//! Minimal Integration Layer for CUDA Execution Engine
//!
//! This module provides a simplified, compilation-safe integration layer
//! for the CUDA execution engine modules, focusing on core functionality
//! without complex dependencies that might cause compilation issues.

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

/// Minimal execution engine for basic optimization tasks
///
/// This is a simplified version of the full integrated execution engine
/// that provides core functionality without complex dependencies.
#[derive(Debug)]
pub struct MinimalExecutionEngine {
    /// Configuration
    config: MinimalEngineConfig,

    /// Active tasks
    active_tasks: Arc<Mutex<HashMap<String, MinimalTask>>>,

    /// Engine state
    state: Arc<Mutex<EngineState>>,

    /// Simple statistics
    stats: Arc<Mutex<MinimalStatistics>>,
}

/// Minimal configuration for the execution engine
#[derive(Debug, Clone)]
pub struct MinimalEngineConfig {
    /// Maximum concurrent tasks
    pub max_concurrent_tasks: usize,

    /// Default task timeout
    pub default_timeout: Duration,

    /// Enable basic monitoring
    pub enable_monitoring: bool,

    /// Enable basic fault tolerance
    pub enable_fault_tolerance: bool,
}

/// Minimal task representation
#[derive(Debug, Clone)]
pub struct MinimalTask {
    /// Task identifier
    pub id: String,

    /// Task type
    pub task_type: String,

    /// Task parameters
    pub parameters: HashMap<String, String>,

    /// Task priority (0 = highest)
    pub priority: u8,

    /// Creation timestamp
    pub created_at: SystemTime,

    /// Current status
    pub status: TaskStatus,

    /// Progress (0.0 to 1.0)
    pub progress: f64,
}

/// Task execution status
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum TaskStatus {
    Pending,
    Running,
    Completed,
    Failed,
    Cancelled,
}

/// Engine state
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum EngineState {
    Stopped,
    Starting,
    Running,
    Stopping,
    Error,
}

/// Minimal statistics tracking
#[derive(Debug, Clone)]
pub struct MinimalStatistics {
    /// Total tasks processed
    pub tasks_processed: u64,

    /// Currently active tasks
    pub active_task_count: usize,

    /// Success rate (0.0 to 1.0)
    pub success_rate: f64,

    /// Average processing time
    pub avg_processing_time: Duration,

    /// Engine uptime
    pub uptime: Duration,

    /// Last update time
    pub last_updated: SystemTime,
}

/// Task execution result
#[derive(Debug, Clone)]
pub struct TaskResult {
    /// Task identifier
    pub task_id: String,

    /// Execution success
    pub success: bool,

    /// Result data
    pub data: HashMap<String, String>,

    /// Execution time
    pub execution_time: Duration,

    /// Error message (if any)
    pub error: Option<String>,
}

/// Simple error type for the minimal engine
#[derive(Debug, Clone)]
pub enum MinimalEngineError {
    TaskNotFound(String),
    EngineNotRunning,
    ExecutionFailed(String),
    ConfigError(String),
    SystemError(String),
}

impl fmt::Display for MinimalEngineError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            MinimalEngineError::TaskNotFound(id) => write!(f, "Task not found: {}", id),
            MinimalEngineError::EngineNotRunning => write!(f, "Engine not running"),
            MinimalEngineError::ExecutionFailed(msg) => write!(f, "Task execution failed: {}", msg),
            MinimalEngineError::ConfigError(msg) => write!(f, "Configuration error: {}", msg),
            MinimalEngineError::SystemError(msg) => write!(f, "System error: {}", msg),
        }
    }
}

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

impl MinimalExecutionEngine {
    /// Create a new minimal execution engine
    pub fn new(config: MinimalEngineConfig) -> Self {
        Self {
            config,
            active_tasks: Arc::new(Mutex::new(HashMap::new())),
            state: Arc::new(Mutex::new(EngineState::Stopped)),
            stats: Arc::new(Mutex::new(MinimalStatistics::new())),
        }
    }

    /// Start the execution engine
    pub fn start(&self) -> Result<(), MinimalEngineError> {
        let mut state = self.state.lock().expect("lock should not be poisoned");

        match *state {
            EngineState::Running => return Ok(()), // Already running
            EngineState::Starting => {
                return Err(MinimalEngineError::SystemError(
                    "Engine is already starting".to_string(),
                ))
            }
            _ => {}
        }

        *state = EngineState::Starting;

        // Simulate startup process
        std::thread::sleep(Duration::from_millis(100));

        *state = EngineState::Running;

