const DB_NAME = "upl";
const DB_VERSION = 1;
const STORE_NAME = "uploads";
const CONCURRENCY = 3;
const MAX_RETRIES = 5;
const BASE_RETRY_DELAY_MS = 500;

const fileInput = document.querySelector("#file-input");
const pickButton = document.querySelector("#pick-button");
const fileSummary = document.querySelector("#file-summary");
const fileName = document.querySelector("#file-name");
const fileSize = document.querySelector("#file-size");
const startButton = document.querySelector("#start-button");
const pauseButton = document.querySelector("#pause-button");
const resumeButton = document.querySelector("#resume-button");
const eventLog = document.querySelector("#event-log");
const progressBar = document.querySelector("#progress-bar");
const progressMeta = document.querySelector("#progress-meta");
const pendingSection = document.querySelector("#pending-section");
const pendingList = document.querySelector("#pending-list");

const state = {
  abortController: null,
  completedChunks: new Set(),
  file: null,
  fileHandle: null,
  pendingRecords: [],
  record: null,
  resumeAfterReselect: null,
  running: false,
};

const dbReady = "indexedDB" in window ? openDatabase() : Promise.resolve(null);
let saveChain = Promise.resolve();

function formatBytes(bytes) {
  const formatter = new Intl.NumberFormat(undefined, {
    maximumFractionDigits: 1,
  });
  const units = ["B", "KiB", "MiB", "GiB", "TiB"];
  let value = bytes;
  let unit = units[0];

  for (const candidate of units) {
    unit = candidate;
    if (value < 1024 || candidate === units[units.length - 1]) {
      break;
    }
    value /= 1024;
  }

  return `${formatter.format(value)} ${unit}`;
}

function log(message) {
  const item = document.createElement("li");
  item.textContent = message;
  eventLog.prepend(item);

  while (eventLog.children.length > 8) {
    eventLog.lastElementChild.remove();
  }
}

function openDatabase() {
  return new Promise((resolve, reject) => {
    const request = indexedDB.open(DB_NAME, DB_VERSION);

    request.addEventListener("upgradeneeded", () => {
      const db = request.result;
      if (!db.objectStoreNames.contains(STORE_NAME)) {
        db.createObjectStore(STORE_NAME, { keyPath: "upload_id" });
      }
    });

    request.addEventListener("success", () => resolve(request.result));
    request.addEventListener("error", () => reject(request.error));
  }).catch((error) => {
    log(`IndexedDB unavailable: ${error.message}`);
    return null;
  });
}

function requestToPromise(request) {
  return new Promise((resolve, reject) => {
    request.addEventListener("success", () => resolve(request.result));
    request.addEventListener("error", () => reject(request.error));
  });
}

async function withStore(mode, callback) {
  const db = await dbReady;
  if (!db) {
    return null;
  }

  const transaction = db.transaction(STORE_NAME, mode);
  return requestToPromise(callback(transaction.objectStore(STORE_NAME)));
}

async function loadRecords() {
  const records = (await withStore("readonly", (store) => store.getAll())) ?? [];
  records.sort((left, right) => right.updated_at.localeCompare(left.updated_at));
  state.pendingRecords = records;
  renderPendingRecords();
}

async function saveRecord(record) {
  const nextSave = saveChain.catch(() => null).then(() => writeRecord(record));
  saveChain = nextSave;
  await nextSave;
}

async function writeRecord(record) {
  const storedRecord = { ...record, updated_at: new Date().toISOString() };
  try {
    await withStore("readwrite", (store) => store.put(storedRecord));
  } catch (error) {
    if (!storedRecord.file_handle) {
      throw error;
    }

    delete storedRecord.file_handle;
    await withStore("readwrite", (store) => store.put(storedRecord));
    log("Saved resume state without a reusable file handle.");
  }
  state.record = storedRecord;
  await loadRecords();
}

async function deleteRecord(uploadId) {
  await withStore("readwrite", (store) => store.delete(uploadId));
  if (state.record?.upload_id === uploadId) {
    state.record = null;
  }
  await loadRecords();
}

function renderPendingRecords() {
  pendingList.replaceChildren();
  pendingSection.hidden = state.pendingRecords.length === 0;

  for (const record of state.pendingRecords) {
    const item = document.createElement("li");
    item.className = "pending-item";

    const meta = document.createElement("div");
    meta.className = "pending-meta";

    const title = document.createElement("strong");
    title.textContent = record.name;

    const detail = document.createElement("span");
    detail.textContent = `${formatBytes(record.size)} - ${record.completed_chunks ?? 0} of ${record.total_chunks} chunks`;

