//! Lock-free history of the input plus the host transport, shared by the audio and GUI threads.
//!
//! The audio thread writes samples with relaxed stores and publishes the frame count with a
//! release store. The GUI thread reads the count with acquire, copies, then checks the count
//! again: anything the writer may have overwritten during the copy is reported, never returned.
use std::sync::atomic::{AtomicU32, AtomicU64, Ordering};

/// Transport markers kept for alignment; one is written at least every half second.
pub const MARKERS: usize = 512;

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Transport {
    pub playing: bool,
    pub tempo: f64,
    /// Song position in quarter notes at the first sample of the block.
    pub beats: f64,
    pub numerator: u32,
    pub denominator: u32,
}
impl Transport {
    /// Bar length in quarter notes.
    pub fn bar(&self) -> f64 {
        self.numerator.max(1) as f64 * 4. / self.denominator.max(1) as f64
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Marker {
    /// Absolute recorded frame index.
    pub frame: u64,
    pub transport: Transport,
}
impl Marker {
    /// Song position at `frame`, extrapolated at this marker's tempo.
    pub fn beats_at(&self, frame: f64, rate: f64) -> f64 {
        self.transport.beats + (frame - self.frame as f64) / rate * self.transport.tempo / 60.
    }
    pub fn frame_at(&self, beats: f64, rate: f64) -> f64 {
        self.frame as f64 + (beats - self.transport.beats) * 60. / self.transport.tempo * rate
    }
}

pub struct Ring {
    rate: f32,
    frames: usize,
    data: Box<[AtomicU32]>,
    written: AtomicU64,
    markers: Box<[[AtomicU64; 4]]>,
    marker_count: AtomicU64,
    peak: AtomicU32,
}
impl Ring {
    /// Stereo history of `seconds` at `rate`.
    pub fn new(rate: f32, seconds: f32) -> Self {
        let frames = (rate * seconds).ceil().max(1.) as usize;
        Self {
            rate,
            frames,
            data: (0..frames * 2).map(|_| AtomicU32::new(0)).collect(),
            written: AtomicU64::new(0),
            markers: (0..MARKERS)
                .map(|_| std::array::from_fn(|_| AtomicU64::new(0)))
                .collect(),
            marker_count: AtomicU64::new(0),
            peak: AtomicU32::new(0),
        }
    }
    pub fn rate(&self) -> f32 {
        self.rate
    }
    pub fn capacity(&self) -> usize {
        self.frames
    }
    pub fn written(&self) -> u64 {
        self.written.load(Ordering::Acquire)
    }
    /// Input peak since the last call, for the editor meter.
    pub fn take_peak(&self) -> f32 {
        f32::from_bits(self.peak.swap(0, Ordering::AcqRel))
    }
    /// Markers that are certainly intact, oldest first.
    pub fn markers(&self) -> Vec<Marker> {
        let count = self.marker_count.load(Ordering::Acquire);
        // A margin keeps slots the writer may be refilling during this read out of the result.
        let first = count.saturating_sub(MARKERS as u64 - 8);
        let mut out: Vec<Marker> = (first..count)
            .map(|i| {
                let s = &self.markers[(i % MARKERS as u64) as usize];
                let meta = s[3].load(Ordering::Relaxed);
                Marker {
                    frame: s[0].load(Ordering::Relaxed),
                    transport: Transport {
                        beats: f64::from_bits(s[1].load(Ordering::Relaxed)),
                        tempo: f64::from_bits(s[2].load(Ordering::Relaxed)),
                        numerator: (meta & 0xffff) as u32,
                        denominator: ((meta >> 16) & 0xffff) as u32,
                        playing: meta >> 32 & 1 == 1,
                    },
                }
            })
            .collect();
        let after = self.marker_count.load(Ordering::Acquire);
        let safe = after.saturating_sub(MARKERS as u64 - 8);
        out.drain(..(safe.saturating_sub(first) as usize).min(out.len()));
        out
    }
    /// Copies frames `[start, end)` as interleaved stereo. Fails if any were overwritten.
    pub fn copy(&self, start: u64, end: u64) -> Result<Vec<f32>, &'static str> {
        let written = self.written();
        if end > written || start > end {
            return Err("Capture range is not recorded yet.");
        }
        if written - start > self.frames as u64 {
            return Err("Capture is longer than the recording buffer.");
        }
        let mut out = Vec::with_capacity(((end - start) * 2) as usize);
        for f in start..end {
            let at = (f % self.frames as u64) as usize * 2;
            out.push(f32::from_bits(self.data[at].load(Ordering::Relaxed)));
            out.push(f32::from_bits(self.data[at + 1].load(Ordering::Relaxed)));
        }
        if self.written() - start > self.frames as u64 {
            return Err("Capture was overwritten while copying. Try again.");
        }
        Ok(out)
    }
}

