/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.atlas.lib;

// NB shifting is "mod 32" -- <<32 is a no-op (not a clear).
// http://mindprod.com/jgloss/masking.html

/**
 * Utilities for manipulating a bit pattern which are held in a 32 bit int.
 * Bits are numbered 0 to 31.
 * Bit 0 is the low bit of the int, and bit 31 the sign bit of the long.
 *
 * @see BitsLong
 */
public final class BitsInt {
    private BitsInt() {}

    private static final int IntLen = Integer.SIZE;

    /**
     * Extract the value packed into bits start (inclusive) and finish (exclusive).
     * The value is returned in the low part of the returned int. The low bit is bit
     * zero.
     *
     * @param bits
     * @param start
     * @param finish
     * @return int
     */
    public static final int unpack(int bits, int start, int finish) {
        check(start, finish);
        if ( finish == 0 )
            return 0;
        // Remove top bits by moving up. Clear bottom bits by them moving down.
        return (bits << (IntLen - finish)) >>> ((IntLen - finish) + start);
    }

    /**
     * Place the value into the bit pattern between start and finish and returns the
     * new int. Leaves other bits alone.
     *
     * @param bits
     * @param value
     * @param start
     * @param finish
     * @return int
     */
    public static final int pack(int bits, int value, int start, int finish) {
        check(start, finish);
        bits = clear$(bits, start, finish);
        int mask = mask(start, finish);
        bits = bits | ((value << start) & mask);
        return bits;
    }

    /**
     * Get bits from a hex string.
     *
     * @param str
     * @param startChar Index of first character (counted from the left, string
     *     style).
     * @param finishChar Index after the last character (counted from the left,
     *     string style).
     * @return int
     * @see #access(int, int, int)
     */

    public static final int unpack(String str, int startChar, int finishChar) {
        String s = str.substring(startChar, finishChar);
        return Integer.parseInt(s, 16);
    }

    /**
     * Set the bits specified.
     *
     * @param bits Pattern
     * @param bitIndex
     * @return Modified pattern
     */
    public static final int set(int bits, int bitIndex) {
        check(bitIndex);
        return set$(bits, bitIndex);
    }

    /**
     * Set the bits from start (inc) to finish (exc) to one
     *
     * @param bits Pattern
     * @param start start (inclusive)
     * @param finish finish (exclusive)
     * @return Modified pattern
     */
    public static final int set(int bits, int start, int finish) {
        check(start, finish);
        return set$(bits, start, finish);
    }

    /**
     * Test whether a bit is the same as isSet
     *
     * @param bits Pattern
     * @param isSet Test whether is set or not.
     * @param bitIndex Bit index
     * @return Boolean
     */
    public static final boolean test(int bits, boolean isSet, int bitIndex) {
        check(bitIndex);
        return test$(bits, isSet, bitIndex);
    }

    /**
     * Test whether a bit is set
     *
     * @param bits Pattern
     * @param bitIndex Bit index
     * @return Boolean
     */
    public static final boolean isSet(int bits, int bitIndex) {
        check(bitIndex);
        return test$(bits, true, bitIndex);
    }

    /**
     * Test whether a range has a specific value or not
     *
     * @param bits Pattern
     * @param value Value to test for
     * @param start start (inclusive)
     * @param finish finish (exclusive)
     * @return Boolean
     */
    public static final boolean test(int bits, int value, int start, int finish) {
        check(start, finish);
        return test$(bits, value, start, finish);
    }

    /**
     * Get the bits from start (inclusive) to finish (exclusive), leaving them
     * aligned in the int. See also {@link #unpack} which returns the value found at
     * that place.
     *
     * @see #unpack(int, int, int)
     * @param bits
     * @param start
     * @param finish
     * @return int
     */
    public static final int access(int bits, int start, int finish) {
        check(start, finish);
        return access$(bits, start, finish);
    }

    /**
     * Clear the bit specified.
     *
     * @param bits
     * @param bitIndex
     * @return int
     */
    public static final int clear(int bits, int bitIndex) {
        check(bitIndex);
        return clear$(bits, bitIndex);
    }

    /**
     * Clear the bits specified.
     *
     * @param bits
     * @param start
     * @param finish
     * @return int
     */
    public static final int clear(int bits, int start, int finish) {
        check(start, finish);
        return clear$(bits, start, finish);
    }

    /**
     * Create a mask that has ones between bit positions start (inc) and finish
     * (exc), and zeros elsewhere.
     *
     * @param start
     * @param finish
     * @return int
     */
    public static final int mask(int start, int finish) {
        check(start, finish);
        return mask$(start, finish);
    }

    /**
     * Create a mask that has zeros between bit positions start (inc) and finish
     * (exc), and ones elsewhere
     *
     * @param start
     * @param finish
     * @return int
     */
    public static final int maskZero(int start, int finish) {
        check(start, finish);
        return maskZero$(start, finish);
    }

    private static final int clear$(int bits, int bitIndex) {
        int mask = maskZero$(bitIndex);
        bits = bits & mask;
        return bits;
    }

    private static final int clear$(int bits, int start, int finish) {
        int mask = maskZero$(start, finish);
        bits = bits & mask;
        return bits;
    }

    private static final int set$(int bits, int bitIndex) {
        int mask = mask$(bitIndex);
        return bits | mask;
    }

    private static final int set$(int bits, int start, int finish) {
        int mask = mask$(start, finish);
        return bits | mask;
    }

    private static final boolean test$(int bits, boolean isSet, int bitIndex) {
        return isSet == access$(bits, bitIndex);
    }

    private static final boolean test$(int bits, int value, int start, int finish) {
        int v = access$(bits, start, finish);
        return v == value;
    }

    private static final boolean access$(int bits, int bitIndex) {
        int mask = mask$(bitIndex);
        return (bits & mask) != 0L;
    }

    private static final int access$(int bits, int start, int finish) {
        // Alternative
        //    int mask = mask$(start, finish);
        //    return bits & mask;
        return ((bits << (IntLen - finish)) >>> (IntLen - finish + start)) << start;
    }

    private static final int mask$(int bitIndex) {
        return 1 << bitIndex;
    }

    private static final int mask$(int start, int finish) {
        if ( finish == 0 )
            // Valid args; start is zero and so the mask is zero.
            return 0;
        int mask = -1;
        return ((mask << (IntLen - finish)) >>> (IntLen - finish + start)) << start;
    }

    private static final int maskZero$(int bitIndex) {
        return ~mask$(bitIndex);
    }

    private static final int maskZero$(int start, int finish) {
        return ~mask$(start, finish);
    }

    private static final
    void check(int bitIndex) {
        if ( bitIndex < 0 || bitIndex >= IntLen ) throw new IllegalArgumentException("Illegal bit index: "+bitIndex);
    }

    private static final
    void check(int start, int finish) {
        if ( start < 0 || start >= IntLen ) throw new IllegalArgumentException("Illegal start: "+start);
        if ( finish < 0 || finish > IntLen ) throw new IllegalArgumentException("Illegal finish: "+finish);
        if ( start > finish )  throw new IllegalArgumentException("Illegal range: ("+start+", "+finish+")");
    }
}
