package btools.util;

/**
 * Something like LinkedHashMap, but purpose build, less dynamic and memory efficient
 *
 * @author ab
 */
public final class LruMap {
  private int hashbins;
  private int maxsize;
  private int size;

  private LruMapNode lru;
  private LruMapNode mru;

  private LruMapNode[] binArray;

  public LruMap(int bins, int size) {
    hashbins = bins;
    maxsize = size;
    binArray = new LruMapNode[hashbins];
  }

  public LruMapNode get(LruMapNode key) {
    int bin = (key.hash & 0xfffffff) % hashbins;

    LruMapNode e = binArray[bin];
    while (e != null) {
      if (key.equals(e)) {
        return e;
      }
      e = e.nextInBin;
    }
    return null;
  }

  // put e to the mru end of the queue
  public void touch(LruMapNode e) {
    LruMapNode n = e.next;
    LruMapNode p = e.previous;

    if (n == null) {
      return; // already at mru
    }
    n.previous = p;
    if (p != null) {
      p.next = n;
    } else {
      lru = n;
    }

    mru.next = e;
    e.previous = mru;
    e.next = null;
    mru = e;
  }

  public LruMapNode removeLru() {
    if (size < maxsize) {
      return null;
    }
    size--;
    // unlink the lru from it's bin-queue
    int bin = (lru.hashCode() & 0xfffffff) % hashbins;
    LruMapNode e = binArray[bin];
    if (e == lru) {
      binArray[bin] = lru.nextInBin;
    } else {
      while (e != null) {
        LruMapNode prev = e;
        e = e.nextInBin;
        if (e == lru) {
          prev.nextInBin = lru.nextInBin;
          break;
        }
      }
    }

    LruMapNode res = lru;
    lru = lru.next;
    lru.previous = null;
    return res;
  }

  public void put(LruMapNode val) {
    int bin = (val.hashCode() & 0xfffffff) % hashbins;
    val.nextInBin = binArray[bin];
    binArray[bin] = val;

    val.previous = mru;
    val.next = null;
    if (mru == null) {
      lru = val;
    } else {
      mru.next = val;
    }
    mru = val;
    size++;
  }
}