/// Spatial receipt parser: row clustering, column logic, and lookahead buffer.
library;

import '../models/line_item.dart';
import '../models/ocr_element.dart';
import '../models/receipt_bounds.dart';
import '../models/receipt_row.dart';
import '../utils/money.dart';
import 'receipt_parse_config.dart';
import 'receipt_row_builder.dart';
import 'receipt_text_parser.dart';

class _PendingItem {
  _PendingItem({
    required this.name,
    this.unitPrice,
    this.lineTotal,
    this.quantity = 1,
    this.bounds,
  });

  String name;
  double? unitPrice;
  double? lineTotal;
  int quantity;
  double discount = 0;
  ReceiptBounds? bounds;

  void mergeBounds(ReceiptBounds? other) {
    if (other == null) return;
    bounds = bounds == null ? other : bounds!.union(other);
  }
}

class ReceiptSpatialParser {
  ReceiptSpatialParser._();

  static int _nextId = 0;
  static String _id() => 'item-${++_nextId}';

  static ReceiptParseResult parse(OcrDocument document) {
    _nextId = 0;
    final config = receiptParseConfig;
    final rows = ReceiptRowBuilder(config).buildRows(document);
    return _parseRows(
      rows,
      rawText: document.flattenedText,
      imageWidth: document.imageWidth,
      imageHeight: document.imageHeight,
    );
  }

  static ReceiptParseResult _parseRows(
    List<ReceiptRow> rows, {
    required String rawText,
    required double imageWidth,
    required double imageHeight,
  }) {
    final config = receiptParseConfig;
    final items = <LineItem>[];
    _PendingItem? pending;
    var receiptTotal = _readTotalFromRows(rows, config);
    var totalDiscount = 0.0;
    var stop = false;

    void emitPending({required bool needsReview}) {
      final current = pending;
      pending = null;
      if (current == null) return;
      final total = current.lineTotal ?? current.unitPrice;
      if (total == null) {
        items.add(
          LineItem(
            id: _id(),
            name: current.name,
            price: 0,
            sourceBounds: current.bounds,
            needsManualReview: true,
          ),
        );
        return;
      }
      items.add(
        LineItem(
          id: _id(),
          name: current.name,
          price: roundMoney(total),
          quantity: current.quantity == 1 ? null : current.quantity,
          unitPrice: current.quantity == 1 ? null : current.unitPrice,
          discount: current.discount == 0 ? 0 : roundMoney(current.discount),
          sourceBounds: current.bounds,
          needsManualReview: needsReview,
        ),
      );
    }

    for (var i = 0; i < rows.length && !stop; i++) {
      final row = rows[i];
      switch (row.kind) {
        case ReceiptRowKind.skip:
          continue;
        case ReceiptRowKind.quantityModifier:
          if (pending != null &&
              row.quantity != null &&
              row.unitPrice != null) {
            pending!
              ..quantity = row.quantity!
              ..unitPrice = row.unitPrice
              ..lineTotal = row.lineTotal ?? roundMoney(row.quantity! * row.unitPrice!);
            pending!.mergeBounds(row.bounds);
            emitPending(needsReview: false);
          }
          continue;
        case ReceiptRowKind.nameOnly:
          emitPending(needsReview: pending?.lineTotal == null);
          pending = _PendingItem(name: row.nameText, bounds: row.bounds);
          final next = i + 1 < rows.length ? rows[i + 1] : null;
          if (next?.kind == ReceiptRowKind.quantityModifier) {
            continue;
          }
          emitPending(needsReview: true);
          continue;
        case ReceiptRowKind.item:
          emitPending(needsReview: pending?.lineTotal == null);
          pending = _PendingItem(
            name: row.nameText,
            unitPrice: row.unitPrice ?? row.price,
            lineTotal: row.lineTotal ?? row.price,
            quantity: row.quantity ?? 1,
            bounds: row.bounds,
          );
          if (row.quantity != null) {
            pending!.unitPrice = row.unitPrice;
          }
          final nextItem = i + 1 < rows.length ? rows[i + 1] : null;
          if (nextItem?.kind == ReceiptRowKind.quantityModifier) {
            continue;
          }
          emitPending(needsReview: false);
          continue;
        case ReceiptRowKind.discount:
          var amount = row.price;
          if (amount == null && i + 1 < rows.length) {
            amount = rows[i + 1].price;
            if (amount != null) i++;
          }
          if (amount == null) continue;
          if (amount > 0) amount = -amount;
          if (pending != null) {
            pending!.discount += amount;
            pending!.lineTotal = roundMoney(
              (pending!.lineTotal ?? pending!.unitPrice ?? 0) + amount,
            );
            pending!.mergeBounds(row.bounds);
          } else {
            totalDiscount += amount;
          }
          continue;
        case ReceiptRowKind.totalDiscount:
          var amount = row.price;
          if (amount == null && i + 1 < rows.length) {
            amount = rows[i + 1].price;
            if (amount != null) i++;
          }
          if (amount != null) {
            totalDiscount += amount > 0 ? -amount : amount;
          }
          continue;
        case ReceiptRowKind.grandTotal:
          emitPending(needsReview: pending?.lineTotal == null);
          if (row.price != null) {
            receiptTotal = row.price;
            stop = true;
          }
          continue;
      }
    }
    emitPending(needsReview: pending?.lineTotal == null);

