let thread_id = null;
let exports = null;

async function init(tid, memory, heap_base) {
    thread_id = tid;

    const result = await WebAssembly.instantiateStreaming(fetch('wasm/lod.wasm'), {
        env: { 'memory': memory }
    });

    exports = result.instance.exports;
    exports.set_sp(heap_base - thread_id * 16 * 4096); // 64K stack

    postMessage({ 'type': 'init_done' });
}

function work(indices_base, indices_count, zoom, offsets) {
    exports.do_lod(
        indices_base, indices_count, zoom,
        offsets['coords_from'],
        offsets['line_threshold'],
        offsets['xs'],
        offsets['ys'],
        offsets['pressures'],
        offsets['result_buffers'] + thread_id * 4,
        offsets['result_counts'] + thread_id * 4,
    );

    postMessage({ 'type': 'lod_done' });
}

onmessage = (e) => {
    const d = e.data;

    if (d.type === 'init') {
        init(d.thread_id, d.memory, d.heap_base);
    } else if (d.type === 'lod') {
        work(d.indices_base, d.indices_count, d.zoom, d.offsets);
    } else {
        console.error('unexpected worker command:', d.type);
    }
}