//! Silero V5 VAD candle port — pure Rust + candle 0.9, NO `ort` /
//! ONNX runtime, NO sentencepiece-protobuf conflict (the issue that
//! deferred this in Phase 8.1.3).
//!
//! Direct port of `Snakers4/silero-vad/src/silero_vad/tinygrad_model.py`
//! (71 LOC, canonical small-framework reference). Architecture facts
//! captured in `docs/silero_vad_port_notes.md`.
//!
//! ## Usage
//!
//! ```ignore
//! let vad = SileroVad::load_default(&device)?;
//! let mut state = SileroState::zero(&device)?;
//! // 512 samples per chunk @ 16 kHz = 32 ms; +64 context prefix.
//! for chunk in audio.chunks(512) {
//!     let p = vad.forward_step(chunk, &mut state)?;
//!     println!("speech prob = {p:.3}");
//! }
//! ```

use candle_core::{D, DType, Device, Module, Result, Tensor};
use candle_nn::{Conv1d, Conv1dConfig, VarBuilder};

const N_FFT: usize = 256;
const STRIDE: usize = 128;
const PAD_RIGHT: usize = 64;
const CHUNK_SAMPLES: usize = 512;
const CONTEXT_SAMPLES: usize = 64;
const CUTOFF: usize = N_FFT / 2 + 1; // 129

/// LSTM hidden + cell state for stateful per-stream detection. Pass
/// the same `SileroState` across consecutive `forward_step` calls on
/// the same audio stream.
pub struct SileroState {
    h: Tensor, // (1, 128)
    c: Tensor, // (1, 128)
}

impl SileroState {
    pub fn zero(device: &Device) -> Result<Self> {
        Ok(Self {
            h: Tensor::zeros((1, 128), DType::F32, device)?,
            c: Tensor::zeros((1, 128), DType::F32, device)?,
        })
    }
}

/// Single LSTM cell port. Uses fused weight_ih (input -> 4*hidden)
/// and weight_hh (hidden -> 4*hidden) tensors as PyTorch does.
struct LstmCell {
    weight_ih: Tensor, // (4*hidden, input)
    weight_hh: Tensor, // (4*hidden, hidden)
    bias_ih: Tensor,   // (4*hidden,)
    bias_hh: Tensor,   // (4*hidden,)
    hidden: usize,
}

impl LstmCell {
    fn new(input_size: usize, hidden: usize, vb: VarBuilder) -> Result<Self> {
        let weight_ih = vb.get((4 * hidden, input_size), "weight_ih")?;
        let weight_hh = vb.get((4 * hidden, hidden), "weight_hh")?;
        let bias_ih = vb.get(4 * hidden, "bias_ih")?;
        let bias_hh = vb.get(4 * hidden, "bias_hh")?;
        Ok(Self {
            weight_ih,
            weight_hh,
            bias_ih,
            bias_hh,
            hidden,
        })
    }

    /// `x`: `(B, input)`. `state.h`/`state.c`: `(B, hidden)`.
    /// Returns updated `(h, c)`.
    fn forward(&self, x: &Tensor, state: &SileroState) -> Result<(Tensor, Tensor)> {
        // gates = x @ Wih.T + bih + h @ Whh.T + bhh
        let gx = x
            .matmul(&self.weight_ih.t()?)?
            .broadcast_add(&self.bias_ih)?;
        let gh = state
            .h
            .matmul(&self.weight_hh.t()?)?
            .broadcast_add(&self.bias_hh)?;
        let gates = (gx + gh)?;
        // Split into [i, f, g, o] along the last dim.
        let h = self.hidden;
        let i = candle_nn::ops::sigmoid(&gates.narrow(D::Minus1, 0, h)?)?;
        let f = candle_nn::ops::sigmoid(&gates.narrow(D::Minus1, h, h)?)?;
        let g = gates.narrow(D::Minus1, 2 * h, h)?.tanh()?;
        let o = candle_nn::ops::sigmoid(&gates.narrow(D::Minus1, 3 * h, h)?)?;
        // c' = f * c + i * g
        let c_new = ((f * &state.c)? + (i * g)?)?;
        // h' = o * tanh(c')
        let h_new = (o * c_new.tanh()?)?;
        Ok((h_new, c_new))
    }
}

