From 5c86a7a7e869f3d15fa1521ba4cfbf6fcb87f9bb Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Mon, 2 Feb 2026 20:27:37 +0100
Subject: [PATCH 1/7] stop on printSummary function

---
 .prettierrc                |   7 +++
 finance-tracker/app.js     |  37 ++++++++++++
 finance-tracker/data.js    |  77 ++++++++++++++++++++++-
 finance-tracker/finance.js | 121 ++++++++++++++++++++++++++++++++-----
 package-lock.json          |  86 ++++++++++++++++++++++++++
 package.json               |  17 ++++++
 6 files changed, 329 insertions(+), 16 deletions(-)
 create mode 100644 .prettierrc
 create mode 100644 package-lock.json
 create mode 100644 package.json

diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 0000000..eba5a68
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,7 @@
+{
+  "semi": true,
+  "singleQuote": true,
+  "trailingComma": "es5",
+  "printWidth": 80,
+  "tabWidth": 2
+}
diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index 7cfcd07..481d9de 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -1,3 +1,40 @@
 // This is the entrypoint for your application.
 // node app.js
+import {
+  addTransaction,
+  getTotalIncome,
+  getTotalExpenses,
+  getBalance,
+  getTransactionsByCategory,
+  getLargestExpense,
+  printAllTransactions,
+  printSummary,
+} from './finance.js';
+import transactions from './data.js';
 
+addTransaction(
+  'expense',
+  'groceries',
+  98,
+  'Weekly supermarket shopping',
+  '2025-01-25'
+);
+
+const totalIncome = getTotalIncome(transactions);
+const totalExpenses = getTotalExpenses(transactions);
+const balance = getBalance(transactions);
+const transactionsByCategory = getTransactionsByCategory(
+  transactions,
+  'groceries'
+);
+const largestExpenseAmount = getLargestExpense(transactions);
+
+console.log(transactions);
+console.log(totalIncome);
+console.log(totalExpenses);
+console.log(balance);
+console.log(transactionsByCategory);
+console.log(largestExpenseAmount);
+
+printAllTransactions(transactions);
+console.log(printSummary(transactions));
diff --git a/finance-tracker/data.js b/finance-tracker/data.js
index d7863ff..8fd4d0d 100644
--- a/finance-tracker/data.js
+++ b/finance-tracker/data.js
@@ -1,2 +1,77 @@
 // Place here the transaction data array. Use it in your application as needed.
-const transactions = [];
\ No newline at end of file
+const transactions = [
+  {
+    id: 1,
+    type: 'income',
+    category: 'salary',
+    amount: 3000,
+    description: 'Monthly salary',
+    date: '2025-01-15',
+  },
+  {
+    id: 2,
+    type: 'expense',
+    category: 'groceries',
+    amount: 120,
+    description: 'Weekly supermarket shopping',
+    date: '2025-01-16',
+  },
+  {
+    id: 3,
+    type: 'expense',
+    category: 'transport',
+    amount: 45,
+    description: 'Monthly public transport pass',
+    date: '2025-01-17',
+  },
+  {
+    id: 4,
+    type: 'income',
+    category: 'freelance',
+    amount: 600,
+    description: 'Freelance web project',
+    date: '2025-01-20',
+  },
+  {
+    id: 5,
+    type: 'expense',
+    category: 'entertainment',
+    amount: 75,
+    description: 'Concert tickets',
+    date: '2025-01-21',
+  },
+  {
+    id: 6,
+    type: 'expense',
+    category: 'utilities',
+    amount: 150,
+    description: 'Electricity and water bill',
+    date: '2025-01-22',
+  },
+  {
+    id: 7,
+    type: 'income',
+    category: 'gift',
+    amount: 200,
+    description: 'Birthday gift from family',
+    date: '2025-01-23',
+  },
+  {
+    id: 8,
+    type: 'expense',
+    category: 'health',
+    amount: 90,
+    description: 'Doctor appointment',
+    date: '2025-01-24',
+  },
+  {
+    id: 9,
+    type: 'expense',
+    category: 'education',
+    amount: 300,
+    description: 'Online course fee',
+    date: '2025-01-25',
+  },
+];
+
+export default transactions;
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index ac2118f..54ff4ca 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -1,27 +1,118 @@
-function addTransaction(transaction) {
-  // TODO: Implement this function
+import transactions from './data.js';
+import chalk from 'chalk';
+
+export function addTransaction(type, category, amount, description, date) {
+  const newTransaction = {
+    id: transactions.length + 1,
+    type,
+    category,
+    amount,
+    description,
+    date,
+  };
+  transactions.push(newTransaction);
+  return newTransaction;
+}
+
+export function getTotalIncome(transactions) {
+  let totalIncome = 0;
+  for (const transaction of transactions) {
+    if (transaction.type === 'income') {
+      totalIncome += transaction.amount;
+    }
+  }
+  return totalIncome;
+}
+
+export function getTotalExpenses(transactions) {
+  let totalExpenses = 0;
+  for (const transaction of transactions) {
+    if (transaction.type === 'expense') {
+      totalExpenses += transaction.amount;
+    }
+  }
+  return totalExpenses;
 }
 
-function getTotalIncome() {
-  // TODO: Implement this function
+export function getBalance(transactions) {
+  const totalIncome = getTotalIncome(transactions);
+  const totalExpenses = getTotalExpenses(transactions);
+  const balance = totalIncome - totalExpenses;
+
+  return balance;
 }
 
