//! Multi-region orchestration module for RustyTorch++ Platform
//! Handles region management, health monitoring, failover, and cross-region coordination

use crate::error::RegionError;
use crate::{PlatformError, PlatformResult};
use dashmap::DashMap;
use std::collections::HashMap;
use std::sync::{
    Arc,
    atomic::{AtomicBool, Ordering},
};
use std::time::{Duration, Instant};
use tokio::sync::{RwLock as AsyncRwLock, broadcast};
use uuid::Uuid;

/// Regional configuration
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct RegionConfig {
    pub id: String,
    pub name: String,
    pub endpoint: String,
    pub capacity_limits: HashMap<String, u64>,
    pub availability_zone_count: u32,
    pub latency_targets_ms: HashMap<String, u64>,
}

/// Region status enumeration
#[derive(Debug, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
pub enum RegionStatus {
    Available,
    Degraded,
    Unavailable,
    Maintenance,
}

/// Region health information
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub enum RegionHealth {
    Healthy {
        uptime: Duration,
        cpu_usage: f64,
        memory_usage: f64,
        #[serde(skip, default = "std::time::Instant::now")]
        last_check: std::time::Instant,
    },
    Degraded {
        issues: Vec<String>,
        #[serde(skip, default = "std::time::Instant::now")]
        last_check: std::time::Instant,
    },
    Unhealthy {
        errors: Vec<String>,
        #[serde(skip, default = "std::time::Instant::now")]
        last_check: std::time::Instant,
    },
}

/// Cross-region operation definition
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct CrossRegionOp {
    pub id: Uuid,
    pub tenant_id: Uuid,
    pub source_region: String,
    pub target_regions: Vec<String>,
    pub operation_type: String,
    pub data_size_bytes: u64,
    pub priority: u32,
    pub timeout_ms: u64,
}

/// Region capacity information
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct RegionCapacity {
    pub region_id: String,
    pub total_gpu: u64,
    pub available_gpu: u64,
    pub reserved_gpu: u64,
    pub used_gpu: u64,
    pub total_memory_gb: u64,
    pub available_memory_gb: u64,
    pub reserved_memory_gb: u64,
    pub used_memory_gb: u64,
}

/// Operation scheduling request
#[derive(Debug, Clone)]
pub struct OperationRequest {
    pub tenant_id: Uuid,
    pub preferred_region: String,
    pub operation_type: String,
    pub data_size_bytes: u64,
    pub resource_requirements: HashMap<String, u64>,
}

/// Operation assignment result
#[derive(Debug, Clone)]
pub struct OperationAssignment {
    pub operation_id: Uuid,
    pub tenant_id: Uuid,
    pub assigned_region: String,
    pub is_failover: bool,
    pub estimated_start_time: chrono::DateTime<chrono::Utc>,
}

/// Cross-region coordination result
#[derive(Debug, Clone)]
pub struct CrossRegionResult {
    pub operation_id: Uuid,
    pub participating_regions: Vec<String>,
    pub latency_ms: u64,
    pub success: bool,
}

/// Latency-sensitive request
#[derive(Debug, Clone)]
pub struct LatencySensitiveRequest {
    pub tenant_id: Uuid,
    pub required_regions: Vec<String>,
    pub max_latency_ms: u64,
    pub operation_type: String,
    pub data_size_bytes: u64,
}

/// Latency-optimized assignment
#[derive(Debug, Clone)]
pub struct LatencyOptimizedAssignment {
    pub operation_id: Uuid,
    pub participating_regions: Vec<String>,
    pub max_inter_region_latency_ms: u64,
    pub latency_matrix: HashMap<String, HashMap<String, f64>>,
}

/// Data locality request
#[derive(Debug, Clone)]
pub struct DataLocalityRequest {
    pub tenant_id: Uuid,
    pub dataset_id: String,
    pub operation_type: String,
    pub resource_types: Vec<String>,
    pub resource_quantity: u64,
}

/// Data locality optimized assignment
#[derive(Debug, Clone)]
pub struct DataLocalityAssignment {
    pub operation_id: Uuid,
    pub assigned_region: String,
    pub data_transfer_required: bool,
    pub estimated_data_transfer_time_ms: u64,
}

/// Capacity reservation
#[derive(Debug, Clone)]
pub struct CapacityReservation {
    pub reservation_id: Uuid,
    pub tenant_id: Uuid,
    pub region_id: String,
    pub resources: HashMap<String, u64>,
    pub expires_at: chrono::DateTime<chrono::Utc>,
}

