//! DQN Checkpoint Loading Tests
//!
//! Tests for loading DQN model weights from safetensors files.
//! Follows TDD methodology - tests written first, then implementation.

use anyhow::Result;
use ml::dqn::{WorkingDQN, WorkingDQNConfig};
use std::fs;
use tempfile::TempDir;

/// Test 1: Basic safetensors loading
///
/// Verifies that the load_from_safetensors() method exists and can load
/// a previously saved checkpoint without errors.
#[test]
fn test_load_safetensors_basic() -> Result<()> {
    // Create temp directory for test files
    let temp_dir = TempDir::new()?;
    let checkpoint_path = temp_dir.path().join("dqn_test.safetensors");

    // Create and save a DQN model
    let config = WorkingDQNConfig::emergency_safe_defaults();
    let dqn = WorkingDQN::new(config.clone())?;

    dqn.get_q_network_vars().save(&checkpoint_path)?;

    // Create a new DQN and load the checkpoint
    let mut dqn2 = WorkingDQN::new(config)?;
    dqn2.load_from_safetensors(checkpoint_path.to_str().unwrap())?;

    Ok(())
}

/// Test 2: Validate weight dimensions match after loading
///
/// Ensures that loaded weights have the same dimensions as the original model.
#[test]
fn test_load_safetensors_weight_dimensions() -> Result<()> {
    let temp_dir = TempDir::new()?;
    let checkpoint_path = temp_dir.path().join("dqn_test.safetensors");

    let config = WorkingDQNConfig::emergency_safe_defaults();
    let dqn = WorkingDQN::new(config.clone())?;

    // Save checkpoint
    dqn.get_q_network_vars().save(&checkpoint_path)?;

    // Get original variable names and count
    let original_vars = dqn.get_q_network_vars();
    let original_data = original_vars.data().lock().unwrap();
    let original_count = original_data.len();
    let original_names: Vec<String> = original_data.keys().cloned().collect();
    drop(original_data);

    // Load into new model
    let mut dqn2 = WorkingDQN::new(config)?;
    dqn2.load_from_safetensors(checkpoint_path.to_str().unwrap())?;

    // Verify variable count matches
    let loaded_vars = dqn2.get_q_network_vars();
    let loaded_data = loaded_vars.data().lock().unwrap();
    assert_eq!(loaded_data.len(), original_count, "Variable count mismatch");

    // Verify all original variable names exist
    for name in original_names {
        assert!(
            loaded_data.contains_key(&name),
            "Missing variable: {}",
            name
        );
    }

    Ok(())
}

/// Test 3: Forward pass produces correct outputs after loading
///
/// Verifies that inference works correctly after loading weights,
/// and produces valid Q-values.
#[test]
fn test_load_safetensors_forward_pass() -> Result<()> {
    let temp_dir = TempDir::new()?;
    let checkpoint_path = temp_dir.path().join("dqn_test.safetensors");

    let config = WorkingDQNConfig::emergency_safe_defaults();
    let dqn = WorkingDQN::new(config.clone())?;

    // Save checkpoint
    dqn.get_q_network_vars().save(&checkpoint_path)?;

    // Load into new model
    let mut dqn2 = WorkingDQN::new(config.clone())?;
    dqn2.load_from_safetensors(checkpoint_path.to_str().unwrap())?;

    // Create test input
    let test_state = vec![0.5f32; config.state_dim];
    let state_tensor =
        candle_core::Tensor::from_vec(test_state.clone(), (1, config.state_dim), dqn2.device())?;

    // Forward pass should work
    let q_values = dqn2.forward(&state_tensor)?;

    // Verify output shape
    assert_eq!(q_values.dims(), &[1, config.num_actions]);

    // Verify Q-values are finite (not NaN or Inf)
    let q_vec = q_values.to_vec2::<f32>()?;
    for q_val in q_vec[0].iter() {
        assert!(q_val.is_finite(), "Q-value is not finite: {}", q_val);
    }

