/*
 * 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.sis.util;

import java.util.Map;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Queue;
import java.util.Set;
import java.util.SortedSet;
import java.util.NavigableSet;
import java.util.Collections;
import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.math.BigInteger;
import org.apache.sis.math.Fraction;
import org.apache.sis.util.resources.Errors;
import org.apache.sis.internal.util.Numerics;
import org.apache.sis.internal.util.CollectionsExt;

import static java.lang.Double.doubleToLongBits;


/**
 * Static methods working with {@link Number} objects, and a few primitive types by extension.
 *
 * @author  Martin Desruisseaux (IRD, Geomatys)
 * @version 1.0
 *
 * @see org.apache.sis.math.MathFunctions
 *
 * @since 0.3
 * @module
 */
@SuppressWarnings({
    "UnnecessaryBoxing",
    "ResultOfObjectAllocationIgnored"
})
public final class Numbers extends Static {
    /**
     * Constant of value {@value} used in {@code switch} statements or as index in arrays.
     * This enumeration provides the following guarantees (some Apache SIS codes rely on them):
     *
     * <ul>
     *   <li>{@code OTHER} value is 0.</li>
     *   <li>Primitive types are enumerated in this exact order
     *       (from lower value to higher value, but not necessarily as consecutive values):
     *       {@code BYTE}, {@code SHORT}, {@code INTEGER}, {@code LONG}, {@code FLOAT}, {@code DOUBLE}.</li>
     *   <li>{@link java.math} types of greater capacity than primitive types ({@code BIG_DECIMAL}
     *       and {@code BIG_INTEGER}) have higher enumeration values.</li>
     *   <li>{@link Fraction} is considered as a kind of floating point value.</li>
     * </ul>
     */
    public static final byte
            BIG_DECIMAL=11, BIG_INTEGER=10, FRACTION=7,
            DOUBLE=9, FLOAT=8, LONG=6, INTEGER=5, SHORT=4, BYTE=3, CHARACTER=2, BOOLEAN=1, OTHER=0;

    /**
     * Mapping between a primitive type and its wrapper, if any.
     *
     * <div class="note"><b>Implementation note:</b>
     * In the particular case of {@code Class} keys, {@code IdentityHashMap} and {@code HashMap} have identical
     * behavior since {@code Class} is final and does not override the {@code equals(Object)} and {@code hashCode()}
     * methods. The {@code IdentityHashMap} Javadoc claims that it is faster than the regular {@code HashMap}.
     * But maybe the most interesting property is that it allocates less objects since {@code IdentityHashMap}
     * implementation does not need the chain of objects created by {@code HashMap}.</div>
     */
    private static final Map<Class<?>,Numbers> MAPPING = new IdentityHashMap<>(12);
    static {
        new Numbers(BigDecimal.class, true, false, BIG_DECIMAL);
        new Numbers(BigInteger.class, false, true, BIG_INTEGER);
        new Numbers(Fraction  .class, true, false, FRACTION);
        new Numbers(Double   .TYPE, Double   .class, true,  false, (byte) Double   .SIZE, DOUBLE,    'D', Numerics .valueOf(Double.NaN));
        new Numbers(Float    .TYPE, Float    .class, true,  false, (byte) Float    .SIZE, FLOAT,     'F', Float    .valueOf(Float .NaN));
        new Numbers(Long     .TYPE, Long     .class, false, true,  (byte) Long     .SIZE, LONG,      'J', Long     .valueOf(        0L));
        new Numbers(Integer  .TYPE, Integer  .class, false, true,  (byte) Integer  .SIZE, INTEGER,   'I', Integer  .valueOf(        0));
        new Numbers(Short    .TYPE, Short    .class, false, true,  (byte) Short    .SIZE, SHORT,     'S', Short    .valueOf((short) 0));
        new Numbers(Byte     .TYPE, Byte     .class, false, true,  (byte) Byte     .SIZE, BYTE,      'B', Byte     .valueOf((byte)  0));
        new Numbers(Character.TYPE, Character.class, false, false, (byte) Character.SIZE, CHARACTER, 'C', Character.valueOf((char)  0));
        new Numbers(Boolean  .TYPE, Boolean  .class, false, false, (byte) 1,              BOOLEAN,   'Z', Boolean.FALSE);
        new Numbers(Void     .TYPE, Void     .class, false, false, (byte) 0,              OTHER,     'V', null);
    }

