001// License: GPL. For details, see LICENSE file.
002package org.openstreetmap.josm.data.projection.datum;
003
004import java.io.IOException;
005import java.io.InputStream;
006import java.util.Collections;
007import java.util.Map;
008import java.util.TreeMap;
009
010/**
011 * Wrapper for {@link NTV2GridShiftFile}.
012 *
013 * Loads the shift file from disk, when it is first accessed.
014 * @since 5226
015 */
016public class NTV2GridShiftFileWrapper {
017
018    private NTV2GridShiftFile instance;
019    private final String gridFileName;
020
021    public static final float NTV2_SOURCE_PRIORITY_LOCAL = 10f;
022    public static final float NTV2_SOURCE_PRIORITY_DOWNLOAD = 5f;
023
024    private static Map<Float, NTV2GridShiftFileSource> sources = new TreeMap<>(Collections.reverseOrder());
025
026    /**
027     * Register a source for NTV2 grid files.
028     * @param priority the priority, sources with higher priority are checked first;
029     * use {@link #NTV2_SOURCE_PRIORITY_LOCAL} for local files and
030     * {@link #NTV2_SOURCE_PRIORITY_DOWNLOAD} for remote downloads
031     * @param source the NTV2 grid file source
032     * @since 12777
033     */
034    public static void registerNTV2GridShiftFileSource(float priority, NTV2GridShiftFileSource source) {
035        sources.put(priority, source);
036    }
037
038    /**
039     * Constructs a new {@code NTV2GridShiftFileWrapper}.
040     * @param filename Path to the grid file (GSB format)
041     */
042    public NTV2GridShiftFileWrapper(String filename) {
043        this.gridFileName = filename;
044    }
045
046    /**
047     * Returns the actual {@link NTV2GridShiftFile} behind this wrapper.
048     * The grid file is only loaded once, when first accessed.
049     * @return The NTv2 grid file
050     * @throws IOException if the grid file cannot be found/loaded
051     */
052    public synchronized NTV2GridShiftFile getShiftFile() throws IOException {
053        if (instance == null) {
054            for (Map.Entry<Float, NTV2GridShiftFileSource> entry : sources.entrySet()) {
055                NTV2GridShiftFileSource source = entry.getValue();
056                try (InputStream is = source.getNTV2GridShiftFile(gridFileName)) {
057                    if (is != null) {
058                        NTV2GridShiftFile ntv2 = new NTV2GridShiftFile();
059                        ntv2.loadGridShiftFile(is, false);
060                        instance = ntv2;
061                        break;
062                    }
063                }
064            }
065        }
066        return instance;
067    }
068}