import type { Attachment } from "@root/model/attachment";

type ReadFileFormat = "text" | "url" | "array" | "binary";

type ReadFileOption<T extends ReadFileFormat> = T extends "text" | "url"
  ? Promise<string>
  : T extends "array"
  ? Promise<ArrayBuffer>
  : T extends "binary"
  ? Promise<Attachment>
  : Promise<null>;

export const readFile = <T extends ReadFileFormat>(
  file: File,
  format?: T
): ReadFileOption<T> => <ReadFileOption<T>>new Promise((resolve, reject) => {
    const reader = new FileReader();

    switch (format) {
      case "text":
        reader.readAsText(file);
        break;

      case "url":
        reader.readAsDataURL(file);
        break;

      case "array":
        reader.readAsArrayBuffer(file);
        break;

      case "binary":
        reader.readAsBinaryString(file);
        break;

      default:
        reader.readAsText(file);
        break;
    }

    reader.onload = (): void => {
      if (!reader.result) {
        return reject(new Error("File is empty"));
      }

      if (format === "binary") {
        return resolve({
          name: file.name,
          content: reader.result as "string",
          mimetype: file.type,
        });
      }

      return resolve(reader.result);
    };

    reader.onerror = (): void => reject(new Error("Data conversion error"));
  });