//! Backend service implementation

use std::sync::Arc;

use crate::metadata::LbMetadataStore;
use fiberlb_api::{
    backend_service_server::BackendService,
    CreateBackendRequest, CreateBackendResponse,
    DeleteBackendRequest, DeleteBackendResponse,
    GetBackendRequest, GetBackendResponse,
    ListBackendsRequest, ListBackendsResponse,
    UpdateBackendRequest, UpdateBackendResponse,
    Backend as ProtoBackend, BackendAdminState as ProtoBackendAdminState,
    BackendStatus as ProtoBackendStatus,
};
use fiberlb_types::{Backend, BackendAdminState, BackendId, BackendStatus, PoolId};
use tonic::{Request, Response, Status};
use uuid::Uuid;

/// Backend service implementation
pub struct BackendServiceImpl {
    metadata: Arc<LbMetadataStore>,
}

impl BackendServiceImpl {
    /// Create a new BackendServiceImpl
    pub fn new(metadata: Arc<LbMetadataStore>) -> Self {
        Self { metadata }
    }
}

/// Convert domain Backend to proto
fn backend_to_proto(backend: &Backend) -> ProtoBackend {
    ProtoBackend {
        id: backend.id.to_string(),
        name: backend.name.clone(),
        pool_id: backend.pool_id.to_string(),
        address: backend.address.clone(),
        port: backend.port as u32,
        weight: backend.weight,
        admin_state: match backend.admin_state {
            BackendAdminState::Enabled => ProtoBackendAdminState::Enabled.into(),
            BackendAdminState::Disabled => ProtoBackendAdminState::Disabled.into(),
            BackendAdminState::Drain => ProtoBackendAdminState::Drain.into(),
        },
        status: match backend.status {
            BackendStatus::Online => ProtoBackendStatus::Online.into(),
            BackendStatus::Offline => ProtoBackendStatus::Offline.into(),
            BackendStatus::Checking => ProtoBackendStatus::Checking.into(),
            BackendStatus::Disabled => ProtoBackendStatus::Offline.into(),
            BackendStatus::Unknown => ProtoBackendStatus::Unknown.into(),
        },
        created_at: backend.created_at,
        updated_at: backend.updated_at,
    }
}

/// Parse BackendId from string
fn parse_backend_id(id: &str) -> Result<BackendId, Status> {
    let uuid: Uuid = id
        .parse()
        .map_err(|_| Status::invalid_argument("invalid backend ID"))?;
    Ok(BackendId::from_uuid(uuid))
}

/// Parse PoolId from string
fn parse_pool_id(id: &str) -> Result<PoolId, Status> {
    let uuid: Uuid = id
        .parse()
        .map_err(|_| Status::invalid_argument("invalid pool ID"))?;
    Ok(PoolId::from_uuid(uuid))
}


#[tonic::async_trait]
impl BackendService for BackendServiceImpl {
    async fn create_backend(
        &self,
        request: Request<CreateBackendRequest>,
    ) -> Result<Response<CreateBackendResponse>, Status> {
        let req = request.into_inner();

        // Validate required fields
        if req.name.is_empty() {
            return Err(Status::invalid_argument("name is required"));
        }
        if req.pool_id.is_empty() {
            return Err(Status::invalid_argument("pool_id is required"));
        }
        if req.address.is_empty() {
            return Err(Status::invalid_argument("address is required"));
        }
        if req.port == 0 {
            return Err(Status::invalid_argument("port is required"));
        }

        let pool_id = parse_pool_id(&req.pool_id)?;

        // Create new backend
        let mut backend = Backend::new(&req.name, pool_id, &req.address, req.port as u16);

        // Apply weight if specified
        if req.weight > 0 {
            backend.weight = req.weight;
        }

        // Save backend
        self.metadata
            .save_backend(&backend)
            .await
            .map_err(|e| Status::internal(format!("failed to save backend: {}", e)))?;

        Ok(Response::new(CreateBackendResponse {
            backend: Some(backend_to_proto(&backend)),
        }))
    }

    async fn get_backend(
        &self,
        request: Request<GetBackendRequest>,
    ) -> Result<Response<GetBackendResponse>, Status> {
        let req = request.into_inner();

        if req.id.is_empty() {
            return Err(Status::invalid_argument("id is required"));
        }

        let _backend_id = parse_backend_id(&req.id)?;

        // Need pool_id context to efficiently look up backend
        // The proto doesn't include pool_id in GetBackendRequest
        Err(Status::unimplemented(
            "get_backend by ID requires pool_id context; use list_backends instead",
        ))
    }

    async fn list_backends(
        &self,
        request: Request<ListBackendsRequest>,
    ) -> Result<Response<ListBackendsResponse>, Status> {
        let req = request.into_inner();

        if req.pool_id.is_empty() {
            return Err(Status::invalid_argument("pool_id is required"));
        }

        let pool_id = parse_pool_id(&req.pool_id)?;

        let backends = self
            .metadata
            .list_backends(&pool_id)
            .await
            .map_err(|e| Status::internal(format!("metadata error: {}", e)))?;

        let proto_backends: Vec<ProtoBackend> = backends.iter().map(backend_to_proto).collect();

        Ok(Response::new(ListBackendsResponse {
            backends: proto_backends,
            next_page_token: String::new(),
        }))
    }

    async fn update_backend(
        &self,
        request: Request<UpdateBackendRequest>,
    ) -> Result<Response<UpdateBackendResponse>, Status> {
        let req = request.into_inner();

        if req.id.is_empty() {
            return Err(Status::invalid_argument("id is required"));
        }

        // For update, we need to know the pool_id to load the backend
        // This is a limitation - the proto doesn't require pool_id for update
        // We'll need to scan or require pool_id in a future update
        return Err(Status::unimplemented(
            "update_backend requires pool_id context; include pool_id in request",
        ));
    }

    async fn delete_backend(
        &self,
        request: Request<DeleteBackendRequest>,
    ) -> Result<Response<DeleteBackendResponse>, Status> {
        let req = request.into_inner();

        if req.id.is_empty() {
            return Err(Status::invalid_argument("id is required"));
        }

        // Same limitation as update - need pool_id context
        return Err(Status::unimplemented(
            "delete_backend requires pool_id context; include pool_id in request",
        ));
    }
}