From e05ba8b9c2a98943d129e664c7615bd3724e069e Mon Sep 17 00:00:00 2001
From: Paul Dicker <paul@pitdicker.nl>
Date: Thu, 21 Mar 2024 07:22:26 +0100
Subject: [PATCH] Add `MappedLocalTime::and_then`

---
 src/offset/local/unix.rs |  2 +-
 src/offset/mod.rs        | 43 +++++++++++++++++++++-------------------
 2 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/src/offset/local/unix.rs b/src/offset/local/unix.rs
index ad99542330..c1942eba7e 100644
--- a/src/offset/local/unix.rs
+++ b/src/offset/local/unix.rs
@@ -166,6 +166,6 @@ impl Cache {
         self.zone
             .find_local_time_type_from_local(d.and_utc().timestamp(), d.year())
             .expect("unable to select local time type")
-            .map(|o| FixedOffset::east_opt(o.offset()).unwrap())
+            .and_then(|o| FixedOffset::east_opt(o.offset()))
     }
 }
diff --git a/src/offset/mod.rs b/src/offset/mod.rs
index c1d1cc5619..89aafb61be 100644
--- a/src/offset/mod.rs
+++ b/src/offset/mod.rs
@@ -121,6 +121,24 @@ impl<T> MappedLocalTime<T> {
             MappedLocalTime::Ambiguous(min, max) => MappedLocalTime::Ambiguous(f(min), f(max)),
         }
     }
+
+    /// Maps a `MappedLocalTime<T>` into `MappedLocalTime<U>` with given function.
+    ///
+    /// Returns `MappedLocalTime::None` if the function returns `None`.
+    #[must_use]
+    pub(crate) fn and_then<U, F: FnMut(T) -> Option<U>>(self, mut f: F) -> MappedLocalTime<U> {
+        match self {
+            MappedLocalTime::None => MappedLocalTime::None,
+            MappedLocalTime::Single(v) => match f(v) {
+                Some(new) => MappedLocalTime::Single(new),
+                None => MappedLocalTime::None,
+            },
+            MappedLocalTime::Ambiguous(min, max) => match (f(min), f(max)) {
+                (Some(min), Some(max)) => MappedLocalTime::Ambiguous(min, max),
+                _ => MappedLocalTime::None,
+            },
+        }
+    }
 }
 
 /// The conversion result from the local time to the timezone-aware datetime types.
@@ -547,26 +565,11 @@ pub trait TimeZone: Sized + Clone {
     /// Converts the local `NaiveDateTime` to the timezone-aware `DateTime` if possible.
     #[allow(clippy::wrong_self_convention)]
     fn from_local_datetime(&self, local: &NaiveDateTime) -> MappedLocalTime<DateTime<Self>> {
-        // Return `MappedLocalTime::None` when the offset pushes a value out of range, instead of
-        // panicking.
-        match self.offset_from_local_datetime(local) {
-            MappedLocalTime::None => MappedLocalTime::None,
-            MappedLocalTime::Single(offset) => match local.checked_sub_offset(offset.fix()) {
-                Some(dt) => {
-                    MappedLocalTime::Single(DateTime::from_naive_utc_and_offset(dt, offset))
-                }
-                None => MappedLocalTime::None,
-            },
-            MappedLocalTime::Ambiguous(o1, o2) => {
-                match (local.checked_sub_offset(o1.fix()), local.checked_sub_offset(o2.fix())) {
-                    (Some(d1), Some(d2)) => MappedLocalTime::Ambiguous(
-                        DateTime::from_naive_utc_and_offset(d1, o1),
-                        DateTime::from_naive_utc_and_offset(d2, o2),
-                    ),
-                    _ => MappedLocalTime::None,
-                }
-            }
-        }
+        self.offset_from_local_datetime(local).and_then(|off| {
+            local
+                .checked_sub_offset(off.fix())
+                .map(|dt| DateTime::from_naive_utc_and_offset(dt, off))
+        })
     }
 
     /// Creates the offset for given UTC `NaiveDate`. This cannot fail.