WIP normalized score merge strategy

meilisearch-types/src/error.rs

@@ -236,6 +236,7 @@ InvalidSearchHighlightPreTag          , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchHitsPerPage              , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchLimit                    , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchMatchingStrategy         , InvalidRequest       , BAD_REQUEST ;
+InvalidMultiSearchMergeStrategy       , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchOffset                   , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchPage                     , InvalidRequest       , BAD_REQUEST ;
 InvalidSearchQ                        , InvalidRequest       , BAD_REQUEST ;

meilisearch/src/routes/multi_search.rs

@@ -2,9 +2,11 @@ use actix_http::StatusCode;
 use actix_web::web::{self, Data};
 use actix_web::{HttpRequest, HttpResponse};
 use deserr::actix_web::AwebJson;
+use deserr::Deserr;
 use index_scheduler::IndexScheduler;
 use log::debug;
 use meilisearch_types::deserr::DeserrJsonError;
+use meilisearch_types::error::deserr_codes::InvalidMultiSearchMergeStrategy;
 use meilisearch_types::error::ResponseError;
 use meilisearch_types::keys::actions;
 use serde::Serialize;
@@ -14,7 +16,7 @@ use crate::extractors::authentication::policies::ActionPolicy;
 use crate::extractors::authentication::{AuthenticationError, GuardedData};
 use crate::extractors::sequential_extractor::SeqHandler;
 use crate::search::{
-    add_search_rules, perform_search, SearchQueryWithIndex, SearchResultWithIndex,
+    add_search_rules, perform_search, SearchHit, SearchQueryWithIndex, SearchResultWithIndex,
 };
 
 pub fn configure(cfg: &mut web::ServiceConfig) {
@@ -23,13 +25,34 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
 
 #[derive(Serialize)]
 struct SearchResults {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    aggregate_hits: Option<Vec<SearchHitWithIndex>>,
     results: Vec<SearchResultWithIndex>,
 }
 
+#[derive(Serialize, Debug, Clone, PartialEq)]
+#[serde(rename_all = "camelCase")]
+struct SearchHitWithIndex {
+    pub index_uid: String,
+    #[serde(flatten)]
+    pub hit: SearchHit,
+}
+
 #[derive(Debug, deserr::Deserr)]
 #[deserr(error = DeserrJsonError, rename_all = camelCase, deny_unknown_fields)]
 pub struct SearchQueries {
     queries: Vec<SearchQueryWithIndex>,
+    #[deserr(default, error = DeserrJsonError<InvalidMultiSearchMergeStrategy>, default)]
+    merge_strategy: MergeStrategy,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Deserr, Default)]
+#[deserr(rename_all = camelCase)]
+pub enum MergeStrategy {
+    #[default]
+    None,
+    ByNormalizedScore,
+    ByScoreDetails,
 }
 
 pub async fn multi_search_with_post(
@@ -38,7 +61,13 @@ pub async fn multi_search_with_post(
     req: HttpRequest,
     analytics: web::Data<dyn Analytics>,
 ) -> Result<HttpResponse, ResponseError> {
-    let queries = params.into_inner().queries;
+    let SearchQueries { queries, merge_strategy } = params.into_inner();
+    // FIXME: REMOVE UNWRAP
+    let max_hits = queries
+        .iter()
+        .map(|SearchQueryWithIndex { limit, hits_per_page, .. }| hits_per_page.unwrap_or(*limit))
+        .max()
+        .unwrap();
 
     let mut multi_aggregate = MultiSearchAggregator::from_queries(&queries, &req);
 
@@ -104,7 +133,49 @@ pub async fn multi_search_with_post(
 
     debug!("returns: {:?}", search_results);
 
-    Ok(HttpResponse::Ok().json(SearchResults { results: search_results }))
+    let aggregate_hits = match merge_strategy {
+        MergeStrategy::None => None,
+        MergeStrategy::ByScoreDetails => todo!(),
+        MergeStrategy::ByNormalizedScore => {
+            Some(merge_by_normalized_score(&search_results, max_hits))
+        }
+    };
+
+    Ok(HttpResponse::Ok().json(SearchResults { aggregate_hits, results: search_results }))
+}
+
+fn merge_by_normalized_score(
+    search_results: &[SearchResultWithIndex],
+    max_hits: usize,
+) -> Vec<SearchHitWithIndex> {
+    let mut iterators: Vec<_> = search_results
+        .iter()
+        .filter_map(|SearchResultWithIndex { index_uid, result }| {
+            let mut it = result.hits.iter();
+            let next = it.next()?;
+            Some((index_uid, it, next))
+        })
+        .collect();
+
+    let mut hits = Vec::with_capacity(max_hits);
+
+    for _ in 0..max_hits {
+        iterators.sort_by_key(|(_, _, peeked)| peeked.ranking_score.unwrap());
+
+        let Some((index_uid, it, next)) = iterators.last_mut()
+        else {
+            break;
+        };
+
+        let hit = SearchHitWithIndex { index_uid: index_uid.clone(), hit: next.clone() };
+        if let Some(next_hit) = it.next() {
+            *next = next_hit;
+        } else {
+            iterators.pop();
+        }
+        hits.push(hit);
+    }
+    hits
 }
 
 /// Local `Result` extension trait to avoid `map_err` boilerplate.