Implement "infinite scroll" for expenses (#95)

* Extract ExpenseCard vom ExpenseList

* Implement simple pagination of expenses (see #30)

- display only this year's entries by default
- a "Show more" button reveals all expenses

* Turn getPrisma() into constant "prisma"

- getPrisma() is not async and doesn't need to be awaited
- turn getPrisma() into exported constant "prisma"

* Select fields to be returned by getGroupExpenses()

- make JSON more concise and less redundant
- some properties were removed (i.e.instead of "expense.paidById" use "expense.paidBy.id")

* Remove "participants" from ExpenseCard

- no need to search for participant by id to get it's name
- name property is already present in expense

* Add option to fetch a slice of group expenses

- specify offset and length to get expenses for [offset, offset+length[
- add function to get total number of group expenses

* Add api route for client to fetch group expenses

* Remove "Show more" button from expense list

* Implement infinite scroll

- in server component Page
  - only load first 200 expenses max
  - pass preloaded expenses and total count

- in client component ExpenseList, if there are more expenses to show
  - test if there are more expenses
  - append preloading "skeletons" to end of list
  - fetch more expenses when last item in list comes into view
  - after each fetch increase fetch-length by factor 1.5
    - rationale: db fetch usually is not the issue here, the longer the list gets, the longer react needs to redraw

* Use server action instead of api endpoint

* Fixes

---------

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

package-lock.json

@@ -43,6 +43,7 @@
         "react": "^18.2.0",
         "react-dom": "^18.2.0",
         "react-hook-form": "^7.47.0",
+        "react-intersection-observer": "^9.8.0",
         "sharp": "^0.33.2",
         "tailwind-merge": "^1.14.0",
         "tailwindcss-animate": "^1.0.7",
@@ -7510,6 +7511,20 @@
         "react": "^16.8.0 || ^17 || ^18"
       }
     },
+    "node_modules/react-intersection-observer": {
+      "version": "9.8.0",
+      "resolved": "https://registry.npmjs.org/react-intersection-observer/-/react-intersection-observer-9.8.0.tgz",
+      "integrity": "sha512-wXHvMQUsTagh3X0Z6jDtGkIXc3VVCd2tjDRYR9kII3GKrZr0XF0xtpfdamo2n8BSF+zzfeeBVOTjxZWpBp9X0g==",
+      "peerDependencies": {
+        "react": "^15.0.0 || ^16.0.0 || ^17.0.0 || ^18.0.0",
+        "react-dom": "^15.0.0 || ^16.0.0 || ^17.0.0 || ^18.0.0"
+      },
+      "peerDependenciesMeta": {
+        "react-dom": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/react-is": {
       "version": "16.13.1",
       "resolved": "https://registry.npmjs.org/react-is/-/react-is-16.13.1.tgz",

package.json

@@ -48,6 +48,7 @@
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
     "react-hook-form": "^7.47.0",
+    "react-intersection-observer": "^9.8.0",
     "sharp": "^0.33.2",
     "tailwind-merge": "^1.14.0",
     "tailwindcss-animate": "^1.0.7",

