export type CsvRow = Record<string, string>;

export type ParsedCsv = { header: string[]; rows: CsvRow[] };

export type CustomerInput = { name: string; email: string; company: string; status: string };
export type ImportResult = {
  total: number;
  valid: CustomerInput[];
  errors: { row: number; message: string }[];
  duplicatesInFile: number[];
};

const KNOWN_STATUSES = ['active', 'lead', 'churned'];

/** Minimal RFC4180-ish CSV parser: quoted fields, escaped quotes, CRLF. */
export function parseCsv(text: string): ParsedCsv {
  const rows: string[][] = [];
  let field = '';
  let row: string[] = [];
  let inQuotes = false;
  const src = text.replace(/\r\n?/g, '\n');

  for (let i = 0; i < src.length; i++) {
    const ch = src[i];
    if (inQuotes) {
      if (ch === '"') {
        if (src[i + 1] === '"') {
          field += '"';
          i++;
        } else inQuotes = false;
      } else field += ch;
    } else if (ch === '"') {
      inQuotes = true;
    } else if (ch === ',') {
      row.push(field);
      field = '';
    } else if (ch === '\n') {
      row.push(field);
      rows.push(row);
      row = [];
      field = '';
    } else field += ch;
  }
  if (field.length > 0 || row.length > 0) {
    row.push(field);
    rows.push(row);
  }

  const cleaned = rows.filter((r) => r.some((c) => c.trim() !== ''));
  const first = cleaned[0];
  if (!first) return { header: [], rows: [] };
  const header = first.map((h) => h.trim().toLowerCase());
  const out: CsvRow[] = cleaned.slice(1).map((r) => {
    const obj: CsvRow = {};
    header.forEach((h, idx) => (obj[h] = (r[idx] ?? '').trim()));
    return obj;
  });
  return { header, rows: out };
}

const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

/** Validate parsed rows for the customer import: required columns, email shape, status enum. */
export function validateCustomerRows(rows: CsvRow[]): ImportResult {
  const errors: { row: number; message: string }[] = [];
  const valid: CustomerInput[] = [];
  const seen = new Map<string, number>();
  const duplicatesInFile: number[] = [];

  rows.forEach((row, idx) => {
    const line = idx + 2; // 1-based + header
    const name = (row.name ?? '').trim();
    const email = (row.email ?? '').trim().toLowerCase();
    const company = (row.company ?? '').trim();
    const status = (row.status ?? 'active').trim().toLowerCase() || 'active';

    if (!name) {
      errors.push({ row: line, message: 'name is required' });
      return;
    }
    if (!email || !EMAIL_RE.test(email)) {
      errors.push({ row: line, message: `invalid email "${row.email ?? ''}"` });
      return;
    }
    if (!KNOWN_STATUSES.includes(status)) {
      errors.push({ row: line, message: `unknown status "${status}" (use ${KNOWN_STATUSES.join('/')})` });
      return;
    }
    const priorLine = seen.get(email);
    if (priorLine !== undefined) {
      duplicatesInFile.push(line);
      return;
    }
    seen.set(email, line);
    valid.push({ name, email, company, status });
  });

  return { total: rows.length, valid, errors, duplicatesInFile };
}

export function toCsv(rows: Record<string, unknown>[], columns: string[]): string {
  const escape = (v: unknown) => {
    const s = v === null || v === undefined ? '' : String(v);
    return /[",\n]/.test(s) ? `"${s.replace(/"/g, '""')}"` : s;
  };
  return [columns.join(','), ...rows.map((r) => columns.map((c) => escape(r[c])).join(','))].join('\n');
}