    /** The primitive type.                     */ private final Class<?> primitive;
    /** The wrapper for the primitive type.     */ private final Class<?> wrapper;
    /** {@code true} for floating point number. */ private final boolean  isFloat;
    /** {@code true} for integer number.        */ private final boolean  isInteger;
    /** The size in bits, or -1 if variable.    */ private final byte     size;
    /** Constant to be used in switch statement.*/ private final byte     ordinal;
    /** The internal form of the primitive name.*/ private final char     internal;
    /** The null, NaN, 0 or false value.        */ private final Object   nullValue;

    /**
     * Creates an entry for a type which is not a primitive type.
     */
    @SuppressWarnings("ThisEscapedInObjectConstruction")
    private Numbers(final Class<?> type, final boolean isFloat, final boolean isInteger, final byte ordinal) {
        primitive = wrapper = type;
        this.isFloat   = isFloat;
        this.isInteger = isInteger;
        this.size      = -1;
        this.ordinal   = ordinal;
        this.internal  = 'L';                           // Defined by Java, and tested elsewhere in this class.
        this.nullValue = null;
        if (MAPPING.put(type, this) != null) {
            throw new AssertionError();                 // Should never happen.
        }
    }

    /**
     * Creates a mapping between a primitive type and its wrapper.
     */
    @SuppressWarnings("ThisEscapedInObjectConstruction")
    private Numbers(final Class<?> primitive, final Class<?> wrapper,
                    final boolean  isFloat,   final boolean  isInteger,
                    final byte     size,      final byte     ordinal,
                    final char     internal,  final Object   nullValue)
    {
        this.primitive = primitive;
        this.wrapper   = wrapper;
        this.isFloat   = isFloat;
        this.isInteger = isInteger;
        this.size      = size;
        this.ordinal   = ordinal;
        this.internal  = internal;
        this.nullValue = nullValue;
        if (MAPPING.put(primitive, this) != null || MAPPING.put(wrapper, this) != null) {
            throw new AssertionError();                         // Should never happen.
        }
    }

    /**
     * Returns the Java letter used for the internal representation of this given primitive type.
     */
    static char getInternal(final Class<?> type) {
        return MAPPING.get(type).internal;
    }

    /**
     * Returns {@code true} if the given {@code type} is a floating point type. The floating point types
     * are {@link Float}, {@code float}, {@link Double}, {@code double} and {@link BigDecimal}.
     * {@link Fraction} is also considered as a kind of floating point values.
     *
     * @param  type  the primitive type or wrapper class to test (can be {@code null}).
     * @return {@code true} if {@code type} is one of the known types capable to represent floating point numbers.
     *
     * @see #isInteger(Class)
     */
    public static boolean isFloat(final Class<?> type) {
        final Numbers mapping = MAPPING.get(type);
        return (mapping != null) && mapping.isFloat;
    }

    /**
     * Returns {@code true} if the given {@code type} is an integer type. The integer types are
     * {@link Byte}, {@code byte}, {@link Short}, {@code short}, {@link Integer}, {@code int},
     * {@link Long}, {@code long} and {@link BigInteger}.
     *
     * @param  type  the primitive type or wrapper class to test (can be {@code null}).
     * @return {@code true} if {@code type} is an integer type.
     *
     * @see #isFloat(Class)
     */
    public static boolean isInteger(final Class<?> type) {
        final Numbers mapping = MAPPING.get(type);
        return (mapping != null) && mapping.isInteger;
    }

    /**
     * Returns the number of bits used by primitive of the specified type.
     * The given type must be a primitive type or its wrapper class.
     *
     * @param  type  the primitive type (can be {@code null}).
     * @return the number of bits, or 0 if {@code type} is null.
     * @throws IllegalArgumentException if the given type is not one of the types supported by this {@code Numbers} class.
     */
    public static int primitiveBitCount(final Class<?> type) throws IllegalArgumentException {
        final Numbers mapping = MAPPING.get(type);
        if (mapping != null) {
            final int size = mapping.size;
            if (size >= 0) {
                return size;
            }
        } else if (type == null) {
            return 0;
        }
        throw unknownType(type);
    }