/// Region manager for multi-region orchestration
#[derive(Debug)]
pub struct RegionManager {
    regions: Arc<DashMap<String, RegionConfig>>,
    region_status: Arc<DashMap<String, RegionStatus>>,
    region_health: Arc<DashMap<String, RegionHealth>>,
    region_capacity: Arc<DashMap<String, RegionCapacity>>,
    reservations: Arc<DashMap<Uuid, CapacityReservation>>,
    data_locality: Arc<DashMap<String, HashMap<Uuid, Vec<String>>>>, // dataset_id -> tenant_id -> regions
    latency_matrix: Arc<AsyncRwLock<HashMap<String, HashMap<String, f64>>>>,
    health_monitor_running: Arc<AtomicBool>,
    shutdown_tx: Option<broadcast::Sender<()>>,
    client: reqwest::Client,
}

impl RegionManager {
    /// Create new RegionManager
    pub async fn new(config: &crate::PlatformConfig) -> PlatformResult<Self> {
        let regions = Arc::new(DashMap::new());
        let region_status = Arc::new(DashMap::new());
        let region_health = Arc::new(DashMap::new());
        let region_capacity = Arc::new(DashMap::new());
        let reservations = Arc::new(DashMap::new());
        let data_locality = Arc::new(DashMap::new());
        let latency_matrix = Arc::new(AsyncRwLock::new(HashMap::new()));
        let health_monitor_running = Arc::new(AtomicBool::new(false));
        let client = reqwest::Client::new();

        // Initialize regions
        for (region_id, region_config) in &config.regions {
            regions.insert(region_id.clone(), region_config.clone());
            region_status.insert(region_id.clone(), RegionStatus::Available);

            // Initialize capacity based on config
            let capacity = RegionCapacity {
                region_id: region_id.clone(),
                total_gpu: region_config
                    .capacity_limits
                    .get("gpu")
                    .copied()
                    .unwrap_or(0),
                available_gpu: region_config
                    .capacity_limits
                    .get("gpu")
                    .copied()
                    .unwrap_or(0),
                reserved_gpu: 0,
                used_gpu: 0,
                total_memory_gb: region_config
                    .capacity_limits
                    .get("memory_gb")
                    .copied()
                    .unwrap_or(0),
                available_memory_gb: region_config
                    .capacity_limits
                    .get("memory_gb")
                    .copied()
                    .unwrap_or(0),
                reserved_memory_gb: 0,
                used_memory_gb: 0,
            };
            region_capacity.insert(region_id.clone(), capacity);

            // Initialize health as healthy
            region_health.insert(
                region_id.clone(),
                RegionHealth::Healthy {
                    uptime: Duration::from_secs(0),
                    cpu_usage: 0.1,
                    memory_usage: 0.1,
                    last_check: Instant::now(),
                },
            );
        }

        // Initialize latency matrix from config
        let mut matrix = HashMap::new();
        for (source_id, source_config) in &config.regions {
            let mut targets = HashMap::new();
            for (target_id, latency) in &source_config.latency_targets_ms {
                targets.insert(target_id.clone(), *latency as f64);
            }
            // Self-latency is 0
            targets.insert(source_id.clone(), 0.0);
            matrix.insert(source_id.clone(), targets);
        }
        *latency_matrix.write().await = matrix;

        Ok(Self {
            regions,
            region_status,
            region_health,
            region_capacity,
            reservations,
            data_locality,
            latency_matrix,
            health_monitor_running,
            shutdown_tx: None,
            client,
        })
    }

    /// Start region manager services
    pub async fn start(&mut self) -> PlatformResult<()> {
        self.start_health_monitoring().await?;
        tracing::info!("RegionManager started");
        Ok(())
    }

    /// Shutdown region manager
    pub async fn shutdown(&mut self) -> PlatformResult<()> {
        self.health_monitor_running.store(false, Ordering::Relaxed);
        if let Some(tx) = self.shutdown_tx.take() {
            let _ = tx.send(());
        }
        tracing::info!("RegionManager shutdown");
        Ok(())
    }

    /// Get region count
    pub async fn get_region_count(&self) -> usize {
        self.regions.len()
    }

    /// Get region configuration
    pub async fn get_region(&self, region_id: &str) -> PlatformResult<RegionConfig> {
        self.regions
            .get(region_id)
            .map(|r| r.clone())
            .ok_or_else(|| {
                PlatformError::Region(RegionError::NotFound {
                    region_id: region_id.to_string(),
                })
            })
    }

