[Goals]add template to set x month average (#2688)

* add template to set x month average

* error on 0

* note

* lint

packages/loot-core/src/server/budget/goal-template.pegjs

@@ -22,6 +22,8 @@ expr
     { return { type: 'schedule', name, priority: +priority, full } }
   / priority: priority? _? remainder: remainder
     { return { type: 'remainder', priority: null, weight: remainder } }
+  / priority: priority? _? 'average'i _ amount: positive _ 'months'i?
+    { return { type: 'average', amount: +amount, priority: +priority }}
 
 
 repeat 'repeat interval'

packages/loot-core/src/server/budget/goals/goalsAverage.ts

+// @ts-strict-ignore
+
+import * as monthUtils from '../../../shared/months';
+import { getSheetValue } from '../actions';
+
+export async function goalsAverage(
+  template,
+  month,
+  category,
+  errors,
+  to_budget,
+) {
+  // simple has an 'amount' param
+  let increment = 0;
+  if (template.amount) {
+    let sum = 0;
+    for (let i = 1; i <= template.amount; i++) {
+      // add up other months
+      const sheetName = monthUtils.sheetForMonth(
+        monthUtils.subMonths(month, i),
+      );
+      sum += await getSheetValue(sheetName, `sum-amount-${category.id}`);
+    }
+    increment = sum / template.amount;
+  } else {
+    errors.push('Number of months to average is not valid');
+    return { to_budget, errors };
+  }
+  to_budget += -Math.round(increment);
+  return { to_budget, errors };
+}

packages/loot-core/src/server/budget/goaltemplates.ts

@@ -7,6 +7,7 @@ import { batchMessages } from '../sync';
 
 import { setBudget, getSheetValue, isReflectBudget, setGoal } from './actions';
 import { parse } from './goal-template.pegjs';
+import { goalsAverage } from './goals/goalsAverage';
 import { goalsBy } from './goals/goalsBy';
 import { goalsPercentage } from './goals/goalsPercentage';
 import { findRemainder, goalsRemainder } from './goals/goalsRemainder';
@@ -609,6 +610,18 @@ async function applyCategoryTemplate(
         to_budget = goalsReturn.to_budget;
         break;
       }
+      case 'average': {
+        const goalsReturn = await goalsAverage(
+          template,
+          current_month,
+          category,
+          errors,
+          to_budget,
+        );
+        to_budget = goalsReturn.to_budget;
+        errors = goalsReturn.errors;
+        break;
+      }
       case 'error':
         return { errors };
       default:

upcoming-release-notes/2688.md

+---
+category: Enhancements
+authors: [youngcw]
+---
+
+Goals: Add template to budget X months average spending.  Matches the funcion of the existing budget page button.