const is_ra_dec = 1;
const crpix = [11924.5, 16791.5];
const crval = [53.12278110761878, -27.80516045555555];
const cdmatrix = [[-8.331872359085824e-06, 8.484786942893281e-13], [7.247535904753022e-13, 8.331873001310441e-06]];

urlParam = function(name){
    // Parse parameters from window.location,,
    // e.g., .../index.html?zoom=8,
    // urlParam(zoom) = 8,
    var results = new RegExp('[\?&]' + name + '=([^&#]*)').exec(window.location.href);
    if (results==null){
        return null;
    }
    else{
        return decodeURI(results[1]) || 0;
    }
}

pixToSky = function(xy){
    // Convert from zero-index pixel to sky coordinate assuming
    // simple North-up WCS
    if (xy.hasOwnProperty('lng')){
        var dx = xy.lng - crpix[0] + 1;
        var dy = xy.lat - crpix[1] + 1;
    } else {
        var dx = xy[0] - crpix[0] + 1;
        var dy = xy[1] - crpix[1] + 1;
    }
    var dra = dx * cdmatrix[0][0];
    var ddec = dy * cdmatrix[1][1];
    // some catalogs are stored in image coords x/y, not ra/dec. When
    // `is_ra_dec`==1 we are doing calculation in ra/dec when `is_ra_dec`==0
    // then we're working in image coords and so multiply by 0 so
    // cos(0)==1
    var ra = crval[0] + dra / Math.cos(crval[1]/180*3.14159 * is_ra_dec);
    var dec = crval[1] + ddec;
    return [ra, dec];
}

skyToPix = function(rd){
    // Convert from sky to zero-index pixel coordinate assuming
    // simple North-up WCS
    var dx = (rd[0] - crval[0]) * Math.cos(crval[1]/180*3.14159 * is_ra_dec);
    var dy = (rd[1] - crval[1]);
    var x = crpix[0] - 1 + dx / cdmatrix[0][0];
    var y = crpix[1] - 1 + dy / cdmatrix[1][1];
    return [x,y];
}

skyToLatLng = function(rd){
    // Convert from sky to Leaflet.latLng coordinate assuming
    // simple North-up WCS
    var xy = skyToPix(rd);
    return L.latLng(xy[1], xy[0]);
}

panToSky = function(rd, zoom, map){
    // Pan map to celestial coordinates
    var ll = skyToLatLng(rd)
    map.setZoom(zoom);
    map.panTo(ll, zoom);
    //console.log('pan to: ' + rd + ' / ll: ' + ll.lng + ',' + ll.lat);
}

panFromUrl = function(map){
    // Pan map based on ra/dec/[zoom] variables in location bar
    var ra = urlParam('ra');
    var dec = urlParam('dec');
    var zoom = urlParam('zoom') || map.getMinZoom();
    if ((ra !== null) & (dec !== null)) {
        panToSky([ra,dec], zoom, map);
    } else {
        // Pan to crval
        panToSky(crval, zoom, map);
    }
}

updateLocationBar = function(){
    var rd = pixToSky(map.getCenter());
    //console.log(rd);
    var params = 'ra=' + rd[0].toFixed(7);
    params += '&dec=' + rd[1].toFixed(7);
    params += '&zoom=' + map.getZoom();
    //console.log(params);
    var param_url = window.location.href.split('?')[0] + '?' + params;
    window.history.pushState('', '', param_url);
}