src/app/groups/[groupId]/expenses/expense-card.tsx

@@ -0,0 +1,78 @@
+'use client'
+import { ActiveUserBalance } from '@/app/groups/[groupId]/expenses/active-user-balance'
+import { CategoryIcon } from '@/app/groups/[groupId]/expenses/category-icon'
+import { Button } from '@/components/ui/button'
+import { getGroupExpenses } from '@/lib/api'
+import { cn, formatCurrency, formatExpenseDate } from '@/lib/utils'
+import { ChevronRight } from 'lucide-react'
+import Link from 'next/link'
+import { useRouter } from 'next/navigation'
+import { Fragment } from 'react'
+
+type Props = {
+  expense: Awaited<ReturnType<typeof getGroupExpenses>>[number]
+  currency: string
+  groupId: string
+}
+
+export function ExpenseCard({ expense, currency, groupId }: Props) {
+  const router = useRouter()
+
+  return (
+    <div
+      key={expense.id}
+      className={cn(
+        'flex justify-between sm:mx-6 px-4 sm:rounded-lg sm:pr-2 sm:pl-4 py-4 text-sm cursor-pointer hover:bg-accent gap-1 items-stretch',
+        expense.isReimbursement && 'italic',
+      )}
+      onClick={() => {
+        router.push(`/groups/${groupId}/expenses/${expense.id}/edit`)
+      }}
+    >
+      <CategoryIcon
+        category={expense.category}
+        className="w-4 h-4 mr-2 mt-0.5 text-muted-foreground"
+      />
+      <div className="flex-1">
+        <div className={cn('mb-1', expense.isReimbursement && 'italic')}>
+          {expense.title}
+        </div>
+        <div className="text-xs text-muted-foreground">
+          Paid by <strong>{expense.paidBy.name}</strong> for{' '}
+          {expense.paidFor.map((paidFor, index) => (
+            <Fragment key={index}>
+              {index !== 0 && <>, </>}
+              <strong>{paidFor.participant.name}</strong>
+            </Fragment>
+          ))}
+        </div>
+        <div className="text-xs text-muted-foreground">
+          <ActiveUserBalance {...{ groupId, currency, expense }} />
+        </div>
+      </div>
+      <div className="flex flex-col justify-between items-end">
+        <div
+          className={cn(
+            'tabular-nums whitespace-nowrap',
+            expense.isReimbursement ? 'italic' : 'font-bold',
+          )}
+        >
+          {formatCurrency(currency, expense.amount)}
+        </div>
+        <div className="text-xs text-muted-foreground">
+          {formatExpenseDate(expense.expenseDate)}
+        </div>
+      </div>
+      <Button
+        size="icon"
+        variant="link"
+        className="self-center hidden sm:flex"
+        asChild
+      >
+        <Link href={`/groups/${groupId}/expenses/${expense.id}/edit`}>
+          <ChevronRight className="w-4 h-4" />
+        </Link>
+      </Button>
+    </div>
+  )
+}

src/app/groups/[groupId]/expenses/expense-list-fetch-action.ts

@@ -0,0 +1,16 @@
+'use server'
+
+import { getGroupExpenses } from '@/lib/api'
+
+export async function getGroupExpensesAction(
+  groupId: string,
+  options?: { offset: number; length: number },
+) {
+  'use server'
+
+  try {
+    return getGroupExpenses(groupId, options)
+  } catch {
+    return null
+  }
+}

src/app/groups/[groupId]/expenses/expense-list.tsx

@@ -1,19 +1,22 @@
 'use client'
-import { ActiveUserBalance } from '@/app/groups/[groupId]/expenses/active-user-balance'
+import { ExpenseCard } from '@/app/groups/[groupId]/expenses/expense-card'
-import { CategoryIcon } from '@/app/groups/[groupId]/expenses/category-icon'
+import { getGroupExpensesAction } from '@/app/groups/[groupId]/expenses/expense-list-fetch-action'
 import { Button } from '@/components/ui/button'
 import { SearchBar } from '@/components/ui/search-bar'
-import { getGroupExpenses } from '@/lib/api'
+import { Skeleton } from '@/components/ui/skeleton'
-import { cn, formatCurrency, formatExpenseDate } from '@/lib/utils'
+import { Participant } from '@prisma/client'
-import { Expense, Participant } from '@prisma/client'
 import dayjs, { type Dayjs } from 'dayjs'
-import { ChevronRight } from 'lucide-react'
 import Link from 'next/link'
-import { useRouter } from 'next/navigation'
+import { useEffect, useMemo, useState } from 'react'
-import { Fragment, useEffect, useState } from 'react'
+import { useInView } from 'react-intersection-observer'
+
+type ExpensesType = NonNullable<
+  Awaited<ReturnType<typeof getGroupExpensesAction>>
+>
 
 type Props = {
-  expenses: Awaited<ReturnType<typeof getGroupExpenses>>
+  expensesFirstPage: ExpensesType
+  expenseCount: number
   participants: Participant[]
   currency: string
   groupId: string
@@ -47,28 +50,32 @@ function getExpenseGroup(date: Dayjs, today: Dayjs) {
   }
 }
 
