/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/* We use APIs that access the standard Unix environ array, which

 * is defined by UNIX98 to look like:

 *

 *    char **environ;

 *

 * These are unsorted, case-sensitive, null-terminated arrays of bytes

 * of the form FOO=BAR\000 which are usually encoded in the user's

 * default encoding (file.encoding is an excellent choice for

 * encoding/decoding these).  However, even though the user cannot

 * directly access the underlying byte representation, we take pains

 * to pass on the child the exact byte representation we inherit from

 * the parent process for any environment name or value not created by

 * Javaland.  So we keep track of all the byte representations.

 *

 * Internally, we define the types Variable and Value that exhibit

 * String/byteArray duality.  The internal representation of the

 * environment then looks like a Map<Variable,Value>.  But we don't

 * expose this to the user -- we only provide a Map<String,String>

 * view, although we could also provide a Map<byte[],byte[]> view.

 *

 * The non-private methods in this class are not for general use even

 * within this package.  Instead, they are the system-dependent parts

 * of the system-independent method of the same name.  Don't even

 * think of using this class unless your method's name appears below.

 *

 * @author  Martin Buchholz

 * @since   1.5

 */

package java.lang;

import java.io.*;

import java.util.*;

final class ProcessEnvironment

{

    private static final HashMap<Variable,Value> theEnvironment;

    private static final Map<String,String> theUnmodifiableEnvironment;

    static final int MIN_NAME_LENGTH = 0;

    static {

        // We cache the C environment.  This means that subsequent calls

        // to putenv/setenv from C will not be visible from Java code.

        byte[][] environ = environ();

        theEnvironment = new HashMap<>(environ.length/2 + 3);

        // Read environment variables back to front,

        // so that earlier variables override later ones.

        for (int i = environ.length-1; i > 0; i-=2)

            theEnvironment.put(Variable.valueOf(environ[i-1]),

                               Value.valueOf(environ[i]));

        theUnmodifiableEnvironment

            = Collections.unmodifiableMap

            (new StringEnvironment(theEnvironment));

    }

    /* Only for use by System.getenv(String) */

    static String getenv(String name) {

        return theUnmodifiableEnvironment.get(name);

    }

    /* Only for use by System.getenv() */

    static Map<String,String> getenv() {

        return theUnmodifiableEnvironment;

    }

    /* Only for use by ProcessBuilder.environment() */

    static Map<String,String> environment() {

        return new StringEnvironment

            ((Map<Variable,Value>)(theEnvironment.clone()));

    }

    /* Only for use by Runtime.exec(...String[]envp...) */

    static Map<String,String> emptyEnvironment(int capacity) {

        return new StringEnvironment(new HashMap<Variable,Value>(capacity));

    }

    private static native byte[][] environ();

    // This class is not instantiable.

    private ProcessEnvironment() {}

    // Check that name is suitable for insertion into Environment map

    private static void validateVariable(String name) {

        if (name.indexOf('=')      != -1 ||

            name.indexOf('\u0000') != -1)

            throw new IllegalArgumentException

                ("Invalid environment variable name: \"" + name + "\"");

    }

    // Check that value is suitable for insertion into Environment map

    private static void validateValue(String value) {

        if (value.indexOf('\u0000') != -1)

            throw new IllegalArgumentException

                ("Invalid environment variable value: \"" + value + "\"");

    }

    // A class hiding the byteArray-String duality of

    // text data on Unixoid operating systems.

    private static abstract class ExternalData {

        protected final String str;

        protected final byte[] bytes;

        protected ExternalData(String str, byte[] bytes) {

            this.str = str;

            this.bytes = bytes;

        }

        public byte[] getBytes() {

            return bytes;

        }

        public String toString() {

            return str;

        }

        public boolean equals(Object o) {

            return o instanceof ExternalData

                && arrayEquals(getBytes(), ((ExternalData) o).getBytes());

        }

        public int hashCode() {

            return arrayHash(getBytes());

        }

    }

    private static class Variable

        extends ExternalData implements Comparable<Variable>

    {

        protected Variable(String str, byte[] bytes) {

            super(str, bytes);

        }

        public static Variable valueOfQueryOnly(Object str) {

            return valueOfQueryOnly((String) str);

        }

        public static Variable valueOfQueryOnly(String str) {

            return new Variable(str, str.getBytes());

        }

        public static Variable valueOf(String str) {

            validateVariable(str);

            return valueOfQueryOnly(str);

