//! Shared data preparation utilities for hyperopt trainers.
//!
//! Provides common functions for loading DBN data, extracting features,
//! normalizing, and building (input, target) tensor pairs for supervised
//! model training during hyperparameter optimization.

use ml_core::device::MlDevice;
use ml_core::cuda_autograd::GpuTensor;
use serde::Serialize;
use std::fmt::Debug;
use std::path::Path;
use tracing::info;

use crate::features::extraction::OHLCVBar;
use crate::MLError;

/// Build flat (input, target) tensor pairs from extracted features and bars.
///
/// Each pair maps a single feature vector (51-dim) to a normalized close-price
/// return target. Features are z-score normalized using training-set statistics.
///
/// # Arguments
/// * `features` - Extracted feature vectors (51-dim each)
/// * `bars` - OHLCV bars aligned with features (offset by warmup period)
/// * `feature_dim` - Feature dimensionality (51)
/// * `device` - NativeDevice for tensor creation
pub fn build_flat_pairs(
    features: &[[f64; 42]],
    bars: &[OHLCVBar],
    feature_dim: usize,
    device: &MlDevice,
) -> Result<Vec<(GpuTensor, GpuTensor)>, MLError> {
    if features.len() < 2 {
        return Err(MLError::ModelError(
            "Need at least 2 feature vectors to build pairs".to_owned(),
        ));
    }

    // The feature extractor has a warmup of 50 bars, so features[i] corresponds
    // to bars[i + warmup]. We use the close-price return from the NEXT bar as target.
    // Since we don't know the exact warmup offset here, we use price returns
    // computed directly from consecutive features' corresponding bars.
    //
    // Simpler approach: target = normalized close-price return from consecutive features.
    // features[i] -> target = (close[i+1] - close[i]) / close[i] where close comes
    // from the bars that produced the features.
    //
    // Since we can't perfectly align bars<->features without the warmup constant,
    // use the last (features.len()) bars for targets.
    let n_bars = bars.len();
    let n_features = features.len();

    // features correspond to bars[offset..offset+n_features] where offset = n_bars - n_features
    let bar_offset = n_bars.saturating_sub(n_features);

    // Compute per-feature mean and std for z-score normalization
    let mut means = vec![0.0_f64; feature_dim];
    let mut vars = vec![0.0_f64; feature_dim];
    let count = n_features as f64;

    for feat in features.iter() {
        for (j, val) in feat.iter().enumerate() {
            if let Some(m) = means.get_mut(j) {
                *m += val;
            }
        }
    }
    for m in means.iter_mut() {
        *m /= count;
    }

    for feat in features.iter() {
        for (j, val) in feat.iter().enumerate() {
            if let (Some(v), Some(m)) = (vars.get_mut(j), means.get(j)) {
                *v += (val - m) * (val - m);
            }
        }
    }
    let stds: Vec<f64> = vars
        .iter()
        .map(|v| (v / count).sqrt().max(1e-8))
        .collect();

    // Compute target return statistics for normalization
    let mut returns = Vec::with_capacity(n_features.saturating_sub(1));
    for i in 0..n_features.saturating_sub(1) {
        let bar_idx = bar_offset + i;
        let next_bar_idx = bar_offset + i + 1;
        let close = bars.get(bar_idx).map(|b| b.close).unwrap_or(1.0);
        let next_close = bars.get(next_bar_idx).map(|b| b.close).unwrap_or(1.0);
        if close.abs() > 1e-12 {
            returns.push((next_close - close) / close);
        } else {
            returns.push(0.0);
        }
    }

    let ret_mean = returns.iter().sum::<f64>() / returns.len().max(1) as f64;
    let ret_std = (returns
        .iter()
        .map(|r| (r - ret_mean) * (r - ret_mean))
        .sum::<f64>()
        / returns.len().max(1) as f64)
        .sqrt()
        .max(1e-8);

    let mut pairs = Vec::with_capacity(returns.len());
    for (i, ret) in returns.iter().enumerate() {
        let feat = features.get(i).ok_or_else(|| {
            MLError::ModelError(format!("Feature index {} out of bounds", i))
        })?;

        // Z-score normalize features
        let normalized: Vec<f32> = feat
            .iter()
            .enumerate()
            .map(|(j, val)| {
                let m = means.get(j).copied().unwrap_or(0.0);
                let s = stds.get(j).copied().unwrap_or(1.0);
                ((val - m) / s) as f32
            })
            .collect();

        let target_normalized = ((ret - ret_mean) / ret_std) as f32;

        let stream = device.cuda_stream()
            .map_err(|e| MLError::ModelError(format!("CUDA stream: {}", e)))?;
        let input = GpuTensor::from_host(normalized.as_slice(), vec![normalized.len()], stream)
            .map_err(|e| MLError::ModelError(format!("Input tensor: {}", e)))?
            .reshape(vec![1, feature_dim])
            .map_err(|e| MLError::ModelError(format!("Input reshape: {}", e)))?;

        let target = GpuTensor::from_host(&[target_normalized], vec![1], stream)
            .map_err(|e| MLError::ModelError(format!("Target tensor: {}", e)))?
            .reshape(vec![1, 1])
            .map_err(|e| MLError::ModelError(format!("Target reshape: {}", e)))?;

        pairs.push((input, target));
    }

    info!(
        "Built {} (input, target) pairs, feature_dim={}, ret_mean={:.6}, ret_std={:.6}",
        pairs.len(),
        feature_dim,
        ret_mean,
        ret_std
    );

