export type ReceiptParseResult = {
  amount: number | null;
  date: Date | null;
  subtotal: number | null;
  tax: number | null;
  vendor: string | null;
  items: ReceiptLineItem[];
  rawLines: string[];
};

export type ReceiptLineItem = {
  id: string;
  name: string;
  amount: number;
  rawLine: string;
};

const AMOUNT_PATTERNS = [
  /(?:total|amount due|balance due|grand total)[:\s]*\$?\s*([\d,]+\.\d{2})/i,
  /\$\s*([\d,]+\.\d{2})\s*(?:total|due)?/i,
  /(?:USD|CAD|EUR)\s*([\d,]+\.\d{2})/i,
];

const DATE_PATTERNS = [
  /(\d{1,2}[/.-]\d{1,2}[/.-]\d{2,4})/,
  /(\d{4}[/.-]\d{1,2}[/.-]\d{1,2})/,
];

const SUBTOTAL_PATTERNS = [
  /(?:sub\s?total|subtotal)[:\s]*\$?\s*([\d,]+\.\d{2})/i,
];

const TAX_PATTERNS = [
  /(?:tax|sales tax|hst|gst|pst|vat)[:\s]*\$?\s*([\d,]+\.\d{2})/i,
];

const NON_ITEM_LINE =
  /(?:total|subtotal|sub total|tax|tip|gratuity|change|cash|visa|mastercard|amex|discover|card|credit|debit|balance|amount due|auth|approval|terminal|merchant|receipt|order|invoice|thank|powered by)/i;

function parseAmount(text: string): number | null {
  for (const pattern of AMOUNT_PATTERNS) {
    const match = text.match(pattern);
    if (!match?.[1]) continue;
    const value = Number(match[1].replace(/,/g, ""));
    if (Number.isFinite(value) && value > 0) return value;
  }

  const amounts = [...text.matchAll(/\$\s*([\d,]+\.\d{2})/g)]
    .map((m) => Number(m[1]!.replace(/,/g, "")))
    .filter((n) => Number.isFinite(n) && n > 0);

  return amounts.length > 0 ? Math.max(...amounts) : null;
}

function parseFirstMatchingAmount(
  text: string,
  patterns: RegExp[],
): number | null {
  for (const pattern of patterns) {
    const match = text.match(pattern);
    if (!match?.[1]) continue;
    const value = Number(match[1].replace(/,/g, ""));
    if (Number.isFinite(value) && value >= 0) return value;
  }
  return null;
}

function parseDate(text: string): Date | null {
  for (const pattern of DATE_PATTERNS) {
    const match = text.match(pattern);
    if (!match?.[1]) continue;
    const parsed = new Date(match[1]);
    if (!Number.isNaN(parsed.getTime())) return parsed;
  }
  return null;
}

function parseVendor(lines: string[]): string | null {
  const candidate = lines.find((line) => line.trim().length >= 3);
  return candidate?.trim().slice(0, 120) ?? null;
}

function parseLineItems(lines: string[]): ReceiptLineItem[] {
  const items: ReceiptLineItem[] = [];

  for (const [index, rawLine] of lines.entries()) {
    const line = rawLine.replace(/\s+/g, " ").trim();
    if (line.length < 5 || NON_ITEM_LINE.test(line)) continue;

    const match = line.match(/^(.{2,}?)\s+\$?(-?[\d,]+\.\d{2})$/);
    if (!match?.[1] || !match[2]) continue;

    const amount = Number(match[2].replace(/,/g, ""));
    const name = match[1]
      .replace(/^\d+\s*[xX]\s+/, "")
      .replace(/\s+\d+\s*[xX]\s*$/, "")
      .trim();

    if (!Number.isFinite(amount) || amount <= 0 || name.length < 2) continue;

    items.push({
      id: `${index}-${name.toLowerCase().replace(/[^a-z0-9]+/g, "-")}-${amount.toFixed(2)}`,
      name: name.slice(0, 80),
      amount,
      rawLine,
    });
  }

  return items.slice(0, 30);
}

export function parseReceiptText(text: string): ReceiptParseResult {
  const normalized = text.replace(/\r/g, "\n").trim();
  const rawLines = normalized
    .split("\n")
    .map((line) => line.trim())
    .filter(Boolean);

  return {
    amount: parseAmount(normalized),
    date: parseDate(normalized),
    subtotal: parseFirstMatchingAmount(normalized, SUBTOTAL_PATTERNS),
    tax: parseFirstMatchingAmount(normalized, TAX_PATTERNS),
    vendor: parseVendor(rawLines),
    items: parseLineItems(rawLines),
    rawLines,
  };
}