import * as downloads from './downloads.js';
import * as platform from './platform.js';

const FILE_ICONS = {
  video: '\u{1F3AC}', audio: '\u{1F3B5}', image: '\u{1F5BC}',
  document: '\u{1F4C4}', archive: '\u{1F4E6}', other: '\u{1F4CE}',
};

function formatSize(bytes) {
  if (bytes < 1024) return bytes + ' B';
  if (bytes < 1024 * 1024) return (bytes / 1024).toFixed(1) + ' KB';
  if (bytes < 1024 * 1024 * 1024) return (bytes / (1024 * 1024)).toFixed(1) + ' MB';
  return (bytes / (1024 * 1024 * 1024)).toFixed(2) + ' GB';
}

function formatDate(ts) {
  return new Date(ts * 1000).toLocaleDateString(undefined, {
    year: 'numeric', month: 'short', day: 'numeric',
  });
}

const PREVIEWABLE_TEXT =
  /\.(txt|md|json|csv|log|xml|yaml|yml|ini|conf|py|js|html|css|sh|c|h|java|rs|go|rb|toml)$/i;

function canPreview(e) {
  return ['image', 'video', 'audio', 'document'].includes(e.type)
    || PREVIEWABLE_TEXT.test(e.name);
}

const CHUNK_SIZE = 1024 * 1024;
// Segments allowed in flight while there is room to put them. This is a window,
// topped up as segments land, and not a debt released in one go: accumulating a
// credit per append and handing the lot over when the buffer finally had room
// sent 6 MB in a burst, overshot the target by a minute of film, and then said
// nothing for the next forty-six seconds. Measured in Chrome against real
// fragmented MP4. A stream that arrives in gulps has no margin for a network
// that hesitates, and looks like a hang while it is quiet.
const PIPELINE_WINDOW = 8;

/**
 * Open somewhere to write, honouring the user's download setting.
 *
 * Returns a target ({writable, name}), null for "no stream available — collect
 * it and hand the browser a blob", or false for "the person dismissed the
 * dialog", which is not an error and must not start a transfer.
 */
async function _openDownloadTarget(filename, size = 0, pickerOpts = {},
                                   swSize = size) {
  // On a desktop build this is the whole answer, and it comes first.
  //
  // The two browser paths below are both unavailable there — `showDirectoryPicker`
  // does not exist, and Chromium refuses a service worker on a custom scheme —
  // so without this the chain fell all the way through to its floor, which
  // collects the file in the page and hands the browser a blob. A gigabyte of
  // film meant a gigabyte of RAM, and a Save As dialog at the *end*.
  if (platform.capabilities.nativeSave) {
    try {
      const native = await platform.nativeSave(
        filename, { auto: downloads.getMode() === 'auto' });
      // Null means the person dismissed the dialog, which is not an error and
      // must not start a transfer.
      return native || false;
    } catch (err) {
      console.warn('[MeshBay] native save failed:', platform.bridgeMessage(err));
      return false;
    }
  }

  try {
    const target = await downloads.openTarget(filename);
    if (target) return target;
  } catch (err) {
    console.warn('[MeshBay] download folder unusable:', err.message);
  }

  // No granted folder. A service worker can still hand the browser a stream to
  // write, which is how this works at all in Firefox: the alternative there is
  // to collect gigabytes in a tab. It goes to the browser's own download
  // folder, without a dialog, which is what "save automatically" meant.
  if (downloads.getMode() === 'auto') {
    const streamed = await downloads.openStreamedDownload(filename, swSize);
    if (streamed) return streamed;
    // Nothing to stream to: small enough for memory, and no dialog.
    if (size < downloads.BLOB_LIMIT) return null;
  }

  if (!window.showSaveFilePicker) return null;
  try {
    const handle = await window.showSaveFilePicker({
      suggestedName: filename, ...pickerOpts,
    });
    return { writable: await handle.createWritable(), name: handle.name || filename };
  } catch (err) {
    if (err.name === 'AbortError') return false;
    throw err;
  }
}

/** The download of last resort, for browsers with no way to stream to disk. */
function _saveBlob(blob, filename) {
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
  URL.revokeObjectURL(url);
}

function _b64ToU8(b64) {
  const bin = atob(b64);
  const arr = new Uint8Array(bin.length);
  for (let i = 0; i < bin.length; i++) arr[i] = bin.charCodeAt(i);
  return arr;
}

async function pipelinedDownload(transport, gekKey, fileId, totalChunks, onChunk,
                                 writable, signal) {
  const results = writable ? null : new Array(totalChunks);
  let nextSend = 0, nextRecv = 0;
  const inflight = new Array(totalChunks);

  const fire = () => {
    while (nextSend < totalChunks && nextSend - nextRecv < PIPELINE_WINDOW) {
      inflight[nextSend] = transport.fetchChunk(fileId, nextSend);
      nextSend++;
    }
  };

  fire();
  while (nextRecv < totalChunks) {
    if (signal && signal.aborted) {
      const err = new Error('Cancelled');
      err.name = 'AbortError';
      throw err;
    }
    const chunkMsg = await inflight[nextRecv];
    let plaintext;
    if (gekKey && chunkMsg.ct) {
      plaintext = await window.MeshBayCrypto.decryptChunkBin(
        gekKey, fileId, nextRecv, chunkMsg.nonce, chunkMsg.ct);
    } else if (gekKey && chunkMsg.ct_b64) {
      plaintext = await window.MeshBayCrypto.decryptChunk(
        gekKey, fileId, nextRecv, chunkMsg.nonce_b64, chunkMsg.ct_b64);
    } else {
      plaintext = _b64ToU8(chunkMsg.ct_b64 || chunkMsg.data_b64);
    }
    if (writable) {
      await writable.write(plaintext);
    } else {
      results[nextRecv] = plaintext;
    }
    nextRecv++;
    fire();
    if (onChunk) onChunk(plaintext.byteLength, nextRecv, totalChunks);
  }
  return results;
}

/**
 * Download one file through the transfers widget: picks a target, streams
 * and decrypts it, and falls back to a blob when there is nowhere to stream
 * to. Shared by the Files table/toolbar and the video/preview modals' own
 * download button — both just want "get this entry to disk".
 */
async function downloadEntry(transfers, transport, gek, entry) {
  const target = await _openDownloadTarget(entry.name, entry.size);
  if (target === false) return;          // the picker was dismissed

  const openRef = { url: null };
  transfers.start({
    kind: 'download', name: (target && target.name) || entry.name,
    total: entry.size, transport,
    open: target
      ? (target.open || null)
      : () => { if (openRef.url) window.open(openRef.url, '_blank'); },
    run: async ({ signal, onProgress }) => {
      const totalChunks = Math.ceil(entry.size / CHUNK_SIZE);
      let done = 0;
      const onChunk = (bytes) => { done += bytes; onProgress(done, entry.size); };

      if (target) {
        try {
          await pipelinedDownload(transport, gek, entry.id, totalChunks,
                                  onChunk, target.writable, signal);
          await target.writable.close();
        } catch (err) {
          await target.writable.abort().catch(() => {});
          throw err;
        }
      } else {
        const chunks = await pipelinedDownload(
          transport, gek, entry.id, totalChunks, onChunk, null, signal);
        const blob = new Blob(chunks);
        _saveBlob(blob, entry.name);
        openRef.url = URL.createObjectURL(blob);
      }
    },
  });
}

export {
  FILE_ICONS,
  formatSize, formatDate, PREVIEWABLE_TEXT, canPreview, CHUNK_SIZE,
  _openDownloadTarget, _saveBlob, _b64ToU8, pipelinedDownload, downloadEntry,
};