Add functions & pipeline for partial tiploca match which requires skipping end stations

Signed-off-by: Fred Boniface <fred@fjla.uk>

src/services/pis.services.ts

@@ -78,8 +78,12 @@ export async function findByTiplocArray(
       if (partialEnd) {
         return convertDocument(partialEnd, "first");
       } else {
-        // Here, I should search for a partialStart match.  For now return null.
-        return null;
+        const partialStart = await findPartialStartMatchByTiploc(tiplocArray);
+        if (partialStart) {
+          return convertDocument(partialEnd, "last");
+        } else {
+          return null;
+        }
       }
     }
   } catch (err) {
@@ -103,6 +107,13 @@ async function findPartialEndMatchByTiploc(array: string[]): Promise<Document> {
   return res[0];
 }
 
+// Uses a pipeline to find a partial match - supporting codes starting with the correct stops.
+async function findPartialStartMatchByTiploc(array: string[]): Promise<Document> {
+  const pipeline = getPartialStartTiplocMatchPipeline(array);
+  const res = await queryAggregate("pis", pipeline);
+  return res[0];
+}
+
 function convertDocument(doc: Document, skipType: string): OB_Pis_SimpleObject {
   return {
     code: doc.code.toString(),

src/utils/pis.utils.ts

@@ -75,6 +75,61 @@ export function getPartialEndTiplocMatchPipeline(query: string[]) {
   ];
 }
 
+export function getPartialStartTiplocMatchPipeline(query: string[]) {
+  return [
+    {
+      '$match': {
+        'tiplocs': {
+          '$all': query
+        }
+      }
+    }, {
+      '$addFields': {
+        'query': query
+      }
+    }, {
+      '$match': {
+        '$expr': {
+          '$eq': [
+            {
+              '$slice': [
+                '$tiplocs', {
+                  '$size': '$query'
+                }
+              ]
+            }, '$query'
+          ]
+        }
+      }
+    }, {
+      '$addFields': {
+        'skipStops': {
+          '$subtract': [
+            {
+              '$size': '$tiplocs'
+            }, {
+              '$size': '$query'
+            }
+          ]
+        }
+      }
+    }, {
+      '$sort': {
+        'skipStops': 1
+      }
+    }, {
+      '$limit': 1
+    }, {
+      '$project': {
+        'code': 1, 
+        'skipStops': 1, 
+        'toc': 1, 
+        '_id': 0
+      }
+    }
+  ]
+}
+
 export function getFullTiplocMatchPipeline(query: string[]) {
   return [
     {