/*-------------------------------------------------------------------------
*
* Copyright (c) 2003-2008, PostgreSQL Global Development Group
*
* IDENTIFICATION
*   $PostgreSQL: pgjdbc/org/postgresql/core/Encoding.java,v 1.23 2008/01/08 06:56:27 jurka Exp $
*
*-------------------------------------------------------------------------
*/
package org.postgresql.core;

import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.io.IOException;
import java.util.HashMap;

/**
 * Representation of a particular character encoding.
 */
public class Encoding
{
    private static final Encoding DEFAULT_ENCODING = new Encoding(null);

    /*
     * Preferred JVM encodings for backend encodings.
     */
    private static final HashMap encodings = new HashMap();

    static {
        //Note: this list should match the set of supported server
        // encodings found in backend/util/mb/encnames.c
        encodings.put("SQL_ASCII", new String[] { "ASCII", "us-ascii" });
        encodings.put("UNICODE", new String[] { "UTF-8", "UTF8" });
        encodings.put("UTF8", new String[] { "UTF-8", "UTF8" }); // 8.1's canonical name for UNICODE changed.
        encodings.put("LATIN1", new String[] { "ISO8859_1" });
        encodings.put("LATIN2", new String[] { "ISO8859_2" });
        encodings.put("LATIN3", new String[] { "ISO8859_3" });
        encodings.put("LATIN4", new String[] { "ISO8859_4" });
        encodings.put("ISO_8859_5", new String[] { "ISO8859_5" });
        encodings.put("ISO_8859_6", new String[] { "ISO8859_6" });
        encodings.put("ISO_8859_7", new String[] { "ISO8859_7" });
        encodings.put("ISO_8859_8", new String[] { "ISO8859_8" });
        encodings.put("LATIN5", new String[] { "ISO8859_9" });
        encodings.put("LATIN7", new String[] { "ISO8859_13" });
        encodings.put("LATIN9", new String[] { "ISO8859_15_FDIS" });
        encodings.put("EUC_JP", new String[] { "EUC_JP" });
        encodings.put("EUC_CN", new String[] { "EUC_CN" });
        encodings.put("EUC_KR", new String[] { "EUC_KR" });
        encodings.put("JOHAB", new String[] { "Johab" });
        encodings.put("EUC_TW", new String[] { "EUC_TW" });
        encodings.put("SJIS", new String[] { "MS932", "SJIS" });
        encodings.put("BIG5", new String[] { "Big5", "MS950", "Cp950" });
        encodings.put("GBK", new String[] { "GBK", "MS936" });
        encodings.put("UHC", new String[] { "MS949", "Cp949", "Cp949C" });
        encodings.put("TCVN", new String[] { "Cp1258" });
        encodings.put("WIN1256", new String[] { "Cp1256" });
        encodings.put("WIN1250", new String[] { "Cp1250" });
        encodings.put("WIN874", new String[] { "MS874", "Cp874" });
        encodings.put("WIN", new String[] { "Cp1251" });
        encodings.put("ALT", new String[] { "Cp866" });
        // We prefer KOI8-U, since it is a superset of KOI8-R.
        encodings.put("KOI8", new String[] { "KOI8_U", "KOI8_R" });
        // If the database isn't encoding-aware then we can't have
        // any preferred encodings.
        encodings.put("UNKNOWN", new String[0]);
        // The following encodings do not have a java equivalent
        encodings.put("MULE_INTERNAL", new String[0]);
        encodings.put("LATIN6", new String[0]);
        encodings.put("LATIN8", new String[0]);
        encodings.put("LATIN10", new String[0]);
    }

    private final String encoding;
    private final boolean fastASCIINumbers;

    protected Encoding(String encoding)
    {
        this.encoding = encoding;
        fastASCIINumbers = testAsciiNumbers();
    }
    
    /**
     * Returns true if this encoding has characters
     * '-' and '0'..'9' in exactly same posision as ascii.
     *  
     * @return true if the bytes can be scanned directly for ascii numbers.
     */
    public boolean hasAsciiNumbers() {
        return fastASCIINumbers;
    }

    /**
     * Construct an Encoding for a given JVM encoding.
     * 
     * @param jvmEncoding the name of the JVM encoding
     * @return an Encoding instance for the specified encoding,
     *   or an Encoding instance for the default JVM encoding if the
     *   specified encoding is unavailable.
     */
    public static Encoding getJVMEncoding(String jvmEncoding) {
        if (isAvailable(jvmEncoding))
        {
            if (jvmEncoding.equals("UTF-8") || jvmEncoding.equals("UTF8"))
                return new UTF8Encoding(jvmEncoding);
            else
                return new Encoding(jvmEncoding);
        }
        else
            return defaultEncoding();
    }

    /**
     * Construct an Encoding for a given database encoding.
     * 
     * @param databaseEncoding the name of the database encoding
     * @return an Encoding instance for the specified encoding,
     *   or an Encoding instance for the default JVM encoding if the
     *   specified encoding is unavailable.
     */
    public static Encoding getDatabaseEncoding(String databaseEncoding)
    {
        // If the backend encoding is known and there is a suitable
        // encoding in the JVM we use that. Otherwise we fall back
        // to the default encoding of the JVM.

