// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.data.imagery;

import static org.openstreetmap.josm.tools.I18n.tr;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.TreeSet;
import java.util.concurrent.ExecutorService;

import org.openstreetmap.josm.Main;
import org.openstreetmap.josm.data.StructUtils;
import org.openstreetmap.josm.data.imagery.ImageryInfo.ImageryPreferenceEntry;
import org.openstreetmap.josm.gui.PleaseWaitRunnable;
import org.openstreetmap.josm.io.CachedFile;
import org.openstreetmap.josm.io.OfflineAccessException;
import org.openstreetmap.josm.io.OnlineResource;
import org.openstreetmap.josm.io.imagery.ImageryReader;
import org.openstreetmap.josm.spi.preferences.Config;
import org.openstreetmap.josm.tools.Logging;
import org.openstreetmap.josm.tools.Utils;
import org.xml.sax.SAXException;

/**
 * Manages the list of imagery entries that are shown in the imagery menu.
 */
public class ImageryLayerInfo {

    /** Unique instance */
    public static final ImageryLayerInfo instance = new ImageryLayerInfo();
    /** List of all usable layers */
    private final List<ImageryInfo> layers = new ArrayList<>();
    /** List of layer ids of all usable layers */
    private final Map<String, ImageryInfo> layerIds = new HashMap<>();
    /** List of all available default layers */
    private static final List<ImageryInfo> defaultLayers = new ArrayList<>();
    /** List of all available default layers (including mirrors) */
    private static final List<ImageryInfo> allDefaultLayers = new ArrayList<>();
    /** List of all layer ids of available default layers (including mirrors) */
    private static final Map<String, ImageryInfo> defaultLayerIds = new HashMap<>();

    private static final String[] DEFAULT_LAYER_SITES = {
        Main.getJOSMWebsite()+"/maps%<?ids=>"
    };

    /**
     * Returns the list of imagery layers sites.
     * @return the list of imagery layers sites
     * @since 7434
     */
    public static Collection<String> getImageryLayersSites() {
        return Config.getPref().getList("imagery.layers.sites", Arrays.asList(DEFAULT_LAYER_SITES));
    }

    private ImageryLayerInfo() {
    }

    /**
     * Constructs a new {@code ImageryLayerInfo} from an existing one.
     * @param info info to copy
     */
    public ImageryLayerInfo(ImageryLayerInfo info) {
        layers.addAll(info.layers);
    }

    /**
     * Clear the lists of layers.
     */
    public void clear() {
        layers.clear();
        layerIds.clear();
    }

    /**
     * Loads the custom as well as default imagery entries.
     * @param fastFail whether opening HTTP connections should fail fast, see {@link ImageryReader#setFastFail(boolean)}
     */
    public void load(boolean fastFail) {
        clear();
        List<ImageryPreferenceEntry> entries = StructUtils.getListOfStructs(
                Config.getPref(), "imagery.entries", null, ImageryPreferenceEntry.class);
        if (entries != null) {
            for (ImageryPreferenceEntry prefEntry : entries) {
                try {
                    ImageryInfo i = new ImageryInfo(prefEntry);
                    add(i);
                } catch (IllegalArgumentException e) {
                    Logging.warn("Unable to load imagery preference entry:"+e);
                }
            }
            Collections.sort(layers);
        }
        loadDefaults(false, null, fastFail);
    }

    /**
     * Loads the available imagery entries.
     *
     * The data is downloaded from the JOSM website (or loaded from cache).
     * Entries marked as "default" are added to the user selection, if not already present.
     *
     * @param clearCache if true, clear the cache and start a fresh download.
     * @param worker executor service which will perform the loading.
     * If null, it should be performed using a {@link PleaseWaitRunnable} in the background
     * @param fastFail whether opening HTTP connections should fail fast, see {@link ImageryReader#setFastFail(boolean)}
     * @since 12634
     */
    public void loadDefaults(boolean clearCache, ExecutorService worker, boolean fastFail) {
        final DefaultEntryLoader loader = new DefaultEntryLoader(clearCache, fastFail);
        if (worker == null) {
            loader.realRun();
            loader.finish();
        } else {
            worker.execute(loader);
        }
    }

    /**
     * Loader/updater of the available imagery entries
     */
    class DefaultEntryLoader extends PleaseWaitRunnable {

        private final boolean clearCache;
        private final boolean fastFail;
        private final List<ImageryInfo> newLayers = new ArrayList<>();
        private ImageryReader reader;
        private boolean canceled;
        private boolean loadError;

