"use strict";

// DuskPNG – PNG export using pngjs (window.PNG)
// Falls back to canvas.toBlob if pngjs is unavailable.

const DuskPNG = (() => {
  function _pngAvailable() {
    return typeof PNG !== "undefined" && PNG.sync && typeof PNG.sync.write === "function";
  }

  // Encode RGBA pixel data into a PNG Buffer via pngjs.
  // Returns a Uint8Array (Buffer) if pngjs is available, otherwise null.
  function encode(width, height, rgbaData) {
    if(!_pngAvailable()) return null;

    const png = new PNG({ width, height });
    const src = rgbaData instanceof Uint8ClampedArray
      ? rgbaData
      : new Uint8ClampedArray(rgbaData);

    for(let i = 0; i < src.length; i++) {
      png.data[i] = src[i];
    }

    return PNG.sync.write(png); // returns a Buffer (Uint8Array subclass)
  }

  // Trigger a browser download of the RGBA data as a PNG file.
  function download(filename, width, height, rgbaData) {
    const buf = encode(width, height, rgbaData);

    if(buf) {
      // pngjs path
      const blob = new Blob([buf], { type: "image/png" });
      _triggerDownload(URL.createObjectURL(blob), filename);
    } else {
      // Canvas fallback
      const canvas = Object.assign(document.createElement("canvas"), { width, height });
      const ctx    = canvas.getContext("2d");
      const src    = rgbaData instanceof Uint8ClampedArray
        ? rgbaData
        : new Uint8ClampedArray(rgbaData);
      ctx.putImageData(new ImageData(src, width, height), 0, 0);
      canvas.toBlob(blob => _triggerDownload(URL.createObjectURL(blob), filename), "image/png");
    }
  }

  function _triggerDownload(url, filename) {
    const a = Object.assign(document.createElement("a"), { href: url, download: filename });
    a.click();
    URL.revokeObjectURL(url);
  }

  return Object.freeze({ encode, download });
})();