add some fft stuff

Cargo.toml

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+[workspace]
+members = ["pleep"]
+resolver = "2"

pleep/Cargo.toml

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+[package]
+name = "pleep"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+num-complex = "0.4.6"
+num-traits = "0.2.19"
+rustfft = "6.2.0"

pleep/src/lib.rs

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+pub mod spectrogram;

pleep/src/spectrogram.rs

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+use std::sync::{Arc, Mutex};
+
+use num_complex::Complex;
+use rustfft::{Fft, FftPlanner};
+
+pub trait Float: rustfft::FftNum + num_traits::Float {}
+impl Float for f64 {}
+impl Float for f32 {}
+
+#[derive(Clone)]
+pub struct Generator<T: Float> {
+    fft_planner: Arc<Mutex<FftPlanner<T>>>,
+}
+
+impl<T: Float> Generator<T> {
+    pub fn new() -> Self {
+        Self {
+            fft_planner: Arc::new(Mutex::new(rustfft::FftPlanner::new())),
+        }
+    }
+
+    pub fn generate_spectrogram(&self, samples: &[T], settings: &Settings) -> Vec<Vec<T>> {
+        let fft = self.get_forward_fft(settings.fft_len);
+        let scratch_size = fft.get_outofplace_scratch_len();
+        let mut scratch = vec![Complex::new(T::zero(), T::zero()); scratch_size];
+
+        let spectrogram = samples
+            .into_iter()
+            .map(|sample| Complex::new(*sample, T::zero()))
+            .collect::<Vec<_>>()
+            .windows(settings.fft_len)
+            .step_by(settings.fft_len - settings.fft_overlap)
+            .map(|sample_group| {
+                let mut group = sample_group.to_vec();
+                fft.process_with_scratch(&mut group, &mut scratch);
+                group
+            })
+            .map(|group| {
+                group
+                    .into_iter()
+                    .take(settings.fft_len / 2)
+                    .map(|v| v.norm())
+                    .collect::<Vec<_>>()
+            })
+            .collect::<Vec<_>>();
+
+        spectrogram
+    }
+
+    fn get_forward_fft(&self, len: usize) -> Arc<dyn Fft<T>> {
+        let mut planner = self.fft_planner.lock().unwrap();
+
+        planner.plan_fft_forward(len)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Settings {
+    fft_len: usize,
+    fft_overlap: usize,
+}