/// Silero V5 VAD model.
pub struct SileroVad {
    stft_conv: Conv1d,
    conv1: Conv1d,
    conv2: Conv1d,
    conv3: Conv1d,
    conv4: Conv1d,
    lstm: LstmCell,
    final_conv: Conv1d,
}

impl SileroVad {
    pub fn new(vb: VarBuilder) -> Result<Self> {
        let stft_conv = candle_nn::conv1d_no_bias(
            1,
            258,
            N_FFT,
            Conv1dConfig {
                padding: 0,
                stride: STRIDE,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("stft_conv"),
        )?;
        let conv1 = candle_nn::conv1d(
            CUTOFF, // 129
            128,
            3,
            Conv1dConfig {
                padding: 1,
                stride: 1,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("conv1"),
        )?;
        let conv2 = candle_nn::conv1d(
            128,
            64,
            3,
            Conv1dConfig {
                padding: 1,
                stride: 2,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("conv2"),
        )?;
        let conv3 = candle_nn::conv1d(
            64,
            64,
            3,
            Conv1dConfig {
                padding: 1,
                stride: 2,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("conv3"),
        )?;
        let conv4 = candle_nn::conv1d(
            64,
            128,
            3,
            Conv1dConfig {
                padding: 1,
                stride: 1,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("conv4"),
        )?;
        let lstm = LstmCell::new(128, 128, vb.pp("lstm_cell"))?;
        let final_conv = candle_nn::conv1d(
            128,
            1,
            1,
            Conv1dConfig {
                padding: 0,
                stride: 1,
                dilation: 1,
                groups: 1,
                cudnn_fwd_algo: None,
            },
            vb.pp("final_conv"),
        )?;
        Ok(Self {
            stft_conv,
            conv1,
            conv2,
            conv3,
            conv4,
            lstm,
            final_conv,
        })
    }

    /// Download (cached) the upstream `Snakers4/silero-vad` 16 kHz
    /// safetensors and load. ~1.24 MB; cached under
    /// `~/.cache/silero-vad/silero_vad_16k.safetensors` after first use.
    pub fn load_default(device: &Device) -> Result<Self> {
        let path = ensure_default_weights()?;
        Self::load_from_file(&path, device)
    }

    pub fn load_from_file(path: &std::path::Path, device: &Device) -> Result<Self> {
        let vb = unsafe { VarBuilder::from_mmaped_safetensors(&[path], DType::F32, device) }?;
        Self::new(vb)
    }

    /// Forward one chunk. `samples` must contain `CONTEXT_SAMPLES + CHUNK_SAMPLES`
    /// samples (576 total). Returns the speech probability in `[0, 1]`
    /// and updates the LSTM state in place.
    pub fn forward_step(&self, samples: &[f32], state: &mut SileroState) -> Result<f32> {
        if samples.len() != CHUNK_SAMPLES + CONTEXT_SAMPLES {
            return Err(candle_core::Error::Msg(format!(
                "silero_vad: expected {} samples, got {}",
                CHUNK_SAMPLES + CONTEXT_SAMPLES,
                samples.len()
            )));
        }
        let device = state.h.device();

        // Build (B=1, T=576) tensor and reflect-pad on the right by 64.
        let mut padded = Vec::with_capacity(samples.len() + PAD_RIGHT);
        padded.extend_from_slice(samples);
        // Reflect padding: last sample, second-to-last, ... up to PAD_RIGHT.
        let n = samples.len();
        for i in 0..PAD_RIGHT {
            // PyTorch reflect skips the boundary sample (idx n-1) for the
            // first reflected sample — i.e. mirror around idx n-1.
            // padded[n + i] = samples[n - 2 - i] for i in 0..pad_right.
            let src = (n as isize - 2 - i as isize).max(0) as usize;
            padded.push(samples[src.min(n - 1)]);
        }
        let x = Tensor::from_vec(padded, (1, 1, samples.len() + PAD_RIGHT), device)?;

        // STFT conv -> (1, 258, n_frames)
        let x = self.stft_conv.forward(&x)?;
        // Magnitude: sqrt(real² + imag²) for the first 129 bins; output
        // has shape (1, 129, n_frames).
        let real = x.narrow(1, 0, CUTOFF)?;
        let imag = x.narrow(1, CUTOFF, CUTOFF)?;
        let mag = (real.sqr()? + imag.sqr()?)?.sqrt()?;

        // 4-layer Conv1d feature extractor.
        let h = self.conv1.forward(&mag)?.relu()?;
        let h = self.conv2.forward(&h)?.relu()?;
        let h = self.conv3.forward(&h)?.relu()?;
        let h = self.conv4.forward(&h)?.relu()?;
        // Collapse the time axis (it's now 1 frame after the strides).
        // Shape: (1, 128, 1) -> (1, 128).
        let h = h.squeeze(D::Minus1)?;