    /// Start health monitoring
    pub async fn start_health_monitoring(&mut self) -> PlatformResult<()> {
        if self.health_monitor_running.load(Ordering::Relaxed) {
            return Ok(());
        }

        self.health_monitor_running.store(true, Ordering::Relaxed);
        let (shutdown_tx, mut shutdown_rx) = broadcast::channel(1);
        self.shutdown_tx = Some(shutdown_tx);

        let region_health = self.region_health.clone();
        let region_status = self.region_status.clone();
        let regions = self.regions.clone();
        let health_running = self.health_monitor_running.clone();
        let client = self.client.clone();

        tokio::spawn(async move {
            let mut interval = tokio::time::interval(Duration::from_secs(10));

            while health_running.load(Ordering::Relaxed) {
                tokio::select! {
                    _ = interval.tick() => {
                        // Perform health checks on all regions
                        for region_entry in regions.iter() {
                            let region_id = region_entry.key();
                            let region_config = region_entry.value();

                            if let Ok(health) = Self::check_region_health(&client, region_config).await {
                                region_health.insert(region_id.clone(), health);
                                region_status.insert(region_id.clone(), RegionStatus::Available);
                            } else {
                                region_health.insert(region_id.clone(), RegionHealth::Unhealthy {
                                    errors: vec!["Health check failed".to_string()],
                                    last_check: Instant::now(),
                                });
                                region_status.insert(region_id.clone(), RegionStatus::Unavailable);
                            }
                        }
                    }
                    _ = shutdown_rx.recv() => {
                        break;
                    }
                }
            }
        });

        Ok(())
    }

    /// Check health of a specific region
    async fn check_region_health(
        client: &reqwest::Client,
        region_config: &RegionConfig,
    ) -> PlatformResult<RegionHealth> {
        // Simulate health check - in real implementation would call region endpoint
        let _response = client
            .get(format!("{}/health", region_config.endpoint))
            .timeout(Duration::from_secs(5))
            .send()
            .await
            .map_err(PlatformError::Network)?;

        Ok(RegionHealth::Healthy {
            uptime: Duration::from_secs(3600), // 1 hour uptime
            cpu_usage: 0.3,
            memory_usage: 0.4,
            last_check: Instant::now(),
        })
    }

    /// Get region health
    pub async fn get_region_health(&self, region_id: &str) -> PlatformResult<RegionHealth> {
        self.region_health
            .get(region_id)
            .map(|h| h.clone())
            .ok_or_else(|| {
                PlatformError::Region(RegionError::NotFound {
                    region_id: region_id.to_string(),
                })
            })
    }

    /// Coordinate cross-region operation
    pub async fn coordinate_cross_region_operation(
        &self,
        operation: CrossRegionOp,
    ) -> PlatformResult<CrossRegionResult> {
        let start_time = Instant::now();

        // Verify all target regions are available
        for region_id in &operation.target_regions {
            if !self.regions.contains_key(region_id) {
                return Err(PlatformError::Region(RegionError::NotFound {
                    region_id: region_id.clone(),
                }));
            }

            let status = self
                .region_status
                .get(region_id)
                .map_or(RegionStatus::Unavailable, |s| s.clone());

            if status != RegionStatus::Available {
                return Err(PlatformError::Region(RegionError::Unavailable {
                    region_id: region_id.clone(),
                }));
            }
        }

        // Calculate maximum latency between participating regions
        let latency_matrix = self.latency_matrix.read().await;
        let mut max_latency = 0u64;

        let all_regions = vec![operation.source_region.clone()]
            .into_iter()
            .chain(operation.target_regions.iter().cloned())
            .collect::<Vec<_>>();

        for source in &all_regions {
            for target in &all_regions {
                if source != target
                    && let Some(source_latencies) = latency_matrix.get(source)
                    && let Some(&latency) = source_latencies.get(target)
                {
                    max_latency = max_latency.max(latency as u64);
                }
            }
        }

        let coordination_latency = start_time.elapsed().as_millis() as u64 + max_latency;

        Ok(CrossRegionResult {
            operation_id: operation.id,
            participating_regions: all_regions,
            latency_ms: coordination_latency,
            success: true,
        })
    }

