/*
 * DSI utilities
 *
 * Copyright (C) 2007-2023 Sebastiano Vigna
 *
 * This program and the accompanying materials are made available under the
 * terms of the GNU Lesser General Public License v2.1 or later,
 * which is available at
 * http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html,
 * or the Apache Software License 2.0, which is available at
 * https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later OR Apache-2.0
 */

package it.unimi.dsi.bits;

import java.io.DataInput;
import java.io.DataInputStream;
import java.io.DataOutput;
import java.io.DataOutputStream;
import java.io.IOException;

import it.unimi.dsi.io.OfflineIterable;


/** A class providing static methods and objects that do useful things with bit vectors.
 *
 * @see BitVector
 */

public class BitVectors {

	private BitVectors() {}

	@Deprecated
	public static <T extends BitVector> TransformationStrategy<T> identity() {
		return TransformationStrategies.identity();
	}

    public static void ensureFromTo(final long bitVectorLength, final long from, final long to) {
        if (from < 0) throw new ArrayIndexOutOfBoundsException("Start index (" + from + ") is negative");
        if (from > to) throw new IllegalArgumentException("Start index (" + from + ") is greater than end index (" + to + ")");
        if (to > bitVectorLength) throw new ArrayIndexOutOfBoundsException("End index (" + to + ") is greater than bit vector length (" + bitVectorLength + ")");
    }

	/** An immutable, singleton empty bit vector. */
	public static final BitVector EMPTY_VECTOR = new AbstractBitVector() {
		@Override
		public final long length() { return 0; }
		@Override
		public final BitVector copy(final long from, final long to) {
			ensureFromTo(0, from, to);
			return EMPTY_VECTOR;
		}
		@Override
		public final boolean getBoolean(final long index) { throw new IndexOutOfBoundsException(); }
		@Override
		public BitVector copy() {
			return this;
		}
		public Object readResolve() {
			return EMPTY_VECTOR;
		}
	};

	/** An immutable bit vector of length one containing a zero. */
	public static final BitVector ZERO = new AbstractBitVector() {
		@Override
		public final long length() { return 1; }
		@Override
		public final BitVector copy(final long from, final long to) {
			ensureFromTo(1, from, to);
			return from == to ? EMPTY_VECTOR : this;
		}
		@Override
		public final boolean getBoolean(final long index) { if (index > 0) throw new IndexOutOfBoundsException(); else return false; }
		@Override
		public BitVector copy() {
			return this;
		}
		public Object readResolve() {
			return ZERO;
		}
	};

	/** An immutable bit vector of length one containing a one. */
	public static final BitVector ONE = new AbstractBitVector() {
		@Override
		public final long length() { return 1; }
		@Override
		public final BitVector copy(final long from, final long to) {
			ensureFromTo(1, from, to);
			return from == to ? EMPTY_VECTOR : this;
		}
		@Override
		public final boolean getBoolean(final long index) { if (index > 0) throw new IndexOutOfBoundsException(); else return true; }
		@Override
		public BitVector copy() {
			return this;
		}
		public Object readResolve() {
			return ONE;
		}
	};

	/** Writes quickly a bit vector to a {@link DataOutputStream}.
	 *
	 * <p>This method writes a bit vector in a simple format: first, a long representing the length.
	 * Then, as many longs as necessary to write the bits in the bit vectors (i.e.,
	 * {@link LongArrayBitVector#words(long)} of the bit vector length), obtained via {@link BitVector#getLong(long, long)}.
	 *
	 * <p>The main purpose of this function is to support {@link OfflineIterable} (see {@link #OFFLINE_SERIALIZER}).
	 *
	 * @param v a bit vector.
	 * @param dos a data output stream.
	 */

	public static void writeFast(final BitVector v, final DataOutput dos) throws IOException {
		final long length = v.length();
		final long l = length & -Long.SIZE;
		dos.writeLong(length);
		long i;
		for(i = 0; i < l; i += Long.SIZE) dos.writeLong(v.getLong(i, i + Long.SIZE));
		if (i < length) dos.writeLong(v.getLong(i, length));
	}

	/** Reads quickly a bit vector from a {@link DataInputStream}.
	 *
	 * <p>This method is the dual of {@link #writeFast(BitVector, DataOutput)}. If you
	 * need to avoid creating a bit vector at each call, please have a look at {@link #readFast(DataInput, LongArrayBitVector)}.
	 *
	 * @param dis a data input stream.
	 * @return the next bit vector in the stream, as saved by {@link  #writeFast(BitVector, DataOutput)}.
	 * @see #writeFast(BitVector, DataOutput)
	 * @see #readFast(DataInput, LongArrayBitVector)
	 */

	public static LongArrayBitVector readFast(final DataInput dis) throws IOException {
		final long length = dis.readLong();
		final long bits[] = new long[LongArrayBitVector.words(length)];
		final int l = bits.length;
		for(int i = 0; i < l; i++) bits[i] = dis.readLong();
		return LongArrayBitVector.wrap(bits, length);
	}

	/** Reads quickly a bit vector from a {@link DataInputStream}.
	 *
	 * <p>This method is similar in purpose to {@link #readFast(DataInput)}, but it allows reuse of the bit vector.
	 *
	 * @param dis a data input stream.
	 * @param bv a long-array bit vector.
	 * @return <code>bv</code>, filled with the next bit vector in the stream, as saved by {@link  #writeFast(BitVector, DataOutput)}.
	 * @see #writeFast(BitVector, DataOutput)
	 * @see #readFast(DataInput)
	 */
	public static LongArrayBitVector readFast(final DataInput dis, final LongArrayBitVector bv) throws IOException {
		final long length = dis.readLong();
		bv.ensureCapacity(length);
		final int l = LongArrayBitVector.words(length);
		for(int i = 0; i < l; i++) bv.bits[i] = dis.readLong();
		bv.length(length);
		return bv;
	}

	private static class BitVectorOfflineSerializer implements OfflineIterable.Serializer<BitVector,LongArrayBitVector> {
		@Override
		public void write(final BitVector bv, final DataOutput dos) throws IOException {
			writeFast(bv, dos);
		}

		@Override
		public void read(final DataInput dis, final LongArrayBitVector bv) throws IOException {
			readFast(dis, bv);
		}
	}

	/** A serializer for {@link LongArrayBitVector} instances that can be used with {@link it.unimi.dsi.io.OfflineIterable}. It can serialize
	 * any implementation of {@link BitVector}, and requires at construction time an instance of {@link LongArrayBitVector} that
	 * will be used to return deserialized elements. */
	public static BitVectorOfflineSerializer OFFLINE_SERIALIZER = new BitVectorOfflineSerializer();
}