export const DOCX_MIME_TYPE = "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
export const XLSX_MIME_TYPE = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
export const PPTX_MIME_TYPE = "application/vnd.openxmlformats-officedocument.presentationml.presentation";
export const EML_MIME_TYPE = "message/rfc822;charset=utf-8";

const pathSeparatorPattern = /[/\\]/;

export function officeTitleFromFileName(fileName: string, fallbackTitle: string) {
  const trimmed = fileName.trim();
  if (!trimmed) {
    return fallbackTitle;
  }

  const parts = trimmed.split(pathSeparatorPattern).filter(Boolean);
  return parts[parts.length - 1] ?? fallbackTitle;
}

export function replaceFileExtension(fileName: string, extension: string) {
  const normalizedExtension = extension.startsWith(".") ? extension : `.${extension}`;
  const baseName = fileName.trim() || "Документ";
  const withoutExtension = baseName.replace(/\.[^.\\/]+$/, "");

  return `${withoutExtension}${normalizedExtension}`;
}

export async function readOfficeFileAsArrayBuffer(file: File) {
  if (typeof file.arrayBuffer !== "function") {
    return readFileWithFileReader(file);
  }

  return file.arrayBuffer();
}

function readFileWithFileReader(file: File): Promise<ArrayBuffer> {
  if (typeof FileReader === "undefined") {
    throw new Error("Не удалось прочитать файл: среда не поддерживает File.arrayBuffer() и FileReader.");
  }

  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.onerror = () => reject(new Error("Не удалось прочитать файл."));
    reader.onload = () => {
      if (reader.result instanceof ArrayBuffer) {
        resolve(reader.result);
        return;
      }

      reject(new Error("Не удалось прочитать файл как ArrayBuffer."));
    };
    reader.readAsArrayBuffer(file);
  });
}