python-by-example/projects/02_expense_tracker/solution.py

"""
================================================================================
Project 02: Expense Tracker
Difficulty: 🟡 Intermediate
================================================================================

A command-line expense tracker that lets users add, view, filter, and analyze
their expenses. Data is persisted to a JSON file between sessions.

Concepts Used:
- Dictionaries and Lists
- File I/O (JSON)
- Functions with parameters
- String formatting
- datetime module
- Data filtering and aggregation

================================================================================
"""

import json
import os
from datetime import datetime


# -----------------------------------------------------------------------------
# Constants
# -----------------------------------------------------------------------------

DATA_FILE = os.path.join(os.path.dirname(__file__), "expenses.json")

CATEGORIES = {
    "food": "🍔",
    "transport": "🚗",
    "entertainment": "🎬",
    "bills": "📄",
    "other": "📦",
}


# -----------------------------------------------------------------------------
# Data Management
# -----------------------------------------------------------------------------

def load_expenses() -> list:
    """Load expenses from the JSON file."""
    if os.path.exists(DATA_FILE):
        with open(DATA_FILE, "r") as f:
            return json.load(f)
    return []


def save_expenses(expenses: list) -> None:
    """Save expenses to the JSON file."""
    with open(DATA_FILE, "w") as f:
        json.dump(expenses, f, indent=2)


def generate_id(expenses: list) -> int:
    """Generate a unique ID for a new expense."""
    if not expenses:
        return 1
    return max(exp["id"] for exp in expenses) + 1


# -----------------------------------------------------------------------------
# Core Features
# -----------------------------------------------------------------------------

def add_expense(expenses: list) -> None:
    """Add a new expense."""
    description = input("  Enter description: ").strip()
    if not description:
        print("  ❌ Description cannot be empty.")
        return

    try:
        amount = float(input("  Enter amount: $"))
        if amount <= 0:
            print("  ❌ Amount must be positive.")
            return
    except ValueError:
        print("  ❌ Invalid amount.")
        return

    print(f"  Categories: {', '.join(CATEGORIES.keys())}")
    category = input("  Enter category: ").strip().lower()
    if category not in CATEGORIES:
        print(f"  ⚠️  Unknown category. Defaulting to 'other'.")
        category = "other"

    expense = {
        "id": generate_id(expenses),
        "description": description,
        "amount": amount,
        "category": category,
        "date": datetime.now().strftime("%Y-%m-%d %H:%M"),
    }

    expenses.append(expense)
    save_expenses(expenses)
    print(f"  ✅ Expense added: {description} — ${amount:.2f} [{category}]")


def view_expenses(expenses: list, filter_category: str = None) -> None:
    """Display expenses in a formatted table."""
    filtered = expenses
    if filter_category:
        filtered = [e for e in expenses if e["category"] == filter_category]

    if not filtered:
        print("  📭 No expenses found.")
        return

    # Header
    print(f"\n  {'ID':<4} {'Date':<18} {'Category':<15} {'Description':<20} {'Amount':>10}")
    print(f"  {'—'*4} {'—'*18} {'—'*15} {'—'*20} {'—'*10}")

    # Rows
    for exp in filtered:
        icon = CATEGORIES.get(exp["category"], "📦")
        print(
            f"  {exp['id']:<4} "
            f"{exp['date']:<18} "
            f"{icon} {exp['category']:<12} "
            f"{exp['description']:<20} "
            f"${exp['amount']:>8.2f}"
        )

    total = sum(e["amount"] for e in filtered)
    print(f"\n  {'Total:':<60} ${total:>8.2f}")


def view_by_category(expenses: list) -> None:
    """Filter and view expenses by category."""
    print(f"  Categories: {', '.join(CATEGORIES.keys())}")
    category = input("  Enter category to filter: ").strip().lower()
    if category not in CATEGORIES:
        print("  ❌ Invalid category.")
        return
    view_expenses(expenses, filter_category=category)


def show_summary(expenses: list) -> None:
    """Display spending summary with category breakdown."""
    if not expenses:
        print("  📭 No expenses to summarize.")
        return

    total = sum(e["amount"] for e in expenses)

    # Group by category
    by_category = {}
    for exp in expenses:
        cat = exp["category"]
        by_category[cat] = by_category.get(cat, 0) + exp["amount"]

    print(f"\n  📊 EXPENSE SUMMARY")
    print(f"  {'='*40}")
    print(f"  Total Expenses: ${total:,.2f}")
    print(f"  Total Items:    {len(expenses)}")
    print(f"  {'—'*40}")

    # Sort categories by amount (descending)
    sorted_cats = sorted(by_category.items(), key=lambda x: x[1], reverse=True)

    for cat, amount in sorted_cats:
        icon = CATEGORIES.get(cat, "📦")
        percentage = (amount / total) * 100
        bar = "█" * int(percentage / 5)
        print(f"  {icon} {cat:<15} ${amount:>8.2f}  ({percentage:>5.1f}%)  {bar}")


def delete_expense(expenses: list) -> None:
    """Delete an expense by its ID."""
    view_expenses(expenses)
    if not expenses:
        return

    try:
        exp_id = int(input("\n  Enter expense ID to delete: "))
    except ValueError:
        print("  ❌ Invalid ID.")
        return

    for i, exp in enumerate(expenses):
        if exp["id"] == exp_id:
            removed = expenses.pop(i)
            save_expenses(expenses)
            print(f"  🗑️  Deleted: {removed['description']} — ${removed['amount']:.2f}")
            return

    print(f"  ❌ Expense with ID {exp_id} not found.")


# -----------------------------------------------------------------------------
# Main Menu
# -----------------------------------------------------------------------------

def display_menu():
    """Display the main menu."""
    print("""
╔══════════════════════════════════════════╗
║         💰 EXPENSE TRACKER 💰           ║
╠══════════════════════════════════════════╣
║  1. Add Expense                         ║
║  2. View All Expenses                   ║
║  3. View by Category                    ║
║  4. Summary                             ║
║  5. Delete Expense                      ║
║  6. Exit                                ║
╚══════════════════════════════════════════╝
    """)


def main():
    """Main entry point."""
    expenses = load_expenses()

    while True:
        display_menu()
        choice = input("  Choose an option (1-6): ").strip()

        if choice == "1":
            add_expense(expenses)
        elif choice == "2":
            view_expenses(expenses)
        elif choice == "3":
            view_by_category(expenses)
        elif choice == "4":
            show_summary(expenses)
        elif choice == "5":
            delete_expense(expenses)
        elif choice == "6":
            print("\n  👋 Goodbye! Keep tracking your expenses!")
            break
        else:
            print("  ❌ Invalid option. Please choose 1-6.")

        input("\n  Press Enter to continue...")


if __name__ == "__main__":
    main()