PHP Financial Data Analysis Script

I need a clean, well-documented PHP script that takes raw financial data as input, runs the necessary analysis, and returns structured results I can feed straight into my reporting stack.

Scope of work
• Ingest financial datasets (CSV, JSON, or an array passed in memory).
• Perform the core data-analysis routines I specify—totals, averages, growth calculations, and any other metrics we agree on.
• Output should be available both as an associative array and, on demand, as a downloadable CSV so I can drop it into Excel or Power BI without extra steps.
• Code must stay framework-agnostic (pure PHP 8.x) and avoid heavy external dependencies; if you rely on a helper library, clear it with me first.
• Efficiency matters: typical files sit around 50 MB, so streaming or chunked processing is essential to keep memory under control.

Deliverables
1. The PHP script(s) with inline comments.
2. A short README explaining required PHP version, any composer installs, and example usage.
3. Sample input file and its expected output for quick verification.

Acceptance criteria
• Script completes analysis of a 50 MB CSV in under 30 seconds on a standard shared-hosting environment (1 vCPU, 1 GB RAM).
• No fatal errors or notices when run with error_reporting(E_ALL).
• Results match the sample output to within 0.1 % tolerance.

Send a brief outline of your approach, including how you will handle memory management and any testing strategy you plan to use.