//! Worker pool adapter for Lambda functions
//!
//! This module adapts the existing worker pool infrastructure for Lambda execution,
//! providing warm start capabilities and cold start tracking.
//!
//! NOTE: This is currently a stub/placeholder. Worker pool integration is planned
//! for Phase 3 of the implementation. For now, Lambda uses ephemeral execution.

use crate::lambda::{
    context::LambdaContext,
    types::{FunctionId, LambdaError},
};
use crate::types::JsExecEvent;
use futures::Stream;
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use std::pin::Pin;

/// Pool adapter for Lambda function execution
///
/// This provides an abstraction over the worker pool, allowing Lambda functions
/// to benefit from warm starts while maintaining proper isolation.
pub struct LambdaPoolAdapter {
    // TODO: Add pool manager when worker pool is implemented
    _phantom: std::marker::PhantomData<()>,
}

impl LambdaPoolAdapter {
    /// Create a new pool adapter
    ///
    /// NOTE: Currently returns a placeholder. Full implementation requires
    /// completing the worker pool in /workspace/src/pool/
    pub fn new(/* pool: Arc<PoolManager> */) -> Self {
        Self {
            _phantom: std::marker::PhantomData,
        }
    }

    /// Execute a function using the worker pool
    ///
    /// This attempts to use a warm worker if available, falling back to
    /// cold start if necessary.
    ///
    /// # Arguments
    /// * `function_id` - The function being executed
    /// * `code` - Function code to execute
    /// * `event` - Event payload
    /// * `context` - Lambda context
    ///
    /// # Returns
    /// Stream of execution events
    ///
    /// # Errors
    /// Returns error if execution fails
    pub async fn execute_function(
        &self,
        _function_id: &FunctionId,
        _code: String,
        _event: serde_json::Value,
        _context: LambdaContext,
    ) -> Result<Pin<Box<dyn Stream<Item = JsExecEvent> + Send>>, LambdaError> {
        // TODO: Implement pool-based execution
        // For now, return an error indicating this feature is not yet implemented
        Err(LambdaError::Internal(
            "Worker pool not yet implemented. Use ephemeral execution mode.".to_string(),
        ))
    }

    /// Get pool statistics
    ///
    /// Returns metrics about worker pool health and performance.
    pub async fn get_pool_stats(&self) -> LambdaPoolStats {
        // TODO: Implement actual stats
        LambdaPoolStats {
            total_workers: 0,
            available_workers: 0,
            busy_workers: 0,
            total_cold_starts: 0,
            total_warm_starts: 0,
            average_cold_start_ms: 0.0,
            average_warm_start_ms: 0.0,
        }
    }
}

/// Statistics about the Lambda worker pool
#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
pub struct LambdaPoolStats {
    /// Total number of workers in the pool
    pub total_workers: usize,
    /// Number of available (idle) workers
    pub available_workers: usize,
    /// Number of busy workers
    pub busy_workers: usize,
    /// Total cold starts since startup
    pub total_cold_starts: u64,
    /// Total warm starts since startup
    pub total_warm_starts: u64,
    /// Average cold start duration (milliseconds)
    pub average_cold_start_ms: f64,
    /// Average warm start duration (milliseconds)
    pub average_warm_start_ms: f64,
}

// TODO: Implement these types when worker pool is ready
// - WorkerHandle
// - WorkerState (Idle, Busy, Evicting)
// - PoolConfiguration
// - Worker lifecycle management
// - Cold/warm start detection
// - Worker eviction policies
