"use strict";

(function (global) {
  const policy = () => global.TarinaiItemUpdatePolicy || {};

  function itemUpdateInterval(item) {
    const interval = policy().itemUpdateInterval?.(item);
    return Number.isFinite(interval) ? interval : Infinity;
  }

  function candidateItems(worldRef) {
    if (policy().candidateItems) return policy().candidateItems(worldRef);
    return (worldRef?.items || []).filter(it => it && !it.dead && it.type !== "grass");
  }

  function ensureBuckets(worldRef) {
    if (policy().ensureBuckets) return policy().ensureBuckets(worldRef);
    if (worldRef?.ensureItemBuckets) worldRef.ensureItemBuckets("item-update-scheduler");
    return undefined;
  }

  function heapPush(heap, entry) {
    heap.push(entry);
    let i = heap.length - 1;
    while (i > 0) {
      const p = (i - 1) >> 1;
      if (heap[p].time <= entry.time) break;
      heap[i] = heap[p];
      i = p;
    }
    heap[i] = entry;
  }

  function heapPop(heap) {
    if (!heap.length) return null;
    const root = heap[0];
    const last = heap.pop();
    if (heap.length && last) {
      let i = 0;
      while (true) {
        let c = i * 2 + 1;
        if (c >= heap.length) break;
        if (c + 1 < heap.length && heap[c + 1].time < heap[c].time) c++;
        if (heap[c].time >= last.time) break;
        heap[i] = heap[c];
        i = c;
      }
      heap[i] = last;
    }
    return root;
  }

  function schedulerSignature(worldRef) {
    return [
      (worldRef.items || []).length,
      worldRef.itemBucketRebuildsTotal || 0,
      worldRef.itemBucketsDirty ? 1 : 0,
    ].join(":");
  }


  function scheduleItem(state, item, now, interval = itemUpdateInterval(item)) {
    if (!item || item.dead || !Number.isFinite(interval)) return false;
    if (interval <= 0) {
      state.realtime.push(item);
      item._schedulerRealtime = true;
      return true;
    }
    const token = (item._schedulerToken || 0) + 1;
    item._schedulerToken = token;
    item._schedulerRealtime = false;
    if (!Number.isFinite(item._schedulerLastAt)) item._schedulerLastAt = now;
    heapPush(state.heap, { time: now + interval, item, token });
    return true;
  }

  function rebuild(worldRef, reason = "manual") {
    ensureBuckets(worldRef);
    const now = worldRef.time || 0;
    const state = {
      heap: [],
      realtime: [],
      signature: schedulerSignature(worldRef),
      rebuilds: ((worldRef._itemUpdateScheduler?.rebuilds || 0) + 1),
      reason,
    };
    for (const item of candidateItems(worldRef)) {
      item._schedulerLastAt = Number.isFinite(item._schedulerLastAt) ? item._schedulerLastAt : now;
      scheduleItem(state, item, now, itemUpdateInterval(item));
    }
    worldRef._itemUpdateScheduler = state;
    worldRef._itemUpdateRealtime = state.realtime;
    return state;
  }

  function ensure(worldRef) {
    const sig = schedulerSignature(worldRef);
    if (!worldRef._itemUpdateScheduler || worldRef._itemUpdateScheduler.signature !== sig) return rebuild(worldRef, "signature");
    return worldRef._itemUpdateScheduler;
  }

  function runRealtime(worldRef, state, dt) {
    let ran = 0;
    const now = worldRef.time || 0;
    const nextRealtime = [];
    for (const item of state.realtime || []) {
      if (!item || item.dead) continue;
      const interval = itemUpdateInterval(item);
      if (!Number.isFinite(interval)) {
        item._schedulerRealtime = false;
        continue;
      }
      if (interval <= 0) {
        if (global.TarinaiItemRuntime?.updateOne) global.TarinaiItemRuntime.updateOne(item, dt, worldRef);
        else item.update(dt, worldRef);
        item._schedulerLastAt = now;
        ran += 1;
        if (Number.isFinite(itemUpdateInterval(item)) && itemUpdateInterval(item) <= 0) nextRealtime.push(item);
        else scheduleItem(state, item, now, itemUpdateInterval(item));
      } else {
        scheduleItem(state, item, now, interval);
      }
    }
    state.realtime = nextRealtime;
    worldRef._itemUpdateRealtime = state.realtime;
    return ran;
  }

  function runDue(worldRef, state) {
    let ran = 0;
    const now = worldRef.time || 0;
    const maxDue = Math.max(24, Math.ceil((state.heap.length || 0) * 0.08));
    let dueRuns = 0;
    while (state.heap.length && state.heap[0].time <= now + 0.0001 && dueRuns < maxDue) {
      const entry = heapPop(state.heap);
      const item = entry?.item;
      if (!item || item.dead || item._schedulerToken !== entry.token) continue;
      const interval = itemUpdateInterval(item);
      if (!Number.isFinite(interval)) continue;
      if (interval <= 0) {
        state.realtime.push(item);
        item._schedulerRealtime = true;
        continue;
      }
      const elapsed = Math.min(10, Math.max(0.001, now - (item._schedulerLastAt ?? entry.time - interval)));
      if (global.TarinaiItemRuntime?.updateOne) global.TarinaiItemRuntime.updateOne(item, elapsed, worldRef);
      else item.update(elapsed, worldRef);
      item._schedulerLastAt = now;
      ran += 1;
      dueRuns += 1;
      scheduleItem(state, item, now, itemUpdateInterval(item));
    }
    return ran;
  }

  function run(worldRef, dt) {
    const end = global.TarinaiPerf?.begin?.("update.items") || null;
    try {
      const state = ensure(worldRef);
      let ran = runRealtime(worldRef, state, dt);
      ran += runDue(worldRef, state);
      state.signature = schedulerSignature(worldRef);
      worldRef._itemUpdateSchedulerStats = {
        heap: state.heap.length,
        realtime: state.realtime.length,
        rebuilds: state.rebuilds,
        lastReason: state.reason,
        lastRan: ran,
      };
      return ran;
    } finally {
      if (end) end();
    }
  }

  function trackedDynamicItems(worldRef) {
    return worldRef?._itemUpdateRealtime || [];
  }

  global.TarinaiItemUpdateScheduler = Object.freeze({ run, rebuild, ensure, itemUpdateInterval, trackedDynamicItems });
})(typeof window !== "undefined" ? window : globalThis);