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use crate::tzdb::offset_info_at_local;
use crate::{
Dt, JD_2000_2_451_545, SEC_PER_DAYI64, Scale, TAI_SECS_1970_MIDNIGHT_TO_2000_NOON, an_err,
error::{DtErr, DtErrKind},
{Meridiem, Offset, TimeParts, Weekday},
};
impl TimeParts {
/// Converts [`TimeParts`] → [`Dt`].
/// - Resulting [`Dt`] is on the TAI timescale.
/// - If this [`TimeParts`] has a unix timestamp then it is used
/// instead of anything else.
pub fn to_dt(&self) -> Result<Dt, DtErr> {
// ──────────────────────────────────────────────────────────────
// Fast path: explicit Unix timestamp
// ──────────────────────────────────────────────────────────────
if let Some(unix_secs) = self.unix_timestamp_seconds {
let sec = unix_secs - TAI_SECS_1970_MIDNIGHT_TO_2000_NOON;
let subsec = self.attos.unwrap_or(0);
return Ok(Dt::from(sec, subsec, Scale::UTC));
}
// ──────────────────────────────────────────────────────────────
// Civil date path
// ──────────────────────────────────────────────────────────────
let mut jd: Option<i64> = None;
if let Some(year) = self.yr {
if let (Some(m), Some(d)) = (self.mo, self.day) {
// Classic YMD – highest priority + full validation
if !Dt::is_valid_ymd(year, m, d) {
return Err(an_err!(DtErrKind::InvalidInput, "ymd"));
}
jd = Some(Dt::ymd_to_jd(year, m, d));
} else if let Some(doy) = self.day_of_yr {
// Ordinal date (%j) – already validated
if doy == 0 || doy > 366 || (doy == 366 && !Dt::is_leap_yr(year)) {
return Err(an_err!(DtErrKind::OutOfRange, "day of year"));
}
jd = Some(Dt::ydoy_to_jd(year, doy));
}
}
if jd.is_none() {
if let (Some(iso_y), Some(iso_w)) = (self.iso_wk_yr, self.iso_wk) {
// ISO week date (%G/%V)
if iso_w == 0 || iso_w > 53 {
return Err(an_err!(DtErrKind::OutOfRange, "iso week"));
}
if iso_w == 53 && !Dt::has_iso_wk_53(iso_y) {
return Err(an_err!(DtErrKind::InvalidItem, "iso week"));
}
let wd = self.wkday.unwrap_or(Weekday::Monday);
jd = Some(Dt::ymd_to_jd_from_iso_wk(iso_y, iso_w, wd));
} else if let (Some(y), Some(w)) = (self.yr, self.wk_sun) {
// Sunday-based week (%U)
if w > 53 {
return Err(an_err!(DtErrKind::OutOfRange, "week number"));
}
let wd = self.wkday.unwrap_or(Weekday::Sunday);
jd = Some(Dt::ymd_to_jd_from_wk_sun(y, w, wd));
} else if let (Some(y), Some(w)) = (self.yr, self.wk_mon) {
// Monday-based week (%W)
if w > 53 {
return Err(an_err!(DtErrKind::OutOfRange, "week number"));
}
let wd = self.wkday.unwrap_or(Weekday::Monday);
jd = Some(Dt::ymd_to_jd_from_wk_mon(y, w, wd));
}
}
let Some(jd) = jd else {
if self.yr.is_none() && self.iso_wk_yr.is_none() {
return Err(an_err!(DtErrKind::Incomplete, "no year"));
} else {
return Err(an_err!(DtErrKind::InvalidInput, "could not create julian"));
}
};
// ──────────────────────────────────────────────────────────────
// Resolve 12-hour time + meridiem (AM/PM) to 24-hour hour
// ──────────────────────────────────────────────────────────────
let hour = match (self.hr, self.meridiem) {
(Some(h), Some(m)) => {
if !(1..=12).contains(&h) {
return Err(an_err!(DtErrKind::OutOfRange, "hour: {}", h));
}
match (h, m) {
(12, Meridiem::AM) => 0,
(12, Meridiem::PM) => 12,
(h, Meridiem::AM) => h,
(h, Meridiem::PM) => h + 12,
}
}
(Some(h), None) => h,
(None, _) => 0,
};
let minute = self.min.unwrap_or(0) as i64;
let second = self.sec.unwrap_or(0) as i64;
let days_since_j2000 = jd.saturating_sub(JD_2000_2_451_545);
let seconds_from_noon_utc = (hour as i64 - 12) * 3600 + minute * 60 + second;
let mut sec_utc: i64 = days_since_j2000
.saturating_mul(SEC_PER_DAYI64)
.saturating_add(seconds_from_noon_utc);
// ──────────────────────────────────────────────────────────────
// Apply timezone correction (IANA or Fixed offset)
// ──────────────────────────────────────────────────────────────
if let Some(name) = &self.iana_name {
let name_str = name.as_str().map_err(|e| {
an_err!(
DtErrKind::InvalidBytes,
"invalid iana ascii: {:?}: {}",
name,
e
)
})?;
if !name_str.is_empty() {
let provisional_unix = sec_utc.saturating_add(TAI_SECS_1970_MIDNIGHT_TO_2000_NOON);
match offset_info_at_local(name_str, provisional_unix) {
Some(info) => {
if info.is_gap {
// Non-existent time (spring-forward gap) — shift forward
sec_utc = sec_utc.saturating_add(info.gap_size); // shift local time into the valid post-gap period
sec_utc = sec_utc.saturating_sub(info.offset as i64); // apply the post-jump offset
} else {
sec_utc = sec_utc.saturating_sub(info.offset as i64);
}
}
None => {
return Err(an_err!(
DtErrKind::InvalidTimezoneOffset,
"invalid iana: {}",
name_str
));
}
}
}
} else if let Some(Offset::Fixed(offset)) = self.offset {
// local civil time → true UTC instant
sec_utc = sec_utc.saturating_sub(offset as i64);
}
Ok(Dt::from(sec_utc, self.attos.unwrap_or(0), Scale::UTC))
}
}