Most Active Cookie

A command line program that processes cookie log files and returns the most active cookie for a specific day.

Task Description

Given a cookie log file with entries in the format:

cookie,timestamp
AtY0laUfhglK3lC7,2018-12-09T14:19:00+00:00
SAZuXPGUrfbcn5UA,2018-12-09T10:13:00+00:00
5UAVanZf6UtGyKVS,2018-12-09T07:25:00+00:00

The program finds the cookie(s) that appear most frequently on a given date.

Usage

# Basic usage (with info logging)
./most-active-cookie -f <filename> -d <date>

# Silent output (production use)
LOG_LEVEL=silent ./most-active-cookie -f <filename> -d <date>

# With debug logging
LOG_LEVEL=debug ./most-active-cookie -f <filename> -d <date>

Parameters

• -f : Path to the cookie log file to process
• -d : Date to analyze (format: YYYY-MM-DD, UTC timezone)

Example

With info logging (default):

./most-active-cookie -f cookie_log.csv -d 2018-12-09

Expected output:

AtY0laUfhglK3lC7
[2025-08-25 14:57:01] INFO: Starting Most Active Cookie analysis
[2025-08-25 14:57:01] INFO: Starting to process cookie_log.csv for date 2018-12-09
[2025-08-25 14:57:01] INFO: Processing completed in 7ms. Found 1 winning cookie(s)

Silent output (clean result only):

LOG_LEVEL=silent ./most-active-cookie -f cookie_log.csv -d 2018-12-09

Expected output:

AtY0laUfhglK3lC7

Installation

# Clone/download the project
cd most-active-cookie

# Install dependencies
bun install

# Build the binary
bun run build

Development

Available Scripts

# Run with test data (debug logging)
bun run dev

# Build production binary
bun run build

# Run comprehensive test suite (error logging)
bun run test

# Test the compiled binary (error logging)
bun run preview

# Run with custom log level
LOG_LEVEL=info bun src/index.ts -f cookie_log.csv -d 2018-12-09

Log Levels

• debug: Full logging (used by bun run dev)
• info: Standard logging (default)
• warn: Warnings and errors only
• error: Errors only (used by bun run test and bun run preview)
• silent: No logging

Project Structure

src/
├── index.ts      # Main entry point
├── cli.ts        # CLI argument parsing
├── processor.ts  # Core streaming logic
├── utils.ts      # Validation utilities
└── types.ts      # Type definitions

test/
├── unit/         # Unit tests
├── integration/  # CLI integration tests
└── fixtures/     # Test data files

Implementation Details

• Streaming Processing: Uses Node.js streams for memory-efficient file processing
• TypeScript: Fully typed with strict compiler settings
• Performance: Single-pass algorithm with O(1) cookie counting
• Error Handling: Comprehensive validation with user-friendly messages
• Testing: 19 tests covering unit, integration, and edge cases

Requirements

• Returns the most active cookie(s) for the specified date
• If multiple cookies have the same highest count, all are returned on separate lines
• Only uses additional libraries for testing, logging, and CLI parsing
• Assumes sufficient memory to load the entire file
• Assumes log entries are sorted by timestamp (most recent first)