feat: initialise a new totals tab with basic UI (#94)

* feat: initialise a new totals tab with basic UI

* fix: update group tabs and add stats page

* fix: styling within the new elements

* Prettier

* Display active user expenses only if active user is set

---------

Co-authored-by: Sebastien Castiel <sebastien@castiel.me>

1 files changed, 66 insertions, 0 deletions

diff --git a/src/lib/totals.ts b/src/lib/totals.ts
new file mode 100644
index 0000000..797318c
--- /dev/null
+++ b/src/lib/totals.ts
@@ -0,0 +1,66 @@
+import { getGroupExpenses } from '@/lib/api'
+
+export function getTotalGroupSpending(
+  expenses: NonNullable<Awaited<ReturnType<typeof getGroupExpenses>>>,
+): number {
+  return expenses.reduce(
+    (total, expense) =>
+      !expense.isReimbursement ? total + expense.amount : total + 0,
+    0,
+  )
+}
+
+export function getTotalActiveUserPaidFor(
+  activeUserId: string | null,
+  expenses: NonNullable<Awaited<ReturnType<typeof getGroupExpenses>>>,
+): number {
+  return expenses.reduce(
+    (total, expense) =>
+      expense.paidBy.id === activeUserId ? total + expense.amount : total + 0,
+    0,
+  )
+}
+
+export function getTotalActiveUserShare(
+  activeUserId: string | null,
+  expenses: NonNullable<Awaited<ReturnType<typeof getGroupExpenses>>>,
+): number {
+  let total = 0
+
+  expenses.forEach((expense) => {
+    const paidFors = expense.paidFor
+    const userPaidFor = paidFors.find(
+      (paidFor) => paidFor.participantId === activeUserId,
+    )
+
+    if (!userPaidFor) {
+      // If the active user is not involved in the expense, skip it
+      return
+    }
+
+    switch (expense.splitMode) {
+      case 'EVENLY':
+        // Divide the total expense evenly among all participants
+        total += expense.amount / paidFors.length
+        break
+      case 'BY_AMOUNT':
+        // Directly add the user's share if the split mode is BY_AMOUNT
+        total += userPaidFor.shares
+        break
+      case 'BY_PERCENTAGE':
+        // Calculate the user's share based on their percentage of the total expense
+        total += (expense.amount * userPaidFor.shares) / 10000 // Assuming shares are out of 10000 for percentage
+        break
+      case 'BY_SHARES':
+        // Calculate the user's share based on their shares relative to the total shares
+        const totalShares = paidFors.reduce(
+          (sum, paidFor) => sum + paidFor.shares,
+          0,
+        )
+        total += (expense.amount * userPaidFor.shares) / totalShares
+        break
+    }
+  })
+
+  return parseFloat(total.toFixed(2))
+}