    final expectedItemCount = _readExpectedItemCount(rows, config);
    return _finalize(
      items: items,
      rawText: rawText,
      receiptTotal: receiptTotal,
      totalDiscount: totalDiscount,
      expectedItemCount: expectedItemCount,
      imageWidth: imageWidth,
      imageHeight: imageHeight,
    );
  }

  static double? _readTotalFromRows(
    List<ReceiptRow> rows,
    ReceiptParseConfig config,
  ) {
    for (final row in rows) {
      if (row.kind != ReceiptRowKind.grandTotal) continue;
      if (config.matchesAny(row.text, [
        ...config.totalDiscountKeywords,
        ...config.taxInclusiveTotalKeywords,
        ...config.subtotalKeywords,
      ])) {
        continue;
      }
      return row.price;
    }
    return null;
  }

  static int? _readExpectedItemCount(
    List<ReceiptRow> rows,
    ReceiptParseConfig config,
  ) {
    final pattern = RegExp(
      r'(\d+)\s*$',
      caseSensitive: false,
    );
    for (final row in rows) {
      if (!config.matchesAny(row.text, config.itemCountKeywords)) continue;
      final match = pattern.firstMatch(row.text);
      if (match != null) {
        return int.tryParse(match.group(1)!);
      }
    }
    return null;
  }

  static ReceiptParseResult _finalize({
    required List<LineItem> items,
    required String rawText,
    double? receiptTotal,
    double totalDiscount = 0,
    int? expectedItemCount,
    required double imageWidth,
    required double imageHeight,
  }) {
    final kept = items
        .where(
          (item) =>
              item.name.trim().isNotEmpty &&
              (item.price > 0 || item.needsManualReview),
        )
        .toList();
    final sum = roundMoney(
      kept
          .where((item) => item.price > 0)
          .fold<double>(0, (total, item) => total + item.price),
    );

    var passed = true;
    if (receiptTotal != null) {
      passed =
          (sum - receiptTotal).abs() <= 0.01 ||
          (sum + totalDiscount - receiptTotal).abs() <= 0.01;
    }
    if (expectedItemCount != null && kept.length != expectedItemCount) {
      passed = false;
    }
    if (kept.any((item) => item.needsManualReview)) {
      passed = false;
    }

    return ReceiptParseResult(
      items: kept,
      store: ReceiptTextParser.detectStore(rawText),
      receiptTotal: receiptTotal,
      totalDiscount: totalDiscount,
      validationPassed: passed,
      expectedItemCount: expectedItemCount,
      ocrImageWidth: imageWidth,
      ocrImageHeight: imageHeight,
    );
  }
}