-function getTotalExpenses() {
-  // TODO: Implement this function
+export function getTransactionsByCategory(transactions, category) {
+  let transactionByCategory = [];
+
+  for (const transaction of transactions) {
+    if (transaction.category === category) {
+      transactionByCategory.push(transaction);
+    }
+  }
+
+  return transactionByCategory;
 }
 
-function getBalance() {
-  // TODO: Implement this function
+export function getLargestExpense(transactions) {
+  const expenseTransactions = transactions.filter(
+    (transaction) => transaction.type === 'expense'
+  );
+
+  let largest = expenseTransactions[0].amount;
+
+  for (const transaction of expenseTransactions) {
+    if (transaction.amount > largest) {
+      largest = transaction.amount;
+    }
+  }
+  return largest;
 }
 
-function getTransactionsByCategory(category) {
-  // TODO: Implement this function
+export function printAllTransactions(transactions) {
+  console.log(chalk.bold('All Transactions:'));
+  for (const transaction of transactions) {
+    const { id, type, category, amount, description } = transaction;
+
+    const typeFormat =
+      type === 'income'
+        ? chalk.green(type.toUpperCase())
+        : chalk.red(type.toUpperCase());
+
+    const categoryFormat = getFirstCharacterToUp(chalk.yellow(category));
+
+    const amountFormat = chalk.bold(amount);
+
+    const descriptionFormat = description.toLowerCase();
+
+    const formattingTransaction = `${id}. [${typeFormat}] ${categoryFormat} - €${amountFormat} (${descriptionFormat})`;
+    console.log(formattingTransaction);
+  }
+}
+
+export function printSummary(transactions) {
+  const totalIncome = chalk.green(getTotalIncome(transactions));
+  const totalExpenses = chalk.red(getTotalExpenses(transactions));
+  const balance =
+    getBalance(transactions) >= 0
+      ? chalk.cyan(getBalance(transactions))
+      : chalk.red(getBalance(transactions));
+  const numOfTransactions = chalk.bold(transactions.length);
+  const largestExpense = getLargestExpense(transactions);
+  const largestExpenseForm = chalk.bold(largestExpense.amount);
+  const largestExpenseDescr = getFirstCharacterToUp(largestExpense.description);
+
+  const summary = `📊 FINANCIAL SUMMARY 📊 \nTotal Income: €${totalIncome}\nTotal Expenses: €${totalExpenses}\nCurrent Balance: €${balance}\n\nLargest Expense: ${largestExpenseDescr} (${largestExpenseForm})\nTotal Transactions: ${numOfTransactions}`;
+
+  return summary;
 }
 
-function getLargestExpense() {
-  // TODO: Implement this function
+function getFirstCharacterToUp(word) {
+  return word[0].toUpperCase() + word.slice(1);
 }
 
-function printAllTransactions() {
-  // TODO: Implement this function
-}
\ No newline at end of file
+// if (balance >= 0) {
+//     return chalk.bold.cyan(balance);
+//   } else {
+//     return chalk.bold.red(balance);
+//   }
diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000..52239c6
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,86 @@
+{
+  "name": "c55-core-week-4",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "c55-core-week-4",
+      "version": "1.0.0",
+      "license": "ISC",
+      "dependencies": {
+        "chalk": "^4.1.2"
+      }
+    },
+    "node_modules/ansi-styles": {
+      "version": "4.3.0",
+      "resolved": "https://registry.npmjs.org/ansi-styles/-/ansi-styles-4.3.0.tgz",
+      "integrity": "sha512-zbB9rCJAT1rbjiVDb2hqKFHNYLxgtk8NURxZ3IZwD3F6NtxbXZQCnnSi1Lkx+IDohdPlFp222wVALIheZJQSEg==",
+      "license": "MIT",
+      "dependencies": {
+        "color-convert": "^2.0.1"
+      },
+      "engines": {
+        "node": ">=8"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/ansi-styles?sponsor=1"
+      }
+    },
+    "node_modules/chalk": {
+      "version": "4.1.2",
+      "resolved": "https://registry.npmjs.org/chalk/-/chalk-4.1.2.tgz",
+      "integrity": "sha512-oKnbhFyRIXpUuez8iBMmyEa4nbj4IOQyuhc/wy9kY7/WVPcwIO9VA668Pu8RkO7+0G76SLROeyw9CpQ061i4mA==",
+      "license": "MIT",
+      "dependencies": {
+        "ansi-styles": "^4.1.0",
+        "supports-color": "^7.1.0"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "funding": {
+        "url": "https://github.com/chalk/chalk?sponsor=1"
+      }
+    },
+    "node_modules/color-convert": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
+      "integrity": "sha512-RRECPsj7iu/xb5oKYcsFHSppFNnsj/52OVTRKb4zP5onXwVF3zVmmToNcOfGC+CRDpfK/U584fMg38ZHCaElKQ==",
+      "license": "MIT",
+      "dependencies": {
+        "color-name": "~1.1.4"
+      },
+      "engines": {
+        "node": ">=7.0.0"
+      }
+    },
+    "node_modules/color-name": {
+      "version": "1.1.4",
+      "resolved": "https://registry.npmjs.org/color-name/-/color-name-1.1.4.tgz",
+      "integrity": "sha512-dOy+3AuW3a2wNbZHIuMZpTcgjGuLU/uBL/ubcZF9OXbDo8ff4O8yVp5Bf0efS8uEoYo5q4Fx7dY9OgQGXgAsQA==",
+      "license": "MIT"
+    },
+    "node_modules/has-flag": {
+      "version": "4.0.0",
+      "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-4.0.0.tgz",
+      "integrity": "sha512-EykJT/Q1KjTWctppgIAgfSO0tKVuZUjhgMr17kqTumMl6Afv3EISleU7qZUzoXDFTAHTDC4NOoG/ZxU3EvlMPQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/supports-color": {
+      "version": "7.2.0",
+      "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-7.2.0.tgz",
+      "integrity": "sha512-qpCAvRl9stuOHveKsn7HncJRvv501qIacKzQlO/+Lwxc9+0q2wLyv4Dfvt80/DPn2pqOBsJdDiogXGR9+OvwRw==",
+      "license": "MIT",
+      "dependencies": {
+        "has-flag": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    }
+  }
+}
diff --git a/package.json b/package.json
new file mode 100644
index 0000000..3134228
--- /dev/null
+++ b/package.json
@@ -0,0 +1,17 @@
+{
+  "name": "c55-core-week-4",
+  "version": "1.0.0",
+  "description": "The week 4 assignment for the HackYourFuture Core program can be found at the following link: https://hub.hackyourfuture.nl/core-program-week-4-assignment",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1",
+    "start": "node finance-tracker/app.js"
+  },
+  "type": "module",
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "chalk": "^4.1.2"
+  }
+}

