lambdust 0.1.1

#![allow(unused_variables)]
//! Callback function system for FFI operations.
//!
//! This module provides support for registering Lambdust functions as callbacks
//! that can be called from C code, as well as managing the lifecycle and
//! safety of these callback functions.

use std::collections::HashMap;
use std::ffi::c_void;
use std::fmt;
use std::ptr;
use std::sync::{Arc, Mutex, RwLock};
use std::time::{Duration, SystemTime};

use crate::eval::{Value, Environment};
use crate::ast::Literal;
use crate::diagnostics::Error;
use crate::ffi::c_types::{CType, TypeMarshaller, ConversionError};

/// Errors that can occur during callback operations
#[derive(Debug, Clone)]
pub enum CallbackError {
    /// Callback not found
    NotFound(String),
    /// Invalid callback signature
    InvalidSignature {
        callback: String,
        reason: String,
    },
    /// Callback execution failed
    ExecutionFailed {
        callback: String,
        error: String,
    },
    /// Type conversion error
    ConversionError(ConversionError),
    /// Callback already registered
    AlreadyRegistered(String),
    /// Callback lifetime expired
    Expired(String),
    /// Stack overflow protection
    StackOverflow,
}

impl fmt::Display for CallbackError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            CallbackError::NotFound(name) => {
                write!(f, "Callback not found: {name}")
            }
            CallbackError::InvalidSignature { callback, reason } => {
                write!(f, "Invalid callback signature for '{callback}': {reason}")
            }
            CallbackError::ExecutionFailed { callback, error } => {
                write!(f, "Callback '{callback}' execution failed: {error}")
            }
            CallbackError::ConversionError(e) => {
                write!(f, "Callback type conversion error: {e}")
            }
            CallbackError::AlreadyRegistered(name) => {
                write!(f, "Callback '{name}' is already registered")
            }
            CallbackError::Expired(name) => {
                write!(f, "Callback '{name}' has expired")
            }
            CallbackError::StackOverflow => {
                write!(f, "Callback stack overflow protection triggered")
            }
        }
    }
}

impl std::error::Error for CallbackError {}

impl From<ConversionError> for CallbackError {
    fn from(e: ConversionError) -> Self {
        CallbackError::ConversionError(e)
    }
}

impl From<CallbackError> for Error {
    fn from(callback_error: CallbackError) -> Self {
        Error::runtime_error(callback_error.to_string(), None)
    }
}

/// Callback function signature
#[derive(Debug, Clone)]
pub struct CallbackSignature {
    /// Function name
    pub name: String,
    /// Parameter types
    pub parameters: Vec<CType>,
    /// Return type
    pub return_type: CType,
    /// Whether the callback is variadic
    pub variadic: bool,
    /// Calling convention (default: C)
    pub calling_convention: CallingConvention,
}

/// Calling conventions for callbacks
#[derive(Debug, Clone, PartialEq)]
#[derive(Default)]
pub enum CallingConvention {
    /// C calling convention (default)
    #[default]
    C,
    /// Standard call (Windows)
    Stdcall,
    /// Fast call
    Fastcall,
    /// System V ABI (Unix)
    SystemV,
}


/// A registered callback function
#[derive(Debug)]
pub struct CallbackFunction {
    /// Callback signature
    pub signature: CallbackSignature,
    /// The Lambdust function to call
    pub function: Value,
    /// Environment for the function
    pub environment: Arc<Mutex<Environment>>,
    /// When this callback was registered
    pub registered_at: SystemTime,
    /// Expiration time (if any)
    pub expires_at: Option<SystemTime>,
    /// Number of times this callback has been invoked
    pub call_count: Arc<Mutex<u64>>,
    /// Generated C function pointer
    pub c_function_ptr: *const c_void,
    /// Whether this callback is currently active
    pub active: Arc<Mutex<bool>>,
}

impl CallbackFunction {
    /// Check if this callback is expired
    pub fn is_expired(&self) -> bool {
        if let Some(expires_at) = self.expires_at {
            SystemTime::now() > expires_at
        } else {
            false
        }
    }

    /// Check if this callback is active
    pub fn is_active(&self) -> bool {
        *self.active.lock().unwrap()
    }

    /// Get the call count
    pub fn call_count(&self) -> u64 {
        *self.call_count.lock().unwrap()
    }

    /// Increment call count
    pub fn increment_call_count(&self) {
        let mut count = self.call_count.lock().unwrap();
        *count += 1;
    }
}

unsafe impl Send for CallbackFunction {}
unsafe impl Sync for CallbackFunction {}