/// Audio-thread writer. Never allocates.
pub struct Recorder {
    last: Option<Marker>,
    frame: u64,
    since_marker: u64,
    peak: f32,
}
impl Default for Recorder {
    fn default() -> Self {
        Self::new()
    }
}
impl Recorder {
    pub fn new() -> Self {
        Self {
            last: None,
            frame: 0,
            since_marker: 0,
            peak: 0.,
        }
    }
    /// Call at the start of every block with the host transport.
    pub fn block(&mut self, ring: &Ring, transport: Option<Transport>) {
        let Some(t) =
            transport.filter(|t| t.tempo.is_finite() && t.tempo > 1. && t.beats.is_finite())
        else {
            return;
        };
        let rate = ring.rate as f64;
        let changed = match self.last {
            None => true,
            Some(m) => {
                let expected = m.beats_at(self.frame as f64, rate);
                m.transport.playing != t.playing
                    || (m.transport.tempo - t.tempo).abs() > 1e-6
                    || m.transport.numerator != t.numerator
                    || m.transport.denominator != t.denominator
                    || (t.playing && (expected - t.beats).abs() > 0.01)
            }
        };
        if changed || self.since_marker as f64 >= rate * 0.5 {
            let m = Marker {
                frame: self.frame,
                transport: t,
            };
            let count = ring.marker_count.load(Ordering::Relaxed);
            let s = &ring.markers[(count % MARKERS as u64) as usize];
            s[0].store(m.frame, Ordering::Relaxed);
            s[1].store(t.beats.to_bits(), Ordering::Relaxed);
            s[2].store(t.tempo.to_bits(), Ordering::Relaxed);
            let meta = (t.numerator as u64 & 0xffff)
                | (t.denominator as u64 & 0xffff) << 16
                | (t.playing as u64) << 32;
            s[3].store(meta, Ordering::Relaxed);
            ring.marker_count.store(count + 1, Ordering::Release);
            self.last = Some(m);
            self.since_marker = 0;
        }
    }
    #[inline]
    pub fn push(&mut self, ring: &Ring, frame: [f32; 2]) {
        let at = (self.frame % ring.frames as u64) as usize * 2;
        ring.data[at].store(frame[0].to_bits(), Ordering::Relaxed);
        ring.data[at + 1].store(frame[1].to_bits(), Ordering::Relaxed);
        self.frame += 1;
        self.since_marker += 1;
        self.peak = self.peak.max(frame[0].abs()).max(frame[1].abs());
    }
    /// Makes the frames pushed so far visible to the GUI thread. Call at the end of a block.
    pub fn publish(&mut self, ring: &Ring) {
        ring.written.store(self.frame, Ordering::Release);
        let old = f32::from_bits(ring.peak.load(Ordering::Relaxed));
        if self.peak > old {
            ring.peak.store(self.peak.to_bits(), Ordering::Relaxed);
        }
        self.peak = 0.;
    }
}