/// Turns raw OCR text into [LineItem]s using line-end prices and a keyword filter.
library;

import '../models/line_item.dart';
import '../utils/money.dart';

/// Headers, payments, and totals — never treated as products.
const Set<String> kHeaderKeywords = {
  'TOTAL',
  'SUBTOTAL',
  'TOTAAL',
  'TAX',
  'VAT',
  'BTW',
  'CASH',
  'CARD',
  'CHANGE',
  'VISA',
  'MASTERCARD',
  'MAESTRO',
  'PIN',
  'DEBIT',
  'CREDIT',
  'OMSCHRIJVING',
  'BEDRAG',
  'AMOUNT',
  'DESCRIPTION',
  'THANK',
  'BEDANKT',
  'WISSELGELD',
  'BETAALD',
  'BETAAL',
  'CONTANT',
  'KASSA',
  'RECEIPT',
  'WWW',
  'HTTP',
};

/// Discount / promo rows. Paired with a price, then dropped.
const Set<String> kDropKeywords = {
  'DISCOUNT',
  'KORTING',
  'ACTIE',
};

final _separatorPattern = RegExp(r'^[=\-_.:\s]+$');
final _postalPattern = RegExp(r'\d{4}\s*[A-Za-z]{2}\b');
final _phonePattern = RegExp(r'^\d{8,}$');
final _streetPattern = RegExp(r"^[A-Za-z. ''-]+\s+\d{1,4}$");
final _urlPattern = RegExp(r'www\.|\.com|\.nl', caseSensitive: false);

class _QtyLine {
  const _QtyLine({required this.count, required this.unitPrice, this.total});

  final int count;
  final double unitPrice;
  final double? total;

  double get lineTotal => total ?? roundMoney(count * unitPrice);
}

class ReceiptParser {
  ReceiptParser._();

  static int _nextId = 0;

  static String _id() => 'item-${++_nextId}';

  /// Parses [rawText] into product rows.
  ///
  /// Prefers same-line `name … price` (with a following `2 x 1.50` line when
  /// the name has no price). If OCR split the receipt into a name column and a
  /// price column, falls back to pairing those columns.
  static List<LineItem> parse(String rawText) {
    final lines = rawText
        .split('\n')
        .map((line) => line.trim())
        .where((line) => line.isNotEmpty)
        .toList();

    final inline = _parseInline(lines);
    final columns = _parseColumns(lines);
    final chosen = columns.length > inline.length ? columns : inline;
    return chosen.where(_keepItem).toList();
  }

  static List<LineItem> _parseInline(List<String> lines) {
    final items = <LineItem>[];

    for (var i = 0; i < lines.length; i++) {
      final line = lines[i];
      if (_shouldSkipLine(line) || isPriceOnly(line)) continue;

      final qty = _parseQty(line);
      if (qty != null) continue;

      final trailing = trailingPricePattern.firstMatch(line);
      if (trailing != null) {
        final name = trailing.group(1)!.trim();
        final price = tryParsePrice(trailing.group(2)!);
        if (name.isEmpty || price == null || _shouldSkipLine(name)) continue;
        items.add(LineItem(id: _id(), name: name, price: price));
        continue;
      }

      if (i + 1 >= lines.length) continue;
      final nextQty = _parseQty(lines[i + 1]);
      if (nextQty == null) continue;
      items.add(
        LineItem(
          id: _id(),
          name: line,
          price: nextQty.lineTotal,
          quantity: nextQty.count,
          unitPrice: nextQty.unitPrice,
        ),
      );
      i++;
    }

    return items;
  }

  static List<LineItem> _parseColumns(List<String> lines) {
    final names = <({String name, int? quantity, double? unitPrice})>[];
    final prices = <double>[];

    for (final line in lines) {
      if (isPriceOnly(line)) {
        final price = tryParsePrice(line);
        if (price != null) prices.add(price);
        continue;
      }
      if (_shouldSkipLine(line)) continue;

      final qty = _parseQty(line);
      if (qty != null) {
        if (names.isNotEmpty) {
          final last = names.removeLast();
          names.add((
            name: last.name,
            quantity: qty.count,
            unitPrice: qty.unitPrice,
          ));
        }
        continue;
      }

      names.add((name: line, quantity: null, unitPrice: null));
    }

    final count = names.length < prices.length ? names.length : prices.length;
    return [
      for (var i = 0; i < count; i++)
        LineItem(
          id: _id(),
          name: names[i].name,
          price: prices[i],
          quantity: names[i].quantity,
          unitPrice: names[i].unitPrice,
        ),
    ];
  }

  static bool _keepItem(LineItem item) {
    if (item.price < 0) return false;
    if (item.name.trim().isEmpty) return false;
    return !_containsKeyword(item.name, kDropKeywords);
  }

  static bool _shouldSkipLine(String line) {
    if (_separatorPattern.hasMatch(line)) return true;
    if (_urlPattern.hasMatch(line)) return true;
    if (_postalPattern.hasMatch(line)) return true;
    if (_phonePattern.hasMatch(line.replaceAll(RegExp(r'\s'), ''))) {
      return true;
    }
    if (_streetPattern.hasMatch(line)) return true;
    if (_containsKeyword(line, kHeaderKeywords)) return true;
    return false;
  }

  static bool _containsKeyword(String line, Set<String> keywords) {
    final upper = line.toUpperCase();
    for (final keyword in keywords) {
      if (RegExp('\\b${RegExp.escape(keyword)}\\b').hasMatch(upper)) {
        return true;
      }
    }
    return false;
  }

  static _QtyLine? _parseQty(String line) {
    final match = quantityPattern.firstMatch(line.trim());
    if (match == null) return null;
    final count = int.tryParse(match.group(1)!);
    final unit = tryParsePrice(match.group(2)!);
    if (count == null || count < 1 || unit == null) return null;
    final totalRaw = match.group(3);
    final total = totalRaw == null ? null : tryParsePrice(totalRaw);
    return _QtyLine(count: count, unitPrice: unit, total: total);
  }
}