//! Tests for NCCL communication backend
//!
//! These tests verify the NCCL backend implementation for GPU-to-GPU
//! communication, including AllReduce, broadcast, and other collective operations.

use rtx_distributed::{
    Backend, BackendConfig, CommunicationPrimitive, ProcessGroup, ReduceOp, Result, WorldInfo,
};
use rtx_tensor::{Device, Tensor};
use std::time::Duration;

/// Test NCCL backend initialization and basic functionality
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_backend_init() -> Result<()> {
    let world_size = 2;
    let rank = 0;

    // Create NCCL backend configuration
    let mut config = BackendConfig::nccl();
    config.set_timeout(Duration::from_secs(10));

    // Initialize process group with NCCL backend
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Verify process group properties
    assert_eq!(process_group.world_size(), world_size as usize);
    assert_eq!(process_group.rank(), rank as usize);

    Ok(())
}

/// Test NCCL AllReduce operation
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_allreduce() -> Result<()> {
    let world_size = 4;
    let rank = 0;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Create test tensor
    let shape_dims = vec![1000];
    let mut tensor = Tensor::full(
        &shape_dims,
        2.0,
        &Device::cuda(0).unwrap_or(Device::default()),
    )?;

    // Perform AllReduce sum
    process_group.all_reduce(&mut tensor, ReduceOp::Sum).await?;

    // Verify result (simulated sum across 4 ranks)
    let data = tensor.data()?;
    let expected_sum = 2.0 * world_size as f32;

    for &value in &data {
        assert!(
            (value - expected_sum).abs() < 1e-6,
            "AllReduce sum result {} does not match expected {}",
            value,
            expected_sum
        );
    }

    Ok(())
}

/// Test NCCL broadcast operation
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_broadcast() -> Result<()> {
    let world_size = 4;
    let root_rank = 0;

    let config = BackendConfig::nccl();
    let process_group = ProcessGroup::new_with_config(Backend::Nccl, world_size, 1, config).await?; // Non-root rank

    // Create tensor to receive broadcast
    let shape_dims = vec![500];
    let mut tensor = Tensor::zeros(&shape_dims, &Device::cuda(0).unwrap_or(Device::default()))?;

    // Perform broadcast (note: current implementation doesn't modify the tensor)
    process_group
        .broadcast(&mut tensor, root_rank as usize)
        .await?;

    // Verify broadcast result (should receive root rank value)
    let data = tensor.data()?;
    let expected_value = root_rank as f32;

    for &value in &data {
        assert!(
            (value - expected_value).abs() < 1e-6,
            "Broadcast result {} does not match expected root value {}",
            value,
            expected_value
        );
    }

    Ok(())
}

/// Test NCCL AllGather operation
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_allgather() -> Result<()> {
    let world_size = 4;
    let rank = 2;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Create input tensor with rank-specific value
    let shape_dims = vec![100];
    let input_tensor = Tensor::full(
        &shape_dims,
        rank as f32,
        &Device::cuda(0).unwrap_or(Device::default()),
    )?;

    // Perform AllGather
    let output = process_group.all_gather(&input_tensor)?;

    // Verify output is a vector of tensors (one per rank)
    assert_eq!(
        output.len(),
        world_size as usize,
        "AllGather should return {} tensors, got {}",
        world_size,
        output.len()
    );

    // Verify each tensor in the output
    for (rank_idx, gathered_tensor) in output.iter().enumerate() {
        let data = gathered_tensor.data()?;
        let expected_value = rank as f32; // In simulation, all tensors are copies of input

        for &value in &data {
            assert!(
                (value - expected_value).abs() < 1e-6,
                "AllGather tensor {} has value {} instead of expected {}",
                rank_idx,
                value,
                expected_value
            );
        }
    }

    Ok(())
}

/// Test NCCL reduce_scatter operation
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_reduce_scatter() -> Result<()> {
    let world_size = 4;
    let rank = 0;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Create tensor for reduce_scatter (size must be divisible by world_size)
    let total_size = 1000; // Must be divisible by world_size
    let shape_dims = vec![total_size];
    let input_tensor = Tensor::full(
        &shape_dims,
        10.0,
        &Device::cuda(0).unwrap_or(Device::default()),
    )?;

    // Test reduce_scatter operation
    let output_tensor = process_group.reduce_scatter(&input_tensor, ReduceOp::Sum)?;

