// Client-side parser for .npy files
// See the specification: http://docs.scipy.org/doc/numpy-dev/neps/npy-format.html

const NumpyLoader = (function NumpyLoader() {
    function asciiDecode(buf) {
        return String.fromCharCode.apply(null, new Uint8Array(buf));
    }

    function readUint16LE(buffer) {
        var view = new DataView(buffer);
        var val = view.getUint8(0);
        val |= view.getUint8(1) << 8;
        return val;
    }

    function fromArrayBuffer(buf) {
      // Check the magic number
      var magic = asciiDecode(buf.slice(0,6));
      if (magic !== "\x93NUMPY") {
          throw new Error("Bad magic number");
      }

      var version = new Uint8Array(buf.slice(6,8)),
          headerLength = readUint16LE(buf.slice(8,10)),
          headerStr = asciiDecode(buf.slice(10, 10+headerLength));
      const offsetBytes = 10 + headerLength;
          //rest = buf.slice(10+headerLength);  XXX -- This makes a copy!!! https://www.khronos.org/registry/typedarray/specs/latest/#5

      // Hacky conversion of dict literal string to JS Object
      const info = JSON.parse(headerStr.toLowerCase()
                              .replace('(','[')
                              .replace('),',']')
                              .replace(/'/g, '"')
                              .replace(',]', ']'));

      // Intepret the bytes according to the specified dtype
      var data;
      if (info.descr === "|u1") {
          data = new Uint8Array(buf, offsetBytes);
      } else if (info.descr === "|i1") {
          data = new Int8Array(buf, offsetBytes);
      } else if (info.descr === "<u2") {
          data = new Uint16Array(buf, offsetBytes);
      } else if (info.descr === "<i2") {
          data = new Int16Array(buf, offsetBytes);
      } else if (info.descr === "<u4") {
          data = new Uint32Array(buf, offsetBytes);
      } else if (info.descr === "<i4") {
          data = new Int32Array(buf, offsetBytes);
      } else if (info.descr === "<f4") {
          data = new Float32Array(buf, offsetBytes);
      } else if (info.descr === "<f8") {
          data = new Float64Array(buf, offsetBytes);
      } else if (info.descr === "<u8") {
          // 8 byte uint64s
          data = new Uint8Array(buf, offsetBytes);
      } else if (info.descr === "<i8") {
          // 8 byte int64s
          data = new Uint8Array(buf, offsetBytes);
      } else if (info.descr === "|s8") {
          // 8 byte strings
          data = new Uint8Array(buf, offsetBytes);
      } else {
          throw new Error('unknown numeric dtype '+info.descr)
      }

      return {
          shape: info.shape,
          fortran_order: info.fortran_order,
          data: data
      };
    }

    function open(file, callback) {
        var reader = new FileReader();
        reader.onload = function() {
            // the file contents have been read as an array buffer
            var buf = reader.result;
            var ndarray = fromArrayBuffer(buf);
            callback(ndarray);
        };
        reader.readAsArrayBuffer(file);
    }

    function promise(url) {
      return new Promise(function(resolve, reject) {
        // Do the usual XHR stuff
        var req = new XMLHttpRequest();
        req.onload = function() {
          // This is called even on 404 etc
          // so check the status
          if (req.status == 200) {
            var buf = req.response; // not responseText
            var ndarray = fromArrayBuffer(buf);
            resolve(ndarray);
          } else {
            // Otherwise reject with the status text
            // which will hopefully be a meaningful error
            reject(Error(req.statusText));
          }
        };

        // Handle network errors
        req.onerror = function() {
          reject(Error("Network Error"));
        };

        // Make the request
        req.open('GET', url, true);
        req.responseType = "arraybuffer";
        req.send(null);
      });
    }

    return {
        open: open,
        promise: promise,
        fromArrayBuffer: fromArrayBuffer,
    };
})();

module.exports = NumpyLoader;