From 8f1222672d9775228ac26064675e8c14ff80e2ab Mon Sep 17 00:00:00 2001
From: Andrea Maria Piana <andrea.maria.piana@gmail.com>
Date: Mon, 18 Aug 2025 13:43:44 +0100
Subject: [PATCH] feat: allow accumulator/current in reduce/map operations

---
 v0/src/jsonLogic.js                | 20 ++++++++++--
 v0/src/tests/jsonLogic.fixtures.js | 52 ++++++++++++++++++++++++++++--
 v0/src/tests/jsonLogic.test.js     | 16 +++++++--
 3 files changed, 81 insertions(+), 7 deletions(-)

diff --git a/v0/src/jsonLogic.js b/v0/src/jsonLogic.js
index e5490d159..47e45fc0d 100644
--- a/v0/src/jsonLogic.js
+++ b/v0/src/jsonLogic.js
@@ -404,26 +404,40 @@ function validateInlineRules(jsonSchema, sampleEmptyObject) {
  * @param {Function} errorMessage - Function to generate custom error message.
  *                                  Receives the invalid rule part and should throw an error message string.
  */
+
 function checkRuleIntegrity(
   rule,
   id,
   data,
   errorMessage = (item) =>
-    `[json-schema-form] json-logic error: rule "${id}" has no variable "${item.var}".`
+    `[json-schema-form] json-logic error: rule "${id}" has no variable "${item.var}".`,
+  inReduceOrMap = false
 ) {
   Object.entries(rule ?? {}).map(([operator, subRule]) => {
     if (!Array.isArray(subRule) && subRule !== null && subRule !== undefined) return;
     throwIfUnknownOperator(operator, subRule, id);
 
+    // If we are within a reduce or map, we allow references to `accumulator` and/or `current`.
+    // We augment the data so that we still validate any other field.
+    const isReduceOrMap = inReduceOrMap || operator === 'reduce' || operator === 'map';
+
+    const validationData = isReduceOrMap
+      ? {
+          ...data,
+          accumulator: 0,
+          current: null,
+        }
+      : data;
+
     subRule.map((item) => {
       const isVar = item !== null && typeof item === 'object' && Object.hasOwn(item, 'var');
       if (isVar) {
-        const exists = jsonLogic.apply({ var: removeIndicesFromPath(item.var) }, data);
+        const exists = jsonLogic.apply({ var: removeIndicesFromPath(item.var) }, validationData);
         if (exists === null) {
           throw Error(errorMessage(item));
         }
       } else {
-        checkRuleIntegrity(item, id, data);
+        checkRuleIntegrity(item, id, data, errorMessage, isReduceOrMap);
       }
     });
   });
diff --git a/v0/src/tests/jsonLogic.fixtures.js b/v0/src/tests/jsonLogic.fixtures.js
index c21d70cf4..2845e38ee 100644
--- a/v0/src/tests/jsonLogic.fixtures.js
+++ b/v0/src/tests/jsonLogic.fixtures.js
@@ -1061,7 +1061,7 @@ export const schemaWithReduceAccumulator = {
       type: 'number',
       'x-jsf-logic-computedAttrs': {
         const: 'computed_work_hours_per_week',
-        defaultValue: 'computed_work_hours_per_week',
+        default: 'computed_work_hours_per_week',
         title: '{{computed_work_hours_per_week}} hours per week',
       },
     },
@@ -1073,7 +1073,7 @@ export const schemaWithReduceAccumulator = {
           '*': [
             { var: 'working_hours_per_day' },
             {
-              reduce: [{ var: 'work_days' }, { '+': [{ var: ['accumulator', 0] }, 1] }, 0],
+              reduce: [{ var: 'work_days' }, { '+': [{ var: 'accumulator' }, 1] }, 0],
             },
           ],
         },
@@ -1081,3 +1081,51 @@ export const schemaWithReduceAccumulator = {
     },
   },
 };
+
+export const schemaWithReduceAccumulatorAndMerge = {
+  properties: {
+    work_days: {
+      items: {
+        anyOf: [
+          { const: 'monday', title: 'Monday' },
+          { const: 'tuesday', title: 'Tuesday' },
+          { const: 'wednesday', title: 'Wednesday' },
+          { const: 'thursday', title: 'Thursday' },
+          { const: 'friday', title: 'Friday' },
+          { const: 'saturday', title: 'Saturday' },
+          { const: 'sunday', title: 'Sunday' },
+        ],
+      },
+      type: 'array',
+      uniqueItems: true,
+      'x-jsf-presentation': {
+        inputType: 'select',
+      },
+    },
+    working_hours_per_day: {
+      type: 'number',
+    },
+    working_hours_per_week: {
+      type: 'number',
+      'x-jsf-logic-computedAttrs': {
+        const: 'computed_work_hours_per_week',
+        default: 'computed_work_hours_per_week',
+        title: '{{computed_work_hours_per_week}} hours per week',
+      },
+    },
+  },
+  'x-jsf-logic': {
+    computedValues: {
+      computed_work_hours_per_week: {
+        rule: {
+          reduce: [
+            { var: 'work_days' },
+            { merge: [{ var: 'accumulator' }, [{ var: 'current' }]] },
+            // note we use the wrong accumulator type
+            0,
+          ],
+        },
+      },
+    },
+  },
+};
diff --git a/v0/src/tests/jsonLogic.test.js b/v0/src/tests/jsonLogic.test.js
index 989b1e312..d49071e73 100644
--- a/v0/src/tests/jsonLogic.test.js
+++ b/v0/src/tests/jsonLogic.test.js
@@ -35,6 +35,7 @@ import {
   schemaWithValidationThatDoesNotExistOnProperty,
   badSchemaThatWillNotSetAForcedValue,
   schemaWithReduceAccumulator,
+  schemaWithReduceAccumulatorAndMerge,
   schemaWithComputedPresentationAttributes,
 } from './jsonLogic.fixtures';
 import { mockConsole, restoreConsoleAndEnsureItWasNotCalled } from './testUtils';
@@ -245,8 +246,7 @@ describe('jsonLogic: cross-values validations', () => {
     });
   });
 
-  // TODO: Implement this test.
-  describe.skip('Reduce', () => {
+  describe('Reduce', () => {
     it('reduce: working_hours_per_day * work_days', () => {
       const { fields, handleValidation } = createHeadlessForm(schemaWithReduceAccumulator, {
         strictInputType: false,
@@ -260,6 +260,18 @@ describe('jsonLogic: cross-values validations', () => {
       expect(field.default).toEqual(16);
       expect(field.label).toEqual('16 hours per week');
     });
+
+    it('reduce: handles when operator is non numerical', () => {
+      const { fields, handleValidation } = createHeadlessForm(schemaWithReduceAccumulatorAndMerge, {
+        strictInputType: false,
+      });
+      handleValidation({
+        work_days: ['monday', 'tuesday'],
+        working_hours_per_day: 8,
+      });
+      const field = fields.find((i) => i.name === 'working_hours_per_week');
+      expect(field.const).toEqual([0, 'monday', 'tuesday']);
+    });
   });
 
   describe('Logical: ||, &&', () => {