        DefaultEntryLoader(boolean clearCache, boolean fastFail) {
            super(tr("Update default entries"));
            this.clearCache = clearCache;
            this.fastFail = fastFail;
        }

        @Override
        protected void cancel() {
            canceled = true;
            Utils.close(reader);
        }

        @Override
        protected void realRun() {
            for (String source : getImageryLayersSites()) {
                if (canceled) {
                    return;
                }
                loadSource(source);
            }
        }

        protected void loadSource(String source) {
            boolean online = true;
            try {
                OnlineResource.JOSM_WEBSITE.checkOfflineAccess(source, Main.getJOSMWebsite());
            } catch (OfflineAccessException e) {
                Logging.log(Logging.LEVEL_WARN, e);
                online = false;
            }
            if (clearCache && online) {
                CachedFile.cleanup(source);
            }
            try {
                reader = new ImageryReader(source);
                reader.setFastFail(fastFail);
                Collection<ImageryInfo> result = reader.parse();
                newLayers.addAll(result);
            } catch (IOException ex) {
                loadError = true;
                Logging.log(Logging.LEVEL_ERROR, ex);
            } catch (SAXException ex) {
                loadError = true;
                Logging.error(ex);
            }
        }

        @Override
        protected void finish() {
            defaultLayers.clear();
            allDefaultLayers.clear();
            defaultLayers.addAll(newLayers);
            for (ImageryInfo layer : newLayers) {
                allDefaultLayers.add(layer);
                for (ImageryInfo sublayer : layer.getMirrors()) {
                    allDefaultLayers.add(sublayer);
                }
            }
            defaultLayerIds.clear();
            Collections.sort(defaultLayers);
            Collections.sort(allDefaultLayers);
            buildIdMap(allDefaultLayers, defaultLayerIds);
            updateEntriesFromDefaults(!loadError);
            buildIdMap(layers, layerIds);
            if (!loadError && !defaultLayerIds.isEmpty()) {
                dropOldEntries();
            }
        }
    }

    /**
     * Build the mapping of unique ids to {@link ImageryInfo}s.
     * @param lst input list
     * @param idMap output map
     */
    private static void buildIdMap(List<ImageryInfo> lst, Map<String, ImageryInfo> idMap) {
        idMap.clear();
        Set<String> notUnique = new HashSet<>();
        for (ImageryInfo i : lst) {
            if (i.getId() != null) {
                if (idMap.containsKey(i.getId())) {
                    notUnique.add(i.getId());
                    Logging.error("Id ''{0}'' is not unique - used by ''{1}'' and ''{2}''!",
                            i.getId(), i.getName(), idMap.get(i.getId()).getName());
                    continue;
                }
                idMap.put(i.getId(), i);
                Collection<String> old = i.getOldIds();
                if (old != null) {
                    for (String id : old) {
                        if (idMap.containsKey(id)) {
                            Logging.error("Old Id ''{0}'' is not unique - used by ''{1}'' and ''{2}''!",
                                    i.getId(), i.getName(), idMap.get(i.getId()).getName());
                        } else {
                            idMap.put(id, i);
                        }
                    }
                }
            }
        }
        for (String i : notUnique) {
            idMap.remove(i);
        }
    }

    /**
     * Update user entries according to the list of default entries.
     * @param dropold if <code>true</code> old entries should be removed
     * @since 11706
     */
    public void updateEntriesFromDefaults(boolean dropold) {
        // add new default entries to the user selection
        boolean changed = false;
        Collection<String> knownDefaults = new TreeSet<>(Config.getPref().getList("imagery.layers.default"));
        Collection<String> newKnownDefaults = new TreeSet<>();
        for (ImageryInfo def : defaultLayers) {
            if (def.isDefaultEntry()) {
                boolean isKnownDefault = false;
                for (String entry : knownDefaults) {
                    if (entry.equals(def.getId())) {
                        isKnownDefault = true;
                        newKnownDefaults.add(entry);
                        knownDefaults.remove(entry);
                        break;
                    } else if (isSimilar(entry, def.getUrl())) {
                        isKnownDefault = true;
                        if (def.getId() != null) {
                            newKnownDefaults.add(def.getId());
                        }
                        knownDefaults.remove(entry);
                        break;
                    }
                }
                boolean isInUserList = false;
                if (!isKnownDefault) {
                    if (def.getId() != null) {
                        newKnownDefaults.add(def.getId());
                        for (ImageryInfo i : layers) {
                            if (isSimilar(def, i)) {
                                isInUserList = true;
                                break;
                            }
                        }
                    } else {
                        Logging.error("Default imagery ''{0}'' has no id. Skipping.", def.getName());
                    }
                }
                if (!isKnownDefault && !isInUserList) {
                    add(new ImageryInfo(def));
                    changed = true;
                }
            }
        }
        if (!dropold && !knownDefaults.isEmpty()) {
            newKnownDefaults.addAll(knownDefaults);
        }
        Config.getPref().putList("imagery.layers.default", new ArrayList<>(newKnownDefaults));