    /**
     * Changes a primitive class to its wrapper (for example {@code int} to {@link Integer}).
     * If the specified class is not a primitive type, then it is returned unchanged.
     *
     * @param  type  the primitive type (can be {@code null}).
     * @return the type as a wrapper.
     *
     * @see #wrapperToPrimitive(Class)
     */
    public static Class<?> primitiveToWrapper(final Class<?> type) {
        final Numbers mapping = MAPPING.get(type);
        return (mapping != null) ? mapping.wrapper : type;
    }

    /**
     * Changes a wrapper class to its primitive (for example {@link Integer} to {@code int}).
     * If the specified class is not a wrapper type, then it is returned unchanged.
     *
     * @param  type  the wrapper type (can be {@code null}).
     * @return the type as a primitive.
     *
     * @see #primitiveToWrapper(Class)
     */
    public static Class<?> wrapperToPrimitive(final Class<?> type) {
        final Numbers mapping = MAPPING.get(type);
        return (mapping != null) ? mapping.primitive : type;
    }

    /**
     * Returns the widest type of two numbers. Numbers {@code n1} and {@code n2} can be instance of
     * {@link Byte}, {@link Short}, {@link Integer}, {@link Long}, {@link Float}, {@link Double},
     * {@link Fraction}, {@link BigInteger} or {@link BigDecimal} types.
     *
     * <p>If one of the given argument is null, then this method returns the class of the non-null argument.
     * If both arguments are null, then this method returns {@code null}.</p>
     *
     * @param  n1  the first number, or {@code null}.
     * @param  n2  the second number, or {@code null}.
     * @return the widest type of the given numbers, or {@code null} if both {@code n1} and {@code n2} are null.
     * @throws IllegalArgumentException if a number is not an instance of a supported type.
     *
     * @see #widestClass(Number, Number)
     * @see #narrowestClass(Number, Number)
     */
    public static Class<? extends Number> widestClass(final Number n1, final Number n2) throws IllegalArgumentException {
        return widestClass((n1 != null) ? n1.getClass() : null,
                           (n2 != null) ? n2.getClass() : null);
    }

    /**
     * Returns the widest of the given types. Classes {@code c1} and {@code c2} can be
     * {@link Byte}, {@link Short}, {@link Integer}, {@link Long}, {@link Float}, {@link Double},
     * {@link Fraction}, {@link BigInteger} or {@link BigDecimal} types.
     *
     * <p>If one of the given argument is null, then this method returns the non-null argument.
     * If both arguments are null, then this method returns {@code null}.</p>
     *
     * <div class="note"><b>Example:</b>
     * in the following code, {@code type} is set to {@code Long.class}:
     *
     * {@preformat java
     *     Class<?> type = widestClass(Short.class, Long.class);
     * }
     * </div>
     *
     * @param  c1  the first number type, or {@code null}.
     * @param  c2  the second number type, or {@code null}.
     * @return the widest of the given types, or {@code null} if both {@code c1} and {@code c2} are null.
     * @throws IllegalArgumentException if one of the given types is not supported by this {@code Numbers} class.
     *
     * @see #widestClass(Class, Class)
     * @see #narrowestClass(Number, Number)
     */
    public static Class<? extends Number> widestClass(final Class<? extends Number> c1,
                                                      final Class<? extends Number> c2)
            throws IllegalArgumentException
    {
        if (c1 == null) return c2;
        if (c2 == null) return c1;
        final Numbers m1 = MAPPING.get(c1);
        if (m1 == null) {
            throw unknownType(c1);
        }
        final Numbers m2 = MAPPING.get(c2);
        if (m2 == null) {
            throw unknownType(c2);
        }
        return (m1.ordinal >= m2.ordinal) ? c1 : c2;
    }

