//! Resource allocation strategies for pipeline optimization
//!
//! This module provides comprehensive system resource monitoring and allocation
//! strategies for optimal pipeline performance across different platforms.

use crate::error::{IoError, Result};
use std::time::{Duration, Instant};

/// Real-time resource monitoring for dynamic optimization
#[derive(Debug)]
pub struct ResourceMonitor {
    system_metrics: SystemMetrics,
    monitoring_interval: Duration,
    last_update: Instant,
}

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

impl ResourceMonitor {
    pub fn new() -> Self {
        Self {
            system_metrics: SystemMetrics::default(),
            monitoring_interval: Duration::from_millis(100),
            last_update: Instant::now(),
        }
    }

    pub fn get_current_metrics(&mut self) -> Result<SystemMetrics> {
        if self.last_update.elapsed() >= self.monitoring_interval {
            self.update_metrics()?;
            self.last_update = Instant::now();
        }
        Ok(self.system_metrics.clone())
    }

    fn update_metrics(&mut self) -> Result<()> {
        // Update CPU usage
        self.system_metrics.cpu_usage = self.get_cpu_usage()?;

        // Update memory usage
        self.system_metrics.memory_usage = self.get_memory_usage()?;

        // Update I/O statistics
        self.system_metrics.io_utilization = self.get_io_utilization()?;

        // Update network usage
        self.system_metrics.network_bandwidth_usage = self.get_network_usage()?;

        // Update cache statistics
        self.system_metrics.cache_performance = self.get_cache_performance()?;

        Ok(())
    }

    fn get_cpu_usage(&self) -> Result<f64> {
        // Platform-specific CPU usage detection
        #[cfg(target_os = "linux")]
        {
            self.get_linux_cpu_usage()
        }
        #[cfg(target_os = "windows")]
        {
            self.get_windows_cpu_usage()
        }
        #[cfg(target_os = "macos")]
        {
            self.get_macos_cpu_usage()
        }
        #[cfg(not(any(target_os = "linux", target_os = "windows", target_os = "macos")))]
        {
            Ok(0.5) // Default fallback
        }
    }

    #[cfg(target_os = "linux")]
    fn get_linux_cpu_usage(&self) -> Result<f64> {
        // Read /proc/stat for CPU usage
        let stat_content = std::fs::read_to_string("/proc/stat")
            .map_err(|e| IoError::Other(format!("Failed to read /proc/stat: {}", e)))?;

        if let Some(cpu_line) = stat_content.lines().next() {
            let values: Vec<u64> = cpu_line
                .split_whitespace()
                .skip(1)
                .take(4)
                .filter_map(|s| s.parse().ok())
                .collect();

            if values.len() >= 4 {
                let idle = values[3];
                let total: u64 = values.iter().sum();
                return Ok(1.0 - (idle as f64) / (total as f64));
            }
        }

        Ok(0.5) // Fallback
    }

    #[cfg(target_os = "windows")]
    fn get_windows_cpu_usage(&self) -> Result<f64> {
        // Windows-specific implementation would go here
        Ok(0.5) // Placeholder
    }

    #[cfg(target_os = "macos")]
    fn get_macos_cpu_usage(&self) -> Result<f64> {
        // macOS-specific implementation would go here
        Ok(0.5) // Placeholder
    }

    fn get_memory_usage(&self) -> Result<MemoryUsage> {
        #[cfg(target_os = "linux")]
        {
            self.get_linux_memory_usage()
        }
        #[cfg(not(target_os = "linux"))]
        {
            Ok(MemoryUsage {
                total: 8 * 1024 * 1024 * 1024,     // 8GB fallback
                available: 4 * 1024 * 1024 * 1024, // 4GB fallback
                used: 4 * 1024 * 1024 * 1024,
                utilization: 0.5,
            })
        }
    }