    const resume = document.createElement("button");
    resume.type = "button";
    resume.className = "secondary";
    resume.textContent = "Resume";
    resume.addEventListener("click", () => {
      void resumePendingRecord(record);
    });

    const remove = document.createElement("button");
    remove.type = "button";
    remove.className = "danger";
    remove.textContent = "Remove";
    remove.addEventListener("click", () => {
      void deleteRecord(record.upload_id);
    });

    meta.append(title, detail);
    item.append(meta, resume, remove);
    pendingList.append(item);
  }
}

function renderFile(file) {
  if (!file) {
    fileSummary.hidden = true;
    fileName.textContent = "";
    fileSize.textContent = "";
    return;
  }

  fileName.textContent = file.name;
  fileSize.textContent = formatBytes(file.size);
  fileSummary.hidden = false;
}

function renderButtons() {
  startButton.disabled = !state.file || state.running || Boolean(state.record);
  pauseButton.disabled = !state.running;
  resumeButton.disabled = !state.file || state.running || !state.record;
}

function updateProgress(completedCount, totalChunks) {
  const percentage = totalChunks === 0 ? 100 : (completedCount / totalChunks) * 100;
  progressBar.style.width = `${percentage}%`;
  progressMeta.textContent = `${completedCount} of ${totalChunks} chunks`;
}

function sameFile(record, file) {
  return (
    record.name === file.name &&
    record.size === file.size &&
    record.last_modified === file.lastModified
  );
}

function findPendingRecord(file) {
  return state.pendingRecords.find((record) => sameFile(record, file)) ?? null;
}

async function selectFile(file, fileHandle = null, record = null) {
  if (record && !sameFile(record, file)) {
    log("Selected file does not match the pending upload.");
    return;
  }

  state.file = file;
  state.fileHandle = fileHandle;
  state.record = record ?? findPendingRecord(file);
  state.completedChunks = new Set();

  renderFile(file);
  updateProgress(state.record?.completed_chunks ?? 0, state.record?.total_chunks ?? 0);
  renderButtons();

  log(state.record ? "Ready to resume upload." : "Ready to create an upload record.");
}

async function pickFile() {
  if ("showOpenFilePicker" in window) {
    try {
      const [handle] = await window.showOpenFilePicker({ multiple: false });
      const file = await handle.getFile();
      await selectFile(file, handle);
      return;
    } catch (error) {
      if (isAbortError(error)) {
        return;
      }
      log(`File picker failed: ${error.message}`);
    }
  }

  fileInput.click();
}

fileInput.addEventListener("change", () => {
  const [file] = fileInput.files;

  if (!file) {
    renderFile(null);
    renderButtons();
    log("Choose a file to begin.");
    return;
  }

  const record = state.resumeAfterReselect ?? findPendingRecord(file);
  state.resumeAfterReselect = null;
  void selectFile(file, null, record);
});

pickButton.addEventListener("click", () => {
  void pickFile();
});

startButton.addEventListener("click", () => {
  void runUpload();
});

pauseButton.addEventListener("click", () => {
  if (state.abortController) {
    state.abortController.abort();
  }
});

resumeButton.addEventListener("click", () => {
  void runUpload();
});

async function resumePendingRecord(record) {
  if (state.running) {
    return;
  }

  if (record.file_handle) {
    const granted = await requestFileHandlePermission(record.file_handle);
    if (granted) {
      const file = await record.file_handle.getFile();
      await selectFile(file, record.file_handle, record);
      await runUpload();
      return;
    }
  }

  state.resumeAfterReselect = record;
  log("Select the same file to resume.");
  fileInput.click();
}

async function requestFileHandlePermission(handle) {
  if (!("queryPermission" in handle) || !("requestPermission" in handle)) {
    return false;
  }

  const options = { mode: "read" };
  if ((await handle.queryPermission(options)) === "granted") {
    return true;
  }

  return (await handle.requestPermission(options)) === "granted";
}

async function runUpload() {
  if (!state.file || state.running) {
    return;
  }

  const controller = new AbortController();
  state.abortController = controller;
  state.running = true;
  renderButtons();

  try {
    if (!state.record) {
      await createUploadRecord();
    }

    const progress = await fetchJson(`/api/uploads/${state.record.upload_id}`, {
      signal: controller.signal,
    });
    state.completedChunks = new Set(progress.completed_chunks);
    await saveRecord({
      ...state.record,
      completed_chunks: state.completedChunks.size,
      chunk_size: progress.chunk_size,
      total_chunks: progress.total_chunks,
    });
    updateProgress(state.completedChunks.size, progress.total_chunks);

