self.onmessage = function (e) {
    var d = e.data;
    if (d.type === 'loadLib') {
        try { importScripts(d.libUrl); } catch (err) {
            self.postMessage({ type: 'error', message: 'importScripts: ' + (err && err.message || err) }); return;
        }
        if (typeof self.occtimportjs !== 'function') {
            self.postMessage({ type: 'error', message: 'STEP parser not found.' }); return;
        }
        self.occtimportjs({ locateFile: function () { return 'occt.wasm'; }, wasmBinary: d.wasm }).then(function (occt) {
            self.occt = occt;
            self.postMessage({ type: 'ready' });
        }).catch(function (err) {
            self.postMessage({ type: 'error', message: 'STEP init: ' + (err && err.message || err) });
        });
        return;
    }
    if (d.type === 'parse' && self.occt) {
        try {
            var result = self.occt.ReadStepFile(d.data, d.params);
            var meshes = [];
            (result.meshes || []).forEach(function (m) {
                if (!m.attributes || !m.attributes.position) return;
                var out = { position: m.attributes.position.array, color: m.color };
                if (m.attributes.index && m.attributes.index.array) out.index = m.attributes.index.array;
                meshes.push(out);
            });
            var transfer = [];
            meshes.forEach(function (m) {
                if (m.position && m.position.buffer) transfer.push(m.position.buffer);
                if (m.index && m.index.buffer) transfer.push(m.index.buffer);
            });
            self.postMessage({ type: 'done', success: !!result.success, meshes: meshes }, transfer);
        } catch (err) {
            self.postMessage({ type: 'error', message: 'parse: ' + (err && err.message || err) });
        }
    }
};