pwaLUPMIS2/src/zip-store.js

/**
 * zip-store.js — a minimal, dependency-free STORED (uncompressed) ZIP writer.
 *
 * Extracted from analysis/xlsx.js so the shapefile writer can share it. Both
 * produce small archives (a few analysis rows, a handful of drawn features)
 * where DEFLATE would save nothing worth a compression dependency, and every
 * reader — Excel, QGIS, GDAL, unzip — accepts stored entries.
 *
 *   zipStore({ 'a/b.txt': 'hello', 'a/c.bin': new Uint8Array([1, 2]) })
 *
 * Values may be strings (encoded UTF-8), Uint8Array, or ArrayBuffer.
 */

const CRC_TABLE = (() => {
  const t = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) c = (c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1);
    t[n] = c >>> 0;
  }
  return t;
})();

function crc32(bytes) {
  let c = 0xFFFFFFFF;
  for (let i = 0; i < bytes.length; i++) c = CRC_TABLE[(c ^ bytes[i]) & 0xFF] ^ (c >>> 8);
  return (c ^ 0xFFFFFFFF) >>> 0;
}

function toBytes(enc, value) {
  if (value instanceof Uint8Array) return value;
  if (value instanceof ArrayBuffer) return new Uint8Array(value);
  if (ArrayBuffer.isView(value)) {
    return new Uint8Array(value.buffer, value.byteOffset, value.byteLength);
  }
  return enc.encode(String(value));
}

/**
 * Pack files (path → string | Uint8Array | ArrayBuffer) into an uncompressed
 * ZIP Blob.
 *
 * @param {Record<string, string|Uint8Array|ArrayBuffer>} files
 * @param {string} [mimeType] Blob type for the result.
 * @returns {Blob}
 */
export function zipStore(files, mimeType = 'application/zip') {
  const enc = new TextEncoder();
  const entries = Object.entries(files).map(([name, value]) => {
    const nameBytes = enc.encode(name);
    return {
      nameBytes,
      data: toBytes(enc, value),
      // Bit 11 declares the name is UTF-8. Only set when it matters, so
      // pure-ASCII archives keep byte-for-byte the output xlsx.js had before.
      flags: nameBytes.length === name.length ? 0 : 0x0800,
    };
  });

  // DOS time/date — a fixed timestamp keeps output deterministic.
  const time = 0, date = ((2020 - 1980) << 9) | (1 << 5) | 1;

  const chunks = [];
  const central = [];
  let offset = 0;

  const u16 = (v) => [v & 0xFF, (v >>> 8) & 0xFF];
  const u32 = (v) => [v & 0xFF, (v >>> 8) & 0xFF, (v >>> 16) & 0xFF, (v >>> 24) & 0xFF];

  for (const e of entries) {
    const crc = crc32(e.data);
    const size = e.data.length;
    const local = [
      ...u32(0x04034b50), ...u16(20), ...u16(e.flags), ...u16(0),
      ...u16(time), ...u16(date), ...u32(crc), ...u32(size), ...u32(size),
      ...u16(e.nameBytes.length), ...u16(0),
    ];
    chunks.push(new Uint8Array(local), e.nameBytes, e.data);

    central.push([
      ...u32(0x02014b50), ...u16(20), ...u16(20), ...u16(e.flags), ...u16(0),
      ...u16(time), ...u16(date), ...u32(crc), ...u32(size), ...u32(size),
      ...u16(e.nameBytes.length), ...u16(0), ...u16(0), ...u16(0), ...u16(0),
      ...u32(0), ...u32(offset),
    ]);
    central.push(e.nameBytes);
    offset += local.length + e.nameBytes.length + size;
  }

  const cdParts = [];
  let cdSize = 0;
  for (const part of central) {
    const arr = part instanceof Uint8Array ? part : new Uint8Array(part);
    cdParts.push(arr); cdSize += arr.length;
  }
  const end = new Uint8Array([
    ...u32(0x06054b50), ...u16(0), ...u16(0),
    ...u16(entries.length), ...u16(entries.length),
    ...u32(cdSize), ...u32(offset), ...u16(0),
  ]);

  return new Blob([...chunks, ...cdParts, end], { type: mimeType });
}

/** Trigger a browser download of a Blob. */
export function downloadBlob(blob, filename) {
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url; a.download = filename;
  document.body.appendChild(a); a.click(); a.remove();
  setTimeout(() => URL.revokeObjectURL(url), 1000);
}