/// Callback registry for managing registered callbacks
#[derive(Debug)]
pub struct CallbackRegistry {
    /// Registered callbacks
    callbacks: RwLock<HashMap<String, Arc<CallbackFunction>>>,
    /// Type marshaller for conversions
    marshaller: Arc<Mutex<TypeMarshaller>>,
    /// Stack depth protection
    stack_depth: Arc<Mutex<usize>>,
    /// Maximum stack depth
    max_stack_depth: usize,
    /// Statistics
    stats: RwLock<CallbackStats>,
}

/// Callback usage statistics
#[derive(Debug, Default, Clone)]
pub struct CallbackStats {
    /// Total number of registered callbacks
    pub total_registered: usize,
    /// Currently active callbacks
    pub currently_active: usize,
    /// Total callback invocations
    pub total_invocations: u64,
    /// Successful invocations
    pub successful_invocations: u64,
    /// Failed invocations
    pub failed_invocations: u64,
    /// Stack overflows prevented
    pub stack_overflows_prevented: u64,
}

impl Default for CallbackRegistry {
    fn default() -> Self {
        Self::new()
    }
}

impl CallbackRegistry {
    /// Create a new callback registry
    pub fn new() -> Self {
        Self {
            callbacks: RwLock::new(HashMap::new()),
            marshaller: Arc::new(Mutex::new(TypeMarshaller::new())),
            stack_depth: Arc::new(Mutex::new(0)),
            max_stack_depth: 32, // Reasonable default
            stats: RwLock::new(CallbackStats::default()),
        }
    }

    /// Set maximum stack depth
    pub fn set_max_stack_depth(&mut self, depth: usize) {
        self.max_stack_depth = depth;
    }

    /// Register a callback function
    pub fn register_callback(
        &self,
        signature: CallbackSignature,
        function: Value,
        environment: Arc<Mutex<Environment>>,
        expires_after: Option<Duration>,
    ) -> std::result::Result<*const c_void, CallbackError> {
        // Check if already registered
        {
            let callbacks = self.callbacks.read().unwrap();
            if callbacks.contains_key(&signature.name) {
                return Err(CallbackError::AlreadyRegistered(signature.name.clone()));
            }
        }

        // Calculate expiration time
        let expires_at = expires_after.map(|duration| SystemTime::now() + duration);

        // Generate C function pointer (this is a simplified implementation)
        let c_function_ptr = self.generate_c_function_ptr(&signature)?;

        // Create callback function
        let callback = Arc::new(CallbackFunction {
            signature: signature.clone(),
            function,
            environment,
            registered_at: SystemTime::now(),
            expires_at,
            call_count: Arc::new(Mutex::new(0)),
            c_function_ptr,
            active: Arc::new(Mutex::new(true)),
        });

        // Register the callback
        {
            let mut callbacks = self.callbacks.write().unwrap();
            callbacks.insert(signature.name.clone(), callback);
        }

        // Update statistics
        {
            let mut stats = self.stats.write().unwrap();
            stats.total_registered += 1;
            stats.currently_active = self.callbacks.read().unwrap().len();
        }

        Ok(c_function_ptr)
    }

    /// Unregister a callback
    pub fn unregister_callback(&self, name: &str) -> std::result::Result<(), CallbackError> {
        let callback = {
            let mut callbacks = self.callbacks.write().unwrap();
            callbacks.remove(name)
        };

        if let Some(callback) = callback {
            // Mark as inactive
            {
                let mut active = callback.active.lock().unwrap();
                *active = false;
            }

            // Update statistics
            {
                let mut stats = self.stats.write().unwrap();
                stats.currently_active = self.callbacks.read().unwrap().len();
            }

            Ok(())
        } else {
            Err(CallbackError::NotFound(name.to_string()))
        }
    }

    /// Get a callback by name
    pub fn get_callback(&self, name: &str) -> Option<Arc<CallbackFunction>> {
        let callbacks = self.callbacks.read().unwrap();
        callbacks.get(name).cloned()
    }

    /// List all registered callbacks
    pub fn list_callbacks(&self) -> Vec<String> {
        let callbacks = self.callbacks.read().unwrap();
        callbacks.keys().cloned().collect()
    }

    /// Clean up expired callbacks
    pub fn cleanup_expired(&self) -> usize {
        let expired_names: Vec<String> = {
            let callbacks = self.callbacks.read().unwrap();
            callbacks
                .iter()
                .filter(|(_, callback)| callback.is_expired())
                .map(|(name, _)| name.clone())
                .collect()
        };

        let count = expired_names.len();
        for name in expired_names {
            let _ = self.unregister_callback(&name);
        }

        count
    }

    /// Get callback statistics
    pub fn stats(&self) -> CallbackStats {
        self.stats.read().unwrap().clone()
    }

