tithi_engine 2.2.0

Accurate Vedic tithi, lunar month, and festival date calculator for any city worldwide. Pure Dart, no dependencies, 200-year accuracy (1900–2100).

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: ^2.1.0

Quick Start

import 'package:tithi_engine/tithi_engine.dart';
import 'package:tithi_engine/data/all.dart'; // city correction tables

// City data is REQUIRED in the constructor — pass a pack's registrar.
// data/all.dart links all cities; a region pack (e.g. data/india.dart → registerIndia)
// links only that region so the tree-shaker drops the rest.
final panchang = Panchang([registerAllCities]);

// 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');

There is no zero-arg Panchang(). The constructor requires a list of data-pack registrars, so you can't accidentally run with no city data. Choosing which packs to import is also what lets the tree-shaker drop unused cities (an India-only consumer links ~30 cities, not 230). Registrars are idempotent, so constructing repeatedly is cheap.

Data packs

Import	Pass to constructor	Links
package:tithi_engine/data/all.dart	Panchang([registerAllCities])	all 230 cities
package:tithi_engine/data/india.dart	Panchang([registerIndia])	India (30 cities)

Combine packs: Panchang([registerIndia, registerEurope]).

API

Panchang is the single entry point. Value types (TithiInfo, LunarMonth, MonthSystem, Paksha, FestivalDef, MuhurtaRule, festivals, FestivalDate, City, CityLocation) are exported; the engine internals are not.

Method	Description
Panchang(data, {system})	Construct with city-data registrars (data required)
panchang.forDate(date, city, {utcOffset})	Gregorian date → full TithiInfo (time-of-day aware)
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.recurringDates(festival, year, city)	Recurring festival → all occurrences in the year
panchang.findNext(month, paksha, tithi, city)	Next occurrence from today
panchang.transitionTime(date, {utcOffset})	UTC moment the tithi changes that day
TithiInfo.fromStored(...)	Render a saved tithi (with optional Purnimant↔Amant display conversion)

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	527 tests, ~87% core line coverage

Cross-Platform

This is the Dart implementation of tithi-engine (Java). Both produce identical tithi/panchang results, validated against Swiss Ephemeris.

License

Licensed under the Apache License 2.0.