From 3dcb5b69911a61b002d7e8b7c775c9d8b88f4ef3 Mon Sep 17 00:00:00 2001
From: Nathan Fisher <jeang3nie@hitchhiker-linux.org>
Date: Sun, 11 Jun 2023 01:45:15 -0400
Subject: [PATCH] Parse `DateTime` from Unix timestamp

---
 src/time/epoch.rs | 116 ++++++++++++++++++++++++++++++++++++++++++++++
 src/time/mod.rs   |   4 +-
 2 files changed, 118 insertions(+), 2 deletions(-)
 create mode 100644 src/time/epoch.rs

diff --git a/src/time/epoch.rs b/src/time/epoch.rs
new file mode 100644
index 0000000..2a45281
--- /dev/null
+++ b/src/time/epoch.rs
@@ -0,0 +1,116 @@
+use super::{DateTime, TimeZone};
+
+pub const SECS_PER_DAY: i64 = 86400;
+
+fn days_since_epoch(ts: i64) -> i64 {
+    ts / SECS_PER_DAY
+}
+
+fn is_leap(year: i64) -> bool {
+    year % 4 == 0 && (year % 100 != 0 || year % 16 == 0)
+}
+
+fn year_from_ts_with_remainder(ts: i64) -> (i64, i64) {
+    let mut year = 1970;
+    let mut days = days_since_epoch(ts);
+    loop {
+        let days_in_year = if is_leap(year) {
+            366
+        } else {
+            365
+        };
+        if days > days_in_year {
+            days -= days_in_year;
+            year += 1;
+        } else {
+            break;
+        }
+    }
+    (year, days)
+}
+
+fn days_in_month(month: u8, year: i64) -> i64 {
+    assert!(month < 13);
+    match month {
+        1 | 3 | 5 | 7 | 10 | 12 => 31,
+        2 => {
+            if is_leap(year) {
+                29
+            } else {
+                28
+            }
+        },
+        4 | 6 | 9 | 11 => 30,
+        _ =>  unreachable!(),
+    }
+}
+
+fn month_and_days_from_ordinal(days: i64, year: i64) -> (u8, i64) {
+    assert!(
+        if is_leap(year) {
+            days < 366
+        } else {
+            days < 365
+        }
+    );
+    let mut days = days;
+    let mut month = 1;
+    while days_in_month(month, year) <= days {
+        days -= days_in_month(month, year);
+        month += 1;
+    }
+    (month, days)
+}
+
+pub(super) fn date_time_from_ts(ts: i64) -> DateTime {
+    let (year, days) = year_from_ts_with_remainder(ts);
+    let (month, days) = month_and_days_from_ordinal(days, year);
+    let seconds = ts % SECS_PER_DAY;
+    println!("Seconds: {seconds}");
+    let minutes = seconds / 60;
+    println!("Minutes: {minutes}");
+    let second = seconds % 60;
+    let hour = minutes / 60;
+    let minute = minutes % 60;
+    DateTime {
+        year: year as u32,
+        month: month.try_into().unwrap(),
+        day: (days + 1).try_into().unwrap(),
+        hour: Some((hour + 1).try_into().unwrap()),
+        minute: Some((minute).try_into().unwrap()),
+        second: Some(second.try_into().unwrap()),
+        tz: Some(TimeZone::UTC),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn get_year() {
+        let ts = 1686459092;
+        let (y, r) = year_from_ts_with_remainder(ts);
+        assert_eq!(y, 2023);
+        assert_eq!(r, 161);
+    }
+
+    #[test]
+    fn get_month_and_days() {
+        let ts = 1686459092;
+        let (year, days) = year_from_ts_with_remainder(ts);
+        let (month, days) = month_and_days_from_ordinal(days, year);
+        assert_eq!(month, 6);
+        assert_eq!(days, 10);
+    }
+
+    #[test]
+    fn get_datetime() {
+        let ts = 1686462068;
+        let dt = date_time_from_ts(ts);
+        assert_eq!(dt.day, 11);
+        assert_eq!(dt.hour, Some(6));
+        assert_eq!(dt.minute, Some(41));
+        assert_eq!(dt.second, Some(8));
+    }
+}
diff --git a/src/time/mod.rs b/src/time/mod.rs
index 6d64680..5a7db17 100644
--- a/src/time/mod.rs
+++ b/src/time/mod.rs
@@ -1,13 +1,13 @@
 //! A container representing a moment in ISO-8601 format Time
-use std::{cmp::Ordering, fmt, str::FromStr};
+use std::{fmt, str::FromStr};
 
+pub mod epoch;
 mod error;
 mod parser;
 pub use {error::Error, parser::Parser};
 
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
-use x509_parser::der_parser::ber::ber_read_element_header;
 
 #[derive(Clone, Copy, Debug, PartialEq)]
 #[cfg_attr(feature = "serde", derive(Deserialize, Serialize))]