taian

A Rust library and CLI tool for calculating Rokuyo (六曜), a traditional Japanese calendar system.

Rokuyo is a calendar annotation system that originated in China and is widely used in Japan. It consists of six days: Sensho, Tomobiki, Senbu, Butsumetsu, Taian, and Shakku, calculated from the lunar calendar's month and day.

Features

• Accurate lunar calendar calculation (using chinese-lunisolar-calendar)
• Provides both library and CLI
• Simple and easy-to-use API

Installation

As a Library

[dependencies]
taian = "0.1"

As a CLI Tool

cargo install taian

Usage

As a Library

use taian::{calculate_rokuyo, Rokuyo};
use chrono::NaiveDate;

fn main() {
    let date = NaiveDate::from_ymd_opt(2026, 2, 17).unwrap();

    if let Some(rokuyo) = calculate_rokuyo(date) {
        println!("Rokuyo: {}", rokuyo); // Rokuyo: Sensho

        match rokuyo {
            Rokuyo::Taian => println!("Taian - Auspicious all day"),
            Rokuyo::Shakku => println!("Shakku - Auspicious only at noon, inauspicious at other times"),
            Rokuyo::Sensho => println!("Sensho - Auspicious in the morning, inauspicious in the afternoon"),
            Rokuyo::Tomobiki => println!("Tomobiki - Auspicious in the morning and evening, inauspicious at noon"),
            Rokuyo::Senbu => println!("Senbu - Inauspicious in the morning, auspicious in the afternoon"),
            Rokuyo::Butsumetsu => println!("Butsumetsu - Inauspicious all day"),
        }
    }
}

As a CLI Tool

# Display today's Rokuyo
$ taian
Rokuyo for March 17, 2026: Taian

# Display Rokuyo for a specific date
$ taian 2026 2 17
Rokuyo for February 17, 2026: Sensho

About Rokuyo

Calculation Method

Rokuyo is calculated from the lunar calendar's month and day:

1. The Rokuyo for the 1st day of each lunar month is fixed:

   • Months 1 & 7: Sensho
   • Months 2 & 8: Tomobiki
   • Months 3 & 9: Senbu
   • Months 4 & 10: Butsumetsu
   • Months 5 & 11: Taian
   • Months 6 & 12: Shakku

2. After that, it cycles through the sequence: Sensho → Tomobiki → Senbu → Butsumetsu → Taian → Shakku

License

MIT License - See LICENSE for details.

References

• Rokuyo Calculation Method - Musashiya (Japanese)