From f2e679518040268e5d64ec857faef37c3d9a2cc0 Mon Sep 17 00:00:00 2001
From: ely-uf <ely-uf@protonmail.com>
Date: Sat, 8 Aug 2020 19:26:33 +0300
Subject: [PATCH] Add SkipDuration.

SkipDuration is a source that skips specified duration of the given
source from it's current position.

The already existing TakeDuration source allows to truncate the given source
from the end. SkipDuration complements it, introducing the option of
truncating the given source from it's current position.
---
 src/source/mod.rs  | 10 ++++++
 src/source/skip.rs | 76 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)
 create mode 100644 src/source/skip.rs

diff --git a/src/source/mod.rs b/src/source/mod.rs
index a26544c..b03d3bb 100644
--- a/src/source/mod.rs
+++ b/src/source/mod.rs
@@ -21,6 +21,7 @@ pub use self::periodic::PeriodicAccess;
 pub use self::repeat::Repeat;
 pub use self::samples_converter::SamplesConverter;
 pub use self::sine::SineWave;
+pub use self::skip::SkipDuration;
 pub use self::spatial::Spatial;
 pub use self::speed::Speed;
 pub use self::stoppable::Stoppable;
@@ -45,6 +46,7 @@ mod periodic;
 mod repeat;
 mod samples_converter;
 mod sine;
+mod skip;
 mod spatial;
 mod speed;
 mod stoppable;
@@ -195,6 +197,14 @@ where
         delay::delay(self, duration)
     }
 
+    #[inline]
+    fn skip_duration(self, duration: Duration) -> SkipDuration<Self>
+    where
+        Self: Sized,
+    {
+        skip::skip_duration(self, duration)
+    }
+
     /// Amplifies the sound by the given value.
     #[inline]
     fn amplify(self, value: f32) -> Amplify<Self>
diff --git a/src/source/skip.rs b/src/source/skip.rs
new file mode 100644
index 0000000..430fc13
--- /dev/null
+++ b/src/source/skip.rs
@@ -0,0 +1,76 @@
+use crate::{Sample, Source};
+use std::time::Duration;
+
+pub fn skip_duration<I>(mut input: I, duration: Duration) -> SkipDuration<I>
+where
+    I: Source,
+    I::Item: Sample,
+{
+    let duration_ns = duration.as_nanos();
+    let samples_to_skip =
+        duration_ns * input.sample_rate() as u128 / 1_000_000_000 * input.channels() as u128;
+
+    for _ in 0..samples_to_skip {
+        if input.next().is_none() {
+            break;
+        }
+    }
+
+    SkipDuration {
+        input,
+        skipped_duration: duration,
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct SkipDuration<I> {
+    input: I,
+    skipped_duration: Duration,
+}
+
+impl<I> Iterator for SkipDuration<I>
+where
+    I: Source,
+    I::Item: Sample,
+{
+    type Item = <I as Iterator>::Item;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.input.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.input.size_hint()
+    }
+}
+
+impl<I> Source for SkipDuration<I>
+where
+    I: Source,
+    I::Item: Sample,
+{
+    #[inline]
+    fn current_frame_len(&self) -> Option<usize> {
+        self.input.current_frame_len()
+    }
+
+    #[inline]
+    fn channels(&self) -> u16 {
+        self.input.channels()
+    }
+
+    #[inline]
+    fn sample_rate(&self) -> u32 {
+        self.input.sample_rate()
+    }
+
+    #[inline]
+    fn total_duration(&self) -> Option<Duration> {
+        self.input.total_duration().map(|val| {
+            val.checked_sub(self.skipped_duration)
+                .unwrap_or(Duration::from_secs(0))
+        })
+    }
+}