//! # MAMBA-2 Gradient Extraction Test (TDD)
//!
//! **Test-Driven Development**: This test verifies that gradients are properly extracted
//! from VarMap parameters after backward() pass.
//!
//! **Root Cause**: backward_pass() uses zeros_like() placeholder gradients instead of
//! extracting real gradients from VarMap.
//!
//! **Expected Behavior**:
//! 1. Call forward() to compute loss
//! 2. Call backward() to compute gradients
//! 3. Extract gradients from VarMap parameters (input_proj, output_proj, layer_norms)
//! 4. Verify gradients are non-zero and valid (not NaN/Inf)

#![allow(unused_crate_dependencies)]

use candle_core::{DType, Device, Tensor};
use ml::mamba::Mamba2SSM;
use ml::MLError;

#[test]
fn test_mamba2_gradient_extraction_from_varmap() -> Result<(), MLError> {
    println!("\n=== MAMBA-2 Gradient Extraction Test ===");

    let device = Device::cuda_if_available(0)?;
    println!("Device: {:?}", device);

    // Create small MAMBA-2 model
    let mut model = Mamba2SSM::default_hft(&device)?;
    println!(
        "Model created: {} parameters",
        model.metadata.num_parameters
    );

    // Create dummy input and target
    let batch_size = model.config.batch_size;
    let seq_len = model.config.seq_len;
    let d_model = model.config.d_model;

    let input_data = vec![0.1f64; batch_size * seq_len * d_model];
    let input = Tensor::from_vec(input_data, (batch_size, seq_len, d_model), &device)?;

    let target_data = vec![0.5f64; batch_size * seq_len];
    let target = Tensor::from_vec(target_data, (batch_size, seq_len, 1), &device)?;

    println!("Input shape: {:?}", input.dims());
    println!("Target shape: {:?}", target.dims());

    // Forward pass
    let output = model.forward(&input)?;
    println!("Output shape: {:?}", output.dims());

    // Compute loss (MSE)
    let diff = output.broadcast_sub(&target)?;
    let loss = diff.sqr()?.mean_all()?;
    let loss_value = loss.to_scalar::<f64>()?;
    println!("Loss: {:.6}", loss_value);

    // Backward pass - THIS SHOULD COMPUTE REAL GRADIENTS
    let grads = loss.backward()?;

    // Extract gradients from GradStore
    println!("\n=== Extracting Gradients from GradStore ===");

    let varmap = &model.varmap;
    let all_vars = varmap.all_vars();
    println!("Total VarMap variables: {}", all_vars.len());

    let mut vars_with_gradients = 0;
    let mut total_grad_norm = 0.0f64;

    for (idx, var) in all_vars.iter().enumerate() {
        if let Some(grad) = grads.get(var) {
            // Compute gradient norm
            let grad_vec = grad.flatten_all()?.to_vec1::<f64>()?;
            let grad_norm: f64 = grad_vec.iter().map(|&g| g.powi(2)).sum::<f64>().sqrt();

            println!("  Var {}: grad_norm={:.6}", idx, grad_norm);

            // Verify gradient is valid
            assert!(!grad_norm.is_nan(), "Gradient {} is NaN", idx);
            assert!(!grad_norm.is_infinite(), "Gradient {} is Inf", idx);

            if grad_norm > 1e-9 {
                vars_with_gradients += 1;
                total_grad_norm += grad_norm;
            }
        } else {
            println!("  Var {}: NO GRADIENT", idx);
        }
    }

    println!("\n=== Gradient Summary ===");
    println!(
        "Variables with gradients: {}/{}",
        vars_with_gradients,
        all_vars.len()
    );
    println!("Total gradient norm: {:.6}", total_grad_norm);

    // CRITICAL ASSERTION: At least some parameters should have non-zero gradients
    assert!(
        vars_with_gradients > 0,
        "FAIL: No variables have gradients! backward() did not compute gradients."
    );

    assert!(
        total_grad_norm > 1e-6,
        "FAIL: Total gradient norm is too small ({:.6}). Gradients may be zeros.",
        total_grad_norm
    );

    println!("\n✅ TEST PASSED: Gradients extracted from VarMap");
    Ok(())
}

#[test]
fn test_mamba2_backward_pass_extracts_real_gradients() -> Result<(), MLError> {
    println!("\n=== MAMBA-2 backward_pass() Real Gradient Test ===");

    let device = Device::cuda_if_available(0)?;
    let mut model = Mamba2SSM::default_hft(&device)?;

    // Create input/target
    let batch_size = model.config.batch_size;
    let seq_len = model.config.seq_len;
    let d_model = model.config.d_model;

    let input = Tensor::ones((batch_size, seq_len, d_model), DType::F64, &device)?;
    let target = Tensor::ones((batch_size, seq_len, 1), DType::F64, &device)?;

    // Forward + loss
    let output = model.forward(&input)?;
    let diff = output.broadcast_sub(&target)?;
    let loss = diff.sqr()?.mean_all()?;

    println!("Loss: {:.6}", loss.to_scalar::<f64>()?);

    // Call backward_pass (current implementation uses zeros_like placeholders)
    model.backward_pass(&loss, &input, &target)?;

    // Check model.gradients HashMap
    println!("\n=== Model Gradients HashMap ===");
    println!("Total entries: {}", model.gradients.len());

    for (key, grad) in model.gradients.iter() {
        let grad_vec = grad.flatten_all()?.to_vec1::<f64>()?;
        let grad_norm: f64 = grad_vec.iter().map(|&g| g.powi(2)).sum::<f64>().sqrt();
        println!("  {}: grad_norm={:.6}", key, grad_norm);

        // CURRENT BUG: All gradients are zeros (zeros_like)
        // AFTER FIX: Gradients should be non-zero
        if grad_norm > 1e-9 {
            println!("    ✅ Non-zero gradient found");
        } else {
            println!("    ❌ ZERO gradient (zeros_like placeholder)");
        }
    }

    // This test will FAIL until we fix backward_pass()
    // After fix, gradients should be non-zero
    let total_grad_norm: f64 = model
        .gradients
        .values()
        .map(|grad| {
            let grad_vec = grad.flatten_all().unwrap().to_vec1::<f64>().unwrap();
            grad_vec.iter().map(|&g| g.powi(2)).sum::<f64>().sqrt()
        })
        .sum();

    println!(
        "\nTotal gradient norm in model.gradients: {:.6}",
        total_grad_norm
    );

    // EXPECTED TO FAIL with current zeros_like implementation
    assert!(
        total_grad_norm > 1e-6,
        "FAIL: backward_pass() produced zero gradients. Need to extract from VarMap."
    );

    println!("\n✅ TEST PASSED: backward_pass() extracts real gradients");
    Ok(())
}