        String[] candidates = (String[]) encodings.get(databaseEncoding);
        if (candidates != null)
        {
            for (int i = 0; i < candidates.length; i++)
            {
                if (isAvailable(candidates[i]))
                {
                    return new Encoding(candidates[i]);
                }
            }
        }

        // Try the encoding name directly -- maybe the charset has been
        // provided by the user.
        if (isAvailable(databaseEncoding))
            return new Encoding(databaseEncoding);

        // Fall back to default JVM encoding.
        return defaultEncoding();
    }

    /**
     * Get the name of the (JVM) encoding used.
     *
     * @return the JVM encoding name used by this instance.
     */
    public String name()
    {
        return encoding;
    }

    /**
     * Encode a string to an array of bytes.
     *
     * @param s the string to encode
     * @return a bytearray containing the encoded string
     * @throws IOException if something goes wrong
     */
    public byte[] encode(String s) throws IOException
    {
        if (s == null)
            return null;

        if (encoding == null)
            return s.getBytes();

        return s.getBytes(encoding);
    }

    /**
     * Decode an array of bytes into a string.
     * 
     * @param encodedString a bytearray containing the encoded string  the string to encod
     * @param offset the offset in <code>encodedString</code> of the first byte of the encoded representation
     * @param length the length, in bytes, of the encoded representation
     * @return the decoded string
     * @throws IOException if something goes wrong
     */
    public String decode(byte[] encodedString, int offset, int length) throws IOException
    {
        if (encoding == null)
            return new String(encodedString, offset, length);

        return new String(encodedString, offset, length, encoding);
    }

    /**
     * Decode an array of bytes into a string.
     *
     * @param encodedString a bytearray containing the encoded string  the string to encod
     * @return the decoded string
     * @throws IOException if something goes wrong
     */
    public String decode(byte[] encodedString) throws IOException
    {
        return decode(encodedString, 0, encodedString.length);
    }

    /**
     * Get a Reader that decodes the given InputStream using this encoding.
     *
     * @param in the underlying stream to decode from
     * @return a non-null Reader implementation.
     * @throws IOException if something goes wrong
     */
    public Reader getDecodingReader(InputStream in) throws IOException
    {
        if (encoding == null)
            return new InputStreamReader(in);

        return new InputStreamReader(in, encoding);
    }

    /**
     * Get a Writer that encodes to the given OutputStream using this encoding.
     *
     * @param out the underlying stream to encode to
     * @return a non-null Writer implementation.
     * @throws IOException if something goes wrong
     */
    public Writer getEncodingWriter(OutputStream out) throws IOException
    {
        if (encoding == null)
            return new OutputStreamWriter(out);

        return new OutputStreamWriter(out, encoding);
    }

    /**
     * Get an Encoding using the default encoding for the JVM.
     * @return an Encoding instance
     */
    public static Encoding defaultEncoding()
    {
        return DEFAULT_ENCODING;
    }

    /**
     * Test if an encoding is available in the JVM.
     *
     * @param encodingName the JVM encoding name to test
     * @return true iff the encoding is supported
     */
    private static boolean isAvailable(String encodingName)
    {
        try
        {
            "DUMMY".getBytes(encodingName);
            return true;
        }
        catch (java.io.UnsupportedEncodingException e)
        {
            return false;
        }
    }

    public String toString() {
        return (encoding == null ? "<default JVM encoding>" : encoding);
    }
    
    /**
     * Checks weather this encoding is compatible with ASCII for the number
     * characters '-' and '0'..'9'. Where compatible means that they are encoded
     * with exactly same values. 
     * 
     * @return If faster ASCII number parsing can be used with this encoding.
     */
    private boolean testAsciiNumbers() {
        // TODO: test all postgres supported encoding to see if there are
        // any which do _not_ have ascii numbers in same location
        // at least all the encoding listed in the encodings hashmap have
        // working ascii numbers
	try {
	    String test = "-0123456789";
	    byte[] bytes = encode(test);
	    String res = new String(bytes, "US-ASCII");
	    return test.equals(res);
	} catch (java.io.UnsupportedEncodingException e) {
	    return false;
	} catch (IOException e) {
	    return false;
	}
    }
}