-function getGroupedExpensesByDate(
+function getGroupedExpensesByDate(expenses: ExpensesType) {
-  expenses: Awaited<ReturnType<typeof getGroupExpenses>>,
-) {
   const today = dayjs()
-  return expenses.reduce(
+  return expenses.reduce((result: { [key: string]: ExpensesType }, expense) => {
-    (result: { [key: string]: Expense[] }, expense: Expense) => {
+    const expenseGroup = getExpenseGroup(dayjs(expense.expenseDate), today)
-      const expenseGroup = getExpenseGroup(dayjs(expense.expenseDate), today)
+    result[expenseGroup] = result[expenseGroup] ?? []
-      result[expenseGroup] = result[expenseGroup] ?? []
+    result[expenseGroup].push(expense)
-      result[expenseGroup].push(expense)
+    return result
-      return result
+  }, {})
-    },
-    {},
-  )
 }
 
 export function ExpenseList({
-  expenses,
+  expensesFirstPage,
+  expenseCount,
   currency,
   participants,
   groupId,
 }: Props) {
+  const firstLen = expensesFirstPage.length
   const [searchText, setSearchText] = useState('')
+  const [dataIndex, setDataIndex] = useState(firstLen)
+  const [dataLen, setDataLen] = useState(firstLen)
+  const [hasMoreData, setHasMoreData] = useState(expenseCount > firstLen)
+  const [isFetching, setIsFetching] = useState(false)
+  const [expenses, setExpenses] = useState(expensesFirstPage)
+  const { ref, inView } = useInView()
+
   useEffect(() => {
     const activeUser = localStorage.getItem('newGroup-activeUser')
     const newUser = localStorage.getItem(`${groupId}-newUser`)
@@ -88,10 +95,43 @@ export function ExpenseList({
     }
   }, [groupId, participants])
 
-  const getParticipant = (id: string) => participants.find((p) => p.id === id)
+  useEffect(() => {
-  const router = useRouter()
+    const fetchNextPage = async () => {
+      setIsFetching(true)
+
+      const newExpenses = await getGroupExpensesAction(groupId, {
+        offset: dataIndex,
+        length: dataLen,
+      })
+
+      if (newExpenses !== null) {
+        const exp = expenses.concat(newExpenses)
+        setExpenses(exp)
+        setHasMoreData(exp.length < expenseCount)
+        setDataIndex(dataIndex + dataLen)
+        setDataLen(Math.ceil(1.5 * dataLen))
+      }
+
+      setTimeout(() => setIsFetching(false), 500)
+    }
+
+    if (inView && hasMoreData && !isFetching) fetchNextPage()
+  }, [
+    dataIndex,
+    dataLen,
+    expenseCount,
+    expenses,
+    groupId,
+    hasMoreData,
+    inView,
+    isFetching,
+  ])
+
+  const groupedExpensesByDate = useMemo(
+    () => getGroupedExpensesByDate(expenses),
+    [expenses],
+  )
 
