import ExcelJS from "exceljs";
import { todayIso } from "./format";

// Shared by every /api/export/* route: define columns once as { header, get },
// get both a semicolon CSV (Excel-DE friendly) and a real .xlsx workbook from
// the same data + column definitions. kind: "date" tells the xlsx writer to
// emit a real date cell (not a text string) for ISO ("YYYY-MM-DD") values.
export type ExportColumn<T> = {
  header: string;
  get: (row: T) => string | number | boolean | null;
  kind?: "date";
};

// CSV/Excel formula injection (CWE-1236): a cell whose text begins with
// =, +, -, or @ is interpreted as a formula by Excel/Sheets/LibreOffice on
// open, not as literal text — dangerous when the source data (employee
// names, job titles, free-text notes, audit details, ...) can contain
// attacker- or user-supplied strings. Prefixing with a single quote is the
// standard mitigation (OWASP CSV Injection cheat sheet); it forces the cell
// to render as text at the cost of a visible leading ' for the rare
// legitimate value that starts with one of these characters.
export function sanitizeForSpreadsheetCell(text: string): string {
  return /^[=+\-@]/.test(text) ? `'${text}` : text;
}

function csvCell(value: string | number | boolean | null): string {
  if (value === null || value === undefined) return "";
  const text = typeof value === "boolean" ? (value ? "Ja" : "Nein") : sanitizeForSpreadsheetCell(String(value));
  return /[";\n\r]/.test(text) ? `"${text.replace(/"/g, '""')}"` : text;
}

// Leading BOM + semicolon delimiter: Excel's German locale default, and what
// makes umlauts render correctly instead of mojibake on open.
export function toCsv<T>(rows: T[], columns: ExportColumn<T>[]): string {
  const lines = [columns.map((c) => csvCell(c.header)).join(";")];
  for (const row of rows) {
    lines.push(columns.map((c) => csvCell(c.get(row))).join(";"));
  }
  return "" + lines.join("\r\n");
}

// Anchored at UTC midnight, not local: ExcelJS converts a JS Date to an Excel
// serial straight off getTime() with no timezone adjustment, so a Date built
// at *local* midnight in a positive-offset zone (Vienna) lands on the previous
// day's serial and every date cell in the workbook renders one day early.
function parseIsoDate(value: string): Date | null {
  const d = new Date(`${value}T00:00:00Z`);
  return Number.isNaN(d.getTime()) ? null : d;
}

export async function toXlsx<T>(rows: T[], columns: ExportColumn<T>[], sheetName: string): Promise<Uint8Array> {
  const workbook = new ExcelJS.Workbook();
  const sheet = workbook.addWorksheet(sheetName.slice(0, 31));

  // Keyed by position, not by header text: split columns take their header
  // from the data (a team name, a weekday), so two columns can legitimately
  // collide — and ExcelJS silently drops the second one when two share a key.
  sheet.columns = columns.map((c, i) => ({
    header: c.header,
    key: String(i),
    width: Math.min(40, Math.max(12, c.header.length + 4)),
    style: c.kind === "date" ? { numFmt: "dd.mm.yyyy" } : undefined,
  }));
  sheet.getRow(1).font = { bold: true };
  sheet.autoFilter = { from: { row: 1, column: 1 }, to: { row: 1, column: columns.length } };
  sheet.views = [{ state: "frozen", ySplit: 1 }];

  for (const row of rows) {
    const record: Record<string, string | number | boolean | Date | null> = {};
    for (const [i, c] of columns.entries()) {
      const value = c.get(row);
      record[String(i)] =
        c.kind === "date" && typeof value === "string" && value
          ? (parseIsoDate(value) ?? value)
          : typeof value === "string"
            ? sanitizeForSpreadsheetCell(value)
            : value;
    }
    sheet.addRow(record);
  }

  const written = await workbook.xlsx.writeBuffer();
  return new Uint8Array(written);
}

// The base carries values that originate in the query string (event type,
// measure, dimension) and ends up inside a Content-Disposition header, so it
// is reduced to a filename-safe slug here rather than trusted. Callers also
// validate those params; this is the backstop that makes header injection
// impossible regardless.
export function exportFilename(base: string, format: "csv" | "xlsx"): string {
  const slug = base
    .normalize("NFKD")
    .replace(/[^a-zA-Z0-9._-]+/g, "-")
    .replace(/^-+|-+$/g, "")
    .slice(0, 80);
  return `${slug || "export"}-${todayIso()}.${format}`;
}

export function exportResponseHeaders(filename: string, format: "csv" | "xlsx"): HeadersInit {
  const contentType =
    format === "xlsx" ? "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" : "text/csv; charset=utf-8";
  return {
    "Content-Type": contentType,
    "Content-Disposition": `attachment; filename="${filename}"`,
  };
}