Sales Tax Calculator

A Ruby application that calculates sales taxes and generates receipts for shopping baskets.

Problem

• Basic sales tax: 10% on all goods, except books, food, and medical products
• Import duty: 5% on all imported goods (no exemptions)
• Rounding: Tax is rounded up to the nearest 0.05

Requirements

• Ruby 3.2+
• Bundler

Setup

bundle install

Usage

# Process a file
./bin/sales_tax examples/input_10.txt

# Process from stdin
cat examples/input_10.txt | ./bin/sales_tax

Input Format

<quantity> <product name> at <price>

Example:

2 book at 12.49
1 music CD at 14.99
1 imported box of chocolates at 10.00

Output

2 book: 24.98
1 music CD: 16.49
1 imported box of chocolates: 10.50
Sales Taxes: 2.00
Total: 47.97

Tests

bundle exec rspec

Structure

lib/sales_tax/
|-- item.rb              # Product with tax exemption logic
|-- input_parser.rb      # Parse text input
|-- tax_calculator.rb    # Calculate taxes with rounding
|-- shopping_basket.rb   # Main orchestrator
|-- rules/
|   |-- tax_rule.rb         # Base interface
|   |-- basic_tax_rule.rb   # 10% basic tax
|   |-- import_tax_rule.rb  # 5% import duty
|-- receipt/
    |-- line_item.rb    # Receipt line
    |-- receipt.rb      # Receipt data
    |-- printer.rb      # Format output

Tax Exemptions

• Books: "book"
• Food: "chocolate", "chocolates", "candy"
• Medical: "pills", "headache", "medicine", "vitamin"