From 0a8e56f80033ce889b38b01f2287cd6fbbe36dd6 Mon Sep 17 00:00:00 2001
From: Sebastien Castiel <sebastien@castiel.me>
Date: Mon, 8 Jan 2024 18:11:11 +0100
Subject: Add splitmode and shares to expenses (#11)

* Add splitmode and shares to expenses

* Update balances based on shares

* Change field size

* Form validation

* Redesign expense form

* Split unevenly by amount
---
 src/lib/balances.ts | 41 +++++++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 16 deletions(-)

(limited to 'src/lib/balances.ts')

diff --git a/src/lib/balances.ts b/src/lib/balances.ts
index 77f4622..0bcd915 100644
--- a/src/lib/balances.ts
+++ b/src/lib/balances.ts
@@ -1,5 +1,6 @@
 import { getGroupExpenses } from '@/lib/api'
 import { Participant } from '@prisma/client'
+import { match } from 'ts-pattern'
 
 export type Balances = Record<
   Participant['id'],
@@ -19,34 +20,42 @@ export function getBalances(
 
   for (const expense of expenses) {
     const paidBy = expense.paidById
-    const paidFors = expense.paidFor.map((p) => p.participantId)
+    const paidFors = expense.paidFor
 
     if (!balances[paidBy]) balances[paidBy] = { paid: 0, paidFor: 0, total: 0 }
     balances[paidBy].paid += expense.amount
     balances[paidBy].total += expense.amount
+
+    const totalPaidForShares = paidFors.reduce(
+      (sum, paidFor) => sum + paidFor.shares,
+      0,
+    )
+    let remaining = expense.amount
     paidFors.forEach((paidFor, index) => {
-      if (!balances[paidFor])
-        balances[paidFor] = { paid: 0, paidFor: 0, total: 0 }
+      if (!balances[paidFor.participantId])
+        balances[paidFor.participantId] = { paid: 0, paidFor: 0, total: 0 }
+
+      const isLast = index === paidFors.length - 1
+
+      const [shares, totalShares] = match(expense.splitMode)
+        .with('EVENLY', () => [1, paidFors.length])
+        .with('BY_SHARES', () => [paidFor.shares, totalPaidForShares])
+        .with('BY_PERCENTAGE', () => [paidFor.shares, totalPaidForShares])
+        .with('BY_AMOUNT', () => [paidFor.shares, totalPaidForShares])
+        .exhaustive()
 
-      const dividedAmount = divide(
-        expense.amount,
-        paidFors.length,
-        index === paidFors.length - 1,
-      )
-      balances[paidFor].paidFor += dividedAmount
-      balances[paidFor].total -= dividedAmount
+      const dividedAmount = isLast
+        ? remaining
+        : Math.floor((expense.amount * shares) / totalShares)
+      remaining -= dividedAmount
+      balances[paidFor.participantId].paidFor += dividedAmount
+      balances[paidFor.participantId].total -= dividedAmount
     })
   }
 
   return balances
 }
 
-function divide(total: number, count: number, isLast: boolean): number {
-  if (!isLast) return Math.floor(total / count)
-
-  return total - divide(total, count, false) * (count - 1)
-}
-
 export function getSuggestedReimbursements(
   balances: Balances,
 ): Reimbursement[] {
-- 
cgit v1.3