!include once #1027304 // Eclipse Collections

// read-only, so far. not thread-safe
final sclass BufferedDiskIntMemory implements IIntMemory, AutoCloseable {
  File file;
  int size;
  RandomAccessFile raf;
  bool bigEndian;
  int pageShift, pageSize, maxCachedPages;
  new IntObjectHashMap<CacheEntry> cache;
  CacheEntry newestCacheEntry, oldestCacheEntry;
  
  sclass CacheEntry {
    int page;
    int[] data;
    CacheEntry newer, older; // MRU list
  }
  
  *() {
    pageShift = highestOneBit(4096);
    pageSize = 1 << pageShift;
    maxCachedPages = (128*1024*1024) >> pageShift;
  }
  
  *(File *file) {
    this();
    size = toInt_safe(fileSize(file)/4);
    raf = randomAccessFileForReading(file);
  }
  
  public void close {
    dispose raf;
  }
  
  public int get(int idx) ctex {
    rangeCheck(idx, size);
    int page = idx >> pageShift;
    CacheEntry e = cache.get(page);
    if (e == null)
      e = loadPage(page);
    else
      touchPage(e);
    ret e.data[idx & (pageSize-1)];
  }
  
  void touchPage(CacheEntry e) {
    if (e == newestCacheEntry) ret;
    if (e.older != null)
      e.older.newer = e.newer;
    else
      oldestCacheEntry = e.newer;
    e.newer.older = e.older;
    e.newer = null;
    newestCacheEntry = e;
  }
  
  bool cacheFull() { ret cache.size() >= maxCachedPages; }
  
  void evictAPage {
    CacheEntry e = oldestCacheEntry;
    cache.remove(e.page);
    oldestCacheEntry = e.newer;
    if (oldestCacheEntry == null) newestCacheEntry = null;
  }
  
  void loadPage(int page) {
    if (cacheFull()) evictAPage();
    raf.seek((((long) (page << pageShift)) << 4);
    byte[] buf = new[pageSize*4];
    raf.read(buf);
    new CacheEntry e;
    e.page = page;
    e.data = bigEndian ? intArrayFromBytes(buf) : intArrayFromBytes_littleEndian(buf);
    e.older = newestCacheEntry;
    cache.put(page, e);
    newestCacheEntry = e;
    if (oldestCacheEntry == null) oldestCacheEntry = e;
  }
  
  public void set(int idx, int val) {
    fail("read-only");
  }
  
  public int size() {
    ret size;
  }
}