How do I calculate the profit impact of discounts?

As an e-commerce business owner, I'm struggling to understand how discounts truly affect my bottom line. I want to move beyond simple percentage calculations and develop a comprehensive method to analyze the financial implications of running promotions. My goal is to create a systematic approach that helps me determine whether a discount campaign will generate net positive returns or potentially harm my profitability. I need a framework that considers not just revenue, but also factors like customer acquisition cost, repeat purchase probability, and long-term customer lifetime value.