//! CUDA graph support for optimized execution

use super::stream::CudaStream;
use crate::cuda::cudaSuccess;
use crate::error::{BackendError, BackendResult};
use cuda_sys::cudart::*;
use std::collections::HashMap;
use std::ffi::c_void;
use std::ptr;
use std::sync::{Arc, Mutex};

/// CUDA graph wrapper
pub struct CudaGraph {
    graph: cudaGraph_t,
    instance: Option<cudaGraphExec_t>,
    captured_kernels: usize,
}

impl std::fmt::Debug for CudaGraph {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("CudaGraph")
            .field("graph", &(self.graph as usize))
            .field("instance", &self.instance.map(|i| i as usize))
            .field("captured_kernels", &self.captured_kernels)
            .finish()
    }
}

impl CudaGraph {
    /// Create a new empty CUDA graph
    pub fn new() -> BackendResult<Self> {
        let mut graph: cudaGraph_t = ptr::null_mut();
        unsafe {
            let result = cudaGraphCreate(&mut graph as *mut _, 0);
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to create CUDA graph: {:?}",
                    result
                )));
            }
        }

        Ok(Self {
            graph,
            instance: None,
            captured_kernels: 0,
        })
    }

    /// Begin capturing operations on a stream
    pub fn begin_capture(stream: &CudaStream) -> BackendResult<()> {
        unsafe {
            let result = cudaStreamBeginCapture(
                stream.stream(),
                cudaStreamCaptureMode::cudaStreamCaptureModeGlobal,
            );
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to begin CUDA graph capture: {:?}",
                    result
                )));
            }
        }
        Ok(())
    }

    /// End capturing and create a graph
    pub fn end_capture(stream: &CudaStream) -> BackendResult<Self> {
        let mut graph: cudaGraph_t = ptr::null_mut();
        unsafe {
            let result = cudaStreamEndCapture(stream.stream(), &mut graph as *mut _);
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to end CUDA graph capture: {:?}",
                    result
                )));
            }
        }

        // Get the number of nodes in the graph
        let mut num_nodes: usize = 0;
        unsafe {
            let result = cudaGraphGetNodes(graph, ptr::null_mut(), &mut num_nodes as *mut _);
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to get graph node count: {:?}",
                    result
                )));
            }
        }

        Ok(Self {
            graph,
            instance: None,
            captured_kernels: num_nodes,
        })
    }

    /// Instantiate the graph for execution
    pub fn instantiate(&mut self) -> BackendResult<()> {
        if self.instance.is_some() {
            return Ok(()); // Already instantiated
        }

        let mut instance: cudaGraphExec_t = ptr::null_mut();
        unsafe {
            let result = cudaGraphInstantiate(
                &mut instance as *mut _,
                self.graph,
                ptr::null_mut(),
                ptr::null_mut(),
                0,
            );
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to instantiate CUDA graph: {:?}",
                    result
                )));
            }
        }

        self.instance = Some(instance);
        Ok(())
    }

    /// Launch the instantiated graph
    pub fn launch(&self, stream: &CudaStream) -> BackendResult<()> {
        let instance = self
            .instance
            .ok_or_else(|| BackendError::CudaError("Graph not instantiated".to_string()))?;

        unsafe {
            let result = cudaGraphLaunch(instance, stream.stream());
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to launch CUDA graph: {:?}",
                    result
                )));
            }
        }
        Ok(())
    }

    /// Update graph parameters (for graphs with updatable nodes)
    pub fn update(&mut self, updates: &GraphUpdate) -> BackendResult<()> {
        // This would update specific nodes in the graph
        // For now, this is a placeholder
        let _ = updates;
        Ok(())
    }

    /// Get the number of captured kernels
    pub fn kernel_count(&self) -> usize {
        self.captured_kernels
    }

    /// Clone the graph
    pub fn clone_graph(&self) -> BackendResult<Self> {
        let mut cloned_graph: cudaGraph_t = ptr::null_mut();
        unsafe {
            let result = cudaGraphClone(&mut cloned_graph as *mut _, self.graph);
            if result != cudaSuccess {
                return Err(BackendError::CudaError(format!(
                    "Failed to clone CUDA graph: {:?}",
                    result
                )));
            }
        }

        Ok(Self {
            graph: cloned_graph,
            instance: None,
            captured_kernels: self.captured_kernels,
        })
    }
}

impl Drop for CudaGraph {
    fn drop(&mut self) {
        unsafe {
            if let Some(instance) = self.instance {
                cudaGraphExecDestroy(instance);
            }
            cudaGraphDestroy(self.graph);
        }
    }
}