        }

        public static Variable valueOf(byte[] bytes) {

            return new Variable(new String(bytes), bytes);

        }

        public int compareTo(Variable variable) {

            return arrayCompare(getBytes(), variable.getBytes());

        }

        public boolean equals(Object o) {

            return o instanceof Variable && super.equals(o);

        }

    }

    private static class Value

        extends ExternalData implements Comparable<Value>

    {

        protected Value(String str, byte[] bytes) {

            super(str, bytes);

        }

        public static Value valueOfQueryOnly(Object str) {

            return valueOfQueryOnly((String) str);

        }

        public static Value valueOfQueryOnly(String str) {

            return new Value(str, str.getBytes());

        }

        public static Value valueOf(String str) {

            validateValue(str);

            return valueOfQueryOnly(str);

        }

        public static Value valueOf(byte[] bytes) {

            return new Value(new String(bytes), bytes);

        }

        public int compareTo(Value value) {

            return arrayCompare(getBytes(), value.getBytes());

        }

        public boolean equals(Object o) {

            return o instanceof Value && super.equals(o);

        }

    }

    // This implements the String map view the user sees.

    private static class StringEnvironment

        extends AbstractMap<String,String>

    {

        private Map<Variable,Value> m;

        private static String toString(Value v) {

            return v == null ? null : v.toString();

        }

        public StringEnvironment(Map<Variable,Value> m) {this.m = m;}

        public int size()        {return m.size();}

        public boolean isEmpty() {return m.isEmpty();}

        public void clear()      {       m.clear();}

        public boolean containsKey(Object key) {

            return m.containsKey(Variable.valueOfQueryOnly(key));

        }

        public boolean containsValue(Object value) {

            return m.containsValue(Value.valueOfQueryOnly(value));

        }

        public String get(Object key) {

            return toString(m.get(Variable.valueOfQueryOnly(key)));

        }

        public String put(String key, String value) {

            return toString(m.put(Variable.valueOf(key),

                                  Value.valueOf(value)));

        }

        public String remove(Object key) {

            return toString(m.remove(Variable.valueOfQueryOnly(key)));

        }

        public Set<String> keySet() {

            return new StringKeySet(m.keySet());

        }

        public Set<Map.Entry<String,String>> entrySet() {

            return new StringEntrySet(m.entrySet());

        }

        public Collection<String> values() {

            return new StringValues(m.values());

        }

        // It is technically feasible to provide a byte-oriented view

        // as follows:

        //      public Map<byte[],byte[]> asByteArrayMap() {

        //          return new ByteArrayEnvironment(m);

        //      }

        // Convert to Unix style environ as a monolithic byte array

        // inspired by the Windows Environment Block, except we work

        // exclusively with bytes instead of chars, and we need only

        // one trailing NUL on Unix.

        // This keeps the JNI as simple and efficient as possible.

        public byte[] toEnvironmentBlock(int[]envc) {

            int count = m.size() * 2; // For added '=' and NUL

            for (Map.Entry<Variable,Value> entry : m.entrySet()) {

                count += entry.getKey().getBytes().length;

                count += entry.getValue().getBytes().length;

            }

            byte[] block = new byte[count];

            int i = 0;

            for (Map.Entry<Variable,Value> entry : m.entrySet()) {

                byte[] key   = entry.getKey  ().getBytes();

                byte[] value = entry.getValue().getBytes();

                System.arraycopy(key, 0, block, i, key.length);

                i+=key.length;

                block[i++] = (byte) '=';

                System.arraycopy(value, 0, block, i, value.length);

                i+=value.length + 1;

                // No need to write NUL byte explicitly

                //block[i++] = (byte) '\u0000';

            }

            envc[0] = m.size();

            return block;

        }

    }

    static byte[] toEnvironmentBlock(Map<String,String> map, int[]envc) {

        return map == null ? null :

            ((StringEnvironment)map).toEnvironmentBlock(envc);

    }

    private static class StringEntry

        implements Map.Entry<String,String>

    {

        private final Map.Entry<Variable,Value> e;

        public StringEntry(Map.Entry<Variable,Value> e) {this.e = e;}

        public String getKey()   {return e.getKey().toString();}

        public String getValue() {return e.getValue().toString();}

        public String setValue(String newValue) {

            return e.setValue(Value.valueOf(newValue)).toString();