    /**
     * Returns the narrowest type of two numbers. Numbers {@code n1} and {@code n2} can be instance of
     * {@link Byte}, {@link Short}, {@link Integer}, {@link Long}, {@link Float}, {@link Double},
     * {@link Fraction}, {@link BigInteger} or {@link BigDecimal} types.
     *
     * @param  n1  the first number, or {@code null}.
     * @param  n2  the second number, or {@code null}.
     * @return the narrowest type of the given numbers, or {@code null} if both {@code n1} and {@code n2} are null.
     * @throws IllegalArgumentException if a number is not an instance of a supported type.
     *
     * @see #narrowestClass(Class, Class)
     * @see #widestClass(Class, Class)
     */
    public static Class<? extends Number> narrowestClass(final Number n1, final Number n2)
            throws IllegalArgumentException
    {
        return narrowestClass((n1 != null) ? n1.getClass() : null,
                              (n2 != null) ? n2.getClass() : null);
    }

    /**
     * Returns the narrowest of the given types. Classes {@code c1} and {@code c2} can be
     * {@link Byte}, {@link Short}, {@link Integer}, {@link Long}, {@link Float}, {@link Double},
     * {@link Fraction}, {@link BigInteger} or {@link BigDecimal} types.
     *
     * <p>If one of the given argument is null, then this method returns the non-null argument.
     * If both arguments are null, then this method returns {@code null}.</p>
     *
     * <div class="note"><b>Example:</b>
     * in the following code, {@code type} is set to {@code Short.class}:
     *
     * {@preformat java
     *     Class<?> type = widestClass(Short.class, Long.class);
     * }
     * </div>
     *
     * @param  c1  the first number type, or {@code null}.
     * @param  c2  the second number type, or {@code null}.
     * @return the narrowest of the given types, or {@code null} if both {@code c1} and {@code c2} are null.
     * @throws IllegalArgumentException if one of the given types is not supported by this {@code Numbers} class.
     *
     * @see #narrowestClass(Number, Number)
     * @see #widestClass(Class, Class)
     */
    public static Class<? extends Number> narrowestClass(final Class<? extends Number> c1,
                                                         final Class<? extends Number> c2)
            throws IllegalArgumentException
    {
        if (c1 == null) return c2;
        if (c2 == null) return c1;
        final Numbers m1 = MAPPING.get(c1);
        if (m1 == null) {
            throw unknownType(c1);
        }
        final Numbers m2 = MAPPING.get(c2);
        if (m2 == null) {
            throw unknownType(c2);
        }
        return (m1.ordinal < m2.ordinal) ? c1 : c2;
    }

    /**
     * Returns the smallest class capable to hold the specified value.
     * This method applies the following choices, in that order:
     *
     * <ul>
     *   <li>If the given value is {@code null}, then this method returns {@code null}.</li>
     *   <li>Otherwise if the given value can not be casted from {@code double} to another type
     *       without precision lost, return {@code Double.class}.</li>
     *   <li>Otherwise if the given value can not be casted from {@code float} to another type
     *       without precision lost, return {@code Float.class}.</li>
     *   <li>Otherwise if the given value is between {@value java.lang.Byte#MIN_VALUE} and
     *       {@value java.lang.Byte#MAX_VALUE}, then this method returns {@code Byte.class};</li>
     *   <li>Otherwise if the given value is between {@value java.lang.Short#MIN_VALUE} and
     *       {@value java.lang.Short#MAX_VALUE}, then this method returns {@code Short.class};</li>
     *   <li>Otherwise if the given value is between {@value java.lang.Integer#MIN_VALUE} and
     *       {@value java.lang.Integer#MAX_VALUE}, then this method returns {@code Integer.class};</li>
     *   <li>Otherwise this method returns {@code Long.class};</li>
     * </ul>
     *
     * @param  value  the value to be wrapped in a finer (if possible) {@link Number}.
     * @return the narrowest type capable to hold the given value.
     *
     * @see #narrowestNumber(Number)
     */
    @SuppressWarnings("fallthrough")
    public static Class<? extends Number> narrowestClass(final Number value) {
        if (value == null) {
            return null;
        }
        boolean isFloat = false;
        final long longValue = value.longValue();
        switch (getEnumConstant(value.getClass())) {
            default: {
                final double doubleValue = value.doubleValue();
                final float  floatValue  = (float) doubleValue;
                isFloat = (doubleToLongBits(floatValue) == doubleToLongBits(doubleValue));
                if (doubleValue != longValue) {
                    return isFloat ? Float.class : Double.class;
                }
                // Fall through.
            }
            case LONG:    if (((int)   longValue) != longValue) return isFloat ? Float.class : Long.class;
            case INTEGER: if (((short) longValue) != longValue) return Integer.class;
            case SHORT:   if (((byte)  longValue) != longValue) return Short  .class;
            case BYTE:    return Byte.class;
        }
    }

