/**
 * ip2region client for nodejs
 *
 * project: https://github.com/lionsoul2014/ip2region
 *
 * @author dongyado<dongyado@gmail.com>
 * */
var fs   = require('fs');

var ipbase = [16777216, 65536, 256, 1]; // for ip2long
var ip2region = {};
ip2region.db_file_path   = null;
ip2region.db_fd          = null;

var totalBlocks         = 0;
var firstIndexPtr       = 0;
var lastIndexPtr        = 0;
var superBlock          = new Buffer(8);

var indexBlockLength    = 12;
var totalHeaderLength   = 4096;


/**
 * binary search
 * */
ip2region.binarySearch = function(ip)
{
    if( typeof(ip) == 'string' ) 
        ip = ip2long(ip);

    // search
    var low     = 0;
    var mid     = 0;
    var high    = totalBlocks;
    var dataPos = 0;
    var pos     = 0;
    var sip     = 0;
    var eip     = 0;
    var indexBuffer = new Buffer(12);

    // binary search
    while( low <= high ) {
        mid = ((low + high) >> 1);
        pos = firstIndexPtr + mid * indexBlockLength;
        fs.readSync(this.db_fd, indexBuffer, 0, indexBlockLength, pos);
        sip = getLong(indexBuffer, 0);

        //console.log( ' sip : ' + sip + ' eip : ' + eip );
        if ( ip < sip) {
            high = mid - 1;
        } else {
            eip = getLong(indexBuffer, 4);
            if ( ip > eip ) {
                low = mid + 1;
            } else {
                dataPos = getLong(indexBuffer, 8);
                break;
            }
        }
    }

    // read data
    if (dataPos == 0) return null;
    var dataLen = ((dataPos >> 24) & 0xFF);
    var dataPos = (dataPos & 0x00FFFFFF);
    var dataBuffer = new Buffer(dataLen);

    fs.readSync(this.db_fd, dataBuffer, 0, dataLen, dataPos);

    var city_id = getLong(dataBuffer, 0);
    var data    = dataBuffer.toString('utf8', 4, dataLen);

    //console.log(city_id);
    //console.log(data);

    return { city: city_id, region: data };
}


/**
 * btree search
 * */
ip2region.btreeSearch = function(ip) 
{
    return ip2long(ip);
}


/**
 * convert ip to long (xxx.xxx.xxx.xxx to a integer)
 * */
function ip2long(ip)
{
    var val = 0;
    ip.split('.').forEach(function(ele, i){
        val += ipbase[i] * ele;
    }); 

    return val;
}


/**
 * get long value from buffer with specified offset
 * */
function getLong(buffer, offset) 
{
    var val =  (   
        (buffer[offset] & 0x000000FF) | 
        ((buffer[offset + 1] <<  8) & 0x0000FF00) | 
        ((buffer[offset + 2] << 16) & 0x00FF0000) |
        ((buffer[offset + 3] << 24) & 0xFF000000)
    );

    // convert to unsigned int
    if (val < 0) {
        val = val >>> 0;
    }
    return val;
}


// api for create
exports.create = function(db_path) {

    // db file check
    if (typeof(db_path) == "undefined" || fs.exists(db_path) ) {
        throw("[ip2region] db file not exists : " + db_path);
    }
    
    ip2region.db_file_path = db_path; 

    try {
        ip2region.db_fd = fs.openSync(ip2region.db_file_path, 'r');
    } catch(e) {
        throw("[ip2region] Can not open ip2region.db file , path : "
                + ip2region.db_file_path);
    }

    // init basic search environment
    if (totalBlocks == 0) {
        fs.readSync(ip2region.db_fd, superBlock, 0, 8, 0);
        firstIndexPtr = getLong(superBlock, 0);
        lastIndexPtr  = getLong(superBlock, 4);
        totalBlocks   = (lastIndexPtr - firstIndexPtr) 
                            / indexBlockLength + 1;
    }

    return ip2region;
}


// api for destroy
exports.destroy = function(ip2rObj){
    ip2rObj.db_file_path = null;
    fs.closeSync(ip2rObj.db_fd);
}