-  const groupedExpensesByDate = getGroupedExpensesByDate(expenses)
   return expenses.length > 0 ? (
     <>
       <SearchBar onValueChange={(value) => setSearchText(value)} />
@@ -114,76 +154,33 @@ export function ExpenseList({
             >
               {expenseGroup}
             </div>
-            {groupExpenses.map((expense: any) => (
+            {groupExpenses.map((expense) => (
-              <div
+              <ExpenseCard
                 key={expense.id}
-                className={cn(
+                expense={expense}
-                  'flex justify-between sm:mx-6 px-4 sm:rounded-lg sm:pr-2 sm:pl-4 py-4 text-sm cursor-pointer hover:bg-accent gap-1 items-stretch',
+                currency={currency}
-                  expense.isReimbursement && 'italic',
+                groupId={groupId}
-                )}
+              />
-                onClick={() => {
-                  router.push(`/groups/${groupId}/expenses/${expense.id}/edit`)
-                }}
-              >
-                <CategoryIcon
-                  category={expense.category}
-                  className="w-4 h-4 mr-2 mt-0.5 text-muted-foreground"
-                />
-                <div className="flex-1">
-                  <div
-                    className={cn('mb-1', expense.isReimbursement && 'italic')}
-                  >
-                    {expense.title}
-                  </div>
-                  <div className="text-xs text-muted-foreground">
-                    Paid by{' '}
-                    <strong>{getParticipant(expense.paidById)?.name}</strong>{' '}
-                    for{' '}
-                    {expense.paidFor.map((paidFor: any, index: number) => (
-                      <Fragment key={index}>
-                        {index !== 0 && <>, </>}
-                        <strong>
-                          {
-                            participants.find(
-                              (p) => p.id === paidFor.participantId,
-                            )?.name
-                          }
-                        </strong>
-                      </Fragment>
-                    ))}
-                  </div>
-                  <div className="text-xs text-muted-foreground">
-                    <ActiveUserBalance {...{ groupId, currency, expense }} />
-                  </div>
-                </div>
-                <div className="flex flex-col justify-between items-end">
-                  <div
-                    className={cn(
-                      'tabular-nums whitespace-nowrap',
-                      expense.isReimbursement ? 'italic' : 'font-bold',
-                    )}
-                  >
-                    {formatCurrency(currency, expense.amount)}
-                  </div>
-                  <div className="text-xs text-muted-foreground">
-                    {formatExpenseDate(expense.expenseDate)}
-                  </div>
-                </div>
-                <Button
-                  size="icon"
-                  variant="link"
-                  className="self-center hidden sm:flex"
-                  asChild
-                >
-                  <Link href={`/groups/${groupId}/expenses/${expense.id}/edit`}>
-                    <ChevronRight className="w-4 h-4" />
-                  </Link>
-                </Button>
-              </div>
             ))}
           </div>
         )
       })}
+      {expenses.length < expenseCount &&
+        [0, 1, 2].map((i) => (
+          <div
+            key={i}
+            className="border-t flex justify-between items-center px-6 py-4 text-sm"
+            ref={i === 0 ? ref : undefined}
+          >
+            <div className="flex flex-col gap-2">
+              <Skeleton className="h-4 w-16 rounded-full" />
+              <Skeleton className="h-4 w-32 rounded-full" />
+            </div>
+            <div>
+              <Skeleton className="h-4 w-16 rounded-full" />
+            </div>
+          </div>
+        ))}
     </>
   ) : (
     <p className="px-6 text-sm py-6">

src/app/groups/[groupId]/expenses/export/json/route.ts

@@ -1,4 +1,4 @@
-import { getPrisma } from '@/lib/prisma'
+import { prisma } from '@/lib/prisma'
 import contentDisposition from 'content-disposition'
 import { NextResponse } from 'next/server'
 
@@ -6,7 +6,6 @@ export async function GET(
   req: Request,
   { params: { groupId } }: { params: { groupId: string } },
 ) {
-  const prisma = await getPrisma()
   const group = await prisma.group.findUnique({
     where: { id: groupId },
     select: {

src/app/groups/[groupId]/expenses/page.tsx

@@ -11,7 +11,11 @@ import {
   CardTitle,
 } from '@/components/ui/card'
 import { Skeleton } from '@/components/ui/skeleton'
-import { getCategories, getGroupExpenses } from '@/lib/api'
+import {
+  getCategories,
+  getGroupExpenseCount,
+  getGroupExpenses,
+} from '@/lib/api'
 import { env } from '@/lib/env'
 import { Download, Plus } from 'lucide-react'
 import { Metadata } from 'next'
@@ -91,7 +95,7 @@ export default async function GroupExpensesPage({
               </div>
             ))}
           >
-            <Expenses groupId={groupId} />
+            <Expenses group={group} />
           </Suspense>
         </CardContent>
       </Card>
@@ -101,14 +105,22 @@ export default async function GroupExpensesPage({
   )
 }
 
