Splitwise++

A modern C++17 implementation of a Splitwise-like expense sharing system with clean object-oriented design, strategy patterns, JSON persistence, and a lightweight CLI.

Features

• Strategy-based splitting (equal, exact, percent) with pluggable factory.
• Thread-safe manager coordinating users, groups, and expenses.
• JSON persistence backed by a lightweight nlohmann::json-compatible implementation.
• Greedy settle-up helper to minimise transfers.
• Interactive CLI for day-to-day usage.
• Catch2-style unit tests and GitHub Actions CI.

Design Overview

• Strategy Pattern: SplitStrategy hierarchy for equal, exact, and percent splits.
• Factory Pattern: SplitStrategyFactory instantiates strategies by name.
• Singleton Friendly: SplitwiseManager can be wrapped as a Meyers singleton if desired.
• Observer Stub: INotifier and ConsoleNotifier allow optional large-expense alerts.
• Thread Safety: mutating operations in SplitwiseManager guard shared state with std::mutex.
• Persistence: JSON save/load with automatic balance recomputation for consistency.

CLI Usage

Build and run the CLI to manage your groups and expenses:

cmake -S . -B build
cmake --build build -j
./build/splitwise

Menu options let you add users, list users, create/list groups, record expenses, view balances, settle up, and persist data. Inputs are validated with friendly error messages and sensible defaults (e.g. blank participant input targets the entire group).

Architecture

For a deeper dive into the relationships between the core classes, persistence pipeline, and concurrency guarantees, see ARCHITECTURE.md.

Build & Run

cmake -S . -B build
cmake --build build -j
./build/splitwise

Tests

cmake -S . -B build
cmake --build build -j
ctest --test-dir build
# or
./build/tests

Example JSON

{
  "users": [
    {"id": "USR1", "name": "Alice"}
  ],
  "groups": [
    {"id": "GRP1", "name": "Trip", "members": ["USR1"]}
  ],
  "expenses": [
    {
      "id": "EXP1",
      "groupId": "GRP1",
      "description": "Hotel",
      "payerId": "USR1",
      "amount": 100.0,
      "participants": ["USR1"],
      "exactShares": [100.0],
      "percentShares": [],
      "strategy": "exact"
    }
  ],
  "balances": {
    "USR1": 0.0
  }
}

Future Enhancements

• Observer implementations for push/email alerts on large expenses.
• REST API wrapper around the manager for web/mobile clients.
• Undo/redo stack for expense modifications.
• Richer CLI tooling (CSV import/export, reporting).