    #[cfg(target_os = "linux")]
    fn get_linux_memory_usage(&self) -> Result<MemoryUsage> {
        let meminfo_content = std::fs::read_to_string("/proc/meminfo")
            .map_err(|e| IoError::Other(format!("Failed to read /proc/meminfo: {}", e)))?;

        let mut total = 0u64;
        let mut available = 0u64;

        for line in meminfo_content.lines() {
            if line.starts_with("MemTotal:") {
                total = line
                    .split_whitespace()
                    .nth(1)
                    .and_then(|s| s.parse().ok())
                    .unwrap_or(0)
                    * 1024; // Convert KB to bytes
            } else if line.starts_with("MemAvailable:") {
                available = line
                    .split_whitespace()
                    .nth(1)
                    .and_then(|s| s.parse().ok())
                    .unwrap_or(0)
                    * 1024; // Convert KB to bytes
            }
        }

        let used = total - available;
        let utilization = if total > 0 {
            used as f64 / total as f64
        } else {
            0.0
        };

        Ok(MemoryUsage {
            total,
            available,
            used,
            utilization,
        })
    }

    fn get_io_utilization(&self) -> Result<f64> {
        // Simplified I/O utilization - could be expanded with platform-specific code
        Ok(0.3) // Placeholder
    }

    fn get_network_usage(&self) -> Result<f64> {
        // Simplified network usage - could be expanded with platform-specific code
        Ok(0.2) // Placeholder
    }

    fn get_cache_performance(&self) -> Result<CachePerformance> {
        Ok(CachePerformance {
            l1_hit_rate: 0.95,
            l2_hit_rate: 0.85,
            l3_hit_rate: 0.75,
            tlb_hit_rate: 0.99,
        })
    }
}

/// System resource metrics
#[derive(Debug, Clone)]
pub struct SystemMetrics {
    pub cpu_usage: f64,
    pub memory_usage: MemoryUsage,
    pub io_utilization: f64,
    pub network_bandwidth_usage: f64,
    pub cache_performance: CachePerformance,
    pub numa_topology: NumaTopology,
}

impl Default for SystemMetrics {
    fn default() -> Self {
        Self {
            cpu_usage: 0.5,
            memory_usage: MemoryUsage {
                total: 8 * 1024 * 1024 * 1024,
                available: 4 * 1024 * 1024 * 1024,
                used: 4 * 1024 * 1024 * 1024,
                utilization: 0.5,
            },
            io_utilization: 0.3,
            network_bandwidth_usage: 0.2,
            cache_performance: CachePerformance {
                l1_hit_rate: 0.95,
                l2_hit_rate: 0.85,
                l3_hit_rate: 0.75,
                tlb_hit_rate: 0.99,
            },
            numa_topology: NumaTopology::default(),
        }
    }
}

#[derive(Debug, Clone)]
pub struct MemoryUsage {
    pub total: u64,
    pub available: u64,
    pub used: u64,
    pub utilization: f64,
}

#[derive(Debug, Clone)]
pub struct CachePerformance {
    pub l1_hit_rate: f64,
    pub l2_hit_rate: f64,
    pub l3_hit_rate: f64,
    pub tlb_hit_rate: f64,
}

#[derive(Debug, Clone)]
pub struct NumaTopology {
    pub nodes: Vec<NumaNode>,
    pub preferred_node: usize,
}

impl Default for NumaTopology {
    fn default() -> Self {
        Self {
            nodes: vec![NumaNode {
                id: 0,
                memory_size: 8 * 1024 * 1024 * 1024,
                cpu_cores: vec![0, 1, 2, 3],
            }],
            preferred_node: 0,
        }
    }
}

#[derive(Debug, Clone)]
pub struct NumaNode {
    pub id: usize,
    pub memory_size: u64,
    pub cpu_cores: Vec<usize>,
}

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

    #[test]
    fn test_resource_monitor_creation() {
        let monitor = ResourceMonitor::new();
        assert!(monitor.monitoring_interval > Duration::from_millis(0));
    }

    #[test]
    fn test_system_metrics_default() {
        let metrics = SystemMetrics::default();
        assert!(metrics.cpu_usage >= 0.0 && metrics.cpu_usage <= 1.0);
        assert!(metrics.memory_usage.total > 0);
        assert!(metrics.cache_performance.l1_hit_rate > 0.0);
    }

    #[test]
    fn test_numa_topology_default() {
        let topology = NumaTopology::default();
        assert!(!topology.nodes.is_empty());
        assert_eq!(topology.preferred_node, 0);
    }
}