    Ok(pairs)
}

/// Build sequenced (input, target) tensor pairs for models requiring sequence input.
///
/// Each input has shape `(1, seq_len, feature_dim)` and target is `(1, 1)`.
///
/// # Arguments
/// * `features` - Extracted feature vectors
/// * `bars` - OHLCV bars
/// * `feature_dim` - Feature dimensionality (51)
/// * `seq_len` - Sequence length
/// * `device` - MlDevice for tensor creation
pub fn build_sequence_pairs(
    features: &[[f64; 42]],
    bars: &[OHLCVBar],
    feature_dim: usize,
    seq_len: usize,
    device: &MlDevice,
) -> Result<Vec<(GpuTensor, GpuTensor)>, MLError> {
    if features.len() < seq_len + 1 {
        return Err(MLError::ModelError(format!(
            "Need at least {} features for seq_len={}, got {}",
            seq_len + 1,
            seq_len,
            features.len()
        )));
    }

    let n_bars = bars.len();
    let n_features = features.len();
    let bar_offset = n_bars.saturating_sub(n_features);

    // Compute per-feature stats for normalization
    let mut means = vec![0.0_f64; feature_dim];
    let count = n_features as f64;
    for feat in features.iter() {
        for (j, val) in feat.iter().enumerate() {
            if let Some(m) = means.get_mut(j) {
                *m += val;
            }
        }
    }
    for m in means.iter_mut() {
        *m /= count;
    }

    let mut vars = vec![0.0_f64; feature_dim];
    for feat in features.iter() {
        for (j, val) in feat.iter().enumerate() {
            if let (Some(v), Some(m)) = (vars.get_mut(j), means.get(j)) {
                *v += (val - m) * (val - m);
            }
        }
    }
    let stds: Vec<f64> = vars
        .iter()
        .map(|v| (v / count).sqrt().max(1e-8))
        .collect();

    // Target: close-price returns
    let mut returns = Vec::with_capacity(n_features.saturating_sub(1));
    for i in 0..n_features.saturating_sub(1) {
        let bar_idx = bar_offset + i;
        let next_bar_idx = bar_offset + i + 1;
        let close = bars.get(bar_idx).map(|b| b.close).unwrap_or(1.0);
        let next_close = bars.get(next_bar_idx).map(|b| b.close).unwrap_or(1.0);
        if close.abs() > 1e-12 {
            returns.push((next_close - close) / close);
        } else {
            returns.push(0.0);
        }
    }

    let ret_mean = returns.iter().sum::<f64>() / returns.len().max(1) as f64;
    let ret_std = (returns
        .iter()
        .map(|r| (r - ret_mean) * (r - ret_mean))
        .sum::<f64>()
        / returns.len().max(1) as f64)
        .sqrt()
        .max(1e-8);

    let num_samples = n_features.saturating_sub(seq_len);
    let mut pairs = Vec::with_capacity(num_samples);

    for i in 0..num_samples {
        // Build sequence of normalized features
        let mut seq_data = Vec::with_capacity(seq_len * feature_dim);
        for t in 0..seq_len {
            let feat_idx = i + t;
            let feat = features.get(feat_idx).ok_or_else(|| {
                MLError::ModelError(format!("Feature index {} out of bounds", feat_idx))
            })?;
            for (j, val) in feat.iter().enumerate() {
                let m = means.get(j).copied().unwrap_or(0.0);
                let s = stds.get(j).copied().unwrap_or(1.0);
                seq_data.push(((val - m) / s) as f32);
            }
        }

        // Target: return at the step after the sequence
        let ret_idx = i + seq_len - 1;
        let target_val = returns
            .get(ret_idx)
            .map(|r| ((r - ret_mean) / ret_std) as f32)
            .unwrap_or(0.0);

        let stream = device.cuda_stream()
            .map_err(|e| MLError::ModelError(format!("CUDA stream: {}", e)))?;
        let input = GpuTensor::from_host(seq_data.as_slice(), vec![seq_data.len()], stream)
            .map_err(|e| MLError::ModelError(format!("Seq input tensor: {}", e)))?
            .reshape(vec![1, seq_len, feature_dim])
            .map_err(|e| MLError::ModelError(format!("Seq input reshape: {}", e)))?;

        let target = GpuTensor::from_host(&[target_val], vec![1], stream)
            .map_err(|e| MLError::ModelError(format!("Seq target tensor: {}", e)))?
            .reshape(vec![1, 1])
            .map_err(|e| MLError::ModelError(format!("Seq target reshape: {}", e)))?;

        pairs.push((input, target));
    }

    info!(
        "Built {} sequence pairs (seq_len={}, feature_dim={})",
        pairs.len(),
        seq_len,
        feature_dim
    );

    Ok(pairs)
}

/// Write a trial result to a JSON file (appending to existing trials).
pub fn write_trial_result_json<P: Serialize + Debug>(
    hyperopt_dir: &Path,
    trial_result: &crate::hyperopt::traits::TrialResult<P>,
) -> Result<(), std::io::Error> {
    let trials_file = hyperopt_dir.join("trials.json");

    let mut all_trials = if trials_file.exists() {
        let content = std::fs::read_to_string(&trials_file)?;
        serde_json::from_str::<Vec<serde_json::Value>>(&content).unwrap_or_default()
    } else {
        Vec::new()
    };

    let trial_json = serde_json::to_value(trial_result)
        .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?;
    all_trials.push(trial_json);

    let content = serde_json::to_string_pretty(&all_trials)
        .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?;
    std::fs::write(&trials_file, content)?;

    Ok(())
}