//! inference.rs — continuous batching loop with dual-trigger flush
//!
//! Architecture:
//!   - Tokio MPSC channel receives VerifyRequests from HTTP handlers
//!   - tokio::select! races: MAX_BATCH_SIZE trigger vs 5 ms timer
//!   - execute_batch: dynamic pad → ndarray → TRT forward → softmax → BLAKE3 seal
//!   - Attestations dispatched to background WORM ledger worker
//!   - Results routed back through oneshot channels (no polling)

use std::sync::Arc;
use std::time::SystemTime;

use ndarray::{s, Array2};
use ort::Session;
use tokio::sync::mpsc;
use tokio::time::{interval, Duration};

use crate::types::{
    DaemonConfig, EntailmentAttestation, Verdict, VerifyRequest, VerifyResponse,
};

// ── Softmax ─────────────────────────────────────────────────────────────────

fn softmax_entailment(logits: &[f32]) -> f32 {
    // logits: [contradiction, neutral, entailment]
    let max_l = logits.iter().cloned().fold(f32::NEG_INFINITY, f32::max);
    let exps: Vec<f32> = logits.iter().map(|l| (l - max_l).exp()).collect();
    let sum: f32 = exps.iter().sum();
    exps[2] / sum   // P(Entailment)
}

// ── Batch execution ──────────────────────────────────────────────────────────

async fn execute_batch(
    batch: &mut Vec<VerifyRequest>,
    session: &Arc<Session>,
    cfg: &DaemonConfig,
    ledger_tx: &mpsc::Sender<([u8; 32], Vec<u8>)>,
) {
    if batch.is_empty() {
        return;
    }

    let batch_size = batch.len();

    // 1. Dynamic padding: pad to the longest sequence in THIS batch (not global max).
    //    Avoids wasting compute padding short sequences to 512.
    let max_len = batch
        .iter()
        .map(|r| r.input_ids.len())
        .max()
        .unwrap_or(0);

    let mut input_ids_arr      = Array2::<i64>::zeros((batch_size, max_len));
    let mut attention_mask_arr = Array2::<i64>::zeros((batch_size, max_len));
    let mut token_types_arr    = Array2::<i64>::zeros((batch_size, max_len));

    for (i, req) in batch.iter().enumerate() {
        let len = req.input_ids.len().min(max_len);
        input_ids_arr
            .slice_mut(s![i, ..len])
            .assign(&ndarray::ArrayView::from(&req.input_ids[..len]));
        attention_mask_arr
            .slice_mut(s![i, ..len])
            .assign(&ndarray::ArrayView::from(&req.attention_mask[..len]));
        token_types_arr
            .slice_mut(s![i, ..len])
            .assign(&ndarray::ArrayView::from(&req.token_type_ids[..len]));
    }

    // 2. Run TRT forward pass on a blocking thread (keeps async reactor free).
    let session_clone = Arc::clone(session);
    let outputs = tokio::task::spawn_blocking(move || {
        let inputs = ort::inputs![
            "input_ids"      => input_ids_arr,
            "attention_mask" => attention_mask_arr,
            "token_type_ids" => token_types_arr,
        ]
        .expect("input construction failed");
        session_clone.run(inputs).expect("TRT inference failed")
    })
    .await
    .expect("spawn_blocking panicked");

    // 3. Extract logits (B, 3) → entailment scores.
    let logits_tensor = outputs["logits"]
        .extract_tensor::<f32>()
        .expect("logits extraction failed");
    let logits_view = logits_tensor.view();   // shape (B, 3)

    let timestamp_ns = SystemTime::now()
        .duration_since(SystemTime::UNIX_EPOCH)
        .unwrap()
        .as_nanos() as u64;

    // 4. For each request: compute score → BLAKE3 seal → route response.
    for (i, req) in batch.drain(..).enumerate() {
        let row: Vec<f32> = logits_view
            .row(i)
            .iter()
            .cloned()
            .collect();
        let score   = softmax_entailment(&row);
        let verdict = Verdict::from_score(score, cfg.threshold);

        // 5. Build deterministic attestation and seal with BLAKE3.
        let attestation = EntailmentAttestation {
            timestamp_ns,
            chunk_id:         req.chunk_id.clone(),
            claim_text:       req.claim_text.clone(),
            entailment_score: score,
            verdict:          format!("{:?}", verdict),
            model_signature:  cfg.model_signature.clone(),
            threshold:        cfg.threshold,
        };
        let (hash, payload) = attestation.seal();

        // 6. Dispatch attestation to WORM ledger (non-blocking).
        let _ = ledger_tx.try_send((hash, payload));

        // 7. Return result to caller through oneshot channel.
        let _ = req.responder.send(VerifyResponse {
            entailment_score: score,
            label: verdict,
            attestation_hash: hash,
        });
    }
}

// ── Continuous batching event loop ───────────────────────────────────────────

/// Dual-trigger: flush when MAX_BATCH_SIZE is reached OR every flush_interval_ms.
/// Guarantees maximum latency = flush_interval_ms (default 5 ms).
pub async fn run_inference_daemon(
    mut rx: mpsc::Receiver<VerifyRequest>,
    session: Arc<Session>,
    cfg: Arc<DaemonConfig>,
    ledger_tx: mpsc::Sender<([u8; 32], Vec<u8>)>,
) {
    let mut batch: Vec<VerifyRequest> = Vec::with_capacity(cfg.max_batch_size);
    let mut flush_timer = interval(Duration::from_millis(cfg.flush_interval_ms));

    log::info!(
        "[daemon] running — max_batch={} flush_interval={}ms threshold={}",
        cfg.max_batch_size,
        cfg.flush_interval_ms,
        cfg.threshold
    );

    loop {
        tokio::select! {
            // New request arrived
            Some(req) = rx.recv() => {
                batch.push(req);
                if batch.len() >= cfg.max_batch_size {
                    execute_batch(&mut batch, &session, &cfg, &ledger_tx).await;
                }
            }
            // Flush timer fired — process whatever is in the queue
            _ = flush_timer.tick() => {
                if !batch.is_empty() {
                    execute_batch(&mut batch, &session, &cfg, &ledger_tx).await;
                }
            }
            // Channel closed — drain remaining requests and exit
            else => {
                if !batch.is_empty() {
                    execute_batch(&mut batch, &session, &cfg, &ledger_tx).await;
                }
                log::info!("[daemon] channel closed, shutting down");
                break;
            }
        }
    }
}