enable when expression can access variable

catalog/src/main/assets/behavior_skip_logic_with_expression.json

@@ -0,0 +1,74 @@
+{
+  "resourceType": "Questionnaire",
+  "extension": [
+    {
+      "url": "http://hl7.org/fhir/StructureDefinition/variable",
+      "valueExpression": {
+        "name": "has-fever",
+        "language": "text/fhirpath",
+        "expression": "%resource.descendants().where(linkId='1').answer.value"
+      }
+    }
+  ],
+  "item": [
+    {
+      "linkId": "1",
+      "type": "boolean",
+      "text": "Does patient has fever?",
+      "item": [
+        {
+          "extension": [
+            {
+              "url": "http://hl7.org/fhir/StructureDefinition/questionnaire-displayCategory",
+              "valueCodeableConcept": {
+                "coding": [
+                  {
+                    "system": "http://hl7.org/fhir/questionnaire-display-category",
+                    "code": "instructions"
+                  }
+                ]
+              }
+            }
+          ],
+          "linkId": "1.1",
+          "text": "Define the questionnaire variable 'has-fever' based on the answer to the question 'Does the patient have a fever?",
+          "type": "display"
+        }
+      ]
+    },
+    {
+      "linkId": "2",
+      "text": "Since when?",
+      "type": "date",
+      "extension": [
+        {
+          "url": "http://hl7.org/fhir/uv/sdc/StructureDefinition/sdc-questionnaire-enableWhenExpression",
+          "valueExpression": {
+            "language": "text/fhirpath",
+            "expression": "%has-fever"
+          }
+        }
+      ],
+      "item": [
+        {
+          "extension": [
+            {
+              "url": "http://hl7.org/fhir/StructureDefinition/questionnaire-displayCategory",
+              "valueCodeableConcept": {
+                "coding": [
+                  {
+                    "system": "http://hl7.org/fhir/questionnaire-display-category",
+                    "code": "instructions"
+                  }
+                ]
+              }
+            }
+          ],
+          "linkId": "2.1",
+          "text": "Enabled if variable 'has-fever' evaluates to true",
+          "type": "display"
+        }
+      ]
+    }
+  ]
+}

catalog/src/main/java/com/google/android/fhir/catalog/BehaviorListViewModel.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 Google LLC
+ * Copyright 2022-2023 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,6 +48,11 @@ class BehaviorListViewModel(application: Application) : AndroidViewModel(applica
       R.string.behavior_name_skip_logic,
       "behavior_skip_logic.json"
     ),
+    SKIP_LOGIC_WITH_EXPRESSION(
+      R.drawable.ic_skiplogic_behavior,
+      R.string.behavior_name_skip_logic_with_expression,
+      "behavior_skip_logic_with_expression.json"
+    ),
     DYNAMIC_QUESTION_TEXT(
       R.drawable.ic_dynamic_text_behavior,
       R.string.behavior_name_dynamic_question_text,

catalog/src/main/res/values/strings.xml

@@ -41,6 +41,9 @@
     <string name="layout_name_review">Review</string>
     <string name="layout_name_read_only">Read only</string>
     <string name="behavior_name_skip_logic">Skip logic</string>
+    <string
+        name="behavior_name_skip_logic_with_expression"
+    >Skip logic with expression</string>
     <string
         name="behavior_name_skip_logic_info"
     >If Yes is selected, a follow-up question is displayed. If No is selected, no follow-up questions are displayed.</string>

datacapture/src/main/java/com/google/android/fhir/datacapture/QuestionnaireViewModel.kt

@@ -46,9 +46,7 @@ import com.google.android.fhir.datacapture.extensions.shouldHaveNestedItemsUnder
 import com.google.android.fhir.datacapture.extensions.unpackRepeatedGroups
 import com.google.android.fhir.datacapture.extensions.validateLaunchContextExtensions
 import com.google.android.fhir.datacapture.extensions.zipByLinkId
-import com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.detectExpressionCyclicDependency
-import com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.evaluateCalculatedExpressions
-import com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator.evaluateExpression
+import com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator
 import com.google.android.fhir.datacapture.validation.Invalid
 import com.google.android.fhir.datacapture.validation.NotValidated
 import com.google.android.fhir.datacapture.validation.QuestionnaireResponseItemValidator
@@ -335,12 +333,30 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
       modificationCount.update { it + 1 }
     }
 
