tithi_engine

A pure Dart library for Hindu lunar calendar (tithi/panchang) calculations. Computes accurate tithis, lunar months, and festival dates for any city worldwide.

Features

Tithi calculation — date → tithi number, name, paksha, lunar month
Festival dates — muhurta-accurate (nishita, madhyahna, pradosh rules)
Month resolution — moment-based adhika/kshaya detection, Purnimant & Amant systems
Date finding — tithi → Gregorian date in any year
230 cities — per-city correction tables verified against Swiss Ephemeris
Pure Dart — no dependencies, works in Flutter, server, CLI, and web (WASM)
200-year accuracy — validated 1900–2100 against Drik Panchang

Installation

dependencies:
  tithi_engine: ^1.0.8

Quick Start

import 'package:tithi_engine/tithi_engine.dart';

final panchang = Panchang(MonthSystem.purnimant);

// Date → Tithi
final info = panchang.forDate(DateTime(2026, 2, 15), City.ujjain);
print(info.displayName); // "Phalguna Krishna Trayodashi"

// Festival date
final shivaratri = panchang.dateFor(
  festivals.firstWhere((f) => f.name == 'Maha Shivaratri'), 2026, City.ujjain);
print('Maha Shivaratri 2026: ${shivaratri?.date}');

// Tithi → Date
final date = panchang.getDate(
  LunarMonth.bhadrapada, Paksha.krishna, 8, 2026, City.seattle);
print('Janmashtami 2026 Seattle: $date');

API

Method	Description
`panchang.forDate(date, city)`	Gregorian date → full TithiInfo
`panchang.getDate(month, paksha, tithi, year, city)`	Tithi spec → Gregorian date
`panchang.getDates(month, paksha, tithi, year, city)`	Tithi spec → all dates (adhika-aware)
`panchang.dateFor(festival, year, city)`	Festival → date with muhurta rules
`panchang.findNext(month, paksha, tithi, city)`	Next occurrence from today

Accuracy

Metric	Value
Tithi vs Swiss Ephemeris	0 mismatches (230 cities × 73,049 days, 1900–2100)
Month boundaries (Purnimant)	100% (200 years, verified cities)
Festival dates vs Drik Panchang	22/22 (2025–2026)
Test coverage	467 tests

Cross-Platform

This is the Dart implementation of tithi-engine (Java). Both libraries produce identical results and share the same correction tables.

License

Licensed under the Apache License 2.0.