//坐标转换
//WGS84：为一种大地坐标系，也是目前广泛使用的GPS全球卫星定位系统使用的坐标系。
//GCJ02：又称火星坐标系，是由中国国家测绘局制订的地理信息系统的坐标系统。由WGS84坐标系经加密后的坐标系
//BD09：为百度坐标系，在GCJ02坐标系基础上再次加密。其中bd09ll表示百度经纬度坐标，bd09mc表示百度墨卡托米制（mercator）坐标。
//h5在微信浏览器里、uniapp是使用 gcj02 国测局坐标系
//WGS84  GCJ02  BD09
const PI = 3.14159265358979324;
const x_pi = 3.14159265358979324 * 3000.0 / 180.0;
const delta = (lat, lon) => {
    // Krasovsky 1940
    //
    // a = 6378245.0, 1/f = 298.3
    // b = a * (1 - f)
    // ee = (a^2 - b^2) / a^2;
    var a = 6378245.0; //  a: 卫星椭球坐标投影到平面地图坐标系的投影因子。
    var ee = 0.00669342162296594323; //  ee: 椭球的偏心率。
    var dLat =  transformLat(lon - 105.0, lat - 35.0);
    var dLon =  transformLon(lon - 105.0, lat - 35.0);
    var radLat = lat / 180.0 *  PI;
    var magic = Math.sin(radLat);
    magic = 1 - ee * magic * magic;
    var sqrtMagic = Math.sqrt(magic);
    dLat = (dLat * 180.0) / ((a * (1 - ee)) / (magic * sqrtMagic) *  PI);
    dLon = (dLon * 180.0) / (a / sqrtMagic * Math.cos(radLat) *  PI);
    return {
        'lat': dLat,
        'lon': dLon
    };
}

//WGS-84 to GCJ-02
const gcj_encrypt = (wgsLat, wgsLon) => {
    if ( outOfChina(wgsLat, wgsLon))
        return {
            'lat': wgsLat,
            'lon': wgsLon
        };

    var d =  delta(wgsLat, wgsLon);
    return {
        'lat': wgsLat + d.lat,
        'lon': wgsLon + d.lon
    };
}

//GCJ-02 to WGS-84
const gcj_decrypt_To_wgs = (gcjLat, gcjLon) => {
    if ( outOfChina(gcjLat, gcjLon))
        return {
            'lat': gcjLat,
            'lon': gcjLon
        };

    var d =  delta(gcjLat, gcjLon);
    return {
        'lat': gcjLat - d.lat,
        'lon': gcjLon - d.lon
    };
}

//GCJ-02 to WGS-84 exactly
const gcj_decrypt_exact = (gcjLat, gcjLon) => {
    var initDelta = 0.01;
    var threshold = 0.000000001;
    var dLat = initDelta,
        dLon = initDelta;
    var mLat = gcjLat - dLat,
        mLon = gcjLon - dLon;
    var pLat = gcjLat + dLat,
        pLon = gcjLon + dLon;
    var wgsLat, wgsLon, i = 0;
    while (1) {
        wgsLat = (mLat + pLat) / 2;
        wgsLon = (mLon + pLon) / 2;
        var tmp =  gcj_encrypt(wgsLat, wgsLon)
        dLat = tmp.lat - gcjLat;
        dLon = tmp.lon - gcjLon;
        if ((Math.abs(dLat) < threshold) && (Math.abs(dLon) < threshold))
            break;

        if (dLat > 0) pLat = wgsLat;
        else mLat = wgsLat;
        if (dLon > 0) pLon = wgsLon;
        else mLon = wgsLon;

        if (++i > 10000) break;
    }
    //console.log(i);
    return {
        'lat': wgsLat,
        'lon': wgsLon
    };
}

