Implement sorting documents

crates/milli/src/facet/facet_sort_recursive.rs

@@ -0,0 +1,68 @@
+use roaring::RoaringBitmap;
+use heed::Database;
+use crate::{facet::{ascending_facet_sort, descending_facet_sort}, heed_codec::{facet::{FacetGroupKeyCodec, FacetGroupValueCodec}, BytesRefCodec}};
+
+pub fn recursive_facet_sort<'t>(
+    rtxn: &'t heed::RoTxn<'t>,
+    number_db: Database<FacetGroupKeyCodec<BytesRefCodec>, FacetGroupValueCodec>,
+    string_db: Database<FacetGroupKeyCodec<BytesRefCodec>, FacetGroupValueCodec>,
+    fields: &[(u16, bool)],
+    candidates: RoaringBitmap,
+) -> heed::Result<RoaringBitmap> {
+    let (field_id, ascending) = match fields.first() {
+        Some(first) => *first,
+        None => return Ok(candidates),
+    };
+
+    let (number_iter, string_iter) = if ascending {
+        let number_iter = ascending_facet_sort(
+            rtxn,
+            number_db,
+            field_id,
+            candidates.clone(),
+        )?;
+        let string_iter = ascending_facet_sort(
+            rtxn,
+            string_db,
+            field_id,
+            candidates,
+        )?;
+
+        (itertools::Either::Left(number_iter), itertools::Either::Left(string_iter))
+    } else {
+        let number_iter = descending_facet_sort(
+            rtxn,
+            number_db,
+            field_id,
+            candidates.clone(),
+        )?;
+        let string_iter = descending_facet_sort(
+            rtxn,
+            string_db,
+            field_id,
+            candidates,
+        )?;
+
+        (itertools::Either::Right(number_iter), itertools::Either::Right(string_iter))
+    };
+
+    let chained_iter = number_iter.chain(string_iter);
+    let mut result = RoaringBitmap::new();
+    for part in chained_iter {
+        let (inner_candidates, _) = part?;
+        if inner_candidates.len() <= 1 || fields.len() <= 1 {
+            result |= inner_candidates;
+        } else {
+            let inner_candidates = recursive_facet_sort(
+                rtxn,
+                number_db,
+                string_db,
+                &fields[1..],
+                inner_candidates,
+            )?;
+            result |= inner_candidates;
+        }
+    }
+
+    Ok(result)
+}

crates/milli/src/facet/mod.rs

@@ -1,6 +1,7 @@
 mod facet_type;
 mod facet_value;
 pub mod value_encoding;
+pub mod facet_sort_recursive;
 
 pub use self::facet_type::FacetType;
 pub use self::facet_value::FacetValue;