+  private val expressionEvaluator: ExpressionEvaluator =
+    ExpressionEvaluator(
+      questionnaire,
+      questionnaireResponse,
+      questionnaireItemParentMap,
+      questionnaireLaunchContextMap
+    )
+
+  private val enablementEvaluator: EnablementEvaluator =
+    EnablementEvaluator(
+      questionnaire,
+      questionnaireResponse,
+      questionnaireItemParentMap,
+      questionnaireLaunchContextMap
+    )
+
   private val answerOptionsEvaluator: EnabledAnswerOptionsEvaluator =
     EnabledAnswerOptionsEvaluator(
       questionnaire,
-      questionnaireLaunchContextMap,
+      questionnaireResponse,
       xFhirQueryResolver,
-      externalValueSetResolver
+      externalValueSetResolver,
+      questionnaireItemParentMap,
+      questionnaireLaunchContextMap
     )
 
   /**
@@ -404,7 +420,9 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
     QuestionnaireResponseValidator.validateQuestionnaireResponse(
         questionnaire,
         questionnaireResponse,
-        getApplication()
+        getApplication(),
+        questionnaireItemParentMap,
+        questionnaireLaunchContextMap,
       )
       .also { result ->
         if (result.values.flatten().filterIsInstance<Invalid>().isNotEmpty()) {
@@ -480,13 +498,14 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
       .withIndex()
       .onEach {
         if (it.index == 0) {
-          detectExpressionCyclicDependency(questionnaire.item)
+          expressionEvaluator.detectExpressionCyclicDependency(questionnaire.item)
           questionnaire.item.flattened().forEach { qItem ->
             updateDependentQuestionnaireResponseItems(
               qItem,
               questionnaireResponse.allItems.find { qrItem -> qrItem.linkId == qItem.linkId }
             )
           }
+          modificationCount.update { count -> count + 1 }
         }
       }
       .map { it.value }
@@ -497,15 +516,13 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
       )
 
   private fun updateDependentQuestionnaireResponseItems(
-    updatedQuestionnaireItem: QuestionnaireItemComponent,
+    questionnaireItem: QuestionnaireItemComponent,
     updatedQuestionnaireResponseItem: QuestionnaireResponseItemComponent?,
   ) {
-    evaluateCalculatedExpressions(
-        updatedQuestionnaireItem,
+    expressionEvaluator
+      .evaluateCalculatedExpressions(
+        questionnaireItem,
         updatedQuestionnaireResponseItem,
-        questionnaire,
-        questionnaireResponse,
-        questionnaireItemParentMap
       )
       .forEach { (questionnaireItem, calculatedAnswers) ->
         // update all response item with updated values
@@ -538,13 +555,10 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
     if (!cqfExpression.isFhirPath) {
       throw UnsupportedOperationException("${cqfExpression.language} not supported yet")
     }
-    return evaluateExpression(
-      questionnaire,
-      questionnaireResponse,
+    return expressionEvaluator.evaluateExpression(
       questionnaireItem,
       questionnaireResponseItem,
       cqfExpression,
-      questionnaireItemParentMap
     )
   }
 
@@ -653,8 +667,10 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
     // Hidden questions should not get QuestionnaireItemViewItem instances
     if (questionnaireItem.isHidden) return emptyList()
     val enabled =
-      EnablementEvaluator(questionnaireResponse)
-        .evaluate(questionnaireItem, questionnaireResponseItem)
+      enablementEvaluator.evaluate(
+        questionnaireItem,
+        questionnaireResponseItem,
+      )
     // Disabled questions should not get QuestionnaireItemViewItem instances
     if (!enabled) {
       cacheDisabledQuestionnaireItemAnswers(questionnaireResponseItem)
@@ -688,8 +704,6 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
       answerOptionsEvaluator.evaluate(
         questionnaireItem,
         questionnaireResponseItem,
-        questionnaireResponse,
-        questionnaireItemParentMap
       )
     if (disabledQuestionnaireResponseAnswers.isNotEmpty()) {
       removeDisabledAnswers(
@@ -713,7 +727,10 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
             enabledDisplayItems =
               questionnaireItem.item.filter {
                 it.isDisplayItem &&
-                  EnablementEvaluator(questionnaireResponse).evaluate(it, questionnaireResponseItem)
+                  enablementEvaluator.evaluate(
+                    it,
+                    questionnaireResponseItem,
+                  )
               },
             questionViewTextConfiguration =
               QuestionTextConfiguration(
@@ -790,7 +807,6 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
     questionnaireItemList: List<QuestionnaireItemComponent>,
     questionnaireResponseItemList: List<QuestionnaireResponseItemComponent>,
   ): List<QuestionnaireResponseItemComponent> {
-    val enablementEvaluator = EnablementEvaluator(questionnaireResponse)
     val responseItemKeys = questionnaireResponseItemList.map { it.linkId }
     return questionnaireItemList
       .asSequence()
@@ -828,11 +844,10 @@ internal class QuestionnaireViewModel(application: Application, state: SavedStat
         ->
         QuestionnairePage(
           index,
-          EnablementEvaluator(questionnaireResponse)
-            .evaluate(
-              questionnaireItem,
-              questionnaireResponseItem,
-            ),
+          enablementEvaluator.evaluate(
+            questionnaireItem,
+            questionnaireResponseItem,
+          ),
           questionnaireItem.isHidden
         )
       }

