesFst<'t, 'i> {
+    pub fn new(wtxn: &'t mut RwTxn<'i>, index: &'i Index) -> WordsPrefixesFst<'t, 'i> {
+        WordsPrefixesFst { wtxn, index, threshold: 100, max_prefix_length: 4 }
+    }
+
+    /// Set the number of words required to make a prefix be part of the words prefixes
+    /// database. If a word prefix is supposed to match more than this number of words in the
+    /// dictionary, therefore this prefix is added to the words prefixes datastructures.
+    ///
+    /// Default value is 100. This value must be higher than 50 and will be clamped
+    /// to this bound otherwise.
+    pub fn threshold(&mut self, value: u32) -> &mut Self {
+        self.threshold = value.max(50);
+        self
+    }
+
+    /// Set the maximum length of prefixes in bytes.
+    ///
+    /// Default value is `4` bytes. This value must be between 1 and 25 will be clamped
+    /// to these bounds, otherwise.
+    pub fn max_prefix_length(&mut self, value: usize) -> &mut Self {
+        self.max_prefix_length = value.clamp(1, 25);
+        self
+    }
+
+    #[tracing::instrument(
+        level = "trace",
+        skip_all,
+        target = "indexing::prefix",
+        name = "words_prefix_fst"
+    )]
+    pub fn execute(self) -> Result<()> {
+        let words_fst = self.index.words_fst(self.wtxn)?;
+
+        let mut current_prefix = vec![SmallString32::new(); self.max_prefix_length];
+        let mut current_prefix_count = vec![0; self.max_prefix_length];
+        let mut builders =
+            repeat_with(SetBuilder::memory).take(self.max_prefix_length).collect::<Vec<_>>();
+
+        let mut stream = words_fst.stream();
+        while let Some(bytes) = stream.next() {
+            for n in 0..self.max_prefix_length {
+                let current_prefix = &mut current_prefix[n];
+                let current_prefix_count = &mut current_prefix_count[n];
+                let builder = &mut builders[n];
+
+                // We try to get the first n bytes out of this string but we only want
+                // to split at valid characters bounds. If we try to split in the middle of
+                // a character we ignore this word and go to the next one.
+                let word = str::from_utf8(bytes)?;
+                let prefix = match word.get(..=n) {
+                    Some(prefix) => prefix,
+                    None => continue,
+                };
+
+                // This is the first iteration of the loop,
+                // or the current word doesn't starts with the current prefix.
+                if *current_prefix_count == 0 || prefix != current_prefix.as_str() {
+                    *current_prefix = SmallString32::from(prefix);
+                    *current_prefix_count = 0;
+                }
+
+                *current_prefix_count += 1;
+
+                // There is enough words corresponding to this prefix to add it to the cache.
+                if *current_prefix_count >= self.threshold {
+                    builder.insert(prefix)?;
+                }
+            }
+        }
+
+        // We merge all of the previously computed prefixes into on final set.
+        let prefix_fsts: Vec<_> = builders.into_iter().map(|sb| sb.into_set()).collect();
+        let op = fst::set::OpBuilder::from_iter(prefix_fsts.iter());
+        let mut builder = fst::SetBuilder::memory();
+        builder.extend_stream(op.r#union())?;
+        let prefix_fst = builder.into_set();
+
+        // Set the words prefixes FST in the dtabase.
+        self.index.put_words_prefixes_fst(self.wtxn, &prefix_fst)?;
+
+        Ok(())
+    }
+}