Portfolio Rebalancer

A simple portfolio rebalancing engine implemented in Go.

This project calculates which stocks should be bought or sold in order to match a desired target allocation.

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Overview

A portfolio consists of:

• Current holdings (stocks with quantity and price)
• Target allocation (desired percentage distribution)

The system:

1. Calculates total portfolio value
2. Determines current allocation
3. Compares against target allocation
4. Generates actions: BUY / SELL / HOLD

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Example

Current Portfolio

Stock	Value
META	600
AAPL	400

Total = 1000

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Target Allocation

Stock	%
META	40%
AAPL	60%

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Result

Stock	Action	Amount
META	SELL	200
AAPL	BUY	200

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Architecture

The project follows a simple layered structure:

cmd/            → entry point (main)
internal/
  domain/       → core business logic
  application/  → use case orchestration
  types/        → shared models

Key Design Decisions

• Domain logic is isolated from application logic
• Rebalancing is deterministic and pure
• No external dependencies (kept intentionally simple)
• Action types use integers (DB and i18n friendly)

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Getting Started

Requirements

• Go 1.20+

Run the project

go run cmd/main.go

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Run tests

go test ./...

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Core Logic

For each stock:

target_value = total_portfolio_value * target_percentage
difference = target_value - current_value

• If difference > 0 → BUY
• If difference < 0 → SELL
• If difference = 0 → HOLD

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Edge Cases Considered

• Stocks present in holdings but not in target → SELL all
• Stocks present in target but not in holdings → BUY from zero
• Empty portfolio handling

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LLM Usage Disclosure

This project was developed with the assistance of an LLM for:

• validating architectural decisions in Golang constraints
• Identifying edge cases

All implementation and final decisions were reviewed and written manually.

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Documentantion

Additional development notes, including design decision and LLM usage, are available in:

 docs/development-notes.pdf

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Future Improvements

(Not implemented to avoid overengineering)

• Transaction fees handling
• Minimum trade thresholds
• Real-time price integration
• API interface (REST)
• AI-driven allocation (external system)

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Author

Jhoan Gutiérrez
Software Engineer (Backend & Systems Focus)