//GCJ-02 to BD-09
const bd_encrypt = (gcjLat, gcjLon) => {
    var x = gcjLon,
        y = gcjLat;
    var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * x_pi);
    var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * x_pi);
    bdLon = z * Math.cos(theta) + 0.0065;
    bdLat = z * Math.sin(theta) + 0.006;
    return {
        'lat': bdLat,
        'lon': bdLon
    };
}
//BD-09 to GCJ-02
const bd_decrypt_To_gcj = (bdLat, bdLon) => {
    var x = bdLon - 0.0065,
        y = bdLat - 0.006;
    var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * x_pi);
    var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * x_pi);
    var gcjLon = z * Math.cos(theta);
    var gcjLat = z * Math.sin(theta);
    return {
        'lat': gcjLat,
        'lon': gcjLon
    };
}
//WGS-84 to Web mercator
//mercatorLat -> y mercatorLon -> x
const mercator_encrypt = (wgsLat, wgsLon) => {
    var x = wgsLon * 20037508.34 / 180.;
    var y = Math.log(Math.tan((90. + wgsLat) *  PI / 360.)) / ( PI / 180.);
    y = y * 20037508.34 / 180.;
    return {
        'lat': y,
        'lon': x
    };
    /*
     if ((Math.abs(wgsLon) > 180 || Math.abs(wgsLat) > 90))
     return null;
     var x = 6378137.0 * wgsLon * 0.017453292519943295;
     var a = wgsLat * 0.017453292519943295;
     var y = 3189068.5 * Math.log((1.0 + Math.sin(a)) / (1.0 - Math.sin(a)));
     return {'lat' : y, 'lon' : x};
     //*/
}
// Web mercator to WGS-84
// mercatorLat -> y mercatorLon -> x
const mercator_decrypt = (mercatorLat, mercatorLon) => {
    var x = mercatorLon / 20037508.34 * 180.;
    var y = mercatorLat / 20037508.34 * 180.;
    y = 180 /  PI * (2 * Math.atan(Math.exp(y *  PI / 180.)) -  PI / 2);
    return {
        'lat': y,
        'lon': x
    };
    /*
     if (Math.abs(mercatorLon) < 180 && Math.abs(mercatorLat) < 90)
     return null;
     if ((Math.abs(mercatorLon) > 20037508.3427892) || (Math.abs(mercatorLat) > 20037508.3427892))
     return null;
     var a = mercatorLon / 6378137.0 * 57.295779513082323;
     var x = a - (Math.floor(((a + 180.0) / 360.0)) * 360.0);
     var y = (1.5707963267948966 - (2.0 * Math.atan(Math.exp((-1.0 * mercatorLat) / 6378137.0)))) * 57.295779513082323;
     return {'lat' : y, 'lon' : x};
     //*/
}
// two point's distance
const distance = (latA, lonA, latB, lonB) => {
    var earthR = 6371000.;
    var x = Math.cos(latA *  PI / 180.) * Math.cos(latB *  PI / 180.) * Math.cos((lonA - lonB) *  PI / 180);
    var y = Math.sin(latA *  PI / 180.) * Math.sin(latB *  PI / 180.);
    var s = x + y;
    if (s > 1) s = 1;
    if (s < -1) s = -1;
    var alpha = Math.acos(s);
    var distance = alpha * earthR;
    return distance;
}
const outOfChina = (lat, lon) => {
    if (lon < 72.004 || lon > 137.8347)
        return true;
    if (lat < 0.8293 || lat > 55.8271)
        return true;
    return false;
}
const transformLat = (x, y) => {
    var ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x *  PI) + 20.0 * Math.sin(2.0 * x *  PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(y *  PI) + 40.0 * Math.sin(y / 3.0 *  PI)) * 2.0 / 3.0;
    ret += (160.0 * Math.sin(y / 12.0 *  PI) + 320 * Math.sin(y *  PI / 30.0)) * 2.0 / 3.0;
    return ret;
}
const transformLon = (x, y) => {
    var ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x));
    ret += (20.0 * Math.sin(6.0 * x *  PI) + 20.0 * Math.sin(2.0 * x *  PI)) * 2.0 / 3.0;
    ret += (20.0 * Math.sin(x *  PI) + 40.0 * Math.sin(x / 3.0 *  PI)) * 2.0 / 3.0;
    ret += (150.0 * Math.sin(x / 12.0 *  PI) + 300.0 * Math.sin(x / 30.0 *  PI)) * 2.0 / 3.0;
    return ret;
}


module.exports = {
    bd_decrypt_To_gcj : bd_decrypt_To_gcj ,
    gcj_decrypt_To_wgs : gcj_decrypt_To_wgs ,
}