Dericer

Dericer is a local-first, open-source personal finance core library.
It focuses on clean domain logic, hexagonal architecture, and JSON-based storage, so you can build desktop, mobile, or web apps around the same engine.

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✅ NPM Install

npm install dericer-core

✨ Features (Core)

• Local-first, single user
  • No backend required. All data is stored locally (via pluggable storage, e.g. JSON files).
• Multi-account support
  • Each account has a fixed currency, initial balance, archive & soft-delete flags.
• Multiple transaction types
  • income, expense, debt, receivable
  • Transfers between accounts are represented as two linked transactions.
• Hierarchical categories
  • Parent / child categories (e.g. Food > Supermarket, Food > Restaurant)
  • Reports can roll up child categories into their parents.
• Tags & counterparty
  • Free-form tags (string list)
  • Simple counterpartyName field (no extra entity).
• Multi-currency
  • Each account has a currency.
  • Per-currency config (decimals, zero threshold).
  • Currency totals can hide “near zero” balances based on zeroMinorValue.
• Budgets
  • Budgets over a time range for a single category (including its subtree).
  • Used for informational warnings & analysis (no hard blocking of spending).
• Goals
  • Simple goals with targetAmount, currency, optional targetDate and notes.
• Soft delete
  • Transactions and accounts are soft-deleted (isDeleted flag).
• Query & reporting
  • Filter transactions by date, type, account, category, tags, counterparty, free text, amount…
  • Sort by date, createdAt, or amount.
  • Aggregate sums by account, category hierarchy, or currency.
• Export
  • Export transaction lists / query results as JSON or CSV.

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🧱 Architecture Overview

Dericer is designed as a core library with hexagonal architecture:

• Domain layer (src/domain/)
  • Pure TypeScript models and business rules.
  • No knowledge of files, JSON, databases, UI, or HTTP.
• Application layer (src/application/)
  • Use-cases / services:
    • Transactions (create / update / soft-delete / query)
    • Reports (aggregations)
    • Budgets (evaluate status)
    • Goals (create / update / list)
    • Account balances
• Ports (src/ports/)
  • Interfaces for infrastructure:
    • StoragePort (persistence)
    • TimePort (clock)
• API layer (src/api/)
  • createCore() builds a CoreApi by injecting StoragePort + TimePort.
  • DTO types for use by UI / other apps.
• Adapters (src/adapters/)
  • Optional implementations for specific environments:
    • JsonFileStorage – a JSON file–based StoragePort (Node / desktop).
    • SystemTimePort – a TimePort based on system clock.

You can build a web app, desktop app (Tauri/Electron), or mobile app (React Native, etc.) that all talk to the same CoreApi.

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📁 Folder Structure

src/
  shared/
    types.ts          # Shared nominal types (IDs, ISO date strings, etc.)
    errors.ts         # Domain / validation / not-found errors
    money.ts          # Money & currency helpers (minor units, validation)

  domain/
    account.ts        # Account model
    transaction.ts    # Transaction model + basic validation
    category.ts       # Category model + tree helpers
    budget.ts         # Budget model
    goal.ts           # Goal model
    currency.ts       # CurrencyConfig + zero-value helpers

  ports/
    storage-port.ts   # StoragePort interface (accounts, transactions, etc.)
    time-port.ts      # TimePort interface

  application/
    transactions/
      transaction-service.ts   # Transaction commands + queries
    reports/
      report-service.ts        # Aggregations (by account/category/currency)
    budgets/
      budget-service.ts        # Budget evaluation
    goals/
      goal-service.ts          # Goal CRUD
    accounts/
      account-service.ts       # Account balance & currency totals

  api/
    types.ts          # Public DTOs & filter types for consumers
    core.ts           # CoreApi + createCore(...)
    export.ts         # Helpers to export reports to JSON / CSV

  adapters/
    json-file-storage.ts   # JSON file implementation of StoragePort (Node)
    system-time-port.ts    # SystemTimePort implementation of TimePort

  index.ts             # Main public exports

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🚀 Getting Started

1. Install dependencies

npm install
# or
pnpm install
# or
yarn install

2. Build the library

npm run build
# outputs compiled JS + d.ts to dist/

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🧩 Using Dericer Core in a Node / desktop app

A minimal example for using Dericer core in a Node-based environment (or a desktop app with a Node backend):

