import org.springframework.dao.EmptyResultDataAccessException;
import org.springframework.jdbc.core.simple.SimpleJdbcTemplate;
import sun.misc.BASE64Decoder;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

/**
 * Extracts the customer id from a Ruby session using a cookie recived in the
 * HttpServletRequest. The environment needs to provide a SimpleJdbcTemplate
 * instance to give access to the database holding the actual session data.
 *
 */
public class RailsSessionIntegrationHelper
{
    private SimpleJdbcTemplate simpleJdbcTemplate;
    private static final String RAILS_SESSION_PROP_NAME = "customer";

    public RailsSessionIntegrationHelper(SimpleJdbcTemplate simpleJdbcTemplate)
    {
        this.simpleJdbcTemplate = simpleJdbcTemplate;
    }

    public int getCustomerId(HttpServletRequest req)
    {
        Integer customerId = (Integer)req.getSession().getAttribute("customerId");
        if (customerId != null) {
            return customerId;
        }

        String cookieKey = null;
        Cookie[] cs = req.getCookies();
        if (cs == null) {
            return 0;
        }
        for (Cookie c : cs) {
            if ("_session_id".equals(c.getName())) {
                cookieKey = c.getValue();
            }
        }
        if (cookieKey == null) {
            return 0;
        }
        String data = getSessionData(cookieKey);
        if (data == null) {
            return 0;
        }
        customerId = extractCustomerId(data);
        if (customerId > 0) {
            req.getSession().setAttribute("customerId", customerId);
        }
        return customerId;
    }



    static int extractCustomerId(String data)
    {
        byte[] bs;
        try {
            bs = new BASE64Decoder().decodeBuffer(data);
            byte[] needle = RAILS_SESSION_PROP_NAME.getBytes("US-ASCII");
            int i = at(needle, bs);
            if (i == -1) {
                return 0;
            }
            i += needle.length;

            return parseIntInQuotes(bs, i);
        } catch (IOException e) {
            throw new Error(e);
        }
    }


    static int parseIntInQuotes(byte[] data, int offset)
    {
        StringBuilder sb = new StringBuilder();
        int start = byteAt(data, (byte)'"', offset);
        if (start == -1) {
            return -1;
        }
        for (int i = start + 1; i < data.length; i++) {
            byte b = data[i];
            if (b >= '0' && b <= '9') {
                sb.append((char)b);
            } else if (b == '"') {
                return Integer.parseInt(sb.toString());
            }
        }
        return 0;
    }

    static int at(byte[] needle, byte[] haystack)
    {
        int needleOffset = 0;
        for (int i = 0; i < haystack.length; i++) {
            if (haystack[i] == needle[needleOffset]) {
                needleOffset++;
                if (needleOffset >= needle.length ) {
                    return i - needle.length + 1;
                }
            } else {
                if (needleOffset > 0) {
                    i = i - needleOffset;
                }
                needleOffset = 0;

            }
        }
        if (needleOffset == needle.length) {
            return haystack.length - needle.length + 1;
        }
        return -1;

    }

    static int byteAt(byte[] data, byte toLookFor, int startAt)
    {
        for (int i = startAt; i < data.length; i++) {
            if (data[i] == toLookFor) {
                return i;
            }
        }
        return -1;
    }

    private String getSessionData(String key)
    {
        try {
            return simpleJdbcTemplate.queryForObject(
                    "select data from sessions where sessid = ?",
                    String.class, key);
        } catch (EmptyResultDataAccessException e) {
            return null;
        }
    }

}