package btools.util;

import java.util.ArrayList;
import java.util.List;

/**
 * Special Memory efficient Map to map a long-key to
 * a "small" value (some bits only) where it is expected
 * that the keys are dense, so that we can use more or less
 * a simple array as the best-fit data model (except for
 * the 32-bit limit of arrays!)
 * <p>
 * Target application are osm-node ids which are in the
 * range 0...3 billion and basically dense (=only few
 * nodes deleted)
 *
 * @author ab
 */
public class DenseLongMap {
  private List<byte[]> blocklist = new ArrayList<>(4096);

  private int blocksize; // bytes per bitplane in one block
  private int blocksizeBits;
  private long blocksizeBitsMask;
  private int maxvalue = 254; // fixed due to 8 bit lookup table
  private int[] bitplaneCount = new int[8];
  private long putCount = 0L;
  private long getCount = 0L;

  /**
   * Creates a DenseLongMap for the default block size
   * ( 512 bytes per bitplane, covering a key range of 4096 keys )
   * Note that one value range is limited to 0..254
   */
  public DenseLongMap() {
    this(512);
  }

  /**
   * Creates a DenseLongMap for the given block size
   *
   * @param blocksize bytes per bit-plane
   */
  public DenseLongMap(int blocksize) {
    int bits = 4;
    while (bits < 28 && (1 << bits) != blocksize) {
      bits++;
    }
    if (bits == 28) {
      throw new RuntimeException("not a valid blocksize: " + blocksize + " ( expected 1 << bits with bits in (4..27) )");
    }
    blocksizeBits = bits + 3;
    blocksizeBitsMask = (1L << blocksizeBits) - 1;
    this.blocksize = blocksize;
  }


  public void put(long key, int value) {
    putCount++;

    if (value < 0 || value > maxvalue) {
      throw new IllegalArgumentException("value out of range (0.." + maxvalue + "): " + value);
    }

    int blockn = (int) (key >> blocksizeBits);
    int offset = (int) (key & blocksizeBitsMask);

    byte[] block = blockn < blocklist.size() ? blocklist.get(blockn) : null;

    int valuebits = 1;
    if (block == null) {
      block = new byte[sizeForBits(valuebits)];
      bitplaneCount[0]++;

      while (blocklist.size() < blockn + 1) {
        blocklist.add(null);
      }
      blocklist.set(blockn, block);
    } else {
      // check how many bitplanes we have from the arraysize
      while (sizeForBits(valuebits) < block.length) {
        valuebits++;
      }
    }
    int headersize = 1 << valuebits;

    byte v = (byte) (value + 1); // 0 is reserved (=unset)

    // find the index in the lookup table or the first entry
    int idx = 1;
    while (idx < headersize) {
      if (block[idx] == 0) {
        block[idx] = v; // create new entry
      }
      if (block[idx] == v) {
        break;
      }
      idx++;
    }
    if (idx == headersize) {
      block = expandBlock(block, valuebits);
      block[idx] = v; // create new entry
      blocklist.set(blockn, block);
      valuebits++;
      headersize = 1 << valuebits;
    }

    int bitmask = 1 << (offset & 0x7);
    int invmask = bitmask ^ 0xff;
    int probebit = 1;
    int blockidx = (offset >> 3) + headersize;

    for (int i = 0; i < valuebits; i++) {
      if ((idx & probebit) != 0) {
        block[blockidx] |= bitmask;
      } else {
        block[blockidx] &= invmask;
      }
      probebit <<= 1;
      blockidx += blocksize;
    }
  }


  private int sizeForBits(int bits) {
    // size is lookup table + datablocks
    return (1 << bits) + blocksize * bits;
  }

  private byte[] expandBlock(byte[] block, int valuebits) {
    bitplaneCount[valuebits]++;
    byte[] newblock = new byte[sizeForBits(valuebits + 1)];
    int headersize = 1 << valuebits;
    System.arraycopy(block, 0, newblock, 0, headersize); // copy header
    System.arraycopy(block, headersize, newblock, 2 * headersize, block.length - headersize); // copy data
    return newblock;
  }

  public int getInt(long key) {
    // bit-stats on first get
    if (getCount++ == 0L) {
      System.out.println("**** DenseLongMap stats ****");
      System.out.println("putCount=" + putCount);
      for (int i = 0; i < 8; i++) {
        System.out.println(i + "-bitplanes=" + bitplaneCount[i]);
      }
      System.out.println("****************************");
    }

    /* actual stats for the 30x45 raster and 512 blocksize with filtered nodes:
     *
     **** DenseLongMap stats ****
     putCount=858518399
     0-bitplanes=783337
     1-bitplanes=771490
     2-bitplanes=644578
     3-bitplanes=210767
     4-bitplanes=439
     5-bitplanes=0
     6-bitplanes=0
     7-bitplanes=0
     *
     * This is a total of 1,2 GB
     * (1.234.232.832+7.381.126+15.666.740 for body/header/object-overhead )
    */

    if (key < 0) {
      return -1;
    }
    int blockn = (int) (key >> blocksizeBits);
    int offset = (int) (key & blocksizeBitsMask);

    byte[] block = blockn < blocklist.size() ? blocklist.get(blockn) : null;

    if (block == null) {
      return -1;
    }

    // check how many bitplanes we have from the arrayzize
    int valuebits = 1;
    while (sizeForBits(valuebits) < block.length) {
      valuebits++;
    }
    int headersize = 1 << valuebits;

    int bitmask = 1 << (offset & 7);
    int probebit = 1;
    int blockidx = (offset >> 3) + headersize;
    int idx = 0; // 0 is reserved (=unset)

    for (int i = 0; i < valuebits; i++) {
      if ((block[blockidx] & bitmask) != 0) {
        idx |= probebit;
      }
      probebit <<= 1;
      blockidx += blocksize;
    }

    // lookup that value in the lookup header
    return ((256 + block[idx]) & 0xff) - 1;
  }

}