From e64a0db0678b3b82fe0a0c4197ae4aef0461c277 Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Tue, 3 Feb 2026 11:55:52 +0100
Subject: [PATCH 2/7] Completed the main part of the assignment

---
 finance-tracker/app.js     | 40 +++++++-----------------
 finance-tracker/finance.js | 64 ++++++++++++++++++++++++--------------
 2 files changed, 51 insertions(+), 53 deletions(-)

diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index 481d9de..48b328f 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -2,39 +2,21 @@
 // node app.js
 import {
   addTransaction,
-  getTotalIncome,
-  getTotalExpenses,
-  getBalance,
   getTransactionsByCategory,
-  getLargestExpense,
-  printAllTransactions,
-  printSummary,
+  printGeneralReport,
 } from './finance.js';
 import transactions from './data.js';
 
-addTransaction(
-  'expense',
-  'groceries',
-  98,
-  'Weekly supermarket shopping',
-  '2025-01-25'
+console.log(
+  addTransaction(
+    'expense',
+    'groceries',
+    98,
+    'Weekly supermarket shopping',
+    '2025-01-25'
+  )
 );
 
-const totalIncome = getTotalIncome(transactions);
-const totalExpenses = getTotalExpenses(transactions);
-const balance = getBalance(transactions);
-const transactionsByCategory = getTransactionsByCategory(
-  transactions,
-  'groceries'
-);
-const largestExpenseAmount = getLargestExpense(transactions);
-
-console.log(transactions);
-console.log(totalIncome);
-console.log(totalExpenses);
-console.log(balance);
-console.log(transactionsByCategory);
-console.log(largestExpenseAmount);
+console.log(getTransactionsByCategory(transactions, 'groceries'));
 
-printAllTransactions(transactions);
-console.log(printSummary(transactions));
+console.log(printGeneralReport(transactions));
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index 54ff4ca..ae707f3 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -10,8 +10,14 @@ export function addTransaction(type, category, amount, description, date) {
     description,
     date,
   };
+
+  // The assignment requires using the spread operator when adding a transaction. In this task, mutating the existing array with push() feels more suitable, and that is the approach I would normally use if there were no requirement. To satisfy the task while keeping the logic I prefer, I include both: spread for the assignment, and push() for the actual update.
+
+  const updated = [...transactions, newTransaction];
+
   transactions.push(newTransaction);
-  return newTransaction;
+
+  return updated;
 }
 
 export function getTotalIncome(transactions) {
@@ -59,60 +65,70 @@ export function getLargestExpense(transactions) {
     (transaction) => transaction.type === 'expense'
   );
 
-  let largest = expenseTransactions[0].amount;
+  let largest = expenseTransactions[0];
 
   for (const transaction of expenseTransactions) {
-    if (transaction.amount > largest) {
-      largest = transaction.amount;
+    if (transaction.amount > largest.amount) {
+      largest = transaction;
     }
   }
+
   return largest;
 }
 
 export function printAllTransactions(transactions) {
-  console.log(chalk.bold('All Transactions:'));
+  let output = chalk.bold('All Transactions:\n');
+
   for (const transaction of transactions) {
     const { id, type, category, amount, description } = transaction;
 
+    //formatting values by task requirements with chalk
     const typeFormat =
       type === 'income'
         ? chalk.green(type.toUpperCase())
         : chalk.red(type.toUpperCase());
 
     const categoryFormat = getFirstCharacterToUp(chalk.yellow(category));
-
     const amountFormat = chalk.bold(amount);
-
     const descriptionFormat = description.toLowerCase();
 
-    const formattingTransaction = `${id}. [${typeFormat}] ${categoryFormat} - €${amountFormat} (${descriptionFormat})`;
-    console.log(formattingTransaction);
+    //collect all in one line for each element
+    const line = `${id}. [${typeFormat}] ${categoryFormat} - €${amountFormat} (${descriptionFormat})`;
+
+    output += `${line}\n`;
   }
+
+  return output;
 }
 
 export function printSummary(transactions) {
-  const totalIncome = chalk.green(getTotalIncome(transactions));
-  const totalExpenses = chalk.red(getTotalExpenses(transactions));
+  //formatting values by task requirements with chalk
+  const totalIncome = chalk.bold.green(getTotalIncome(transactions));
+  const totalExpenses = chalk.bold.red(getTotalExpenses(transactions));
+  const numOfTransactions = chalk.bold(transactions.length);
+
   const balance =
     getBalance(transactions) >= 0
-      ? chalk.cyan(getBalance(transactions))
-      : chalk.red(getBalance(transactions));
-  const numOfTransactions = chalk.bold(transactions.length);
-  const largestExpense = getLargestExpense(transactions);
-  const largestExpenseForm = chalk.bold(largestExpense.amount);
-  const largestExpenseDescr = getFirstCharacterToUp(largestExpense.description);
+      ? chalk.bold.cyan(getBalance(transactions))
+      : chalk.bold.red(getBalance(transactions));
+
+  const { amount, description } = getLargestExpense(transactions);
+  const largestExpense = chalk.bold(amount);
 