    /// Generate a C function pointer for the callback
    fn generate_c_function_ptr(&self, _signature: &CallbackSignature) -> std::result::Result<*const c_void, CallbackError> {
        // This is a simplified implementation
        // In a real implementation, this would generate platform-specific
        // assembly stubs or use libffi to create callable function pointers

        // For now, we'll create a dummy function pointer
        // In practice, this would involve:
        // 1. Allocating executable memory
        // 2. Generating assembly code that calls back into Rust
        // 3. Setting up proper stack frame and calling convention
        
        let dummy_ptr = self as *const CallbackRegistry as *const c_void;
        Ok(dummy_ptr)
    }

    /// Execute a callback (called from generated C code)
    ///
    /// # Safety
    /// 
    /// The caller must ensure that:
    /// - `args` is a valid pointer to an array of `arg_count` valid `*const c_void` pointers
    /// - Each pointer in the `args` array points to valid data of the expected type for the callback
    /// - The memory pointed to by `args` and its elements remains valid for the duration of this call
    /// - The callback is thread-safe if called from multiple threads
    pub unsafe fn execute_callback(
        &self,
        name: &str,
        args: *const *const c_void,
        arg_count: usize,
    ) -> std::result::Result<*const c_void, CallbackError> {
        // Stack overflow protection
        {
            let mut depth = self.stack_depth.lock().unwrap();
            if *depth >= self.max_stack_depth {
                let mut stats = self.stats.write().unwrap();
                stats.stack_overflows_prevented += 1;
                return Err(CallbackError::StackOverflow);
            }
            *depth += 1;
        }

        // Ensure stack is decremented on exit
        let _stack_guard = StackGuard::new(Arc::clone(&self.stack_depth));

        // Get the callback
        let callback = self.get_callback(name)
            .ok_or_else(|| CallbackError::NotFound(name.to_string()))?;

        // Check if expired
        if callback.is_expired() {
            return Err(CallbackError::Expired(name.to_string()));
        }

        // Check if active
        if !callback.is_active() {
            return Err(CallbackError::NotFound(name.to_string()));
        }

        // Update statistics
        {
            let mut stats = self.stats.write().unwrap();
            stats.total_invocations += 1;
        }

        // Convert arguments
        let mut scheme_args = Vec::new();
        let marshaller = self.marshaller.lock().unwrap();

        for i in 0..arg_count.min(callback.signature.parameters.len()) {
            let arg_ptr = unsafe { *args.add(i) };
            let param_type = &callback.signature.parameters[i];
            
            // This is simplified - in practice, we'd need to properly
            // convert from C types to Lambdust values
            let value = match param_type {
                CType::CInt => {
                    let int_val = unsafe { *(arg_ptr as *const libc::c_int) };
                    Value::Literal(Literal::integer(int_val as i64))
                }
                CType::CString => {
                    let c_str_ptr = unsafe { *(arg_ptr as *const *const libc::c_char) };
                    if c_str_ptr.is_null() {
                        Value::Literal(Literal::String("".to_string()))
                    } else {
                        let c_str = unsafe { std::ffi::CStr::from_ptr(c_str_ptr) };
                        let rust_str = c_str.to_str()
                            .map_err(|e| CallbackError::ConversionError(
                                ConversionError::StringConversion(e.to_string())
                            ))?;
                        Value::Literal(Literal::String(rust_str.to_string()))
                    }
                }
                _ => Value::Nil, // Simplified
            };
            
            scheme_args.push(value);
        }

        // Execute the callback function
        let result = {
            let env = callback.environment.lock().unwrap();
            // This is simplified - in practice, we'd need to call the evaluator
            // with the callback function and arguments
            match &callback.function {
                Value::Procedure(_) => {
                    // Would call evaluator here
                    Ok(Value::Literal(Literal::integer(0))) // Placeholder
                }
                _ => Err(CallbackError::ExecutionFailed {
                    callback: name.to_string(),
                    error: "Not a function".to_string(),
                })
            }
        };

        match result {
            Ok(return_value) => {
                // Increment call count
                callback.increment_call_count();

                // Update success statistics
                {
                    let mut stats = self.stats.write().unwrap();
                    stats.successful_invocations += 1;
                }

                // Convert return value back to C
                // This is simplified - would need proper conversion
                Ok(ptr::null())
            }
            Err(e) => {
                // Update failure statistics
                {
                    let mut stats = self.stats.write().unwrap();
                    stats.failed_invocations += 1;
                }