/// Graph update information
pub struct GraphUpdate {
    pub node_id: usize,
    pub new_params: Vec<f32>,
}

/// Graph capture context for automatic capture management
#[derive(Debug)]
pub struct GraphCaptureContext {
    stream: Arc<CudaStream>,
    capturing: bool,
}

impl GraphCaptureContext {
    /// Create a new capture context
    pub fn new(stream: Arc<CudaStream>) -> Self {
        Self {
            stream,
            capturing: false,
        }
    }

    /// Start capturing
    pub fn start(&mut self) -> BackendResult<()> {
        if self.capturing {
            return Err(BackendError::CudaError(
                "Already capturing a graph".to_string(),
            ));
        }

        CudaGraph::begin_capture(&self.stream)?;
        self.capturing = true;
        Ok(())
    }

    /// End capturing and return the graph
    pub fn end(&mut self) -> BackendResult<CudaGraph> {
        if !self.capturing {
            return Err(BackendError::CudaError("Not capturing a graph".to_string()));
        }

        let graph = CudaGraph::end_capture(&self.stream)?;
        self.capturing = false;
        Ok(graph)
    }

    /// Check if currently capturing
    pub fn is_capturing(&self) -> bool {
        self.capturing
    }
}

/// Graph cache for reusing instantiated graphs
#[derive(Debug)]
pub struct GraphCache {
    cache: Mutex<HashMap<String, Arc<Mutex<CudaGraph>>>>,
}

impl GraphCache {
    /// Create a new graph cache
    pub fn new() -> Self {
        Self {
            cache: Mutex::new(HashMap::new()),
        }
    }

    /// Get or create a graph with the given key
    pub fn get_or_create<F>(&self, key: &str, creator: F) -> BackendResult<Arc<Mutex<CudaGraph>>>
    where
        F: FnOnce() -> BackendResult<CudaGraph>,
    {
        let mut cache = self.cache.lock().expect("lock should not be poisoned");

        if let Some(graph) = cache.get(key) {
            return Ok(graph.clone());
        }

        let graph = creator()?;
        let graph_arc = Arc::new(Mutex::new(graph));
        cache.insert(key.to_string(), graph_arc.clone());
        Ok(graph_arc)
    }

    /// Remove a graph from the cache
    pub fn remove(&self, key: &str) {
        let mut cache = self.cache.lock().expect("lock should not be poisoned");
        cache.remove(key);
    }

    /// Clear all cached graphs
    pub fn clear(&self) {
        let mut cache = self.cache.lock().expect("lock should not be poisoned");
        cache.clear();
    }

    /// Get the number of cached graphs
    pub fn size(&self) -> usize {
        let cache = self.cache.lock().expect("lock should not be poisoned");
        cache.len()
    }
}

/// Helper macro for graph capture
#[macro_export]
macro_rules! cuda_graph_capture {
    ($stream:expr, $code:block) => {{
        let mut capture_ctx = GraphCaptureContext::new($stream.clone());
        capture_ctx.start()?;
        $code
        capture_ctx.end()
    }};
}

/// Graph optimization hints
#[derive(Debug, Clone)]
pub struct GraphOptimizationHints {
    /// Enable memory optimization
    pub optimize_memory: bool,
    /// Enable kernel fusion
    pub enable_fusion: bool,
    /// Prefer shared memory over global memory
    pub prefer_shared_memory: bool,
    /// Target specific compute capability
    pub target_sm: Option<(u32, u32)>,
}

impl Default for GraphOptimizationHints {
    fn default() -> Self {
        Self {
            optimize_memory: true,
            enable_fusion: true,
            prefer_shared_memory: true,
            target_sm: None,
        }
    }
}

/// Optimize a captured graph
pub fn optimize_graph(graph: &mut CudaGraph, hints: &GraphOptimizationHints) -> BackendResult<()> {
    // This would apply various optimizations to the graph
    // For now, this is a placeholder
    let _ = hints;
    Ok(())
}

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

    #[test]
    fn test_graph_creation() {
        // Note: These tests would require CUDA runtime
        // They are marked as #[test] but would need proper CUDA setup
        if cuda_available() {
            let graph = CudaGraph::new();
            assert!(graph.is_ok());
        }
    }

    #[test]
    fn test_graph_cache() {
        let cache = GraphCache::new();
        assert_eq!(cache.size(), 0);

        // Test operations would go here with actual CUDA runtime
    }

    fn cuda_available() -> bool {
        // Check if CUDA is available on the system
        unsafe {
            let mut device_count: i32 = 0;
            let result = cudaGetDeviceCount(&mut device_count as *mut _);
            result == cudaSuccess && device_count > 0
        }
    }
}