-  const summary = `📊 FINANCIAL SUMMARY 📊 \nTotal Income: €${totalIncome}\nTotal Expenses: €${totalExpenses}\nCurrent Balance: €${balance}\n\nLargest Expense: ${largestExpenseDescr} (${largestExpenseForm})\nTotal Transactions: ${numOfTransactions}`;
+  //collect summary
+  const summary = `📊 ${chalk.bold('financial summary'.toUpperCase())} 📊 \nTotal Income: €${totalIncome}\nTotal Expenses: €${totalExpenses}\nCurrent Balance: €${balance}\n\nLargest Expense: ${description} (€${largestExpense})\nTotal Transactions: ${numOfTransactions}`;
 
   return summary;
 }
 
+export function printGeneralReport(transactions) {
+  const allTransactions = printAllTransactions(transactions);
+  const summary = printSummary(transactions);
+
+  return `💰 ${chalk.bold('personal finance tracker'.toUpperCase())} 💰\n\n${allTransactions}\n${summary}`;
+}
+
 function getFirstCharacterToUp(word) {
+  if (!word) return '';
   return word[0].toUpperCase() + word.slice(1);
 }
-
-// if (balance >= 0) {
-//     return chalk.bold.cyan(balance);
-//   } else {
-//     return chalk.bold.red(balance);
-//   }

From 18de2047bb4ef2d031a34df4e81fd3daa8368436 Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Tue, 3 Feb 2026 16:18:17 +0100
Subject: [PATCH 3/7] wrote searchTransactionsByDate and
 groupTransactionByMonth functions

---
 finance-tracker/app.js     | 15 +++++++++++---
 finance-tracker/data.js    |  4 ++--
 finance-tracker/finance.js | 42 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index 48b328f..df553d1 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -3,7 +3,9 @@
 import {
   addTransaction,
   getTransactionsByCategory,
+  groupTransactionByMonth,
   printGeneralReport,
+  searchTransactionsByDate,
 } from './finance.js';
 import transactions from './data.js';
 
@@ -13,10 +15,17 @@ console.log(
     'groceries',
     98,
     'Weekly supermarket shopping',
-    '2025-01-25'
+    '2026-01-25'
   )
 );
 
-console.log(getTransactionsByCategory(transactions, 'groceries'));
+// console.log(getTransactionsByCategory(transactions, 'groceries'));
 
-console.log(printGeneralReport(transactions));
+// console.log(printGeneralReport(transactions));
+
+//Bonus Challenges output
+// console.log(searchTransactionsByDate(transactions, '2025-01-22', '2025-01-25'));
+
+// Node.js collapses nested objects inside arrays and prints them as [Object]. To see the full structure, I use JSON.stringify(). The second argument (null)means no custom replacer, and the third argument (2) adds indentation for readability.
+
+console.log(JSON.stringify(groupTransactionByMonth(transactions), null, 2));
diff --git a/finance-tracker/data.js b/finance-tracker/data.js
index 8fd4d0d..19e8c18 100644
--- a/finance-tracker/data.js
+++ b/finance-tracker/data.js
@@ -62,7 +62,7 @@ const transactions = [
     category: 'health',
     amount: 90,
     description: 'Doctor appointment',
-    date: '2025-01-24',
+    date: '2025-02-24',
   },
   {
     id: 9,
@@ -70,7 +70,7 @@ const transactions = [
     category: 'education',
     amount: 300,
     description: 'Online course fee',
-    date: '2025-01-25',
+    date: '2025-03-25',
   },
 ];
 
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index ae707f3..a896d49 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -132,3 +132,45 @@ function getFirstCharacterToUp(word) {
   if (!word) return '';
   return word[0].toUpperCase() + word.slice(1);
 }
+
+//Bonus Challenges functions
+
+export function searchTransactionsByDate(transactions, startDate, endDate) {
+  const sorted = transactions
+    .slice()
+    .sort((a, b) => a.date.localeCompare(b.date));
+
+  const startIndex = sorted.findIndex(
+    (transaction) => transaction.date >= startDate
+  );
+  const endIndex = sorted.findIndex(
+    (transaction) => transaction.date > endDate
+  );
+
+  const range = sorted.slice(
+    startIndex,
+    endIndex === -1 ? sorted.length : endIndex
+  );
+
+  return range;
+}
+
+export function groupTransactionByMonth(transactions) {
+  let groupedTransactions = {};
+
+  for (const transaction of transactions) {
+    const [year, month] = transaction.date.split('-');
+
+    if (!groupedTransactions[year]) {
+      groupedTransactions[year] = {};
+    }
+
+    if (!groupedTransactions[year][month]) {
+      groupedTransactions[year][month] = [];
+    }
+
+    groupedTransactions[year][month].push(transaction);
+  }
+
+  return groupedTransactions;
+}

From 6185a5301f03d949bd4bacb9d04c973fc6bf9675 Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Tue, 3 Feb 2026 16:57:05 +0100
Subject: [PATCH 4/7] added function calculateAverageExpensesPerCategory

---
 finance-tracker/app.js     |  7 +++++--
 finance-tracker/data.js    |  8 ++++++++
 finance-tracker/finance.js | 28 ++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index df553d1..a2883ac 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -2,6 +2,7 @@
 // node app.js
 import {
   addTransaction,
+  calculateAverageExpensesPerCategory,
   getTransactionsByCategory,
   groupTransactionByMonth,
   printGeneralReport,
@@ -24,8 +25,10 @@ console.log(
 // console.log(printGeneralReport(transactions));
 
 //Bonus Challenges output
-// console.log(searchTransactionsByDate(transactions, '2025-01-22', '2025-01-25'));
+// console.log(searchTransactionsByDate(transactions, '2025-01-22', '2025-02-24'));
 
 // Node.js collapses nested objects inside arrays and prints them as [Object]. To see the full structure, I use JSON.stringify(). The second argument (null)means no custom replacer, and the third argument (2) adds indentation for readability.
 
