//! Cluster: routes arrivals, performs the L0 / L1 / remote-RDMA fetch chain
//! described in the design diagram, and bookkeeps the global meta store.

use crate::cluster::meta_store::MetaStore;
use crate::config::{Config, ModelConfig};
use crate::instance::instance::AdmittedRequest;
use crate::instance::Instance;
use crate::router::{self, RouteDecision, Router};
use crate::trace::RequestRecord;
use crate::types::InstanceId;

#[derive(Debug, Clone)]
pub struct AdmissionStats {
    pub instance: InstanceId,
    pub l0_hit_blocks: u32,
    pub l1_hit_blocks: u32,
    pub remote_hit_blocks: u32,
    pub miss_blocks: u32,
    pub rdma_bytes: u64,
    pub pcie_bytes: u64,
    pub fetch_time_s: f64,
    pub probe_overhead_s: f64,
    pub ready_at: f64,
    pub decision: RouteDecision,
}

pub struct Cluster {
    pub instances: Vec<Instance>,
    pub meta_store: MetaStore,
    pub router: Box<dyn Router>,
    pub block_size_tokens: u32,
    pub kv_block_bytes: u64,
}

impl Cluster {
    pub fn new(config: &Config, model: &ModelConfig) -> Self {
        let mut instances = Vec::with_capacity(config.cluster.num_instances as usize);
        for id in 0..config.cluster.num_instances {
            instances.push(Instance::new(id as InstanceId, model, &config.hardware));
        }
        let meta_store = MetaStore::new(config.cluster.meta_store.ttl_seconds);
        let router = router::build(config, config.sim.seed);
        Self {
            instances,
            meta_store,
            router,
            block_size_tokens: model.block_size_tokens,
            kv_block_bytes: model.kv_block_bytes(),
        }
    }

    /// Route + admit a request. Returns the chosen instance plus rich
    /// per-request stats for metrics. Does NOT schedule the BatchTick — the
    /// simulator driver does that based on the returned `ready_at`.
    pub fn route_and_admit(&mut self, req: &RequestRecord, now: f64) -> AdmissionStats {
        let decision = self.router.route(req, &self.instances, &self.meta_store, now);
        let inst_id = decision.chosen;
        let probe_overhead_s = decision.probe_overhead_s;

        // The router probe overhead delays the request's effective start time.
        let effective_now = now + probe_overhead_s;

        let inst = &mut self.instances[inst_id as usize];
        let total_blocks = req.hash_ids.len() as u32;

        // 1. L0 lookup (touches matched blocks).
        let l0_hits = inst.cache.l0.longest_prefix(&req.hash_ids) as u32;

        // 2. L1 lookup on the remaining suffix.
        let suffix_after_l0 = &req.hash_ids[l0_hits as usize..];
        let l1_hits = inst.cache.l1.longest_prefix(suffix_after_l0) as u32;
        // L1->L0 transfer cost
        let l1_bytes = (l1_hits as u64) * self.kv_block_bytes;
        let mut t = effective_now;
        if l1_hits > 0 {
            t = inst.links.pcie.reserve(t, l1_bytes);
            // Promote those blocks into L0
            let mut evicted = Vec::new();
            inst.cache.l0.insert_blocks(
                &suffix_after_l0[..l1_hits as usize],
                &mut evicted,
            );
        }

        // 3. Remote v6d lookup for the still-remaining suffix.
        let suffix_after_l1 = &suffix_after_l0[l1_hits as usize..];
        let mut remote_hit_blocks: u32 = 0;
        for &h in suffix_after_l1 {
            // A block is remotely available iff some instance other than
            // `inst_id` lists it (and not expired).
            let owners = self.meta_store.instances_for(h, now);
            let any_remote = owners.iter().any(|o| *o != inst_id);
            if any_remote {
                remote_hit_blocks += 1;
            } else {
                break; // contiguous prefix - stop on first miss
            }
        }
        let remote_bytes = (remote_hit_blocks as u64) * self.kv_block_bytes;
        if remote_hit_blocks > 0 {
            // RDMA from peer host -> local DRAM, then PCIe -> GPU
            let inst = &mut self.instances[inst_id as usize];
            t = inst.links.rdma.reserve(t, remote_bytes);
            t = inst.links.pcie.reserve(t, remote_bytes);
            // Insert into local L1 (occupies LRU space) AND into L0
            let pulled = &suffix_after_l1[..remote_hit_blocks as usize];
            let mut evicted_l1 = Vec::new();
            inst.cache.l1.insert_blocks(pulled, &mut evicted_l1);
            let mut evicted_l0 = Vec::new();
            inst.cache.l0.insert_blocks(pulled, &mut evicted_l0);
            // The local instance now also owns these blocks - update meta_store.
            for &h in pulled {
                self.meta_store.insert(h, inst_id, now);
            }
        }

        // 4. Miss = remaining tokens to prefill from scratch.
        let miss_blocks = total_blocks - l0_hits - l1_hits - remote_hit_blocks;
        let miss_tokens = miss_blocks * self.block_size_tokens;

        // The newly-prefilled blocks (after the request runs) are inserted
        // into L0 here, and into L1 / meta_store via async writeback. Doing
        // this at admission time is OK because we're tracking presence, not
        // actually moving bytes — the writeback latency is hidden behind
        // request execution and we don't model meta_store inconsistency
        // window beyond the TTL itself.
        let inst = &mut self.instances[inst_id as usize];
        let new_input_blocks = &req.hash_ids[(l0_hits + l1_hits + remote_hit_blocks) as usize..];
        let mut evicted_l0 = Vec::new();
        inst.cache.l0.insert_blocks(new_input_blocks, &mut evicted_l0);
        let mut evicted_l1 = Vec::new();
        inst.cache.l1.insert_blocks(new_input_blocks, &mut evicted_l1);
        for &h in new_input_blocks {
            self.meta_store.insert(h, inst_id, now);
        }

        // 5. Reserve KV slots for this request's prefill residency.
        //    PD disaggregation: decode runs elsewhere, so only the input
        //    blocks occupy HBM on this instance.
        let reserved_blocks = total_blocks;
        let admitted = AdmittedRequest {
            req_id: req.req_id,
            arrival: req.arrival,
            ready_at: t,
            prefill_tokens_remaining: miss_tokens,
            reserved_blocks,
        };
        inst.admit(admitted);

        let pcie_bytes = l1_bytes + remote_bytes;
        let fetch_time_s = (t - effective_now).max(0.0);

        AdmissionStats {
            instance: inst_id,
            l0_hit_blocks: l0_hits,
            l1_hit_blocks: l1_hits,
            remote_hit_blocks,
            miss_blocks,
            rdma_bytes: remote_bytes,
            pcie_bytes,
            fetch_time_s,
            probe_overhead_s,
            ready_at: t,
            decision,
        }
    }
}