/*
**********************************************************************
* Copyright (c) 2003, International Business Machines
* Corporation and others.  All Rights Reserved.
**********************************************************************
* Author: Alan Liu
* Created: September 4 2003
* Since: ICU 2.8
**********************************************************************
*/
package com.ibm.icu.impl;

import java.util.Arrays;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
import java.util.TreeSet;

/**
 * This class, not to be instantiated, implements the meta-data
 * missing from the underlying core JDK implementation of time zones.
 * There are two missing features: Obtaining a list of available zones
 * for a given country (as defined by the Olson database), and
 * obtaining a list of equivalent zones for a given zone (as defined
 * by Olson links).
 *
 * This class uses a data class, ZoneMetaData, which is created by the
 * tool tz2icu.
 *
 * @author Alan Liu
 * @since ICU 2.8
 */
public final class ZoneMeta {

    /**
     * Returns a String array containing all system TimeZone IDs
     * associated with the given country.  These IDs may be passed to
     * <code>TimeZone.getTimeZone()</code> to construct the
     * corresponding TimeZone object.
     * @param a two-letter ISO 3166 country code, or <code>null</code>
     * to return zones not associated with any country
     * @return an array of IDs for system TimeZones in the given
     * country.  If there are none, return a zero-length array.
     */
    public static synchronized String[] getAvailableIDs(String country) {
        if (country == null) {
            country = "";
        }
        if (COUNTRY_MAP == null) {
            Set valid = getValidIDs();
            Set unused = new TreeSet(valid);

            ArrayList list = new ArrayList(); // reuse this below

            COUNTRY_MAP = new TreeMap();
            for (int i=0; i<ZoneMetaData.COUNTRY.length; ++i) {
                String[] z = ZoneMetaData.COUNTRY[i];

                // Add all valid IDs to list
                list.clear();
                for (int j=1; j<z.length; ++j) {
                    if (valid.contains(z[j])) {
                        list.add(z[j]);
                        unused.remove(z[j]);
                    }
                }
                
                COUNTRY_MAP.put(z[0], list.toArray(EMPTY));
            }

            // If there are zones in the underlying JDK that are NOT
            // in our metadata, then assign them to the non-country.
            // (Better than nothing.)
            if (unused.size() > 0) {
                list.clear();
                list.addAll(Arrays.asList((String[]) COUNTRY_MAP.get("")));
                list.addAll(unused);
                Collections.sort(list);                
                COUNTRY_MAP.put("", list.toArray(EMPTY));
            }
        }
        String[] result = (String[]) COUNTRY_MAP.get(country);
        if (result == null) {
            result = EMPTY; // per API spec
        }
        return result;
    }

    /**
     * Returns the number of IDs in the equivalency group that
     * includes the given ID.  An equivalency group contains zones
     * that behave identically to the given zone.
     *
     * <p>If there are no equivalent zones, then this method returns
     * 0.  This means either the given ID is not a valid zone, or it
     * is and there are no other equivalent zones.
     * @param id a system time zone ID
     * @return the number of zones in the equivalency group containing
     * 'id', or zero if there are no equivalent zones.
     * @see #getEquivalentID
     */
    public static synchronized int countEquivalentIDs(String id) {
        if (EQUIV_MAP == null) {
            createEquivMap();
        }
        String[] result = (String[]) EQUIV_MAP.get(id);
        return (result == null) ? 0 : result.length;
    }

    /**
     * Returns an ID in the equivalency group that includes the given
     * ID.  An equivalency group contains zones that behave
     * identically to the given zone.
     *
     * <p>The given index must be in the range 0..n-1, where n is the
     * value returned by <code>countEquivalentIDs(id)</code>.  For
     * some value of 'index', the returned value will be equal to the
     * given id.  If the given id is not a valid system time zone, or
     * if 'index' is out of range, then returns an empty string.
     * @param id a system time zone ID
     * @param index a value from 0 to n-1, where n is the value
     * returned by <code>countEquivalentIDs(id)</code>
     * @return the ID of the index-th zone in the equivalency group
     * containing 'id', or an empty string if 'id' is not a valid
     * system ID or 'index' is out of range
     * @see #countEquivalentIDs
     */
    public static synchronized String getEquivalentID(String id, int index) {
        if (EQUIV_MAP == null) {
            createEquivMap();
        }
        String[] a = (String[]) EQUIV_MAP.get(id);
        return (a != null && index >= 0 && index < a.length) ?
            a[index] : "";
    }

    /**
     * Create the equivalency map.
     */
    private static void createEquivMap() {
        EQUIV_MAP = new TreeMap();

        Set valid = getValidIDs();

        ArrayList list = new ArrayList(); // reuse this below

        for (int i=0; i<ZoneMetaData.EQUIV.length; ++i) {
            String[] z = ZoneMetaData.EQUIV[i];
            list.clear();
            for (int j=0; j<z.length; ++j) {
                if (valid.contains(z[j])) {
                    list.add(z[j]);
                }
            }
            if (list.size() > 1) {
                String[] a = (String[]) list.toArray(EMPTY);
                for (int j=0; j<a.length; ++j) {
                    EQUIV_MAP.put(a[j], a);
                }
            }
        }
    }

    private static Set getValidIDs() {
        // Construct list of time zones that are valid, according
        // to the current underlying core JDK.  We have to do this
        // at runtime since we don't know what we're running on.
        Set valid = new TreeSet();
        valid.addAll(Arrays.asList(java.util.TimeZone.getAvailableIDs()));
        return valid;
    }

    /**
     * Empty string array.
     */
    private static final String[] EMPTY = new String[0];

    /**
     * Map of country codes to zone lists.
     */
    private static Map COUNTRY_MAP = null;

    /**
     * Map of zones to equivalent zone lists.
     */
    private static Map EQUIV_MAP = null;
}