/**
 * Structured PO number generator.
 * Format: COMPANY_CODE/VESSEL_CODE/PO_ID/FY
 *   - COMPANY_CODE: company.code (fallback "PMS")
 *   - VESSEL_CODE:  vessel.code  (fallback "GEN")
 *   - PO_ID:        globally sequential integer, starting from 200
 *   - FY:           Indian financial year "XXYY" e.g. "2526" for Apr 2025–Mar 2026
 *
 * Example: PMS/HNR1/200/2526
 */

import { db } from "@/lib/db";

/** Indian financial year string. April–March cycle. */
function currentFY(): string {
  const now = new Date();
  const month = now.getMonth() + 1; // 1-indexed
  const year = now.getFullYear();
  const fyStart = month >= 4 ? year : year - 1;
  const fyEnd = fyStart + 1;
  return `${fyStart}-${String(fyEnd).slice(-2)}`;
}

/** Find the next sequential PO ID (min 200) by scanning existing structured PO numbers. */
async function nextPoId(): Promise<number> {
  const pos = await db.purchaseOrder.findMany({ select: { poNumber: true } });
  // Floor at 8999 so the first generated ID is 9000, avoiding clashes with
  // imported POs that retain their original IDs (which typically start from 1).
  let maxId = 8999;
  for (const { poNumber } of pos) {
    const parts = poNumber.split("/");
    if (parts.length === 4) {
      const n = parseInt(parts[2], 10);
      if (!isNaN(n) && n > maxId) maxId = n;
    }
  }
  return maxId + 1;
}

/**
 * Generate a structured PO number.
 * Pass vesselId and companyId so we can resolve their codes from the DB.
 * Either may be null — sensible defaults are used.
 */
export async function generatePoNumber(
  vesselId?: string | null,
  companyId?: string | null,
): Promise<string> {
  const [vessel, company, id] = await Promise.all([
    vesselId  ? db.vessel .findUnique({ where: { id: vesselId  }, select: { code: true } }) : null,
    companyId ? db.company.findUnique({ where: { id: companyId }, select: { code: true } }) : null,
    nextPoId(),
  ]);

  const companyCode = company?.code ?? "PMS";
  const vesselCode  = vessel?.code  ?? "GEN";
  const fy = currentFY();

  return `${companyCode}/${vesselCode}/${id}/${fy}`;
}

/** Parse a structured PO number into its parts. Returns null for old-format numbers. */
export function parsePoNumber(poNumber: string): {
  companyCode: string;
  vesselCode: string;
  poId: number;
  fy: string;
} | null {
  const parts = poNumber.split("/");
  if (parts.length !== 4) return null;
  const poId = parseInt(parts[2], 10);
  if (isNaN(poId)) return null;
  return { companyCode: parts[0], vesselCode: parts[1], poId, fy: parts[3] };
}