    /**
     * Returns the given number wrapped in the smallest class capable to hold the specified value.
     * This method is equivalent to the following code, in a slightly more efficient way:
     *
     * {@preformat java
     *     return cast(value, narrowestClass(value));
     * }
     *
     * @param  value  the value to be wrapped in a finer (if possible) {@link Number}.
     * @return the narrowest type capable to hold the given value.
     *
     * @see #narrowestClass(Number)
     * @see #cast(Number, Class)
     */
    @SuppressWarnings("fallthrough")
    public static Number narrowestNumber(final Number value) {
        if (value == null) {
            return null;
        }
        final Number candidate;
        boolean isFloat = false;
        final long longValue = value.longValue();
        switch (getEnumConstant(value.getClass())) {
            default: {
                final double doubleValue = value.doubleValue();
                final float  floatValue  = (float) doubleValue;
                isFloat = (doubleToLongBits(floatValue) == doubleToLongBits(doubleValue));
                if (doubleValue != longValue) {
                    // Do not use "isFloat ? … : …" operator as it inserts undesired automatic auto-(un)boxing.
                    if (isFloat) candidate = Float   .valueOf(floatValue);
                    else         candidate = Numerics.valueOf(doubleValue);
                    break;
                }
                // Fall through everywhere.
            }
            case LONG: {
                if (((int) longValue) != longValue) {
                    // Do not use "isFloat ? … : …" operator as it inserts undesired automatic auto-(un)boxing.
                    if (isFloat) candidate = Float.valueOf(longValue);
                    else         candidate = Long .valueOf(longValue);
                    break;
                }
            }
            case INTEGER: {
                if (((short) longValue) != longValue) {
                    candidate = Integer.valueOf((int) longValue);
                    break;
                }
            }
            case SHORT: {
                if (((byte) longValue) != longValue) {
                    candidate = Short.valueOf((short) longValue);
                    break;
                }
            }
            case BYTE: {
                candidate = Byte.valueOf((byte) longValue);
                break;
            }
        }
        // Keep the existing instance if possible.
        return value.equals(candidate) ? value : candidate;
    }

    /**
     * Returns the smallest number capable to hold the specified value.
     *
     * @param  value  the value to be wrapped in a {@link Number}.
     * @return the narrowest type capable to hold the given value.
     * @throws NumberFormatException if the given value can not be parsed as a number.
     *
     * @see #narrowestNumber(Number)
     */
    public static Number narrowestNumber(final String value) throws NumberFormatException {
        /*
         * Do not trim whitespaces. It is up to the caller to do that if he wants.
         * For such low level function, we are better to avoid hidden initiative.
         */
        final int length = value.length();
        for (int i=0; i<length; i++) {
            final char c = value.charAt(i);
            if (c == '.' || c == 'e' || c == 'E') {
                return narrowestNumber(Double.parseDouble(value));
            }
        }
        return narrowestNumber(Long.parseLong(value));
    }