-console.log(JSON.stringify(groupTransactionByMonth(transactions), null, 2));
+// console.log(JSON.stringify(groupTransactionByMonth(transactions), null, 2));
+
+// console.log(calculateAverageExpensesPerCategory(transactions));
diff --git a/finance-tracker/data.js b/finance-tracker/data.js
index 19e8c18..f0febec 100644
--- a/finance-tracker/data.js
+++ b/finance-tracker/data.js
@@ -70,6 +70,14 @@ const transactions = [
     category: 'education',
     amount: 300,
     description: 'Online course fee',
+    date: '2025-03-15',
+  },
+  {
+    id: 10,
+    type: 'expense',
+    category: 'education',
+    amount: 135,
+    description: 'Online course fee',
     date: '2025-03-25',
   },
 ];
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index a896d49..b9caba7 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -174,3 +174,31 @@ export function groupTransactionByMonth(transactions) {
 
   return groupedTransactions;
 }
+
+export function calculateAverageExpensesPerCategory(transactions) {
+  const expenses = transactions.filter(
+    (transaction) => transaction.type === 'expense'
+  );
+
+  let expenseCategories = {};
+
+  for (const transaction of expenses) {
+    const { category, amount } = transaction;
+
+    if (!expenseCategories[category]) {
+      expenseCategories[category] = { total: 0, count: 0 };
+    }
+
+    expenseCategories[category].total += amount;
+    expenseCategories[category].count += 1;
+  }
+
+  let averages = {};
+
+  for (const category in expenseCategories) {
+    const { total, count } = expenseCategories[category];
+    averages[category] = total / count;
+  }
+
+  return averages;
+}

From 4bef68115a1fcdb44292cda723b33e270e7a2d2b Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Wed, 4 Feb 2026 13:08:42 +0100
Subject: [PATCH 5/7] done bonus challenge tasks

---
 finance-tracker/app.js     |  54 ++++++++++++-----
 finance-tracker/data.js    | 120 +++++++++++++++++++++++++++++++++++++
 finance-tracker/finance.js | 108 ++++++++++++++++++++++++++++-----
 3 files changed, 254 insertions(+), 28 deletions(-)

diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index a2883ac..f8c33ad 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -3,32 +3,58 @@
 import {
   addTransaction,
   calculateAverageExpensesPerCategory,
+  findConsecutiveExpensiveMonth,
   getTransactionsByCategory,
   groupTransactionByMonth,
   printGeneralReport,
-  searchTransactionsByDate,
+  removeTransactions,
+  searchTransactionsByDateRange,
 } from './finance.js';
 import transactions from './data.js';
 
-console.log(
-  addTransaction(
-    'expense',
-    'groceries',
-    98,
-    'Weekly supermarket shopping',
-    '2026-01-25'
-  )
+const newTransaction = addTransaction(
+  'expense',
+  'groceries',
+  98,
+  'Weekly supermarket shopping',
+  '2026-01-25'
+);
+
+const transactionByCategory = getTransactionsByCategory(
+  transactions,
+  'groceries'
 );
 
-// console.log(getTransactionsByCategory(transactions, 'groceries'));
+const financeReport = printGeneralReport(transactions);
 
-// console.log(printGeneralReport(transactions));
+console.log(newTransaction, transactionByCategory, financeReport);
 
 //Bonus Challenges output
-// console.log(searchTransactionsByDate(transactions, '2025-01-22', '2025-02-24'));
+const transactionsByDateRange = searchTransactionsByDateRange(
+  transactions,
+  '2025-01-22',
+  '2025-02-24'
+);
 
 // Node.js collapses nested objects inside arrays and prints them as [Object]. To see the full structure, I use JSON.stringify(). The second argument (null)means no custom replacer, and the third argument (2) adds indentation for readability.
 
-// console.log(JSON.stringify(groupTransactionByMonth(transactions), null, 2));
+const transactionsGroupByMonth = JSON.stringify(
+  groupTransactionByMonth(transactions),
+  null,
+  2
+);
+
+const averageExpensesPerCategory =
+  calculateAverageExpensesPerCategory(transactions);
+
+const arrayWithoutRemoveTransaction = removeTransactions(transactions, 3);
+
+const consecutiveExpensiveMonths = findConsecutiveExpensiveMonth(transactions);
 
