iztro 0.3.1

Strongly typed Zi Wei Dou Shu chart generation aligned with iztro.
Documentation 
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//! Lunar-date normalization backed by `lunar-lite`.
//!
//! Upstream `iztro.byLunar(date, _, _, isLeapMonth, _)` delegates to
//! `lunar-lite.lunar2solar(date, isLeapMonth)`, which only honors
//! `isLeapMonth = true` when the requested lunar year actually has a leap month
//! equal to the requested month. If the requested month is not the year's leap
//! month, the flag is ignored and the date is treated as the ordinary month.
//!
//! [`resolve_lunar_date`] reproduces that rule: it never blindly trusts the
//! caller's `is_leap_month`. It resolves the flag with `lunar-lite` and returns
//! the corrected facts.
//! Like the rest of this module, it exposes only the crate's own domain types.

use lunar_lite::{LunarDate, LunarError, normalize_lunar_date};

use crate::core::error::ChartError;
use crate::core::placement::natal::life_body::{LunarDay, LunarMonth};

/// A lunar date whose leap-month flag has been resolved against the real
/// calendar (the leap flag is kept only when the month is actually leap).
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) struct ResolvedLunarDate {
    lunar_year: i32,
    lunar_month: LunarMonth,
    lunar_day: LunarDay,
    is_leap_month: bool,
    month_days: u8,
}

impl ResolvedLunarDate {
    /// Returns the resolved lunar year.
    pub(crate) const fn lunar_year(&self) -> i32 {
        self.lunar_year
    }

    /// Returns the resolved lunar month number (`1..=12`, leap-insensitive).
    pub(crate) const fn lunar_month(&self) -> LunarMonth {
        self.lunar_month
    }

    /// Returns the resolved lunar day of the month.
    pub(crate) const fn lunar_day(&self) -> LunarDay {
        self.lunar_day
    }

    /// Returns whether the resolved lunar month is actually a leap month.
    pub(crate) const fn is_leap_month(&self) -> bool {
        self.is_leap_month
    }

    /// Returns the number of days in the resolved lunar month.
    pub(crate) const fn month_days(&self) -> u8 {
        self.month_days
    }
}

/// Resolves an explicit lunar date and its leap-month flag against the real
/// calendar, mirroring upstream `lunar2solar` leap handling.
///
/// `is_leap_month` is honored only when `lunar_year` actually has a leap month
/// equal to `lunar_month`; otherwise it is ignored and the ordinary month is
/// used. Returns [`ChartError::UnsupportedCalendarDate`] when the day does not
/// exist in the resolved month.
pub(crate) fn resolve_lunar_date(
    lunar_year: i32,
    lunar_month: LunarMonth,
    lunar_day: LunarDay,
    is_leap_month: bool,
) -> Result<ResolvedLunarDate, ChartError> {
    let month = lunar_month.value();
    let day = lunar_day.value();
    let conversion_failed = || ChartError::CalendarConversionFailed {
        year: lunar_year,
        month,
        day,
    };

    let date = normalize_lunar_date(LunarDate {
        year: lunar_year,
        month,
        day,
        is_leap_month,
    })
    .map_err(|err| map_lunar_normalize_error(err, lunar_year, month, day))?;

    let month_days = match normalize_lunar_date(LunarDate { day: 30, ..date }) {
        Ok(_) => 30,
        Err(LunarError::InvalidLunarDate { .. }) => 29,
        Err(err) => return Err(map_lunar_normalize_error(err, lunar_year, month, day)),
    };

    Ok(ResolvedLunarDate {
        lunar_year: date.year,
        lunar_month: LunarMonth::new(date.month).map_err(|_| conversion_failed())?,
        lunar_day: LunarDay::new(date.day).map_err(|_| conversion_failed())?,
        is_leap_month: date.is_leap_month,
        month_days,
    })
}

fn map_lunar_normalize_error(err: LunarError, year: i32, month: u8, day: u8) -> ChartError {
    match err {
        LunarError::InvalidLunarDate { .. } | LunarError::YearOutOfRange { .. } => {
            ChartError::UnsupportedCalendarDate { year, month, day }
        }
        LunarError::InvalidSolarDate { .. }
        | LunarError::InvalidTime { .. }
        | LunarError::InvalidTimeIndex { .. }
        | LunarError::SolarTermOutOfRange { .. } => {
            ChartError::CalendarConversionFailed { year, month, day }
        }
    }
}

#[cfg(test)]
mod tests;