        // Update statistics
        {
            let mut stats = self.stats.lock().expect("lock should not be poisoned");
            stats.last_updated = SystemTime::now();
        }

        Ok(())
    }

    /// Stop the execution engine
    pub fn stop(&self) -> Result<(), MinimalEngineError> {
        let mut state = self.state.lock().expect("lock should not be poisoned");

        match *state {
            EngineState::Stopped => return Ok(()), // Already stopped
            EngineState::Stopping => {
                return Err(MinimalEngineError::SystemError(
                    "Engine is already stopping".to_string(),
                ))
            }
            _ => {}
        }

        *state = EngineState::Stopping;

        // Cancel all active tasks
        {
            let mut tasks = self.active_tasks.lock().expect("lock should not be poisoned");
            for task in tasks.values_mut() {
                if task.status == TaskStatus::Running || task.status == TaskStatus::Pending {
                    task.status = TaskStatus::Cancelled;
                }
            }
        }

        *state = EngineState::Stopped;
        Ok(())
    }

    /// Submit a task for execution
    pub fn submit_task(&self, mut task: MinimalTask) -> Result<String, MinimalEngineError> {
        // Check engine state
        {
            let state = self.state.lock().expect("lock should not be poisoned");
            if *state != EngineState::Running {
                return Err(MinimalEngineError::EngineNotRunning);
            }
        }

        // Check capacity
        {
            let tasks = self.active_tasks.lock().expect("lock should not be poisoned");
            if tasks.len() >= self.config.max_concurrent_tasks {
                return Err(MinimalEngineError::SystemError(
                    "Maximum concurrent tasks reached".to_string(),
                ));
            }
        }

        // Set initial status
        task.status = TaskStatus::Pending;
        task.progress = 0.0;

        let task_id = task.id.clone();

        // Add to active tasks
        {
            let mut tasks = self.active_tasks.lock().expect("lock should not be poisoned");
            tasks.insert(task_id.clone(), task);
        }

        Ok(task_id)
    }

    /// Execute a pending task
    pub fn execute_task(&self, task_id: &str) -> Result<TaskResult, MinimalEngineError> {
        // Get and update task
        let task = {
            let mut tasks = self.active_tasks.lock().expect("lock should not be poisoned");
            match tasks.get_mut(task_id) {
                Some(task) => {
                    if task.status != TaskStatus::Pending {
                        return Err(MinimalEngineError::ExecutionFailed(
                            "Task is not in pending state".to_string(),
                        ));
                    }
                    task.status = TaskStatus::Running;
                    task.progress = 0.1;
                    task.clone()
                }
                None => return Err(MinimalEngineError::TaskNotFound(task_id.to_string())),
            }
        };

        let start_time = std::time::Instant::now();

        // Simulate task execution
        let result = self.simulate_task_execution(&task);

        let execution_time = start_time.elapsed();

        // Update task status
        {
            let mut tasks = self.active_tasks.lock().expect("lock should not be poisoned");
            if let Some(active_task) = tasks.get_mut(task_id) {
                active_task.status = if result.success {
                    TaskStatus::Completed
                } else {
                    TaskStatus::Failed
                };
                active_task.progress = 1.0;
            }
        }

        // Update statistics
        {
            let mut stats = self.stats.lock().expect("lock should not be poisoned");
            stats.tasks_processed += 1;
            stats.last_updated = SystemTime::now();

            // Update success rate
            let total_completed = stats.tasks_processed;
            let success_count = if result.success { 1 } else { 0 };
            stats.success_rate = (stats.success_rate * (total_completed - 1) as f64
                + success_count as f64)
                / total_completed as f64;

            // Update average processing time
            stats.avg_processing_time = Duration::from_nanos(
                ((stats.avg_processing_time.as_nanos() * (total_completed - 1) as u128
                    + execution_time.as_nanos())
                    / total_completed as u128) as u64,
            );
        }

        Ok(TaskResult {
            task_id: task_id.to_string(),
            success: result.success,
            data: result.data,
            execution_time,
            error: result.error,
        })
    }

    /// Get current engine state
    pub fn get_state(&self) -> EngineState {
        *self.state.lock().expect("lock should not be poisoned")
    }

    /// Get current statistics
    pub fn get_statistics(&self) -> MinimalStatistics {
        let mut stats = self.stats.lock().expect("lock should not be poisoned");
        stats.active_task_count = self.active_tasks.lock().expect("lock should not be poisoned").len();
        stats.clone()
    }

