Merge pull request #135 from AnyRoad/rescore

adds query rescoring

search-client/src/commonTest/kotlin/com/jillesvangurp/ktsearch/SearchTest.kt

@@ -217,6 +217,44 @@ class SearchTest : SearchTestBase() {
         response.responses shouldHaveSize 2
     }
 
+    @Test
+    fun shouldApplyRescore() = coRun {
+        val indexName = testDocumentIndex()
+        client.bulk(target = indexName, refresh = Refresh.WaitFor) {
+            index(TestDocument("doc 1", tags = listOf("rescore")).json())
+            index(TestDocument("doc 2", tags = listOf("nope")).json())
+            index(TestDocument("doc 3", tags = listOf("another")).json())
+        }
+        val response = client.search(indexName, explain = true) {
+            query = matchAll()
+            val firstRescoreQuery = constantScore {
+                filter = match(TestDocument::tags, "rescore")
+            }
+
+            val secondRescoreQuery = constantScore {
+                filter = match(TestDocument::tags, "another")
+            }
+            rescore(
+                rescorer(3) {
+                    scoreMode = RescoreScoreMode.total
+                    rescoreQueryWeight = 20.0
+                    queryWeight = 2.0
+                    rescoreQuery = firstRescoreQuery
+                },
+                rescorer(3) {
+                    scoreMode = RescoreScoreMode.multiply
+                    rescoreQueryWeight = 5.0
+                    queryWeight = 1.0
+                    rescoreQuery = secondRescoreQuery
+                }
+            )
+        }
+
+        response.hits!!.hits shouldHaveSize 3
+        response.parseHits<TestDocument>().map(TestDocument::name) shouldBe listOf("doc 1", "doc 3", "doc 2")
+        response.hits!!.hits.map(SearchResponse.Hit::score) shouldBe listOf(22.0, 10.0, 2.0)
+    }
+
     @Test
     fun shouldExposeSeqNo() = coRun {
         val indexName = testDocumentIndex()

search-dsls/src/commonMain/kotlin/com/jillesvangurp/searchdsls/querydsl/search-dsl.kt

@@ -255,3 +255,80 @@ fun SearchDSL.dotted(vararg elements: Any) = elements.joinToString(".") { pathCo
         else -> pathComponent.toString()
     }
 }
+
+fun SearchDSL.rescore(vararg rescores: Rescorer) = getOrCreateMutableList("rescore").addAll(rescores)
+
+/**
+ * Rescoring can help to improve precision by reordering just the top (e.g. 100 - 500) documents
+ * returned by the query and post_filter phases, using a secondary (usually more costly) algorithm,
+ * instead of applying the costly algorithm to all documents in the index.
+ */
+class Rescorer : JsonDsl() {
+    /**
+     * The number of docs which will be examined on each shard
+     */
+    var windowSize by property<Int>()
+
+    /**
+     * Second query excuted only on the Top-K results returned by the query and post_filter phases.
+     */
+    var query by property<RescoreQuery>()
+}
+
+class RescoreQuery : JsonDsl() {
+    /**
+     * Query to apply
+     */
+    var rescoreQuery by esQueryProperty()
+
+    /**
+     * The relative importance of the original query
+     */
+    var queryWeight by property<Double>()
+
+    /**
+     * The relative importance of the rescore query
+     */
+    var rescoreQueryWeight by property<Double>()
+
+    /**
+     * way the original score and rescore score are combined
+     */
+    var scoreMode by property<RescoreScoreMode>()
+}
+
+/**
+ * Controls the way the original score and rescore score are combined
+ */
+enum class RescoreScoreMode {
+    /**
+     * Average the original score and the rescore query score.
+     */
+    avg,
+
+    /**
+     * Take the min of the original score and the rescore query score.
+     */
+    min,
+
+    /**
+     * Take the max of original score and the rescore query score.
+     */
+    max,
+
+    /**
+     * Add the original score and the rescore query score. The default.
+     */
+    total,
+
+    /**
+     * Multiply the original score by the rescore query score.
+     */
+    multiply
+}
+
+fun SearchDSL.rescorer(windowSize: Int, queryBlock: RescoreQuery.() -> Unit) =
+    Rescorer().apply {
+        this.windowSize = windowSize
+        this.query = RescoreQuery().apply(queryBlock)
+    }