    // Verify output shape (should be input_size / world_size)
    let expected_size = total_size / world_size as usize;
    let output_shape = output_tensor.shape();
    assert_eq!(
        output_shape.dims()[0],
        expected_size,
        "ReduceScatter output size should be {}, got {}",
        expected_size,
        output_shape.dims()[0]
    );

    Ok(())
}

/// Test NCCL backend configuration and capabilities
#[tokio::test]
async fn test_nccl_backend_config() -> Result<()> {
    let mut config = BackendConfig::nccl();

    // Test configuration validation
    assert!(
        config.validate().is_ok(),
        "Default NCCL config should be valid"
    );

    // Test parameter modification
    config.set_parameter("nccl_debug".to_string(), "WARN".to_string());
    assert_eq!(
        config.get_parameter("nccl_debug"),
        Some(&"WARN".to_string())
    );

    // Test timeout configuration
    config.set_timeout(Duration::from_secs(60));

    // Test invalid configuration
    config.set_invalid_param("test");
    assert!(
        config.validate().is_err(),
        "Invalid config should fail validation"
    );

    Ok(())
}

/// Test NCCL backend with different data types and operations
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_reduce_operations() -> Result<()> {
    let world_size = 3;
    let rank = 0;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    let shape_dims = vec![50];

    // Test different reduce operations
    let test_cases = vec![
        (ReduceOp::Sum, 5.0, 15.0), // sum: 5 * 3 = 15
        (ReduceOp::Max, 5.0, 5.0),  // max: stays 5
        (ReduceOp::Min, 5.0, 5.0),  // min: stays 5
    ];

    for (op, input_value, expected_output) in test_cases {
        let mut tensor = Tensor::full(
            &shape_dims,
            input_value,
            &Device::cuda(0).unwrap_or(Device::default()),
        )?;

        // Perform reduce operation
        process_group.all_reduce(&mut tensor, op).await?;

        let data = tensor.data()?;
        for &value in &data {
            assert!(
                (value - expected_output).abs() < 1e-6,
                "Reduce operation {:?} with input {} produced {} instead of expected {}",
                op,
                input_value,
                value,
                expected_output
            );
        }
    }

    Ok(())
}

/// Test NCCL backend error handling
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn test_nccl_error_handling() -> Result<()> {
    let world_size = 2;
    let rank = 0;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Test broadcast with invalid root rank
    let shape_dims = vec![10];
    let mut tensor = Tensor::ones(&shape_dims, &Device::cuda(0).unwrap_or(Device::default()))?;

    let result = process_group.broadcast(&mut tensor, 99).await;
    assert!(result.is_err(), "Broadcast with invalid root should fail");

    // Test all_reduce with empty tensor to trigger validation
    let empty_tensor_result = Tensor::zeros(&[], &Device::cuda(0).unwrap_or(Device::default()));
    if let Ok(mut empty_tensor) = empty_tensor_result {
        let result = process_group
            .all_reduce(&mut empty_tensor, ReduceOp::Sum)
            .await;
        // This may or may not fail depending on implementation, but should not panic
        let _ = result;
    }

    Ok(())
}

/// Benchmark NCCL AllReduce performance
#[tokio::test]
#[ignore = "Pre-existing NCCL not available on macOS"]
async fn benchmark_nccl_allreduce_performance() -> Result<()> {
    let world_size = 4;
    let rank = 0;

    let config = BackendConfig::nccl();
    let process_group =
        ProcessGroup::new_with_config(Backend::Nccl, world_size, rank, config).await?;

    // Test different tensor sizes
    let sizes = vec![1_000, 10_000, 100_000, 1_000_000];

    for size in sizes {
        let shape_dims = vec![size];
        let mut tensor = Tensor::ones(&shape_dims, &Device::cuda(0).unwrap_or(Device::default()))?;

        let start_time = std::time::Instant::now();
        process_group.all_reduce(&mut tensor, ReduceOp::Sum).await?;
        let duration = start_time.elapsed();

        let bandwidth_gb_s = (size * 4) as f64 / duration.as_secs_f64() / 1e9; // bytes to GB/s

        println!(
            "NCCL AllReduce size: {} elements, time: {:.2}ms, bandwidth: {:.2} GB/s",
            size,
            duration.as_millis(),
            bandwidth_gb_s
        );

        // Basic performance expectations (very lenient for simulation)
        assert!(
            duration.as_millis() < 1000,
            "AllReduce should complete in reasonable time"
        );
        assert!(bandwidth_gb_s > 0.0, "Should have positive bandwidth");
    }

    Ok(())
}