    /// Get active tasks
    pub fn get_active_tasks(&self) -> Vec<MinimalTask> {
        self.active_tasks
            .lock()
            .expect("active_tasks lock should not be poisoned")
            .values()
            .cloned()
            .collect()
    }

    /// Get task by ID
    pub fn get_task(&self, task_id: &str) -> Option<MinimalTask> {
        self.active_tasks.lock().expect("lock should not be poisoned").get(task_id).cloned()
    }

    /// Cancel a task
    pub fn cancel_task(&self, task_id: &str) -> Result<(), MinimalEngineError> {
        let mut tasks = self.active_tasks.lock().expect("lock should not be poisoned");
        match tasks.get_mut(task_id) {
            Some(task) => {
                if task.status == TaskStatus::Pending || task.status == TaskStatus::Running {
                    task.status = TaskStatus::Cancelled;
                    Ok(())
                } else {
                    Err(MinimalEngineError::ExecutionFailed(
                        "Task cannot be cancelled in current state".to_string(),
                    ))
                }
            }
            None => Err(MinimalEngineError::TaskNotFound(task_id.to_string())),
        }
    }

    /// Simulate task execution (placeholder implementation)
    fn simulate_task_execution(&self, task: &MinimalTask) -> TaskResult {
        // Simulate different types of tasks
        match task.task_type.as_str() {
            "optimization" => self.simulate_optimization_task(task),
            "training" => self.simulate_training_task(task),
            "inference" => self.simulate_inference_task(task),
            _ => self.simulate_generic_task(task),
        }
    }

    fn simulate_optimization_task(&self, task: &MinimalTask) -> TaskResult {
        // Simulate optimization computation
        std::thread::sleep(Duration::from_millis(50));

        let mut data = HashMap::new();
        data.insert("loss".to_string(), "0.0123".to_string());
        data.insert("accuracy".to_string(), "0.987".to_string());
        data.insert("iterations".to_string(), "100".to_string());

        TaskResult {
            task_id: task.id.clone(),
            success: true,
            data,
            execution_time: Duration::from_millis(50),
            error: None,
        }
    }

    fn simulate_training_task(&self, task: &MinimalTask) -> TaskResult {
        // Simulate training computation
        std::thread::sleep(Duration::from_millis(100));

        let mut data = HashMap::new();
        data.insert("epochs".to_string(), "10".to_string());
        data.insert("final_loss".to_string(), "0.0456".to_string());
        data.insert("validation_accuracy".to_string(), "0.923".to_string());

        TaskResult {
            task_id: task.id.clone(),
            success: true,
            data,
            execution_time: Duration::from_millis(100),
            error: None,
        }
    }

    fn simulate_inference_task(&self, task: &MinimalTask) -> TaskResult {
        // Simulate inference computation
        std::thread::sleep(Duration::from_millis(20));

        let mut data = HashMap::new();
        data.insert(
            "predictions".to_string(),
            "[[0.1, 0.9], [0.8, 0.2]]".to_string(),
        );
        data.insert("latency_ms".to_string(), "15".to_string());

        TaskResult {
            task_id: task.id.clone(),
            success: true,
            data,
            execution_time: Duration::from_millis(20),
            error: None,
        }
    }

    fn simulate_generic_task(&self, task: &MinimalTask) -> TaskResult {
        // Simulate generic computation
        std::thread::sleep(Duration::from_millis(30));

        let mut data = HashMap::new();
        data.insert("result".to_string(), "completed".to_string());
        data.insert("processing_time".to_string(), "30ms".to_string());

        TaskResult {
            task_id: task.id.clone(),
            success: true,
            data,
            execution_time: Duration::from_millis(30),
            error: None,
        }
    }
}

impl Default for MinimalEngineConfig {
    fn default() -> Self {
        Self {
            max_concurrent_tasks: 10,
            default_timeout: Duration::from_secs(300),
            enable_monitoring: true,
            enable_fault_tolerance: true,
        }
    }
}

impl MinimalStatistics {
    fn new() -> Self {
        Self {
            tasks_processed: 0,
            active_task_count: 0,
            success_rate: 1.0,
            avg_processing_time: Duration::from_secs(0),
            uptime: Duration::from_secs(0),
            last_updated: SystemTime::now(),
        }
    }
}

impl MinimalTask {
    /// Create a new minimal task
    pub fn new(id: String, task_type: String) -> Self {
        Self {
            id,
            task_type,
            parameters: HashMap::new(),
            priority: 5, // Default medium priority
            created_at: SystemTime::now(),
            status: TaskStatus::Pending,
            progress: 0.0,
        }
    }

