import 'dart:convert';

import 'package:drift/drift.dart';

import '../models/remote_command.dart';
import '../models/tab_event.dart';
import 'app_database.dart';

/// A product as the catalog and this tablet's unsent changes make it.
class _Product {
  String name;
  String category;
  int priceInCents;
  int lowStockThreshold;
  bool active;
  String? imageId;
  String? imagePath;

  _Product(ProductRow row)
    : name = row.name,
      category = row.category,
      priceInCents = row.priceInCents,
      lowStockThreshold = row.lowStockThreshold,
      active = row.active,
      imageId = row.imageId,
      imagePath = row.imagePath;

  _Product.fromServer(ServerProduct product)
    : name = product.name,
      category = product.category ?? '',
      priceInCents = product.priceInCents,
      lowStockThreshold = product.lowStockThreshold ?? 0,
      active = !product.archived,
      imageId = product.imageId,
      imagePath = null;

  bool sameAs(ProductRow row) =>
      name == row.name &&
      category == row.category &&
      priceInCents == row.priceInCents &&
      lowStockThreshold == row.lowStockThreshold &&
      active == row.active &&
      imageId == row.imageId &&
      imagePath == row.imagePath;

  ProductsCompanion toCompanion() => ProductsCompanion(
    name: Value(name),
    category: Value(category),
    priceInCents: Value(priceInCents),
    lowStockThreshold: Value(lowStockThreshold),
    active: Value(active),
    imageId: Value(imageId),
    imagePath: Value(imagePath),
  );

  /// Applies the fields of a `product_created` / `product_updated` event.
  void apply(Map<String, dynamic> fields) {
    if (fields['name'] case final String value) name = value;
    if (fields.containsKey('category')) {
      category = fields['category'] as String? ?? '';
    }
    if (fields['priceInCents'] case final int value) priceInCents = value;
    if (fields.containsKey('lowStockThreshold')) {
      lowStockThreshold = fields['lowStockThreshold'] as int? ?? 0;
    }
    if (fields.containsKey('imageId')) imageId = fields['imageId'] as String?;
  }
}

/// The product catalog: the website's, with this tablet's changes on top.
extension CatalogQueries on AppDatabase {
  /// Makes the local products match [catalog], then replays this tablet's
  /// product changes the server hasn't applied yet on top, so an offline
  /// edit stays visible until the server has it (the same idea as the tabs).
  ///
  /// New products are added; archived ones, and products the server doesn't
  /// know and this tablet didn't create (such as the default products of a
  /// new tablet), are hidden: open tabs and the history refer to them.
  ///
  /// Pictures: a changed one keeps showing the old file until
  /// [ProductImageSync] downloaded the new one; a picture waiting to be
  /// uploaded from this tablet is left alone. The stock is not touched here:
  /// the stock rebase that follows sets it.
  Future<void> applyServerCatalog(List<ServerProduct> catalog) {
    return transaction(() async {
      final rows = {
        for (final row in await select(products).get()) row.id: row,
      };
      final uploading = {
        for (final row in await select(pendingImageUploads).get())
          row.productId,
      };
      final desired = {for (final row in rows.values) row.id: _Product(row)};

      final listed = <String>{};
      for (final product in catalog) {
        listed.add(product.id);
        final local = desired[product.id];
        final next = _Product.fromServer(product);
        if (local == null) {
          desired[product.id] = next;
          continue;
        }
        if (uploading.contains(product.id)) {
          next
            ..imageId = local.imageId
            ..imagePath = local.imagePath;
        } else if (next.imageId != null && next.imageId == local.imageId) {
          next.imagePath = local.imagePath;
        } else if (next.imageId != null) {
          // Until the new picture is downloaded, the old one is better than none
          next.imagePath = local.imagePath;
        }
        desired[product.id] = next;
      }
      for (final entry in desired.entries) {
        if (!listed.contains(entry.key)) entry.value.active = false;
      }

      for (final event in await _pendingProductEvents()) {
        final productId = event['productId'] as String?;
        final local = productId == null ? null : desired[productId];
        if (local == null) continue;
        switch (TabEventType.fromValue(event['type'] as String? ?? '')) {
          case TabEventType.productCreated || TabEventType.productUpdated:
            local.apply(event['product'] as Map<String, dynamic>? ?? {});
            if (event['type'] == TabEventType.productCreated.value) {
              local.active = true;
            }
          case TabEventType.productArchived:
            local.active = false;
          default:
            break;
        }
      }

      for (final MapEntry(key: id, value: product) in desired.entries) {
        final row = rows[id];
        if (row == null) {
          await into(products).insert(
            product.toCompanion().copyWith(
              id: Value(id),
              // Untracked until the stock rebase sets its stock
              stockQuantity: const Value(0),
              infiniteStock: const Value(true),
            ),
          );
        } else if (!product.sameAs(row)) {
          await (update(
            products,
          )..where((r) => r.id.equals(id))).write(product.toCompanion());
        }
      }
    });
  }

  /// Queues a picture taken on this tablet for upload; a newer picture of the
  /// same product replaces one still waiting.
  Future<void> queueImageUpload(String productId, String localPath) async {
    await into(pendingImageUploads).insertOnConflictUpdate(
      PendingImageUploadsCompanion.insert(
        productId: productId,
        localPath: localPath,
        createdAt: DateTime.now(),
      ),
    );
  }

  Future<List<Map<String, dynamic>>> _pendingProductEvents() async {
    final types = TabEventType.products.map((type) => type.value).toSet();
    final rows =
        await (select(tabEvents)..orderBy([
              (row) => OrderingTerm.asc(row.createdAt),
              (row) => OrderingTerm.asc(const CustomExpression<int>('rowid')),
            ]))
            .get();
    return [
      for (final row in rows)
        if (jsonDecode(row.payload) case final Map<String, dynamic> event
            when types.contains(event['type']))
          event,
    ];
  }
}