-async function Expenses({ groupId }: { groupId: string }) {
+type Props = {
-  const group = await cached.getGroup(groupId)
+  group: NonNullable<Awaited<ReturnType<typeof cached.getGroup>>>
-  if (!group) notFound()
+}
-  const expenses = await getGroupExpenses(group.id)
+
+async function Expenses({ group }: Props) {
+  const expenseCount = await getGroupExpenseCount(group.id)
+
+  const expenses = await getGroupExpenses(group.id, {
+    offset: 0,
+    length: 200,
+  })
 
   return (
     <ExpenseList
-      expenses={expenses}
+      expensesFirstPage={expenses}
+      expenseCount={expenseCount}
       groupId={group.id}
       currency={group.currency}
       participants={group.participants}

src/lib/api.ts

@@ -1,4 +1,4 @@
-import { getPrisma } from '@/lib/prisma'
+import { prisma } from '@/lib/prisma'
 import { ExpenseFormValues, GroupFormValues } from '@/lib/schemas'
 import { Expense } from '@prisma/client'
 import { nanoid } from 'nanoid'
@@ -8,7 +8,6 @@ export function randomId() {
 }
 
 export async function createGroup(groupFormValues: GroupFormValues) {
-  const prisma = await getPrisma()
   return prisma.group.create({
     data: {
       id: randomId(),
@@ -42,7 +41,6 @@ export async function createExpense(
       throw new Error(`Invalid participant ID: ${participant}`)
   }
 
-  const prisma = await getPrisma()
   return prisma.expense.create({
     data: {
       id: randomId(),
@@ -78,7 +76,6 @@ export async function createExpense(
 }
 
 export async function deleteExpense(expenseId: string) {
-  const prisma = await getPrisma()
   await prisma.expense.delete({
     where: { id: expenseId },
     include: { paidFor: true, paidBy: true },
@@ -90,15 +87,14 @@ export async function getGroupExpensesParticipants(groupId: string) {
   return Array.from(
     new Set(
       expenses.flatMap((e) => [
-        e.paidById,
+        e.paidBy.id,
-        ...e.paidFor.map((pf) => pf.participantId),
+        ...e.paidFor.map((pf) => pf.participant.id),
       ]),
     ),
   )
 }
 
 export async function getGroups(groupIds: string[]) {
-  const prisma = await getPrisma()
   return (
     await prisma.group.findMany({
       where: { id: { in: groupIds } },
@@ -129,7 +125,6 @@ export async function updateExpense(
       throw new Error(`Invalid participant ID: ${participant}`)
   }
 
-  const prisma = await getPrisma()
   return prisma.expense.update({
     where: { id: expenseId },
     data: {
@@ -198,7 +193,6 @@ export async function updateGroup(
   const existingGroup = await getGroup(groupId)
   if (!existingGroup) throw new Error('Invalid group ID')
 
-  const prisma = await getPrisma()
   return prisma.group.update({
     where: { id: groupId },
     data: {
@@ -230,7 +224,6 @@ export async function updateGroup(
 }
 
 export async function getGroup(groupId: string) {
-  const prisma = await getPrisma()
   return prisma.group.findUnique({
     where: { id: groupId },
     include: { participants: true },
@@ -238,25 +231,43 @@ export async function getGroup(groupId: string) {
 }
 
 export async function getCategories() {
-  const prisma = await getPrisma()
   return prisma.category.findMany()
 }
 
-export async function getGroupExpenses(groupId: string) {
+export async function getGroupExpenses(
-  const prisma = await getPrisma()
+  groupId: string,
+  options?: { offset: number; length: number },
+) {
   return prisma.expense.findMany({
-    where: { groupId },
+    select: {
-    include: {
+      amount: true,
-      paidFor: { include: { participant: true } },
-      paidBy: true,
       category: true,
+      createdAt: true,
+      expenseDate: true,
+      id: true,
+      isReimbursement: true,
+      paidBy: { select: { id: true, name: true } },
+      paidFor: {
+        select: {
+          participant: { select: { id: true, name: true } },
+          shares: true,
+        },
+      },
+      splitMode: true,
+      title: true,
     },
+    where: { groupId },
     orderBy: [{ expenseDate: 'desc' }, { createdAt: 'desc' }],
+    skip: options && options.offset,
+    take: options && options.length,
   })
 }
 