    /// Add a parameter to the task
    pub fn with_parameter(mut self, key: String, value: String) -> Self {
        self.parameters.insert(key, value);
        self
    }

    /// Set task priority
    pub fn with_priority(mut self, priority: u8) -> Self {
        self.priority = priority;
        self
    }
}

/// Convenience functions for creating common task types
impl MinimalTask {
    /// Create an optimization task
    pub fn optimization(id: String) -> Self {
        Self::new(id, "optimization".to_string())
    }

    /// Create a training task
    pub fn training(id: String) -> Self {
        Self::new(id, "training".to_string())
    }

    /// Create an inference task
    pub fn inference(id: String) -> Self {
        Self::new(id, "inference".to_string())
    }
}

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

    #[test]
    fn test_engine_lifecycle() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        // Test starting
        assert!(engine.start().is_ok());
        assert_eq!(engine.get_state(), EngineState::Running);

        // Test stopping
        assert!(engine.stop().is_ok());
        assert_eq!(engine.get_state(), EngineState::Stopped);
    }

    #[test]
    fn test_task_submission() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        let task = MinimalTask::optimization("test_task_001".to_string())
            .with_parameter("learning_rate".to_string(), "0.01".to_string())
            .with_priority(1);

        let task_id = engine.submit_task(task).unwrap();
        assert_eq!(task_id, "test_task_001");

        let retrieved_task = engine.get_task(&task_id).unwrap();
        assert_eq!(retrieved_task.task_type, "optimization");
        assert_eq!(retrieved_task.status, TaskStatus::Pending);
    }

    #[test]
    fn test_task_execution() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        let task = MinimalTask::optimization("test_execution_001".to_string());
        let task_id = engine.submit_task(task).unwrap();

        let result = engine.execute_task(&task_id).unwrap();
        assert!(result.success);
        assert_eq!(result.task_id, "test_execution_001");
        assert!(result.data.contains_key("loss"));
        assert!(result.execution_time > Duration::from_secs(0));
    }

    #[test]
    fn test_task_cancellation() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        let task = MinimalTask::training("test_cancel_001".to_string());
        let task_id = engine.submit_task(task).unwrap();

        assert!(engine.cancel_task(&task_id).is_ok());

        let cancelled_task = engine.get_task(&task_id).unwrap();
        assert_eq!(cancelled_task.status, TaskStatus::Cancelled);
    }

    #[test]
    fn test_statistics_tracking() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        let initial_stats = engine.get_statistics();
        assert_eq!(initial_stats.tasks_processed, 0);

        let task = MinimalTask::inference("test_stats_001".to_string());
        let task_id = engine.submit_task(task).unwrap();
        engine.execute_task(&task_id).unwrap();

        let updated_stats = engine.get_statistics();
        assert_eq!(updated_stats.tasks_processed, 1);
        assert!(updated_stats.success_rate > 0.0);
        assert!(updated_stats.avg_processing_time > Duration::from_secs(0));
    }

    #[test]
    fn test_concurrent_task_limit() {
        let config = MinimalEngineConfig {
            max_concurrent_tasks: 2,
            ..Default::default()
        };
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        // Submit tasks up to the limit
        let task1 = MinimalTask::optimization("task_001".to_string());
        let task2 = MinimalTask::optimization("task_002".to_string());

        assert!(engine.submit_task(task1).is_ok());
        assert!(engine.submit_task(task2).is_ok());

        // Try to submit one more (should fail)
        let task3 = MinimalTask::optimization("task_003".to_string());
        assert!(engine.submit_task(task3).is_err());
    }

    #[test]
    fn test_different_task_types() {
        let config = MinimalEngineConfig::default();
        let engine = MinimalExecutionEngine::new(config);

        engine.start().unwrap();

        // Test optimization task
        let opt_task = MinimalTask::optimization("opt_001".to_string());
        let opt_id = engine.submit_task(opt_task).unwrap();
        let opt_result = engine.execute_task(&opt_id).unwrap();
        assert!(opt_result.data.contains_key("loss"));

        // Test training task
        let train_task = MinimalTask::training("train_001".to_string());
        let train_id = engine.submit_task(train_task).unwrap();
        let train_result = engine.execute_task(&train_id).unwrap();
        assert!(train_result.data.contains_key("epochs"));

        // Test inference task
        let infer_task = MinimalTask::inference("infer_001".to_string());
        let infer_id = engine.submit_task(infer_task).unwrap();
        let infer_result = engine.execute_task(&infer_id).unwrap();
        assert!(infer_result.data.contains_key("predictions"));
    }
}
