feat: add a nanos_at function

Author: frectonz

README.md

@@ -15,6 +15,7 @@ SELECT when_is('5 days ago at this hour in Asia/Tokyo');
 SELECT seconds_at('5 days ago at this hour in Asia/Tokyo');
 SELECT millis_at('5 days ago at this hour in Asia/Tokyo');
 SELECT micros_at('5 days ago at this hour in Asia/Tokyo');
+SELECT nanos_at('5 days ago at this hour in Asia/Tokyo');
 ```
 
 </details>
@@ -30,6 +31,7 @@ SELECT when_is('next friday at 8:00 pm in America/New_York');
 SELECT seconds_at('next friday at 8:00 pm in America/New_York');
 SELECT millis_at('next friday at 8:00 pm in America/New_York');
 SELECT micros_at('next friday at 8:00 pm in America/New_York');
+SELECT nanos_at('next friday at 8:00 pm in America/New_York');
 ```
 
 </details>
@@ -45,6 +47,7 @@ SELECT when_is('in 2 months at midnight in UTC-8');
 SELECT seconds_at('in 2 months at midnight in UTC-8');
 SELECT millis_at('in 2 months at midnight in UTC-8');
 SELECT micros_at('in 2 months at midnight in UTC-8');
+SELECT nanos_at('in 2 months at midnight in UTC-8');
 ```
 
 </details>
@@ -60,6 +63,7 @@ SELECT when_is('last monday at 22:30');
 SELECT seconds_at('last monday at 22:30');
 SELECT millis_at('last monday at 22:30');
 SELECT micros_at('last monday at 22:30');
+SELECT nanos_at('last monday at 22:30');
 ```
 
 </details>
@@ -75,6 +79,7 @@ SELECT when_is('December 31, 2026 at evening');
 SELECT seconds_at('December 31, 2026 at evening');
 SELECT millis_at('December 31, 2026 at evening');
 SELECT micros_at('December 31, 2026 at evening');
+SELECT nanos_at('December 31, 2026 at evening');
 ```
 
 </details>
@@ -169,6 +174,7 @@ The following functions are provided by the Postgres extension.
 | `seconds_at`  | `BIGINT`                   | Returns the total seconds since the UNIX epoch.      |
 | `millis_at`   | `BIGINT`                   | Returns the total milliseconds since the UNIX epoch. |
 | `micros_at`   | `BIGINT`                   | Returns the total microseconds since the UNIX epoch. |
+| `nanos_at`    | `BIGINT`                   | Returns the total microseconds since the UNIX epoch. |
 
 ## Usage
 

src/when_is.rs

@@ -55,3 +55,13 @@ fn micros_at(input: &str) -> i64 {
     let zoned = input.to_timestamp().unwrap_or_report();
     zoned.timestamp().as_microsecond()
 }
+
+#[pg_extern(strict, immutable, parallel_safe)]
+fn nanos_at(input: &str) -> i64 {
+    let input = parse_input(input);
+    let zoned = input.to_timestamp().unwrap_or_report();
+    match zoned.timestamp().as_nanosecond().try_into() {
+        Ok(nanos) => nanos,
+        Err(_) => error!("nanosecond can not be represented as a bigint"),
+    }
+}