// Minimal CSV parse for a client-side dictionary upload (#TBD). Handles quoted
// fields, escaped quotes (""), embedded commas and newlines, and CRLF. Returns
// one object per data row keyed by the trimmed header cells; blank lines are
// skipped. No library needed for a dictionary of a few hundred variables.
export function parseCsv(text: string): Record<string, string>[] {
  const rows: string[][] = [];
  let field = "";
  let row: string[] = [];
  let inQuotes = false;
  const s = text.replace(/\r\n/g, "\n").replace(/\r/g, "\n");
  for (let i = 0; i < s.length; i++) {
    const c = s[i];
    if (inQuotes) {
      if (c === '"') {
        if (s[i + 1] === '"') {
          field += '"';
          i += 1;
        } else {
          inQuotes = false;
        }
      } else {
        field += c;
      }
    } else if (c === '"') {
      inQuotes = true;
    } else if (c === ",") {
      row.push(field);
      field = "";
    } else if (c === "\n") {
      row.push(field);
      rows.push(row);
      row = [];
      field = "";
    } else {
      field += c;
    }
  }
  if (field.length > 0 || row.length > 0) {
    row.push(field);
    rows.push(row);
  }
  if (rows.length === 0) return [];
  const header = rows[0].map((h) => h.trim());
  return rows
    .slice(1)
    .filter((r) => r.some((cell) => cell.trim() !== ""))
    .map((r) => {
      const record: Record<string, string> = {};
      header.forEach((h, idx) => {
        record[h] = (r[idx] ?? "").trim();
      });
      return record;
    });
}

// Minimal CSV serialization for client-side export downloads. No library
// needed for data this small (a few hundred rows, flat objects).
export function toCsv<T extends object>(rows: T[]): string {
  if (rows.length === 0) return "";
  const columns = Array.from(
    rows.reduce((set, row) => {
      Object.keys(row).forEach((k) => set.add(k));
      return set;
    }, new Set<string>()),
  );

  const escape = (value: unknown): string => {
    if (value === null || value === undefined) return "";
    const s = String(value);
    return /[",\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
  };

  const lines = [columns.join(",")];
  for (const row of rows) {
    const record = row as Record<string, unknown>;
    lines.push(columns.map((c) => escape(record[c])).join(","));
  }
  return lines.join("\n");
}

export function downloadCsv<T extends object>(filename: string, rows: T[]): void {
  const blob = new Blob([toCsv(rows)], { type: "text/csv;charset=utf-8;" });
  const url = URL.createObjectURL(blob);
  const link = document.createElement("a");
  link.href = url;
  link.download = filename;
  link.click();
  URL.revokeObjectURL(url);
}