+export async function getGroupExpenseCount(groupId: string) {
+  return prisma.expense.count({ where: { groupId } })
+}
+
 export async function getExpense(groupId: string, expenseId: string) {
-  const prisma = await getPrisma()
   return prisma.expense.findUnique({
     where: { id: expenseId },
     include: { paidBy: true, paidFor: true, category: true, documents: true },

src/lib/balances.ts

@@ -19,7 +19,7 @@ export function getBalances(
   const balances: Balances = {}
 
   for (const expense of expenses) {
-    const paidBy = expense.paidById
+    const paidBy = expense.paidBy.id
     const paidFors = expense.paidFor
 
     if (!balances[paidBy]) balances[paidBy] = { paid: 0, paidFor: 0, total: 0 }
@@ -31,8 +31,8 @@ export function getBalances(
     )
     let remaining = expense.amount
     paidFors.forEach((paidFor, index) => {
-      if (!balances[paidFor.participantId])
+      if (!balances[paidFor.participant.id])
-        balances[paidFor.participantId] = { paid: 0, paidFor: 0, total: 0 }
+        balances[paidFor.participant.id] = { paid: 0, paidFor: 0, total: 0 }
 
       const isLast = index === paidFors.length - 1
 
@@ -47,7 +47,7 @@ export function getBalances(
         ? remaining
         : (expense.amount * shares) / totalShares
       remaining -= dividedAmount
-      balances[paidFor.participantId].paidFor += dividedAmount
+      balances[paidFor.participant.id].paidFor += dividedAmount
     })
   }
 

src/lib/prisma.ts

@@ -1,20 +1,21 @@
 import { PrismaClient } from '@prisma/client'
 
-let prisma: PrismaClient
+declare const global: Global & { prisma?: PrismaClient }
 
-export async function getPrisma() {
+export let p: PrismaClient = undefined as any as PrismaClient
+
+if (typeof window === 'undefined') {
   // await delay(1000)
-  if (!prisma) {
+  if (process.env['NODE_ENV'] === 'production') {
-    if (process.env.NODE_ENV === 'production') {
+    p = new PrismaClient()
-      prisma = new PrismaClient()
+  } else {
-    } else {
+    if (!global.prisma) {
-      if (!(global as any).prisma) {
+      global.prisma = new PrismaClient({
-        ;(global as any).prisma = new PrismaClient({
+        // log: [{ emit: 'stdout', level: 'query' }],
-          // log: [{ emit: 'stdout', level: 'query' }],
+      })
-        })
-      }
-      prisma = (global as any).prisma
     }
+    p = global.prisma
   }
-  return prisma
 }
+
+export const prisma = p

src/lib/totals.ts

@@ -34,7 +34,7 @@ export function getTotalActiveUserShare(
 
     const paidFors = expense.paidFor
     const userPaidFor = paidFors.find(
-      (paidFor) => paidFor.participantId === activeUserId,
+      (paidFor) => paidFor.participant.id === activeUserId,
     )
 
     if (!userPaidFor) {

src/scripts/migrate.ts

@@ -1,6 +1,6 @@
 // @ts-nocheck
 import { randomId } from '@/lib/api'
-import { getPrisma } from '@/lib/prisma'
+import { prisma } from '@/lib/prisma'
 import { Prisma } from '@prisma/client'
 import { Client } from 'pg'
 
@@ -8,8 +8,6 @@ process.env.NODE_TLS_REJECT_UNAUTHORIZED = '0'
 
 async function main() {
   withClient(async (client) => {
-    const prisma = await getPrisma()
-
     // console.log('Deleting all groups…')
     // await prisma.group.deleteMany({})