        // automatically update user entries with same id as a default entry
        for (int i = 0; i < layers.size(); i++) {
            ImageryInfo info = layers.get(i);
            if (info.getId() == null) {
                continue;
            }
            ImageryInfo matchingDefault = defaultLayerIds.get(info.getId());
            if (matchingDefault != null && !matchingDefault.equalsPref(info)) {
                layers.set(i, matchingDefault);
                Logging.info(tr("Update imagery ''{0}''", info.getName()));
                changed = true;
            }
        }

        if (changed) {
            save();
        }
    }

    /**
     * Drop entries with Id which do no longer exist (removed from defaults).
     * @since 11527
     */
    public void dropOldEntries() {
        List<String> drop = new ArrayList<>();

        for (Map.Entry<String, ImageryInfo> info : layerIds.entrySet()) {
            if (!defaultLayerIds.containsKey(info.getKey())) {
                remove(info.getValue());
                drop.add(info.getKey());
                Logging.info(tr("Drop old imagery ''{0}''", info.getValue().getName()));
            }
        }

        if (!drop.isEmpty()) {
            for (String id : drop) {
                layerIds.remove(id);
            }
            save();
        }
    }

    private static boolean isSimilar(ImageryInfo iiA, ImageryInfo iiB) {
        if (iiA == null)
            return false;
        if (!iiA.getImageryType().equals(iiB.getImageryType()))
            return false;
        if (iiA.getId() != null && iiB.getId() != null) return iiA.getId().equals(iiB.getId());
        return isSimilar(iiA.getUrl(), iiB.getUrl());
    }

    // some additional checks to respect extended URLs in preferences (legacy workaround)
    private static boolean isSimilar(String a, String b) {
        return Objects.equals(a, b) || (a != null && b != null && !a.isEmpty() && !b.isEmpty() && (a.contains(b) || b.contains(a)));
    }

    /**
     * Add a new imagery entry.
     * @param info imagery entry to add
     */
    public void add(ImageryInfo info) {
        layers.add(info);
    }

    /**
     * Remove an imagery entry.
     * @param info imagery entry to remove
     */
    public void remove(ImageryInfo info) {
        layers.remove(info);
    }

    /**
     * Save the list of imagery entries to preferences.
     */
    public void save() {
        List<ImageryPreferenceEntry> entries = new ArrayList<>();
        for (ImageryInfo info : layers) {
            entries.add(new ImageryPreferenceEntry(info));
        }
        StructUtils.putListOfStructs(Config.getPref(), "imagery.entries", entries, ImageryPreferenceEntry.class);
    }

    /**
     * List of usable layers
     * @return unmodifiable list containing usable layers
     */
    public List<ImageryInfo> getLayers() {
        return Collections.unmodifiableList(layers);
    }

    /**
     * List of available default layers
     * @return unmodifiable list containing available default layers
     */
    public List<ImageryInfo> getDefaultLayers() {
        return Collections.unmodifiableList(defaultLayers);
    }

    /**
     * List of all available default layers (including mirrors)
     * @return unmodifiable list containing available default layers
     * @since 11570
     */
    public List<ImageryInfo> getAllDefaultLayers() {
        return Collections.unmodifiableList(allDefaultLayers);
    }

    public static void addLayer(ImageryInfo info) {
        instance.add(info);
        instance.save();
    }

    public static void addLayers(Collection<ImageryInfo> infos) {
        for (ImageryInfo i : infos) {
            instance.add(i);
        }
        instance.save();
        Collections.sort(instance.layers);
    }

    /**
     * Get unique id for ImageryInfo.
     *
     * This takes care, that no id is used twice (due to a user error)
     * @param info the ImageryInfo to look up
     * @return null, if there is no id or the id is used twice,
     * the corresponding id otherwise
     */
    public String getUniqueId(ImageryInfo info) {
        if (info.getId() != null && layerIds.get(info.getId()) == info) {
            return info.getId();
        }
        return null;
    }
}