    /**
     * Casts a number to the specified type. The target type can be one of {@link Byte},
     * {@link Short}, {@link Integer}, {@link Long}, {@link Float}, {@link Double},
     * {@link Fraction}, {@link BigInteger} or {@link BigDecimal}.
     * This method makes the following choice:
     *
     * <ul>
     *   <li>If the given value is {@code null} or an instance of the given type, then it is returned unchanged.</li>
     *   <li>Otherwise if the given type is {@code Double.class}, then this method returns
     *       <code>{@linkplain Double#valueOf(double) Double.valueOf}(number.doubleValue())</code>;</li>
     *   <li>Otherwise if the given type is {@code Float.class}, then this method returns
     *       <code>{@linkplain Float#valueOf(float) Float.valueOf}(number.floatValue())</code>;</li>
     *   <li>And likewise for all remaining known types.</li>
     * </ul>
     *
     * This method does not verify if the given type is wide enough for the given value,
     * because the type has typically been calculated by {@link #widestClass(Class, Class)}
     * or {@link #narrowestClass(Number)}. If nevertheless the given type is not wide enough,
     * then the behavior depends on the implementation of the corresponding
     * {@code Number.fooValue()} method - typically, the value is just rounded or truncated.
     *
     * @param  <N>     the class to cast to.
     * @param  number  the number to cast, or {@code null}.
     * @param  type    the destination type.
     * @return the number casted to the given type, or {@code null} if the given value was null.
     * @throws IllegalArgumentException if the given type is not supported by this {@code Numbers} class,
     *         or the type is {@link #FRACTION} and the given number can not be converted to that type.
     */
    @SuppressWarnings("unchecked")
    public static <N extends Number> N cast(final Number number, final Class<N> type) throws IllegalArgumentException {
        if (number == null || number.getClass() == type) {
            return (N) number;
        }
        switch (getEnumConstant(type)) {
            case BYTE:     return (N) Byte    .valueOf(number.  byteValue());
            case SHORT:    return (N) Short   .valueOf(number. shortValue());
            case INTEGER:  return (N) Integer .valueOf(number.   intValue());
            case LONG:     return (N) Long    .valueOf(number.  longValue());
            case FLOAT:    return (N) Float   .valueOf(number. floatValue());
            case DOUBLE:   return (N) Numerics.valueOf(number.doubleValue());
            case FRACTION: return (N) Fraction.valueOf(number.doubleValue());
            case BIG_INTEGER: {
                final BigInteger c;
                if (number instanceof BigInteger) {
                    c = (BigInteger) number;
                } else if (number instanceof BigDecimal) {
                    c = ((BigDecimal) number).toBigInteger();
                } else {
                    c = BigInteger.valueOf(number.longValue());
                }
                return (N) c;
            }
            case BIG_DECIMAL: {
                final BigDecimal c;
                if (number instanceof BigDecimal) {
                    c = (BigDecimal) number;
                } else if (number instanceof BigInteger) {
                    c = new BigDecimal((BigInteger) number);
                } else if (isInteger(number.getClass())) {
                    c = BigDecimal.valueOf(number.longValue());
                } else {
                    /*
                     * Same implementation as BigDecimal.valueOf(double)
                     * but better result if number is a Float instance.
                     */
                    c = new BigDecimal(number.toString());
                }
                return (N) c;
            }
            default: {
                if (type.isInstance(number)) {
                    return (N) number;
                }
                throw unknownType(type);
            }
        }
    }

    /**
     * Wraps the given floating-point value in a {@code Number} of the specified class.
     * The given type shall be one of {@link Byte}, {@link Short}, {@link Integer}, {@link Long},
     * {@link Float}, {@link Double}, {@link Fraction}, {@link BigInteger} and {@link BigDecimal} classes.
     * Furthermore, the given value shall be convertible to the given class without precision lost,
     * otherwise an {@link IllegalArgumentException} will be thrown.
     *
     * @param  <N>    the wrapper class.
     * @param  value  the value to wrap.
     * @param  type   the desired wrapper class.
     * @return the value wrapped in an object of the given class.
     * @throws IllegalArgumentException if the given type is not supported by this {@code Numbers} class,
     *         or if the given value can not be wrapped in an instance of the given class without precision lost.
     */
    @SuppressWarnings("unchecked")
    public static <N extends Number> N wrap(final double value, final Class<N> type) throws IllegalArgumentException {
        final N number;
        switch (getEnumConstant(type)) {
            case BYTE:        number = (N) Byte      .valueOf((byte)  value); break;
            case SHORT:       number = (N) Short     .valueOf((short) value); break;
            case INTEGER:     number = (N) Integer   .valueOf((int)   value); break;
            case LONG:        number = (N) Long      .valueOf((long)  value); break;
            case FLOAT:       number = (N) Float     .valueOf((float) value); break;
            case DOUBLE:      return   (N) Numerics  .valueOf(value); // No need to verify.
            case FRACTION:    return   (N) Fraction  .valueOf(value); // No need to verify.
            case BIG_INTEGER: number = (N) BigInteger.valueOf((long) value); break;
            case BIG_DECIMAL: return   (N) BigDecimal.valueOf(value); // No need to verify.
            default: throw unknownType(type);
        }
        if (doubleToLongBits(number.doubleValue()) != doubleToLongBits(value)) {
            throw new IllegalArgumentException(Errors.format(Errors.Keys.CanNotConvertValue_2, value, type));
        }
        return number;
    }