    /// Create operation request
    pub fn create_operation_request(
        &self,
        tenant_id: Uuid,
        preferred_region: &str,
        operation_type: &str,
        data_size_bytes: u64,
    ) -> OperationRequest {
        OperationRequest {
            tenant_id,
            preferred_region: preferred_region.to_string(),
            operation_type: operation_type.to_string(),
            data_size_bytes,
            resource_requirements: HashMap::new(),
        }
    }

    /// Schedule operation with failover support
    pub async fn schedule_operation(
        &self,
        request: OperationRequest,
    ) -> PlatformResult<OperationAssignment> {
        let operation_id = Uuid::new_v4();

        // Check if preferred region is available
        let preferred_status = self
            .region_status
            .get(&request.preferred_region)
            .map_or(RegionStatus::Unavailable, |s| s.clone());

        let (assigned_region, is_failover) = if preferred_status == RegionStatus::Available {
            (request.preferred_region.clone(), false)
        } else {
            // Find alternative region
            let alternative = self
                .find_alternative_region(&request.preferred_region)
                .await?;
            (alternative, true)
        };

        Ok(OperationAssignment {
            operation_id,
            tenant_id: request.tenant_id,
            assigned_region,
            is_failover,
            estimated_start_time: chrono::Utc::now(),
        })
    }

    /// Mark region as unavailable
    pub async fn mark_region_unavailable(
        &self,
        region_id: &str,
        reason: &str,
    ) -> PlatformResult<()> {
        if !self.regions.contains_key(region_id) {
            return Err(PlatformError::Region(RegionError::NotFound {
                region_id: region_id.to_string(),
            }));
        }

        self.region_status
            .insert(region_id.to_string(), RegionStatus::Unavailable);
        self.region_health.insert(
            region_id.to_string(),
            RegionHealth::Unhealthy {
                errors: vec![reason.to_string()],
                last_check: Instant::now(),
            },
        );

        tracing::warn!("Region {} marked unavailable: {}", region_id, reason);
        Ok(())
    }

    /// Find alternative region for failover
    async fn find_alternative_region(&self, failed_region: &str) -> PlatformResult<String> {
        // Find first available region that's not the failed one
        for region_entry in self.region_status.iter() {
            let region_id = region_entry.key();
            let status = region_entry.value();

            if region_id != failed_region && *status == RegionStatus::Available {
                return Ok(region_id.clone());
            }
        }

        Err(PlatformError::Region(RegionError::Unavailable {
            region_id: "no_alternatives".to_string(),
        }))
    }

    /// Get region capacity
    pub async fn get_region_capacity(&self, region_id: &str) -> PlatformResult<RegionCapacity> {
        self.region_capacity
            .get(region_id)
            .map(|c| c.clone())
            .ok_or_else(|| {
                PlatformError::Region(RegionError::NotFound {
                    region_id: region_id.to_string(),
                })
            })
    }

    /// Reserve capacity in a region
    pub async fn reserve_capacity(
        &self,
        region_id: &str,
        tenant_id: Uuid,
        resources: HashMap<String, u64>,
    ) -> PlatformResult<CapacityReservation> {
        let mut capacity = self.region_capacity.get_mut(region_id).ok_or_else(|| {
            PlatformError::Region(RegionError::NotFound {
                region_id: region_id.to_string(),
            })
        })?;

        // Check if resources are available
        for (resource_type, requested) in &resources {
            match resource_type.as_str() {
                "gpu" => {
                    if capacity.available_gpu < *requested {
                        return Err(PlatformError::Region(RegionError::CapacityExhausted {
                            region_id: region_id.to_string(),
                        }));
                    }
                }
                "memory_gb" => {
                    if capacity.available_memory_gb < *requested {
                        return Err(PlatformError::Region(RegionError::CapacityExhausted {
                            region_id: region_id.to_string(),
                        }));
                    }
                }
                _ => {} // Ignore unknown resource types for now
            }
        }

        // Reserve the resources
        for (resource_type, requested) in &resources {
            match resource_type.as_str() {
                "gpu" => {
                    capacity.available_gpu -= requested;
                    capacity.reserved_gpu += requested;
                }
                "memory_gb" => {
                    capacity.available_memory_gb -= requested;
                    capacity.reserved_memory_gb += requested;
                }
                _ => {}
            }
        }

        let reservation = CapacityReservation {
            reservation_id: Uuid::new_v4(),
            tenant_id,
            region_id: region_id.to_string(),
            resources: resources.clone(),
            expires_at: chrono::Utc::now() + chrono::Duration::hours(1),
        };

        self.reservations
            .insert(reservation.reservation_id, reservation.clone());
        Ok(reservation)
    }