// example.ts
import {
  createCore,
  createJsonFileStorage,
  createSystemTimePort,
  CurrencyCode,
  AccountId,
  TransactionKindDTO
} from "dericer-core"; // or relative path if not yet published

async function main() {
  // 1. Create ports (storage + time)
  const dataDir = "./dericer-data"; // this directory will store JSON files
  const storage = createJsonFileStorage(dataDir);
  const time = createSystemTimePort();

  // 2. Create core
  const core = createCore({ storage, time });

  // 3. Suppose you already created an account and have its ID.
  //    For demo: pretend we have an existing AccountId string.
  const accountId = "my-account-id" as AccountId;
  const currency: CurrencyCode = "IRR";

  // 4. Create a transaction (expense)
  const tx = await core.transactions.create({
    accountId,
    kind: "expense" as TransactionKindDTO,
    amountMinor: 150000, // e.g. 150,000 rials (1,500.00 with 2 decimals)
    currency,
    date: "2025-01-15",
    note: "Groceries",
    tags: ["market", "food"]
  });

  console.log("Created transaction:", tx);

  // 5. Query transactions for this account
  const result = await core.transactions.query(
    { accountIds: [accountId] },
    { field: "date", direction: "asc" }
  );

  console.log("Found transactions:", result.transactions.length);

  // 6. Get account balances
  const balances = await core.accounts.getBalances();
  console.log("Account balances:", balances);

  // 7. Get currency totals (with zero-value filter)
  const currencyTotals = await core.accounts.getCurrencyTotals();
  console.log("Currency totals:", currencyTotals);
}

main().catch((err) => {
  console.error(err);
  process.exit(1);
});

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💾 JSON File Storage Layout

JsonFileStorage uses a directory as a simple local “database”.
Each entity type is stored in a separate JSON file:

dericer-data/
  accounts.json         # Array<Account>
  transactions.json     # Array<Transaction>
  categories.json       # Array<Category>
  budgets.json          # Array<Budget>
  goals.json            # Array<Goal>
  currency-configs.json # Array<CurrencyConfig>

Each file is a simple JSON array of the corresponding entities.
The core only talks to these files via StoragePort;
you are free to backup / sync / edit them externally if you like.

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📊 Exporting Reports (JSON / CSV)

Dericer core can export transaction data and query results as JSON or CSV.
Example:

import {
  createCore,
  createJsonFileStorage,
  createSystemTimePort,
  exportTransactionQueryResultToJson,
  exportTransactionQueryResultToCsv
} from "dericer-core";

async function exportExample() {
  const core = createCore({
    storage: createJsonFileStorage("./dericer-data"),
    time: createSystemTimePort()
  });

  const result = await core.transactions.query(
    { /* any filters you want */ },
    { field: "date", direction: "asc" }
  );

  const json = exportTransactionQueryResultToJson(result);
  const csv = exportTransactionQueryResultToCsv(result);

  // In your app, you can now write these strings to files:
  //   transactions.json, transactions.csv, etc.
  console.log(json);
  console.log(csv);
}

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🧪 Testing

A typical test setup for Dericer might use:

• Vitest or Jest for unit tests
• Tests organized alongside layers, e.g.:

test/
  domain/
    transaction.test.ts
    category.test.ts
  application/
    transaction-service.test.ts
    budget-service.test.ts
    account-service.test.ts
  api/
    core.test.ts

The exact setup is up to you, but the architecture is designed so that:

• Domain can be tested in isolation (pure functions / models).
• Application services can be tested with in-memory or fake storage/time ports.
• API layer can be tested end-to-end with a simple JSON storage adapter.

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⚠️ Limitations / Notes

• Designed for single-user, local-first scenarios.
  • No guarantees for concurrent writes from multiple processes.
• Sync between devices is not handled by the core:
  • You can use Git, Syncthing, cloud drives, or your own tooling to sync the data directory.
• ID generation uses simple UUID-like strings based on Math.random():
  • Perfectly fine for personal use.
  • You can swap this out for a stronger strategy if needed.

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💬 Contributing / Ideas

• Add more advanced reports (cashflow, monthly charts, etc.).
• Implement different storage adapters (SQLite, IndexedDB, etc.).
• Extend the plugin API when UI layers (desktop/web/mobile) are ready.

Enjoy hacking on Dericer 🌱