    /**
     * Wraps the given integer value in a {@code Number} of the specified class.
     * The given type shall be one of {@link Byte}, {@link Short}, {@link Integer}, {@link Long},
     * {@link Float}, {@link Double}, {@link Fraction}, {@link BigInteger} and {@link BigDecimal} classes.
     * Furthermore, the given value shall be convertible to the given class without precision lost,
     * otherwise an {@link IllegalArgumentException} will be thrown.
     *
     * @param  <N>    the wrapper class.
     * @param  value  the value to wrap.
     * @param  type   the desired wrapper class.
     * @return the value wrapped in an object of the given class.
     * @throws IllegalArgumentException if the given type is not supported by this {@code Numbers} class,
     *         or if the given value can not be wrapped in an instance of the given class without precision lost.
     *
     * @since 0.8
     */
    @SuppressWarnings("unchecked")
    public static <N extends Number> N wrap(final long value, final Class<N> type) throws IllegalArgumentException {
        final N number;
        switch (getEnumConstant(type)) {
            case BYTE:        number = (N) Byte      .valueOf((byte)   value); break;
            case SHORT:       number = (N) Short     .valueOf((short)  value); break;
            case INTEGER:     number = (N) Integer   .valueOf((int)    value); break;
            case LONG:        return   (N) Long      .valueOf(value);  // No need to verify.
            case FLOAT:       number = (N) Float     .valueOf((float)  value); break;
            case DOUBLE:      number = (N) Numerics  .valueOf((double) value); break;
            case FRACTION:    number = (N) new Fraction      ((int) value, 1); break;
            case BIG_INTEGER: return   (N) BigInteger.valueOf(value);  // No need to verify.
            case BIG_DECIMAL: return   (N) BigDecimal.valueOf(value);  // No need to verify.
            default: throw unknownType(type);
        }
        if (number.longValue() != value) {
            throw new IllegalArgumentException(Errors.format(Errors.Keys.CanNotConvertValue_2, value, type));
        }
        return number;
    }

    /**
     * Converts the specified string into a value object.
     * The value object can be an instance of {@link BigDecimal}, {@link BigInteger}, {@link Fraction},
     * {@link Double}, {@link Float}, {@link Long}, {@link Integer}, {@link Short}, {@link Byte},
     * {@link Boolean}, {@link Character} or {@link String} according the specified type.
     * This method makes the following choice:
     *
     * <ul>
     *   <li>If the given type is {@code Double.class}, then this method returns
     *       <code>{@linkplain Double#valueOf(String) Double.valueOf}(value)</code>;</li>
     *   <li>If the given type is {@code Float.class}, then this method returns
     *       <code>{@linkplain Float#valueOf(String) Float.valueOf}(value)</code>;</li>
     *   <li>And likewise for all remaining known types.</li>
     * </ul>
     *
     * @param  <T>    the requested type.
     * @param  value  the value to parse.
     * @param  type   the requested type.
     * @return the value object, or {@code null} if {@code value} was null.
     * @throws IllegalArgumentException if {@code type} is not a recognized type.
     * @throws NumberFormatException if {@code type} is a subclass of {@link Number}
     *         and the string value is not parsable as a number of the specified type.
     */
    @SuppressWarnings("unchecked")
    public static <T> T valueOf(final String value, final Class<T> type)
            throws IllegalArgumentException, NumberFormatException
    {
        if (value == null || type == String.class) {
            return (T) value;
        }
        switch (getEnumConstant(type)) {
            case CHARACTER: {
                /*
                 * If the string is empty, returns 0 which means "end of string" in C/C++
                 * and NULL in Unicode standard. If non-empty, take only the first char.
                 * This is somewhat consistent with Boolean.valueOf(...) which is quite
                 * lenient about the parsing as well, and throwing a NumberFormatException
                 * for those would not be appropriate.
                 */
                return (T) Character.valueOf(value.isEmpty() ? 0 : value.charAt(0));
            }
            // Do not trim whitespaces. It is up to the caller to do that if he wants.
            // For such low level function, we are better to avoid hidden initiative.
            case BOOLEAN:     return (T) Boolean.valueOf(value);
            case BYTE:        return (T) Byte   .valueOf(value);
            case SHORT:       return (T) Short  .valueOf(value);
            case INTEGER:     return (T) Integer.valueOf(value);
            case LONG:        return (T) Long   .valueOf(value);
            case FLOAT:       return (T) Float  .valueOf(value);
            case DOUBLE:      return (T) Double .valueOf(value);
            case FRACTION:    return (T) new Fraction  (value);
            case BIG_INTEGER: return (T) new BigInteger(value);
            case BIG_DECIMAL: return (T) new BigDecimal(value);
            default: throw unknownType(type);
        }
    }

