Goals: add flag to percent goals to use previous month income instead of this months (#1403)

This is a more elegant way of implementing a month ahead version of the
percent goals. To use it add the `previous` flag to the percent goal, ex
`#template 10% of previous Paycheck`.

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

@@ -1,8 +1,8 @@
 // https://peggyjs.org
 
 expr
-  = priority: priority? _? percent: percent _ of _ category: name
-    { return { type: 'percentage', percent: +percent, category, priority: +priority }}
+  = priority: priority? _? percentOf:percentOf category: name
+    { return { type: 'percentage', percent: +percentOf.percent, previous: percentOf.prev, category, priority: +priority }}
   / priority: priority? _? amount: amount _ repeatEvery _ weeks: weekCount _ starting _ starting: date limit: limit?
     { return { type: 'week', amount, weeks, starting, limit, priority: +priority }}
   / priority: priority? _? amount: amount _ by _ month: month from: spendFrom? repeat: (_ repeatEvery _ repeat)?
@@ -33,6 +33,8 @@ repeat 'repeat interval'
 limit =  _? upTo _ amount: amount _ 'hold'i { return {amount: amount, hold: true } }
         / _? upTo _ amount: amount { return {amount: amount, hold: false } }
 
+percentOf = percent:percent _ of _ 'previous'i _ { return { percent: percent, prev: true} }
+		/ percent:percent _ of _ { return { percent: percent, prev: false} }
 
 weekCount
   = week { return null }

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

@@ -554,8 +554,19 @@ async function applyCategoryTemplate(
       case 'percentage': {
         let percent = template.percent;
         let monthlyIncome = 0;
+
         if (template.category.toLowerCase() === 'all income') {
-          monthlyIncome = await getSheetValue(sheetName, `total-income`);
+          if (template.previous) {
+            let sheetName_lastmonth = monthUtils.sheetForMonth(
+              monthUtils.addMonths(month, -1),
+            );
+            monthlyIncome = await getSheetValue(
+              sheetName_lastmonth,
+              'total-income',
+            );
+          } else {
+            monthlyIncome = await getSheetValue(sheetName, `total-income`);
+          }
         } else if (template.category.toLowerCase() === 'available funds') {
           monthlyIncome = available_start;
         } else {
@@ -568,11 +579,22 @@ async function applyCategoryTemplate(
             errors.push(`Could not find category “${template.category}”`);
             return { errors };
           }
-          monthlyIncome = await getSheetValue(
-            sheetName,
-            `sum-amount-${income_category.id}`,
-          );
+          if (template.previous) {
+            let sheetName_lastmonth = monthUtils.sheetForMonth(
+              monthUtils.addMonths(month, -1),
+            );
+            monthlyIncome = await getSheetValue(
+              sheetName_lastmonth,
+              `sum-amount-${income_category.id}`,
+            );
+          } else {
+            monthlyIncome = await getSheetValue(
+              sheetName,
+              `sum-amount-${income_category.id}`,
+            );
+          }
         }
+
         let increment = Math.max(
           0,
           Math.round(monthlyIncome * (percent / 100)),

upcoming-release-notes/1403.md

@@ -0,0 +1,6 @@
+---
+category: Enhancements
+authors: [youngcw]
+---
+
+Goals: add "prev" flag to percent goal to use previous month income.