    /// Create latency-sensitive request
    pub fn create_latency_sensitive_request(
        &self,
        tenant_id: Uuid,
        required_regions: Vec<String>,
        max_latency_ms: u64,
        operation_type: &str,
        data_size_bytes: u64,
    ) -> LatencySensitiveRequest {
        LatencySensitiveRequest {
            tenant_id,
            required_regions,
            max_latency_ms,
            operation_type: operation_type.to_string(),
            data_size_bytes,
        }
    }

    /// Optimize operation for latency
    pub async fn optimize_for_latency(
        &self,
        request: LatencySensitiveRequest,
    ) -> PlatformResult<LatencyOptimizedAssignment> {
        let operation_id = Uuid::new_v4();
        let latency_matrix = self.latency_matrix.read().await;

        // Verify latency constraints can be met
        let mut max_latency: f64 = 0.0;
        let mut assignment_matrix = HashMap::new();

        for source in &request.required_regions {
            let mut target_latencies = HashMap::new();

            for target in &request.required_regions {
                if source != target {
                    let latency = latency_matrix
                        .get(source)
                        .and_then(|targets| targets.get(target))
                        .copied()
                        .unwrap_or(1000.0); // Default high latency if unknown

                    target_latencies.insert(target.clone(), latency);
                    max_latency = max_latency.max(latency);
                }
            }
            assignment_matrix.insert(source.clone(), target_latencies);
        }

        if max_latency > request.max_latency_ms as f64 {
            return Err(PlatformError::Region(RegionError::CrossRegionFailed {
                src: "optimization".to_string(),
                dst: "latency_constraint_violation".to_string(),
            }));
        }

        Ok(LatencyOptimizedAssignment {
            operation_id,
            participating_regions: request.required_regions,
            max_inter_region_latency_ms: max_latency as u64,
            latency_matrix: assignment_matrix,
        })
    }

    /// Register data locality information
    pub async fn register_data_locality(
        &self,
        tenant_id: Uuid,
        dataset_id: String,
        regions: Vec<String>,
        _data_size_bytes: u64,
    ) -> PlatformResult<()> {
        let mut tenant_data = HashMap::new();
        tenant_data.insert(tenant_id, regions);
        self.data_locality.insert(dataset_id, tenant_data);
        Ok(())
    }

    /// Create data locality request
    pub fn create_data_locality_request(
        &self,
        tenant_id: Uuid,
        dataset_id: String,
        operation_type: &str,
        resource_types: Vec<String>,
        resource_quantity: u64,
    ) -> DataLocalityRequest {
        DataLocalityRequest {
            tenant_id,
            dataset_id,
            operation_type: operation_type.to_string(),
            resource_types,
            resource_quantity,
        }
    }

    /// Optimize operation for data locality
    pub async fn optimize_for_data_locality(
        &self,
        request: DataLocalityRequest,
    ) -> PlatformResult<DataLocalityAssignment> {
        let operation_id = Uuid::new_v4();

        // Find regions where data is available
        let data_regions = if let Some(tenant_data) = self.data_locality.get(&request.dataset_id) {
            tenant_data
                .get(&request.tenant_id)
                .cloned()
                .unwrap_or_else(Vec::new)
        } else {
            Vec::new()
        };

        if data_regions.is_empty() {
            // Data not found, assign to first available region
            let first_available = self
                .region_status
                .iter()
                .find(|entry| *entry.value() == RegionStatus::Available)
                .map(|entry| entry.key().clone())
                .ok_or_else(|| {
                    PlatformError::Region(RegionError::Unavailable {
                        region_id: "no_available_regions".to_string(),
                    })
                })?;

            return Ok(DataLocalityAssignment {
                operation_id,
                assigned_region: first_available,
                data_transfer_required: true,
                estimated_data_transfer_time_ms: 30000, // 30 seconds estimate
            });
        }

        // Prefer first region where data exists and region is available
        let assigned_region = data_regions
            .into_iter()
            .find(|region| {
                self.region_status
                    .get(region)
                    .is_some_and(|status| *status == RegionStatus::Available)
            })
            .ok_or_else(|| {
                PlatformError::Region(RegionError::Unavailable {
                    region_id: "no_available_data_regions".to_string(),
                })
            })?;

        Ok(DataLocalityAssignment {
            operation_id,
            assigned_region,
            data_transfer_required: false,
            estimated_data_transfer_time_ms: 0,
        })
    }
}