// SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
// SPDX-License-Identifier: Apache-2.0

use super::*;

use utils::*;
use zmq::*;

use derive_builder::Builder;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::time::Duration;
use tokio::sync::Notify;
use tokio::sync::OnceCell;
use tokio::sync::oneshot;
use tokio::time::sleep;

#[derive(Builder, Clone, Debug, Default)]
pub struct KvbmLeaderNumBlocksConfig {
    #[builder(default = "0.0")]
    pub cache_size_in_gb: f64,

    #[builder(default = "0")]
    pub num_blocks_overriden: usize,
}

fn compute_num_blocks(
    num_blocks_config: &KvbmLeaderNumBlocksConfig,
    bytes_per_block: usize,
) -> usize {
    if num_blocks_config.num_blocks_overriden > 0 {
        num_blocks_config.num_blocks_overriden
    } else {
        ((num_blocks_config.cache_size_in_gb * 1_000_000_000.0) / bytes_per_block as f64) as usize
    }
}

#[derive(Builder, Clone, Debug)]
pub struct KvbmLeaderConfig {
    /// The world size.
    #[builder(default = "1")]
    world_size: usize,

    /// The leader-worker init connection timeout seconds.
    #[builder(default = "120")]
    leader_init_timeout_secs: u64,

    #[builder(default = "KvbmLeaderNumBlocksConfig::default()")]
    host_blocks_config: KvbmLeaderNumBlocksConfig,

    #[builder(default = "KvbmLeaderNumBlocksConfig::default()")]
    disk_blocks_config: KvbmLeaderNumBlocksConfig,

    #[builder(default = "String::from(\"tcp://127.0.0.1:56001\")")]
    leader_pub_url: String,

    #[builder(default = "String::from(\"tcp://127.0.0.1:56002\")")]
    leader_ack_url: String,
}

impl KvbmLeaderConfig {
    pub fn builder() -> KvbmLeaderConfigBuilder {
        KvbmLeaderConfigBuilder::default()
    }

    pub fn sanity_check(&self) -> anyhow::Result<()> {
        if self.leader_pub_url == self.leader_ack_url {
            anyhow::bail!(
                "leader_pub_url and leader_ack_url must differ (same endpoint would fail to bind)."
            );
        }

        let cpu = &self.host_blocks_config;
        let disk = &self.disk_blocks_config;
        let cpu_configured = cpu.num_blocks_overriden > 0 || cpu.cache_size_in_gb > 0.0;
        let disk_configured = disk.num_blocks_overriden > 0 || disk.cache_size_in_gb > 0.0;
        if !cpu_configured && !disk_configured {
            panic!(
                "KVBM Configuration Error: At least one cache tier must be configured.\n\
                \n\
                Configure CPU cache (G2) for CPU memory offloading:\n\
                • DYN_KVBM_CPU_CACHE_GB=<size_in_gb>     (e.g., DYN_KVBM_CPU_CACHE_GB=4)\n\
                • DYN_KVBM_CPU_CACHE_OVERRIDE_NUM_BLOCKS=<num_blocks>  (e.g., DYN_KVBM_CPU_CACHE_OVERRIDE_NUM_BLOCKS=1000)\n\
                \n\
                OR configure disk cache (G3) for direct GPU->Disk offloading:\n\
                • DYN_KVBM_DISK_CACHE_GB=<size_in_gb>     (e.g., DYN_KVBM_DISK_CACHE_GB=8)\n\
                • DYN_KVBM_DISK_CACHE_OVERRIDE_NUM_BLOCKS=<num_blocks>\n\
                \n\
                Note: If only disk cache is configured, KVBM will offload directly from GPU (G1) to Disk (G3), bypassing CPU memory (G2)."
            );
        }
        Ok(())
    }
}

#[derive(Debug, Default)]
pub struct KvbmLeaderState {
    pub num_device_blocks: Arc<AtomicUsize>,
    pub num_host_blocks: Arc<AtomicUsize>,
    pub num_disk_blocks: Arc<AtomicUsize>,
    pub workers_allocation_ready: Arc<AtomicBool>,
    pub workers_ready_notify: Arc<Notify>,
}