-// console.log(calculateAverageExpensesPerCategory(transactions));
+console.log(
+  transactionsByDateRange,
+  transactionsGroupByMonth,
+  averageExpensesPerCategory,
+  arrayWithoutRemoveTransaction,
+  consecutiveExpensiveMonths
+);
diff --git a/finance-tracker/data.js b/finance-tracker/data.js
index f0febec..5893f51 100644
--- a/finance-tracker/data.js
+++ b/finance-tracker/data.js
@@ -80,6 +80,126 @@ const transactions = [
     description: 'Online course fee',
     date: '2025-03-25',
   },
+  {
+    id: 11,
+    type: 'expense',
+    category: 'groceries',
+    amount: 95,
+    description: 'Weekly supermarket shopping',
+    date: '2025-02-02',
+  },
+  {
+    id: 12,
+    type: 'expense',
+    category: 'transport',
+    amount: 45,
+    description: 'Monthly public transport pass',
+    date: '2025-02-10',
+  },
+  {
+    id: 13,
+    type: 'income',
+    category: 'salary',
+    amount: 3000,
+    description: 'Monthly salary',
+    date: '2025-02-15',
+  },
+  {
+    id: 14,
+    type: 'expense',
+    category: 'entertainment',
+    amount: 60,
+    description: 'Cinema tickets',
+    date: '2025-02-18',
+  },
+  {
+    id: 15,
+    type: 'expense',
+    category: 'utilities',
+    amount: 155,
+    description: 'Electricity and water bill',
+    date: '2025-02-22',
+  },
+  {
+    id: 16,
+    type: 'income',
+    category: 'freelance',
+    amount: 400,
+    description: 'Small freelance task',
+    date: '2025-03-05',
+  },
+  {
+    id: 17,
+    type: 'expense',
+    category: 'health',
+    amount: 120,
+    description: 'Pharmacy purchase',
+    date: '2025-03-12',
+  },
+  {
+    id: 18,
+    type: 'expense',
+    category: 'groceries',
+    amount: 130,
+    description: 'Weekly supermarket shopping',
+    date: '2025-03-20',
+  },
+  {
+    id: 19,
+    type: 'expense',
+    category: 'transport',
+    amount: 50,
+    description: 'Taxi ride',
+    date: '2025-03-28',
+  },
+  {
+    id: 20,
+    type: 'income',
+    category: 'bonus',
+    amount: 500,
+    description: 'Quarterly bonus',
+    date: '2025-04-01',
+  },
+  {
+    id: 21,
+    type: 'expense',
+    category: 'education',
+    amount: 200,
+    description: 'Books and materials',
+    date: '2025-04-03',
+  },
+  {
+    id: 22,
+    type: 'expense',
+    category: 'entertainment',
+    amount: 90,
+    description: 'Theatre tickets',
+    date: '2025-04-10',
+  },
+  {
+    id: 23,
+    type: 'expense',
+    category: 'utilities',
+    amount: 160,
+    description: 'Electricity and water bill',
+    date: '2025-04-15',
+  },
+  {
+    id: 24,
+    type: 'expense',
+    category: 'health',
+    amount: 80,
+    description: 'Dentist visit',
+    date: '2025-04-20',
+  },
+  {
+    id: 25,
+    type: 'income',
+    category: 'salary',
+    amount: 3100,
+    description: 'Monthly salary',
+    date: '2025-03-15',
+  },
 ];
 
 export default transactions;
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index b9caba7..dc0ac5b 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -17,7 +17,7 @@ export function addTransaction(type, category, amount, description, date) {
 
   transactions.push(newTransaction);
 
-  return updated;
+  return newTransaction;
 }
 
 export function getTotalIncome(transactions) {
@@ -61,9 +61,8 @@ export function getTransactionsByCategory(transactions, category) {
 }
 
 export function getLargestExpense(transactions) {
-  const expenseTransactions = transactions.filter(
-    (transaction) => transaction.type === 'expense'
-  );
+  //I moved the logic for filtering "expense" transactions into a separate function, because this code is reused in several bonus tasks.
+  const expenseTransactions = getExpenseTransactions(transactions);
 
   let largest = expenseTransactions[0];
 
@@ -128,14 +127,14 @@ export function printGeneralReport(transactions) {
   return `💰 ${chalk.bold('personal finance tracker'.toUpperCase())} 💰\n\n${allTransactions}\n${summary}`;
 }
 
-function getFirstCharacterToUp(word) {
-  if (!word) return '';
-  return word[0].toUpperCase() + word.slice(1);
-}
-
 //Bonus Challenges functions
 
-export function searchTransactionsByDate(transactions, startDate, endDate) {
+//Search transactions by date range using slice
+export function searchTransactionsByDateRange(
+  transactions,
+  startDate,
+  endDate
+) {
   const sorted = transactions
     .slice()
     .sort((a, b) => a.date.localeCompare(b.date));
@@ -155,6 +154,7 @@ export function searchTransactionsByDate(transactions, startDate, endDate) {
   return range;
 }
 
+//Group transactions by month using nested objects
 export function groupTransactionByMonth(transactions) {
   let groupedTransactions = {};
 
@@ -175,10 +175,9 @@ export function groupTransactionByMonth(transactions) {
   return groupedTransactions;
 }
 
+//Calculate average expense per category
 export function calculateAverageExpensesPerCategory(transactions) {
-  const expenses = transactions.filter(
-    (transaction) => transaction.type === 'expense'
-  );
+  const expenses = getExpenseTransactions(transactions);
 
   let expenseCategories = {};
 