        // LSTM step.
        let (h_new, c_new) = self.lstm.forward(&h, state)?;
        // unsqueeze -> (1, 128, 1) -> ReLU -> final 1x1 conv -> sigmoid
        let y = h_new.unsqueeze(D::Minus1)?;
        let y = y.relu()?;
        let y = self.final_conv.forward(&y)?;
        let y = candle_nn::ops::sigmoid(&y)?;
        // y shape: (1, 1, 1). Squeeze + mean -> scalar.
        let prob: f32 = y.flatten_all()?.to_vec1::<f32>()?[0];

        // Update state.
        state.h = h_new;
        state.c = c_new;

        Ok(prob)
    }

    /// Sweep the model over a multi-chunk audio buffer. Returns one
    /// probability per `CHUNK_SAMPLES` chunk. Pads the input with
    /// `CONTEXT_SAMPLES` zeros at the front and zero-pads the tail to
    /// a whole-chunk multiple. State is owned internally.
    pub fn forward_audio(&self, samples: &[f32], device: &Device) -> Result<Vec<f32>> {
        let mut state = SileroState::zero(device)?;
        // Front-pad with CONTEXT_SAMPLES zeros (the "context" the model
        // expects on the first chunk).
        let mut padded: Vec<f32> = vec![0.0; CONTEXT_SAMPLES];
        padded.extend_from_slice(samples);
        // Tail-pad to whole-chunk multiple.
        let extra = (CHUNK_SAMPLES - (samples.len() % CHUNK_SAMPLES)) % CHUNK_SAMPLES;
        padded.extend(std::iter::repeat_n(0.0, extra));

        let mut probs = Vec::new();
        let mut i = 0;
        while i + CHUNK_SAMPLES + CONTEXT_SAMPLES <= padded.len() + CONTEXT_SAMPLES {
            // Window: padded[i .. i + CHUNK_SAMPLES + CONTEXT_SAMPLES]
            let end = i + CHUNK_SAMPLES + CONTEXT_SAMPLES;
            if end > padded.len() {
                break;
            }
            let window = &padded[i..end];
            let p = self.forward_step(window, &mut state)?;
            probs.push(p);
            i += CHUNK_SAMPLES;
        }
        Ok(probs)
    }
}

/// Ensure the upstream Silero V5 safetensors is cached locally and
/// return its path. Downloads from the Snakers4/silero-vad GitHub
/// raw URL on first use; ~1.24 MB. Cache lives at
/// `~/.cache/rtx-csm/silero_vad_16k.safetensors`.
pub fn ensure_default_weights() -> Result<std::path::PathBuf> {
    const URL: &str = "https://raw.githubusercontent.com/snakers4/silero-vad/master/src/silero_vad/data/silero_vad_16k.safetensors";
    let cache_dir = dirs_cache_dir().join("rtx-csm");
    let path = cache_dir.join("silero_vad_16k.safetensors");
    if path.exists() {
        return Ok(path);
    }
    std::fs::create_dir_all(&cache_dir)
        .map_err(|e| candle_core::Error::Msg(format!("create cache dir: {e}")))?;
    let bytes = ureq::get(URL)
        .call()
        .map_err(|e| candle_core::Error::Msg(format!("fetch silero weights: {e}")))?
        .into_body()
        .read_to_vec()
        .map_err(|e| candle_core::Error::Msg(format!("read silero body: {e}")))?;
    std::fs::write(&path, &bytes)
        .map_err(|e| candle_core::Error::Msg(format!("write silero cache: {e}")))?;
    Ok(path)
}

fn dirs_cache_dir() -> std::path::PathBuf {
    if let Some(home) = std::env::var_os("HOME") {
        std::path::PathBuf::from(home).join(".cache")
    } else {
        std::env::temp_dir()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn loads_default_weights_and_runs_one_step() {
        let device = Device::Cpu;
        let model = SileroVad::load_default(&device).expect("load weights");
        let mut state = SileroState::zero(&device).expect("state");
        // Random-ish input chunk (576 samples).
        let samples: Vec<f32> = (0..576).map(|i| ((i as f32 * 0.01).sin() * 0.1)).collect();
        let prob = model
            .forward_step(&samples, &mut state)
            .expect("forward_step");
        assert!(
            (0.0..=1.0).contains(&prob),
            "speech prob out of range: {prob}"
        );
    }
}