/// The leader of the KVBM.
///
/// This is responsible for:
/// - Establishing a ZMQ connection with workers.
/// - Syncing the leader barrier with workers.
/// - Sending messages to workers.
pub struct KvbmLeader {
    state: Arc<KvbmLeaderState>,
    zmq_leader: Arc<OnceCell<ZmqActiveMessageLeader>>,
    config: KvbmLeaderConfig,
}

impl KvbmLeader {
    pub async fn new(config: KvbmLeaderConfig) -> anyhow::Result<Self> {
        let leader_sockets = new_leader_sockets(&config.leader_pub_url, &config.leader_ack_url)?;

        let leader = Self {
            state: Arc::new(KvbmLeaderState::default()),
            zmq_leader: Arc::new(tokio::sync::OnceCell::new()),
            config,
        };

        let cancel_token = tokio_util::sync::CancellationToken::new();
        leader.spawn_zmq_task(leader_sockets, cancel_token);

        Ok(leader)
    }

    fn spawn_zmq_task(
        &self,
        leader_sockets: LeaderSockets,
        cancel: tokio_util::sync::CancellationToken,
    ) {
        let cell = self.zmq_leader.clone();
        let state = self.state.clone();
        let world_size = self.config.world_size;
        let timeout = self.config.leader_init_timeout_secs;
        let host_cfg = self.config.host_blocks_config.clone();
        let disk_cfg = self.config.disk_blocks_config.clone();

        // capture num_device_blocks so we can set it inside the closure
        let num_device_blocks_cell = state.num_device_blocks.clone();
        let num_host_blocks_cell = state.num_host_blocks.clone();
        let num_disk_blocks_cell = state.num_disk_blocks.clone();

        tokio::spawn(async move {
            let res = ZmqActiveMessageLeader::new_with_handshake(
                leader_sockets,
                world_size,
                std::time::Duration::from_secs(timeout),
                cancel.clone(),
                move |workers: &[WorkerMetadata]| -> LeaderMetadata {
                    // Record device blocks: min across workers
                    if let Some(min_dev) = workers.iter().map(|w| w.num_device_blocks).min() {
                        num_device_blocks_cell.store(min_dev, Ordering::Release);
                    }

                    // For TP, sum bytes_per_block; adjust policy for DP/PP if needed.
                    let bytes_per_block: usize = workers.iter().map(|w| w.bytes_per_block).sum();
                    let num_host_blocks = compute_num_blocks(&host_cfg, bytes_per_block);
                    let num_disk_blocks = compute_num_blocks(&disk_cfg, bytes_per_block);

                    // store into leader state
                    num_host_blocks_cell.store(num_host_blocks, Ordering::Release);
                    num_disk_blocks_cell.store(num_disk_blocks, Ordering::Release);

                    LeaderMetadata {
                        num_host_blocks,
                        num_disk_blocks,
                    }
                },
            )
            .await;

            match res {
                Ok(zmq) => {
                    let _ = cell.set(zmq);
                    state
                        .workers_allocation_ready
                        .store(true, Ordering::Release);
                    state.workers_ready_notify.notify_waiters();
                    tracing::info!("ZMQ handshake complete; workers allocation ready");
                }
                Err(e) => {
                    tracing::error!("ZMQ init/handshake failed: {e:?}");
                }
            }
        });
    }

    pub async fn transfer_blocks_request(
        &self,
        request: BlockTransferRequest,
    ) -> anyhow::Result<oneshot::Receiver<()>> {
        let zmq = self
            .zmq_leader
            .get()
            .ok_or_else(|| anyhow::anyhow!("ZMQ leader not ready"))?;
        let data = vec![serde_json::to_vec(&request)?];
        zmq.broadcast(ZMQ_TRANSFER_BLOCKS_MESSAGE, data).await
    }

    pub fn num_device_blocks(&self) -> usize {
        self.state.num_device_blocks.load(Ordering::Acquire)
    }

    pub fn num_host_blocks(&self) -> usize {
        self.state.num_host_blocks.load(Ordering::Acquire)
    }

    pub fn num_disk_blocks(&self) -> usize {
        self.state.num_disk_blocks.load(Ordering::Acquire)
    }

    pub async fn wait_worker_sync_ready(&self) -> bool {
        if self.state.workers_allocation_ready.load(Ordering::Acquire) {
            return true;
        }
        let notified = self.state.workers_ready_notify.notified();
        tokio::select! {
            _ = notified => true,
            _ = sleep(Duration::from_secs(self.config.leader_init_timeout_secs)) => false,
        }
    }
}