@@ -197,8 +196,89 @@ export function calculateAverageExpensesPerCategory(transactions) {
 
   for (const category in expenseCategories) {
     const { total, count } = expenseCategories[category];
-    averages[category] = total / count;
+    averages[category] = Number((total / count).toFixed(2));
   }
 
   return averages;
 }
+
+//Add ability to remove transactions by id
+export function removeTransactions(transactions, id) {
+  const newTransactions = transactions.filter(
+    (transaction) => transaction.id !== id
+  );
+  return newTransactions;
+}
+
+//Create a function that finds consecutive expensive months (use while loop)
+//Use multi-line commenting to explain your most complex function
+
+/* This function returns a list of months where expenses increase consecutively.
+  It follows these steps:
+
+  1. It filters all transactions using getExpenseTransactions() to keep only those with type "expense".
+
+  2. It creates an empty object (monthlyTotal) to store total expenses per month.
+
+  3. It iterates through all expense transactions. For each one:
+    - extracts the date and amount,
+    - derives the month in "YYYY-MM" format using slice(),
+    - initializes monthlyTotal[month] to 0 if it doesn't exist yet,
+    - adds the transaction amount to that month's total.
+
+  4. It collects all month keys from monthlyTotal and sorts them to ensure chronological comparison.
+
+  5. It prepares a while loop index (i) and an empty result array.
+
+  6. Using a while loop, it compares each month with the next one.
+    If the next month has a higher total expense than the current month:
+      - it adds the current month to the result (only if not already included),
+      - it always adds the next month.
+    This builds a sequence of months with increasing expenses.
+
+  7. After the loop finishes, it returns the result array containing all months that form consecutive increasing expense periods. */
+
+export function findConsecutiveExpensiveMonth(transactions) {
+  const expenses = getExpenseTransactions(transactions);
+  const monthlyTotal = {};
+
+  for (const transaction of expenses) {
+    const { date, amount } = transaction;
+    const month = date.slice(0, 7);
+
+    if (!monthlyTotal[month]) monthlyTotal[month] = 0;
+    monthlyTotal[month] += amount;
+  }
+
+  const months = Object.keys(monthlyTotal).sort();
+
+  let i = 0;
+  const result = [];
+
+  while (i < months.length - 1) {
+    const current = months[i];
+    const next = months[i + 1];
+
+    if (monthlyTotal[current] < monthlyTotal[next]) {
+      if (!result.includes(current)) result.push(current);
+      result.push(next);
+    }
+    i++;
+  }
+
+  return result;
+}
+
+//reused functions
+
+function getExpenseTransactions(transactions) {
+  const expenses = transactions.filter(
+    (transaction) => transaction.type === 'expense'
+  );
+  return expenses;
+}
+
+function getFirstCharacterToUp(word) {
+  if (!word) return '';
+  return word[0].toUpperCase() + word.slice(1);
+}

From 3d93d31cd66bd2dbc338174cd8e2e6b87cf23bc4 Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Wed, 4 Feb 2026 14:05:19 +0100
Subject: [PATCH 6/7] change addTransaction function

---
 finance-tracker/app.js     | 29 +++++++++++++++--------------
 finance-tracker/finance.js | 16 ++--------------
 2 files changed, 17 insertions(+), 28 deletions(-)

diff --git a/finance-tracker/app.js b/finance-tracker/app.js
index f8c33ad..f9c9c24 100644
--- a/finance-tracker/app.js
+++ b/finance-tracker/app.js
@@ -12,22 +12,23 @@ import {
 } from './finance.js';
 import transactions from './data.js';
 
-const newTransaction = addTransaction(
-  'expense',
-  'groceries',
-  98,
-  'Weekly supermarket shopping',
-  '2026-01-25'
-);
-
-const transactionByCategory = getTransactionsByCategory(
+const newTransaction = addTransaction({
+  id: 31,
+  type: 'expense',
+  category: 'groceries',
+  amount: 98,
+  description: 'Weekly supermarket shopping',
+  date: '2026-01-25',
+});
+
+const transactionsByCategory = getTransactionsByCategory(
   transactions,
   'groceries'
 );
 
 const financeReport = printGeneralReport(transactions);
 
-console.log(newTransaction, transactionByCategory, financeReport);
+console.log(newTransaction, transactionsByCategory, financeReport);
 
 //Bonus Challenges output
 const transactionsByDateRange = searchTransactionsByDateRange(
@@ -38,7 +39,7 @@ const transactionsByDateRange = searchTransactionsByDateRange(
 
 // Node.js collapses nested objects inside arrays and prints them as [Object]. To see the full structure, I use JSON.stringify(). The second argument (null)means no custom replacer, and the third argument (2) adds indentation for readability.
 
-const transactionsGroupByMonth = JSON.stringify(
+const transactionsGroupedByMonth = JSON.stringify(
   groupTransactionByMonth(transactions),
   null,
   2
@@ -47,14 +48,14 @@ const transactionsGroupByMonth = JSON.stringify(
 const averageExpensesPerCategory =
   calculateAverageExpensesPerCategory(transactions);
 
-const arrayWithoutRemoveTransaction = removeTransactions(transactions, 3);
+const remainingTransactions = removeTransactions(transactions, 3);
 
 const consecutiveExpensiveMonths = findConsecutiveExpensiveMonth(transactions);
 
 console.log(
   transactionsByDateRange,
-  transactionsGroupByMonth,
+  transactionsGroupedByMonth,
   averageExpensesPerCategory,
-  arrayWithoutRemoveTransaction,
+  remainingTransactions,
   consecutiveExpensiveMonths
 );
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index dc0ac5b..0a60556 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -1,20 +1,8 @@
 import transactions from './data.js';
 import chalk from 'chalk';
 
-export function addTransaction(type, category, amount, description, date) {
-  const newTransaction = {
-    id: transactions.length + 1,
-    type,
-    category,
-    amount,
-    description,
-    date,
-  };
-
-  // The assignment requires using the spread operator when adding a transaction. In this task, mutating the existing array with push() feels more suitable, and that is the approach I would normally use if there were no requirement. To satisfy the task while keeping the logic I prefer, I include both: spread for the assignment, and push() for the actual update.
-
-  const updated = [...transactions, newTransaction];
-
+export function addTransaction(transaction) {
+  const newTransaction = { ...transaction };
   transactions.push(newTransaction);
 
   return newTransaction;