datacapture/src/main/java/com/google/android/fhir/datacapture/enablement/EnablementEvaluator.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022 Google LLC
+ * Copyright 2022-2023 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,10 +19,12 @@ package com.google.android.fhir.datacapture.enablement
 import com.google.android.fhir.compareTo
 import com.google.android.fhir.datacapture.extensions.allItems
 import com.google.android.fhir.datacapture.extensions.enableWhenExpression
+import com.google.android.fhir.datacapture.fhirpath.ExpressionEvaluator
 import com.google.android.fhir.datacapture.fhirpath.evaluateToBoolean
 import com.google.android.fhir.equals
 import org.hl7.fhir.r4.model.Questionnaire
 import org.hl7.fhir.r4.model.QuestionnaireResponse
+import org.hl7.fhir.r4.model.Resource
 
 /**
  * Evaluator for the enablement status of a [Questionnaire.QuestionnaireItemComponent].
@@ -50,16 +52,39 @@ import org.hl7.fhir.r4.model.QuestionnaireResponse
  * is shown or hidden. However, it is also possible that only user interaction is enabled or
  * disabled (e.g. grayed out) with the [Questionnaire.QuestionnaireItemComponent] always shown.
  *
- * The evaluator does not track the changes in the `questionnaire` and `questionnaireResponse`.
- * Therefore, a new evaluator should be created if they were modified.
+ * The evaluator works in the context of a Questionnaire and the corresponding
+ * QuestionnaireResponse. It is the caller's responsibility to make sure to call the evaluator with
+ * QuestionnaireItems and QuestionnaireResponseItems that belong to the Questionnaire and the
+ * QuestionnaireResponse.
  *
  * For more information see
  * [Questionnaire.item.enableWhen](https://www.hl7.org/fhir/questionnaire-definitions.html#Questionnaire.item.enableWhen)
  * and
  * [Questionnaire.item.enableBehavior](https://www.hl7.org/fhir/questionnaire-definitions.html#Questionnaire.item.enableBehavior)
  * .
+ *
+ * @param questionnaire the [Questionnaire] where the expression belong to
+ * @param questionnaireResponse the [QuestionnaireResponse] related to the [Questionnaire]
+ * @param questionnaireItemParentMap the [Map] of items parent
+ * @param questionnaireLaunchContextMap the [Map] of launchContext names to their resource values
  */
-internal class EnablementEvaluator(val questionnaireResponse: QuestionnaireResponse) {
+internal class EnablementEvaluator(
+  private val questionnaire: Questionnaire,
+  private val questionnaireResponse: QuestionnaireResponse,
+  private val questionnaireItemParentMap:
+    Map<Questionnaire.QuestionnaireItemComponent, Questionnaire.QuestionnaireItemComponent> =
+    emptyMap(),
+  private val questionnaireLaunchContextMap: Map<String, Resource>? = emptyMap(),
+) {
+
+  private val expressionEvaluator =
+    ExpressionEvaluator(
+      questionnaire,
+      questionnaireResponse,
+      questionnaireItemParentMap,
+      questionnaireLaunchContextMap
+    )
+
   /**
    * The pre-order traversal trace of the items in the [QuestionnaireResponse]. This essentially
    * represents the order in which all items are displayed in the UI.
@@ -95,6 +120,7 @@ internal class EnablementEvaluator(val questionnaireResponse: QuestionnaireRespo
   /**
    * Returns whether [questionnaireItem] should be enabled.
    *
+   * @param questionnaireItem the corresponding questionnaire item.
    * @param questionnaireResponseItem the corresponding questionnaire response item.
    */
   fun evaluate(
@@ -110,10 +136,16 @@ internal class EnablementEvaluator(val questionnaireResponse: QuestionnaireRespo
 
     // Evaluate `enableWhenExpression`.
     if (enableWhenExpression != null && enableWhenExpression.hasExpression()) {
+      val contextMap =
+        expressionEvaluator.extractDependentVariables(
+          questionnaireItem.enableWhenExpression!!,
+          questionnaireItem,
+        )
       return evaluateToBoolean(
         questionnaireResponse,
         questionnaireResponseItem,
-        enableWhenExpression.expression
+        enableWhenExpression.expression,
+        contextMap,
       )
     }