const multer = require("multer");
const { UPLOAD_DIR } = require("../config/upload.config");

const CSV_UPLOAD_FIELD = "file";

const upload = multer({
  dest: UPLOAD_DIR,
  limits: { fileSize: 10 * 1024 * 1024 },
});

function respondCsvUploadError(res, statusCode, message, extra = {}) {
  return res.status(statusCode).json({
    status: "failed",
    message,
    ...extra,
  });
}

/**
 * Parses multipart upload and sets req.file from form field "file".
 * Returns helpful errors when Swagger/Postman sends the wrong shape.
 */
function handleCsvUpload(req, res, next) {
  upload.any()(req, res, (err) => {
    if (err) {
      if (err.code === "LIMIT_FILE_SIZE") {
        return respondCsvUploadError(
          res,
          400,
          "CSV file is too large. Maximum allowed size is 10 MB."
        );
      }
      if (err.code === "LIMIT_UNEXPECTED_FILE") {
        return respondCsvUploadError(
          res,
          400,
          `Unexpected file field "${err.field}". Use form field name "${CSV_UPLOAD_FIELD}" for the CSV.`,
          { expected_field: CSV_UPLOAD_FIELD, received_field: err.field }
        );
      }
      return respondCsvUploadError(
        res,
        400,
        "Could not read uploaded file. Please upload a valid .csv file.",
        { detail: err.message }
      );
    }

    const files = Array.isArray(req.files) ? req.files : [];

    if (files.length === 0) {
      const contentType = req.headers["content-type"] || "";

      if (!contentType.includes("multipart/form-data")) {
        return respondCsvUploadError(
          res,
          400,
          "CSV upload must use multipart/form-data, not JSON.",
          {
            hint: `Send your .csv in form field "${CSV_UPLOAD_FIELD}". In Swagger: choose the file under "${CSV_UPLOAD_FIELD}" before Execute.`,
            expected_field: CSV_UPLOAD_FIELD,
            received_content_type: contentType || "(missing)",
          }
        );
      }

      return respondCsvUploadError(
        res,
        400,
        `No CSV file received. Attach a .csv file to form field "${CSV_UPLOAD_FIELD}".`,
        {
          hint:
            'In Swagger UI: click "Try it out" → use the file picker for "' +
            CSV_UPLOAD_FIELD +
            '" (e.g. hs-codes-sample.csv) → then Execute. Do not leave the file field empty.',
          expected_field: CSV_UPLOAD_FIELD,
          example_curl:
            'curl -F "file=@hs-codes-sample.csv;type=text/csv" ...',
        }
      );
    }

    const csvFile = files.find((f) => f.fieldname === CSV_UPLOAD_FIELD);

    if (!csvFile) {
      const receivedFields = [...new Set(files.map((f) => f.fieldname))];
      return respondCsvUploadError(
        res,
        400,
        `CSV must use form field "${CSV_UPLOAD_FIELD}", but received: ${receivedFields.join(", ")}.`,
        {
          hint: `Change the form field name to "${CSV_UPLOAD_FIELD}" and upload again.`,
          expected_field: CSV_UPLOAD_FIELD,
          received_fields: receivedFields,
        }
      );
    }

    if (files.length > 1) {
      return respondCsvUploadError(
        res,
        400,
        "Only one CSV file can be uploaded per request.",
        {
          hint: `Send a single file in field "${CSV_UPLOAD_FIELD}".`,
          received_file_count: files.length,
        }
      );
    }

    req.file = csvFile;
    return next();
  });
}

module.exports = { handleCsvUpload, CSV_UPLOAD_FIELD };