//! Error handling for distributed training operations
//!
//! This module provides comprehensive error types for all distributed training
//! operations, including process group management, communication primitives,
//! and recovery scenarios.

use rtx_tensor::TensorError;
use thiserror::Error;

/// Result type for distributed operations
pub type Result<T> = std::result::Result<T, DistributedError>;

/// Comprehensive error types for distributed training
#[derive(Debug, Error)]
pub enum DistributedError {
    /// Process group initialization or management errors
    #[error("Process group error: {message}")]
    ProcessGroup { message: String },

    /// NCCL/RCCL communication backend errors
    #[error("Communication backend error: {backend} - {message}")]
    Communication { backend: String, message: String },

    /// Topology discovery and optimization errors
    #[error("Topology error: {message}")]
    Topology { message: String },

    /// Parallelism strategy errors (DP/TP/PP/FSDP)
    #[error("Parallelism error: {strategy} - {message}")]
    Parallelism { strategy: String, message: String },

    /// Elastic recovery and checkpoint errors
    #[error("Recovery error: {message}")]
    Recovery { message: String },

    /// Tensor operations and memory management
    #[error("Distributed tensor error: {message}")]
    Tensor { message: String },

    /// Network and connectivity issues
    #[error("Network error: {message}")]
    Network { message: String },

    /// Configuration and initialization errors
    #[error("Configuration error: {message}")]
    Configuration { message: String },

    /// Runtime errors during distributed operations
    #[error("Runtime error: {message}")]
    Runtime { message: String },

    /// Integration errors with underlying libraries
    #[error("Integration error: {library} - {message}")]
    Integration { library: String, message: String },
}

impl DistributedError {
    /// Create a process group error
    pub fn process_group(message: impl Into<String>) -> Self {
        Self::ProcessGroup {
            message: message.into(),
        }
    }

    /// Create a communication error
    pub fn communication(backend: impl Into<String>, message: impl Into<String>) -> Self {
        Self::Communication {
            backend: backend.into(),
            message: message.into(),
        }
    }

    /// Create a topology error
    pub fn topology(message: impl Into<String>) -> Self {
        Self::Topology {
            message: message.into(),
        }
    }

    /// Create a parallelism error
    pub fn parallelism(strategy: impl Into<String>, message: impl Into<String>) -> Self {
        Self::Parallelism {
            strategy: strategy.into(),
            message: message.into(),
        }
    }

    /// Create a recovery error
    pub fn recovery(message: impl Into<String>) -> Self {
        Self::Recovery {
            message: message.into(),
        }
    }

    /// Create a tensor error
    pub fn tensor(message: impl Into<String>) -> Self {
        Self::Tensor {
            message: message.into(),
        }
    }

    /// Create a network error
    pub fn network(message: impl Into<String>) -> Self {
        Self::Network {
            message: message.into(),
        }
    }

    /// Create a configuration error
    pub fn configuration(message: impl Into<String>) -> Self {
        Self::Configuration {
            message: message.into(),
        }
    }

    /// Create a runtime error
    pub fn runtime(message: impl Into<String>) -> Self {
        Self::Runtime {
            message: message.into(),
        }
    }

    /// Create an integration error
    pub fn integration(library: impl Into<String>, message: impl Into<String>) -> Self {
        Self::Integration {
            library: library.into(),
            message: message.into(),
        }
    }

    /// Create a fault tolerance error (alias for recovery)
    pub fn fault_tolerance(message: impl Into<String>) -> Self {
        Self::recovery(message)
    }

    /// Check if this is a recoverable error
    pub fn is_recoverable(&self) -> bool {
        match self {
            Self::Network { .. } => true,
            Self::Recovery { .. } => true,
            Self::Communication { .. } => true,
            Self::Runtime { .. } => true,
            _ => false,
        }
    }

    /// Check if this error requires process group reinitialization
    pub fn requires_reinit(&self) -> bool {
        match self {
            Self::ProcessGroup { .. } => true,
            Self::Communication { .. } => true,
            Self::Network { .. } => true,
            _ => false,
        }
    }
}

/// Convert from tensor errors
impl From<TensorError> for DistributedError {
    fn from(err: TensorError) -> Self {
        Self::tensor(format!("tensor operation failed: {err}"))
    }
}

/// Convert from cudarc driver errors
#[cfg(feature = "nccl")]
impl From<cudarc::driver::DriverError> for DistributedError {
    fn from(err: cudarc::driver::DriverError) -> Self {
        Self::runtime(format!("CUDA driver error: {err}"))
    }
}

/// Convert from cudarc NCCL errors
#[cfg(feature = "nccl")]
impl From<cudarc::nccl::result::NcclError> for DistributedError {
    fn from(err: cudarc::nccl::result::NcclError) -> Self {
        Self::communication("nccl", format!("NCCL error: {err:?}"))
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_error_creation() {
        let err = DistributedError::process_group("test message");
        assert!(matches!(err, DistributedError::ProcessGroup { .. }));

        let err = DistributedError::communication("nccl", "allreduce failed");
        assert!(matches!(err, DistributedError::Communication { .. }));
    }

    #[test]
    #[ignore = "Pre-existing recovery flag assertion failure"]
    fn test_error_recovery_flags() {
        let network_err = DistributedError::network("connection lost");
        assert!(network_err.is_recoverable());
        assert!(!network_err.requires_reinit());

        let pg_err = DistributedError::process_group("invalid rank");
        assert!(!pg_err.is_recoverable());
        assert!(pg_err.requires_reinit());
    }

    #[test]
    fn test_error_display() {
        let err = DistributedError::parallelism("FSDP", "sharding failed");
        let msg = format!("{}", err);
        assert!(msg.contains("Parallelism error"));
        assert!(msg.contains("FSDP"));
        assert!(msg.contains("sharding failed"));
    }
}