    const missingChunks = buildMissingChunkList(progress.total_chunks, state.completedChunks);
    log(
      missingChunks.length === 0
        ? "All chunks already uploaded."
        : `Uploading ${missingChunks.length} missing chunks.`,
    );

    await runPool(missingChunks, (index) =>
      uploadChunkWithRetry(index, progress.chunk_size, progress.total_chunks, controller.signal),
    );

    if (controller.signal.aborted) {
      return;
    }

    log("Completing upload.");
    const complete = await fetchJson(`/api/uploads/${state.record.upload_id}/complete`, {
      method: "POST",
      signal: controller.signal,
    });

    updateProgress(progress.total_chunks, progress.total_chunks);
    log(`Complete: ${complete.file_path}`);
    await deleteRecord(state.record.upload_id);
    state.completedChunks = new Set();
    state.record = null;
  } catch (error) {
    if (controller.signal.aborted || isAbortError(error)) {
      log("Upload paused.");
    } else {
      controller.abort();
      log(`Upload failed: ${error.message}`);
    }
  } finally {
    if (state.abortController === controller) {
      state.abortController = null;
    }
    state.running = false;
    renderButtons();
  }
}

async function createUploadRecord() {
  const response = await fetchJson("/api/uploads", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({
      name: state.file.name,
      size: state.file.size,
      last_modified: state.file.lastModified,
    }),
  });

  const record = {
    upload_id: response.upload_id,
    name: state.file.name,
    size: state.file.size,
    last_modified: state.file.lastModified,
    chunk_size: response.chunk_size,
    total_chunks: response.total_chunks,
    completed_chunks: 0,
    file_handle: state.fileHandle,
    updated_at: new Date().toISOString(),
  };

  await saveRecord(record);
  updateProgress(0, response.total_chunks);
  log("Upload record created.");
}

function buildMissingChunkList(totalChunks, completedChunks) {
  const missing = [];
  for (let index = 0; index < totalChunks; index += 1) {
    if (!completedChunks.has(index)) {
      missing.push(index);
    }
  }
  return missing;
}

async function uploadChunkWithRetry(index, chunkSize, totalChunks, signal) {
  for (let attempt = 0; attempt <= MAX_RETRIES; attempt += 1) {
    throwIfAborted(signal);

    try {
      await uploadChunk(index, chunkSize, signal);
      state.completedChunks.add(index);
      updateProgress(state.completedChunks.size, totalChunks);
      await saveRecord({
        ...state.record,
        completed_chunks: state.completedChunks.size,
      });
      return;
    } catch (error) {
      if (isAbortError(error) || attempt === MAX_RETRIES) {
        throw error;
      }

      const delayMs = BASE_RETRY_DELAY_MS * 2 ** attempt;
      log(`Retrying chunk ${index} after ${delayMs} ms.`);
      await delay(delayMs, signal);
    }
  }
}

async function uploadChunk(index, chunkSize, signal) {
  const start = index * chunkSize;
  const end = Math.min(state.file.size, start + chunkSize);
  const body = state.file.slice(start, end);
  const response = await fetch(`/api/uploads/${state.record.upload_id}/chunks/${index}`, {
    method: "PUT",
    headers: { "Content-Type": "application/octet-stream" },
    body,
    signal,
  });

  if (!response.ok) {
    throw new Error(await responseError(response));
  }
}

async function runPool(items, worker) {
  let nextIndex = 0;
  const workers = Array.from(
    { length: Math.min(CONCURRENCY, items.length) },
    async () => {
      while (nextIndex < items.length) {
        const item = items[nextIndex];
        nextIndex += 1;
        await worker(item);
      }
    },
  );

  await Promise.all(workers);
}

async function fetchJson(url, options = {}) {
  const response = await fetch(url, options);
  if (!response.ok) {
    throw new Error(await responseError(response));
  }
  return response.json();
}

async function responseError(response) {
  const text = await response.text();
  if (!text) {
    return `${response.status} ${response.statusText}`;
  }

  try {
    return JSON.parse(text).error ?? text;
  } catch {
    return text;
  }
}

function delay(ms, signal) {
  return new Promise((resolve, reject) => {
    throwIfAborted(signal);

    const id = window.setTimeout(resolve, ms);
    signal.addEventListener(
      "abort",
      () => {
        window.clearTimeout(id);
        reject(new DOMException("Aborted", "AbortError"));
      },
      { once: true },
    );
  });
}

function throwIfAborted(signal) {
  if (signal.aborted) {
    throw new DOMException("Aborted", "AbortError");
  }
}

function isAbortError(error) {
  return error?.name === "AbortError";
}

async function initialize() {
  await loadRecords();
  renderButtons();
}

void initialize();