refactor: Extract normalizeFindSelector method from executeQuery

We want to extract this code logic into its own method in order to ease
readability and testing

Also we refactored the code to make it easier to read

This replies to #1506 (comment)

packages/cozy-pouch-link/src/CozyPouchLink.js

@@ -556,25 +556,11 @@ class PouchLink extends CozyLink {
       res = withoutDesignDocuments(res)
       withRows = true
     } else {
-      let findSelector = selector
-      const shouldAddId = !findSelector
-      if (shouldAddId) {
-        findSelector = {}
-      }
-      if (indexedFields) {
-        for (const indexedField of indexedFields) {
-          if (!Object.keys(findSelector).includes(indexedField)) {
-            findSelector[indexedField] = {
-              $gt: null
-            }
-          }
-        }
-      }
-      if (shouldAddId) {
-        findSelector['_id'] = {
-          $gt: null
-        }
-      }
+      const findSelector = helpers.normalizeFindSelector(
+        selector,
+        indexedFields
+      )
+
       const findOpts = {
         sort,
         selector: findSelector,

packages/cozy-pouch-link/src/CozyPouchLink.spec.js

@@ -4,6 +4,8 @@ import { find, allDocs, withoutDesignDocuments } from './helpers'
 jest.mock('./helpers', () => ({
   find: jest.fn(),
   allDocs: jest.fn(),
+  normalizeFindSelector: jest.requireActual('./helpers').default
+    .normalizeFindSelector,
   withoutDesignDocuments: jest.fn()
 }))
 

packages/cozy-pouch-link/src/helpers.js

@@ -61,4 +61,21 @@ helpers.insertBulkDocs = async (db, docs) => {
   return db.bulkDocs(docs, { new_edits: false })
 }
 
+helpers.normalizeFindSelector = (selector, indexedFields) => {
+  let findSelector = selector || {}
+  if (indexedFields) {
+    for (const indexedField of indexedFields) {
+      if (!Object.keys(findSelector).includes(indexedField)) {
+        findSelector[indexedField] = {
+          $gt: null
+        }
+      }
+    }
+  }
+
+  return Object.keys(findSelector).length > 0
+    ? findSelector
+    : { _id: { $gt: null } } // PouchDB does not accept empty selector
+}
+
 export default helpers

packages/cozy-pouch-link/src/helpers.spec.js

@@ -1,5 +1,10 @@
 import helpers from './helpers'
-const { withoutDesignDocuments, isDeletedDocument, isDesignDocument } = helpers
+const {
+  withoutDesignDocuments,
+  isDeletedDocument,
+  isDesignDocument,
+  normalizeFindSelector
+} = helpers
 
 import PouchDB from 'pouchdb-browser'
 import PouchDBFind from 'pouchdb-find'
@@ -113,4 +118,37 @@ describe('Helpers', () => {
       expect(isDeletedDocument({ _id: 'notdeleted' })).toBeFalsy()
     })
   })
+
+  describe('normalizeFindSelector', () => {
+    it('should add indexed fields in the selector if they are missing', () => {
+      const selector = {
+        SOME_FIELD: { $gt: null }
+      }
+      const indexedFields = ['SOME_INDEXED_FIELD']
+
+      const findSelector = normalizeFindSelector(selector, indexedFields)
+      expect(findSelector).toStrictEqual({
+        SOME_FIELD: { $gt: null },
+        SOME_INDEXED_FIELD: { $gt: null }
+      })
+    })
+
+    it('should prevent empty selector by adding a selector on _id when no selector is provided', () => {
+      const selector = undefined
+      const indexedFields = undefined
+
+      const findSelector = normalizeFindSelector(selector, indexedFields)
+      expect(findSelector).toStrictEqual({ _id: { $gt: null } })
+    })
+
+    it('should not add selector on _id when no selector is provided but there are some indexed fields', () => {
+      const selector = undefined
+      const indexedFields = ['SOME_INDEXED_FIELD']
+
+      const findSelector = normalizeFindSelector(selector, indexedFields)
+      expect(findSelector).toStrictEqual({
+        SOME_INDEXED_FIELD: { $gt: null }
+      })
+    })
+  })
 })