const crypto = require("node:crypto");

function decodeMarker(imageBase64) {
  try {
    return Buffer.from(imageBase64, "base64").toString("utf8");
  } catch {
    return "";
  }
}

function buildInvoiceKey(markerText) {
  const duplicateMatch = markerText.match(/MOCK_DUP:([A-Za-z0-9_-]+)/);
  if (duplicateMatch?.[1]) {
    return `dup:${duplicateMatch[1]}`;
  }

  const hash = crypto.createHash("sha256").update(markerText || "mock-empty").digest("hex");
  return `hash:${hash.slice(0, 20)}`;
}

function toAmount(seedHex, fallback) {
  const value = Number.parseInt(seedHex.slice(0, 8), 16);
  if (!Number.isFinite(value)) {
    return fallback;
  }

  return ((value % 50000) / 100 + fallback).toFixed(2);
}

async function runMockOcr({ ocrType, imageBase64 }) {
  const markerText = decodeMarker(imageBase64);
  if (markerText.includes("MOCK_OCR_FAIL")) {
    throw new Error("mock_ocr_failed");
  }

  const invoiceKey = buildInvoiceKey(markerText);
  const hash = crypto.createHash("sha256").update(invoiceKey).digest("hex");
  const invoiceCode = `MOCK${hash.slice(0, 8).toUpperCase()}`;
  const invoiceNumber = hash.slice(8, 16).toUpperCase();

  return {
    invoiceCode,
    invoiceNumber,
    invoiceDate: "2026-02-08",
    amount: toAmount(hash.slice(16, 24), 100),
    taxAmount: toAmount(hash.slice(24, 32), 10),
    totalAmount: toAmount(hash.slice(32, 40), 110),
    sellerName: `Mock Seller (${ocrType})`,
    buyerName: "Mock Buyer",
    raw: {
      provider: "mock",
      invoiceKey,
      marker: markerText.slice(0, 128),
    },
  };
}

module.exports = {
  runMockOcr,
};