    Ok(())
}

/// Test 4: End-to-end train→save→load→infer
///
/// Complete workflow test: train model, save checkpoint, load in new instance,
/// verify inference works correctly.
#[test]
fn test_load_safetensors_e2e_workflow() -> Result<()> {
    let temp_dir = TempDir::new()?;
    let checkpoint_path = temp_dir.path().join("dqn_e2e.safetensors");

    let mut config = WorkingDQNConfig::emergency_safe_defaults();
    config.min_replay_size = 4;
    config.batch_size = 4;

    // Create and train original model
    let mut dqn = WorkingDQN::new(config.clone())?;

    // Add training experiences
    for i in 0..10 {
        let experience = ml::dqn::Experience::new(
            vec![i as f32 * 0.1; config.state_dim],
            (i % config.num_actions) as u8,
            i as f32,
            vec![(i + 1) as f32 * 0.1; config.state_dim],
            i == 9,
        );
        dqn.store_experience(experience)?;
    }

    // Train for a few steps
    for _ in 0..5 {
        let _ = dqn.train_step(None)?;
    }

    // Save checkpoint
    dqn.get_q_network_vars().save(&checkpoint_path)?;

    // Create test state for inference comparison
    let test_state = vec![0.5f32; config.state_dim];
    let state_tensor =
        candle_core::Tensor::from_vec(test_state.clone(), (1, config.state_dim), dqn.device())?;

    // Get Q-values from original model
    let original_q_values = dqn.forward(&state_tensor)?;
    let original_q_vec = original_q_values.to_vec2::<f32>()?;

    // Load into new model
    let mut dqn2 = WorkingDQN::new(config.clone())?;
    dqn2.load_from_safetensors(checkpoint_path.to_str().unwrap())?;

    // Get Q-values from loaded model
    let loaded_q_values = dqn2.forward(&state_tensor)?;
    let loaded_q_vec = loaded_q_values.to_vec2::<f32>()?;

    // Verify Q-values match (within floating point tolerance)
    // Note: Small differences can occur due to GPU/CPU variations and target network updates
    for (i, (orig, loaded)) in original_q_vec[0]
        .iter()
        .zip(loaded_q_vec[0].iter())
        .enumerate()
    {
        let diff = (orig - loaded).abs();
        assert!(
            diff < 0.01,
            "Q-value mismatch at index {}: orig={}, loaded={}, diff={}",
            i,
            orig,
            loaded,
            diff
        );
    }

    Ok(())
}

/// Test 5: Error cases (file not found, corrupted file)
///
/// Verifies proper error handling for invalid checkpoint files.
#[test]
fn test_load_safetensors_error_cases() -> Result<()> {
    let config = WorkingDQNConfig::emergency_safe_defaults();
    let mut dqn = WorkingDQN::new(config)?;

    // Test 1: File not found
    let result = dqn.load_from_safetensors("/nonexistent/path/model.safetensors");
    assert!(result.is_err(), "Should fail for nonexistent file");

    // Test 2: Corrupted file
    let temp_dir = TempDir::new()?;
    let corrupted_path = temp_dir.path().join("corrupted.safetensors");
    fs::write(&corrupted_path, b"not a valid safetensors file")?;

    let result = dqn.load_from_safetensors(corrupted_path.to_str().unwrap());
    assert!(result.is_err(), "Should fail for corrupted file");

    // Test 3: Extension handling (.safetensors auto-append)
    let checkpoint_path = temp_dir.path().join("test_model");
    dqn.get_q_network_vars()
        .save(format!("{}.safetensors", checkpoint_path.display()))?;

    // Should work without .safetensors extension
    let result = dqn.load_from_safetensors(checkpoint_path.to_str().unwrap());
    assert!(result.is_ok(), "Should auto-append .safetensors extension");

    Ok(())
}