        }

        public String toString() {return getKey() + "=" + getValue();}

        public boolean equals(Object o) {

            return o instanceof StringEntry

                && e.equals(((StringEntry)o).e);

        }

        public int hashCode()    {return e.hashCode();}

    }

    private static class StringEntrySet

        extends AbstractSet<Map.Entry<String,String>>

    {

        private final Set<Map.Entry<Variable,Value>> s;

        public StringEntrySet(Set<Map.Entry<Variable,Value>> s) {this.s = s;}

        public int size()        {return s.size();}

        public boolean isEmpty() {return s.isEmpty();}

        public void clear()      {       s.clear();}

        public Iterator<Map.Entry<String,String>> iterator() {

            return new Iterator<Map.Entry<String,String>>() {

                Iterator<Map.Entry<Variable,Value>> i = s.iterator();

                public boolean hasNext() {return i.hasNext();}

                public Map.Entry<String,String> next() {

                    return new StringEntry(i.next());

                }

                public void remove() {i.remove();}

            };

        }

        private static Map.Entry<Variable,Value> vvEntry(final Object o) {

            if (o instanceof StringEntry)

                return ((StringEntry)o).e;

            return new Map.Entry<Variable,Value>() {

                public Variable getKey() {

                    return Variable.valueOfQueryOnly(((Map.Entry)o).getKey());

                }

                public Value getValue() {

                    return Value.valueOfQueryOnly(((Map.Entry)o).getValue());

                }

                public Value setValue(Value value) {

                    throw new UnsupportedOperationException();

                }

            };

        }

        public boolean contains(Object o) { return s.contains(vvEntry(o)); }

        public boolean remove(Object o)   { return s.remove(vvEntry(o)); }

        public boolean equals(Object o) {

            return o instanceof StringEntrySet

                && s.equals(((StringEntrySet) o).s);

        }

        public int hashCode() {return s.hashCode();}

    }

    private static class StringValues

          extends AbstractCollection<String>

    {

        private final Collection<Value> c;

        public StringValues(Collection<Value> c) {this.c = c;}

        public int size()        {return c.size();}

        public boolean isEmpty() {return c.isEmpty();}

        public void clear()      {       c.clear();}

        public Iterator<String> iterator() {

            return new Iterator<String>() {

                Iterator<Value> i = c.iterator();

                public boolean hasNext() {return i.hasNext();}

                public String next()     {return i.next().toString();}

                public void remove()     {i.remove();}

            };

        }

        public boolean contains(Object o) {

            return c.contains(Value.valueOfQueryOnly(o));

        }

        public boolean remove(Object o) {

            return c.remove(Value.valueOfQueryOnly(o));

        }

        public boolean equals(Object o) {

            return o instanceof StringValues

                && c.equals(((StringValues)o).c);

        }

        public int hashCode() {return c.hashCode();}

    }

    private static class StringKeySet extends AbstractSet<String> {

        private final Set<Variable> s;

        public StringKeySet(Set<Variable> s) {this.s = s;}

        public int size()        {return s.size();}

        public boolean isEmpty() {return s.isEmpty();}

        public void clear()      {       s.clear();}

        public Iterator<String> iterator() {

            return new Iterator<String>() {

                Iterator<Variable> i = s.iterator();

                public boolean hasNext() {return i.hasNext();}

                public String next()     {return i.next().toString();}

                public void remove()     {       i.remove();}

            };

        }

        public boolean contains(Object o) {

            return s.contains(Variable.valueOfQueryOnly(o));

        }

        public boolean remove(Object o) {

            return s.remove(Variable.valueOfQueryOnly(o));

        }

    }

    // Replace with general purpose method someday

    private static int arrayCompare(byte[]x, byte[] y) {

        int min = x.length < y.length ? x.length : y.length;

        for (int i = 0; i < min; i++)

            if (x[i] != y[i])

                return x[i] - y[i];

        return x.length - y.length;

    }

    // Replace with general purpose method someday

    private static boolean arrayEquals(byte[] x, byte[] y) {

        if (x.length != y.length)

            return false;

        for (int i = 0; i < x.length; i++)

            if (x[i] != y[i])

                return false;

        return true;

    }

    // Replace with general purpose method someday

    private static int arrayHash(byte[] x) {

        int hash = 0;

        for (int i = 0; i < x.length; i++)

            hash = 31 * hash + x[i];

        return hash;

    }

}