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Standard set of models for geo coding, access control and elastic search abstraction
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package io.polyglotted.pgmodel.geo;

import lombok.Getter;
import lombok.RequiredArgsConstructor;
import lombok.experimental.Accessors;

import java.util.BitSet;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;

import static io.polyglotted.pgmodel.util.ModelUtil.jsonEquals;

@Getter
@Accessors(fluent = true)
@RequiredArgsConstructor
public final class GeoHash {

    private static int numbits = 6 * 5;
    final static char[] digits = {'0', '1', '2', '3', '4', '5', '6', '7', '8',
       '9', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'm', 'n', 'p',
       'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};

    final static Map lookup = new HashMap<>();

    static {
        int i = 0;
        for (char c : digits)
            lookup.put(c, i++);
    }

    public final GeoPoint point;

    @Override
    public boolean equals(Object o) {
        return jsonEquals(this, o);
    }

    @Override
    public int hashCode() {
        return Objects.hash(point);
    }

    @Override
    public String toString() {
        return encode(point.lat, point.lon);
    }

    public static GeoHash decodeGeoHash(String geohash) {
        StringBuilder buffer = new StringBuilder();
        for (char c : geohash.toCharArray()) {

            int i = lookup.get(c) + 32;
            buffer.append(Integer.toString(i, 2).substring(1));
        }

        BitSet lonset = new BitSet();
        BitSet latset = new BitSet();

        //even bits
        int j = 0;
        for (int i = 0; i < numbits * 2; i += 2) {
            boolean isSet = false;
            if (i < buffer.length())
                isSet = buffer.charAt(i) == '1';
            lonset.set(j++, isSet);
        }

        //odd bits
        j = 0;
        for (int i = 1; i < numbits * 2; i += 2) {
            boolean isSet = false;
            if (i < buffer.length())
                isSet = buffer.charAt(i) == '1';
            latset.set(j++, isSet);
        }

        return new GeoHash(new GeoPoint(decode(latset, -90, 90), decode(lonset, -180, 180)));
    }

    static String encode(double lat, double lon) {
        BitSet latbits = getBits(lat, -90, 90);
        BitSet lonbits = getBits(lon, -180, 180);
        StringBuilder buffer = new StringBuilder();
        for (int i = 0; i < numbits; i++) {
            buffer.append((lonbits.get(i)) ? '1' : '0');
            buffer.append((latbits.get(i)) ? '1' : '0');
        }
        return base32(Long.parseLong(buffer.toString(), 2));
    }

    private static BitSet getBits(double lat, double floor, double ceiling) {
        BitSet buffer = new BitSet(numbits);
        for (int i = 0; i < numbits; i++) {
            double mid = (floor + ceiling) / 2;
            if (lat >= mid) {
                buffer.set(i);
                floor = mid;
            } else {
                ceiling = mid;
            }
        }
        return buffer;
    }

    private static String base32(long i) {
        char[] buf = new char[65];
        int charPos = 64;
        boolean negative = (i < 0);
        if (!negative)
            i = -i;
        while (i <= -32) {
            buf[charPos--] = digits[(int) (-(i % 32))];
            i /= 32;
        }
        buf[charPos] = digits[(int) (-i)];

        if (negative)
            buf[--charPos] = '-';
        return new String(buf, charPos, (65 - charPos));
    }

    private static double decode(BitSet bs, double floor, double ceiling) {
        double mid = 0;
        for (int i = 0; i < bs.length(); i++) {
            mid = (floor + ceiling) / 2;
            if (bs.get(i))
                floor = mid;
            else
                ceiling = mid;
        }
        return mid;
    }
}