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Java library for reading and writing FITS files. FITS, the Flexible Image Transport System, is the format commonly used in the archiving and transport of astronomical data.
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package nom.tam.fits.header;

/*
 * #%L
 * nom.tam FITS library
 * %%
 * Copyright (C) 1996 - 2015 nom-tam-fits
 * %%
 * This is free and unencumbered software released into the public domain.
 * 
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 * 
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
 * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
 * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 * #L%
 */

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

import nom.tam.fits.header.IFitsHeader.HDU;
import nom.tam.fits.header.IFitsHeader.SOURCE;
import nom.tam.fits.header.IFitsHeader.VALUE;

/**
 * generic key interface, create an IFitsHeader from a key.
 *
 * @author ritchie
 */
public final class GenericKey {

    private static final int NUMBER_BASE = 10;

    /**
     * cache of all standard keys, for reusing the standards.
     */
    private static final Map STANDARD_KEYS;

    static {
        Map headers = new HashMap();
        for (IFitsHeader key : Standard.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : Checksum.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : Compression.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : DataDescription.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : InstrumentDescription.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : NonStandard.values()) {
            headers.put(key.key(), key);
        }
        for (IFitsHeader key : ObservationDescription.values()) {
            headers.put(key.key(), key);
        }
        STANDARD_KEYS = Collections.unmodifiableMap(headers);
    }

    /**
     * create a fits header key from a free string
     *
     * @param key
     *            the string to create the key for
     * @return the IFitsHeader implementation for the key.
     */
    public static IFitsHeader create(String key) {
        IFitsHeader result = STANDARD_KEYS.get(key);
        if (result == null) {
            result = new FitsHeaderImpl(key, SOURCE.UNKNOWN, HDU.ANY, VALUE.ANY, "");
        }
        return result;
    }

    /**
     * create a array of generic fits header keys from a array of string keys.
     *
     * @param keys
     *            the array of string keys
     * @return the array of IFitsHeaderKeys.
     */
    public static IFitsHeader[] create(String[] keys) {
        IFitsHeader[] result = new IFitsHeader[keys.length];
        for (int index = 0; index < result.length; index++) {
            result[index] = create(keys[index]);
        }
        return result;
    }

    public static int getN(String card) {
        int index = card.length() - 1;
        int n = 0;
        int numberBase = 1;
        while (index >= 0 && Character.isDigit(card.charAt(index))) {
            n = n + (card.charAt(index) - '0') * numberBase;
            numberBase *= NUMBER_BASE;
            index--;
        }
        return n;
    }

    /**
     * lookup a string key in the standard key sets.
     *
     * @param key
     *            the fits key to search.
     * @return the found fits key or null
     */
    public static IFitsHeader lookup(String key) {
        int keyLength = key.length();
        if (keyLength > 0 && Character.isDigit(key.charAt(keyLength - 1))) {
            StringBuilder builder = new StringBuilder();
            for (int index = 0; index < keyLength; index++) {
                char character = key.charAt(index);
                if (Character.isDigit(character)) {
                    if (builder.charAt(builder.length() - 1) != 'n') {
                        builder.append('n');
                    }
                } else {
                    builder.append(character);
                }
            }
            return STANDARD_KEYS.get(builder.toString());
        }
        return STANDARD_KEYS.get(key);
    }

    /**
     * utility class do not instanciate it.
     */
    private GenericKey() {
    }
}