    /**
     * Returns a {@code NaN}, zero, empty or {@code null} value of the given type. This method
     * tries to return the closest value that can be interpreted as <cite>"none"</cite>, which
     * is usually not the same than <cite>"zero"</cite>. More specifically:
     *
     * <ul>
     *   <li>If the given type is a floating point <strong>primitive</strong> type ({@code float}
     *       or {@code double}), then this method returns {@link Float#NaN} or {@link Double#NaN}
     *       depending on the given type.</li>
     *
     *   <li>If the given type is an integer <strong>primitive</strong> type or the character type
     *       ({@code long}, {@code int}, {@code short}, {@code byte} or {@code char}), then this
     *       method returns the zero value of the given type.</li>
     *
     *   <li>If the given type is the {@code boolean} <strong>primitive</strong> type, then this
     *       method returns {@link Boolean#FALSE}.</li>
     *
     *   <li>If the given type is an array or a collection, then this method returns an empty
     *       array or collection. The given type is honored on a <cite>best effort</cite> basis.</li>
     *
     *   <li>For all other cases, including the wrapper classes of primitive types, this method
     *       returns {@code null}.</li>
     * </ul>
     *
     * Despite being defined in the {@code Numbers} class, the scope of this method has been
     * extended to array and collection types because those objects can also be seen as
     * mathematical concepts.
     *
     * @param  <T>   the compile-time type of the requested object.
     * @param  type  the type of the object for which to get a nil value.
     * @return an object of the given type which represents a nil value, or {@code null}.
     *
     * @see org.apache.sis.xml.NilObject
     */
    @SuppressWarnings("unchecked")
    public static <T> T valueOfNil(final Class<T> type) {
        final Numbers mapping = MAPPING.get(type);
        if (mapping != null) {
            if (type.isPrimitive()) {
                return (T) mapping.nullValue;
            }
        } else if (type != null && type != Object.class) {
            if (type == Map         .class) return (T) Collections.EMPTY_MAP;
            if (type == List        .class) return (T) Collections.EMPTY_LIST;
            if (type == Queue       .class) return (T) CollectionsExt.emptyQueue();
            if (type == SortedSet   .class) return (T) Collections.emptySortedSet();
            if (type == NavigableSet.class) return (T) Collections.emptyNavigableSet();
            if (type.isAssignableFrom(Set.class)) {
                return (T) Collections.EMPTY_SET;
            }
            final Class<?> element = type.getComponentType();
            if (element != null) {
                return (T) Array.newInstance(element, 0);
            }
        }
        return null;
    }

    /**
     * Returns a numeric constant for the given type.
     * The constants are {@link #BIG_DECIMAL}, {@link #BIG_INTEGER}, {@link #FRACTION},
     * {@link #DOUBLE}, {@link #FLOAT}, {@link #LONG}, {@link #INTEGER},
     * {@link #SHORT}, {@link #BYTE}, {@link #CHARACTER}, {@link #BOOLEAN}, or {@link #OTHER}
     * constants for the given type. This is a commodity for usage in {@code switch} statements.
     *
     * @param  type  a type (usually either a primitive type or its wrapper), or {@code null}.
     * @return the constant for the given type, or {@link #OTHER} if unknown.
     */
    public static byte getEnumConstant(final Class<?> type) {
        final Numbers mapping = MAPPING.get(type);
        return (mapping != null) ? mapping.ordinal : OTHER;
    }

    /**
     * Returns an exception for an unknown type.
     */
    private static IllegalArgumentException unknownType(final Class<?> type) {
        return new IllegalArgumentException(Errors.format(Errors.Keys.NotAPrimitiveWrapper_1, type));
    }
}
