From af484658565920005a502553422530493a5d91de Mon Sep 17 00:00:00 2001
From: Jacob Lee <jacob@unabridgedsoftware.com>
Date: Wed, 24 Nov 2021 23:32:31 -0500
Subject: Refactor envelope to use line iterator

---
 klangfarbrs/src/line.rs | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)
 create mode 100644 klangfarbrs/src/line.rs

(limited to 'klangfarbrs/src/line.rs')

diff --git a/klangfarbrs/src/line.rs b/klangfarbrs/src/line.rs
new file mode 100644
index 0000000..f57b103
--- /dev/null
+++ b/klangfarbrs/src/line.rs
@@ -0,0 +1,68 @@
+use super::{Millisecond, Amplitude, SamplesPerSecond};
+
+pub struct Line {
+    pub start: Amplitude,
+    pub end: Amplitude,
+    pub duration: Millisecond,
+    pub index: u32,
+    slope: f32,
+    samples: u32
+}
+
+impl Line {
+    pub fn new(
+        start: Amplitude, end: Amplitude, duration: Millisecond, sample_rate: SamplesPerSecond
+    ) -> Self {
+        Self { start, end, duration, index: 0, slope: slope(start, end, ms_to_samples(duration, sample_rate)), samples: ms_to_samples(duration, sample_rate) }
+    }
+}
+
+impl Iterator for Line {
+    type Item = Amplitude;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let idx = self.index;
+        let val = self.slope * idx as f32 + self.start;
+        self.index += 1;
+ 
+        if idx <= self.samples {
+            Some(val)
+        } else {
+            None
+        }
+          
+    }
+}
+
+fn slope(start: Amplitude, end: Amplitude, duration: Millisecond) -> f32 {
+  return (end - start) / duration as f32 ;
+}
+
+fn ms_to_samples(ms: Millisecond, sample_rate: SamplesPerSecond) -> u32 {
+    let multiplier = sample_rate as u32 / 1000;
+    multiplier * ms
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_calculates_a_slope() {
+      let expected = 0.5;
+      let slope = slope(0.0, 0.5, 1);
+      assert_eq! (expected, slope)
+    }
+
+    #[test]
+    fn it_calculates_the_next_values() {
+      let mut line = Line::new(0.0, 0.5, 1, 5000.0);
+      assert_eq!(0.0, line.next().unwrap());
+      assert_eq!(0.1, line.next().unwrap());
+      assert_eq!(0.2, line.next().unwrap());
+      assert_eq!(0.3, line.next().unwrap());
+      assert_eq!(0.4, line.next().unwrap());
+      assert_eq!(0.5, line.next().unwrap());
+      assert_eq!(None, line.next());
+    }
+}
-- 
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