fix(expenses): Ensure shares are consistent for 'EVENLY' split mode

This commit addresses a data inconsistency issue where expenses with a split mode of 'EVENLY' could have non-normalized shares, leading to calculation errors in features like CSV exports.

This is a comprehensive fix that includes two parts:

1.  **Application-level fix:**
    The createExpense and updateExpense functions in src/lib/api.ts are updated to explicitly check if the split mode is 'EVENLY'. If it is, the shares for all participants are normalized to 1, ensuring that all new and updated expenses are stored with consistent data.

2.  **Data migration:**
    A new data migration is introduced to clean up existing inconsistent data. The migration updates the shares to 1 for all ExpensePaidFor entries associated with an Expense where splitMode is 'EVENLY'.

Together, these changes guarantee data integrity for all 'EVENLY' split expenses, both past and future.

Author: Uli-Z

prisma/migrations/20250701155133_cleanup_evenly_shares/migration.sql

@@ -0,0 +1,11 @@
+-- This migration cleans up existing data where the split mode is 'EVENLY'
+-- but the shares are not set to 1. This ensures data consistency for
+-- all expenses that should be split equally.
+
+UPDATE "ExpensePaidFor"
+SET "shares" = 1
+WHERE "expenseId" IN (
+  SELECT "id"
+  FROM "Expense"
+  WHERE "splitMode" = 'EVENLY'
+);

src/lib/api.ts

@@ -64,6 +64,14 @@ export async function createExpense(
     groupId,
   )
 
+  const paidFor =
+    expenseFormValues.splitMode === 'EVENLY'
+      ? expenseFormValues.paidFor.map(({ participant }) => ({
+          participant,
+          shares: 1,
+        }))
+      : expenseFormValues.paidFor
+
   return prisma.expense.create({
     data: {
       id: expenseId,
@@ -87,7 +95,7 @@ export async function createExpense(
       },
       paidFor: {
         createMany: {
-          data: expenseFormValues.paidFor.map((paidFor) => ({
+          data: paidFor.map((paidFor) => ({
             participantId: paidFor.participant,
             shares: paidFor.shares,
           })),
@@ -204,6 +212,14 @@ export async function updateExpense(
     existingExpense.expenseDate,
   )
 
+  const paidFor =
+    expenseFormValues.splitMode === 'EVENLY'
+      ? expenseFormValues.paidFor.map(({ participant }) => ({
+          participant,
+          shares: 1,
+        }))
+      : expenseFormValues.paidFor
+
   return prisma.expense.update({
     where: { id: expenseId },
     data: {
@@ -218,7 +234,7 @@ export async function updateExpense(
       splitMode: expenseFormValues.splitMode,
       recurrenceRule: expenseFormValues.recurrenceRule,
       paidFor: {
-        create: expenseFormValues.paidFor
+        create: paidFor
           .filter(
             (p) =>
               !existingExpense.paidFor.some(
@@ -229,7 +245,7 @@ export async function updateExpense(
             participantId: paidFor.participant,
             shares: paidFor.shares,
           })),
-        update: expenseFormValues.paidFor.map((paidFor) => ({
+        update: paidFor.map((paidFor) => ({
           where: {
             expenseId_participantId: {
               expenseId,