From 149859f3ad94b6c224ddc78c34e97aa50b766f8e Mon Sep 17 00:00:00 2001
From: Yana Pechenenko <pechenenko.ya@gmail.com>
Date: Sat, 28 Feb 2026 17:46:41 +0100
Subject: [PATCH 7/7] Add changes after review

---
 .hyf/README.md             |  2 +-
 .hyf/score.example.json    |  2 +-
 .prettierignore            |  1 +
 README.md                  |  6 ++++--
 finance-tracker/finance.js |  7 ++-----
 package-lock.json          | 19 +++++++++++++++++++
 package.json               |  6 +++++-
 7 files changed, 33 insertions(+), 10 deletions(-)
 create mode 100644 .prettierignore

diff --git a/.hyf/README.md b/.hyf/README.md
index 38f1a4d..7475329 100644
--- a/.hyf/README.md
+++ b/.hyf/README.md
@@ -1,6 +1,7 @@
 # Auto grade tool
 
 ## How it works
+
 1. The auto grade tool runs the `test.sh` script located in this directory.
 2. `test.sh` should write to a file named `score.json` with following JSON format:
    ```json
@@ -12,4 +13,3 @@
    ```
    All scores are out of 100. It is up to the assignment to determine how to calculate the score.
 3. The auto grade runs via a github action on PR creation and updates the PR with the score.
-
diff --git a/.hyf/score.example.json b/.hyf/score.example.json
index 8d931f5..e048aec 100644
--- a/.hyf/score.example.json
+++ b/.hyf/score.example.json
@@ -2,4 +2,4 @@
   "score": 75,
   "pass": true,
   "passingScore": 50
-}
\ No newline at end of file
+}
diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..b512c09
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1 @@
+node_modules
\ No newline at end of file
diff --git a/README.md b/README.md
index 2de48c5..d410295 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,9 @@
 # Core program week 4 assignment
+
 The week 4 assignment for the HackYourFuture Core program can be found at the following link: https://hub.hackyourfuture.nl/core-program-week-4-assignment
 
 ## Implementation Instructions
-- Implement the requirements in the `finance-tracker` folder. 
-- Use the existing file structure. 
+
+- Implement the requirements in the `finance-tracker` folder.
+- Use the existing file structure.
 - You are allowed to create additional files if needed.
diff --git a/finance-tracker/finance.js b/finance-tracker/finance.js
index 0a60556..92bfd5e 100644
--- a/finance-tracker/finance.js
+++ b/finance-tracker/finance.js
@@ -94,16 +94,13 @@ export function printSummary(transactions) {
   const totalExpenses = chalk.bold.red(getTotalExpenses(transactions));
   const numOfTransactions = chalk.bold(transactions.length);
 
-  const balance =
-    getBalance(transactions) >= 0
-      ? chalk.bold.cyan(getBalance(transactions))
-      : chalk.bold.red(getBalance(transactions));
+  const balance = getBalance(transactions);
 
   const { amount, description } = getLargestExpense(transactions);
   const largestExpense = chalk.bold(amount);
 
   //collect summary
-  const summary = `📊 ${chalk.bold('financial summary'.toUpperCase())} 📊 \nTotal Income: €${totalIncome}\nTotal Expenses: €${totalExpenses}\nCurrent Balance: €${balance}\n\nLargest Expense: ${description} (€${largestExpense})\nTotal Transactions: ${numOfTransactions}`;
+  const summary = `📊 ${chalk.bold('financial summary'.toUpperCase())} 📊 \nTotal Income: €${totalIncome}\nTotal Expenses: €${totalExpenses}\nCurrent Balance: €${balance > 0 ? chalk.bold.cyan(balance) : chalk.bold.red(balance)}\n\nLargest Expense: ${description} (€${largestExpense})\nTotal Transactions: ${numOfTransactions}`;
 
   return summary;
 }
diff --git a/package-lock.json b/package-lock.json
index 52239c6..228d484 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10,6 +10,9 @@
       "license": "ISC",
       "dependencies": {
         "chalk": "^4.1.2"
+      },
+      "devDependencies": {
+        "prettier": "^3.8.1"
       }
     },
     "node_modules/ansi-styles": {
@@ -70,6 +73,22 @@
         "node": ">=8"
       }
     },
+    "node_modules/prettier": {
+      "version": "3.8.1",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.8.1.tgz",
+      "integrity": "sha512-UOnG6LftzbdaHZcKoPFtOcCKztrQ57WkHDeRD9t/PTQtmT0NHSeWWepj6pS0z/N7+08BHFDQVUrfmfMRcZwbMg==",
+      "dev": true,
+      "license": "MIT",
+      "bin": {
+        "prettier": "bin/prettier.cjs"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier?sponsor=1"
+      }
+    },
     "node_modules/supports-color": {
       "version": "7.2.0",
       "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-7.2.0.tgz",
diff --git a/package.json b/package.json
index 3134228..b2ed093 100644
--- a/package.json
+++ b/package.json
@@ -5,7 +5,8 @@
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
-    "start": "node finance-tracker/app.js"
+    "start": "node finance-tracker/app.js",
+    "format": "prettier --write ."
   },
   "type": "module",
   "keywords": [],
@@ -13,5 +14,8 @@
   "license": "ISC",
   "dependencies": {
     "chalk": "^4.1.2"
+  },
+  "devDependencies": {
+    "prettier": "^3.8.1"
   }
 }