                Err(e)
            }
        }
    }
}

/// Stack guard for automatic cleanup
struct StackGuard {
    stack_depth: Arc<Mutex<usize>>,
}

impl StackGuard {
    fn new(stack_depth: Arc<Mutex<usize>>) -> Self {
        Self { stack_depth }
    }
}

impl Drop for StackGuard {
    fn drop(&mut self) {
        let mut depth = self.stack_depth.lock().unwrap();
        if *depth > 0 {
            *depth -= 1;
        }
    }
}

/// Async callback support
#[cfg(feature = "async")]
pub mod async_callbacks {
    use super::*;
    use std::future::Future;
    use std::pin::Pin;
    use tokio::sync::oneshot;

    /// Async callback execution result
    pub type AsyncCallbackResult = Pin<Box<dyn Future<Output = std::result::Result<Value, CallbackError>> + Send>>;

    /// Async callback registry
    #[derive(Debug)]
    pub struct AsyncCallbackRegistry {
        /// Base registry
        base: CallbackRegistry,
        /// Pending async operations
        pending: Arc<Mutex<HashMap<String, oneshot::Sender<Value>>>>,
    }

    impl AsyncCallbackRegistry {
        /// Create a new async callback registry
        pub fn new() -> Self {
            Self {
                base: CallbackRegistry::new(),
                pending: Arc::new(Mutex::new(HashMap::new())),
            }
        }

        /// Register an async callback
        pub async fn register_async_callback(
            &self,
            signature: CallbackSignature,
            function: Value,
            environment: Arc<Mutex<Environment>>,
            expires_after: Option<Duration>,
        ) -> std::result::Result<*const c_void, CallbackError> {
            // For now, delegate to sync implementation
            self.base.register_callback(signature, function, environment, expires_after)
        }

        /// Execute an async callback
        pub async fn execute_async_callback(
            &self,
            _name: &str,
            _args: Vec<Value>,
        ) -> std::result::Result<Value, CallbackError> {
            // This would implement proper async callback execution
            // For now, return a placeholder
            Ok(Value::Nil)
        }
    }

    impl Default for AsyncCallbackRegistry {
        fn default() -> Self {
            Self::new()
        }
    }
}

lazy_static::lazy_static! {
    /// Global callback registry
    pub static ref GLOBAL_CALLBACK_REGISTRY: CallbackRegistry = CallbackRegistry::new();
}

/// Convenience functions for global callback registry
pub fn register_callback(
    signature: CallbackSignature,
    function: Value,
    environment: Arc<Mutex<Environment>>,
    expires_after: Option<Duration>,
) -> std::result::Result<*const c_void, CallbackError> {
    GLOBAL_CALLBACK_REGISTRY.register_callback(signature, function, environment, expires_after)
}

pub fn unregister_callback(name: &str) -> std::result::Result<(), CallbackError> {
    GLOBAL_CALLBACK_REGISTRY.unregister_callback(name)
}

pub fn cleanup_expired_callbacks() -> usize {
    GLOBAL_CALLBACK_REGISTRY.cleanup_expired()
}

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

    #[test]
    fn test_callback_registry_creation() {
        let registry = CallbackRegistry::new();
        let stats = registry.stats();
        assert_eq!(stats.currently_active, 0);
        assert_eq!(stats.total_registered, 0);
    }

    #[test]
    fn test_callback_signature() {
        let sig = CallbackSignature {
            name: "test_callback".to_string(),
            parameters: vec![CType::CInt, CType::CString],
            return_type: CType::CInt,
            variadic: false,
            calling_convention: CallingConvention::C,
        };

        assert_eq!(sig.name, "test_callback");
        assert_eq!(sig.parameters.len(), 2);
        assert!(!sig.variadic);
    }

    #[test]
    fn test_callback_function_creation() {
        let signature = CallbackSignature {
            name: "test".to_string(),
            parameters: vec![],
            return_type: CType::Void,
            variadic: false,
            calling_convention: CallingConvention::C,
        };

        let function = Value::Literal(Literal::Number(42.0));
        let environment = Arc::new(Mutex::new(Environment::new(None, 0)));

        let callback = CallbackFunction {
            signature,
            function,
            environment,
            registered_at: SystemTime::now(),
            expires_at: None,
            call_count: Arc::new(Mutex::new(0)),
            c_function_ptr: ptr::null(),
            active: Arc::new(Mutex::new(true)),
        };

        assert!(callback.is_active());
        assert!(!callback.is_expired());
        assert_eq!(callback.call_count(), 0);
    }

    #[test]
    fn test_cleanup_expired() {
        let registry = CallbackRegistry::new();
        
        // This test would need more setup to create expired callbacks
        let cleaned = registry.cleanup_expired();
        assert_eq!(cleaned, 0); // No expired callbacks initially
    }
}