using Lagerbestand.Data;
using Lagerbestand.Models;
using Microsoft.EntityFrameworkCore;

namespace Lagerbestand.Services;

public interface IInventoryService
{
    Task<List<InventoryItem>> GetAllAsync();
    Task<InventoryItem?> GetByIdAsync(Guid id);
    Task<InventoryItem?> GetByQrCodeAsync(string qrCode);
    Task<bool> ExistsAsync(string qrCode);
    Task<InventoryItem> AddItemAsync(string qrCode, Guid? catalogItemId = null, string? name = null);
    Task<List<InventoryItem>> AddItemsAsync(List<string> qrCodes, Guid? catalogItemId = null);
    Task<bool> RemoveItemAsync(string qrCode);
    Task<int> RemoveItemsAsync(List<string> qrCodes);
    Task<InventoryItem> UpdateCategoryAsync(Guid id, Guid? catalogItemId);
    Task<int> UpdateCategoryForItemsAsync(List<Guid> itemIds, Guid? catalogItemId);
    Task DeleteAsync(Guid id);
}

public class InventoryService : IInventoryService
{
    private readonly AppDbContext _context;
    private readonly ILogger<InventoryService> _logger;

    public InventoryService(AppDbContext context, ILogger<InventoryService> logger)
    {
        _context = context;
        _logger = logger;
    }

    public async Task<List<InventoryItem>> GetAllAsync()
    {
        return await _context.InventoryItems
            .AsNoTracking()
            .Include(x => x.CatalogItem)
            .OrderByDescending(x => x.CreatedAt)
            .ToListAsync();
    }

    public async Task<InventoryItem?> GetByIdAsync(Guid id)
    {
        return await _context.InventoryItems
            .Include(x => x.CatalogItem)
            .FirstOrDefaultAsync(x => x.Id == id);
    }

    public async Task<InventoryItem?> GetByQrCodeAsync(string qrCode)
    {
        return await _context.InventoryItems
            .Include(x => x.CatalogItem)
            .FirstOrDefaultAsync(x => x.QrCode == qrCode);
    }

    public async Task<bool> ExistsAsync(string qrCode)
    {
        return await _context.InventoryItems.AnyAsync(x => x.QrCode == qrCode);
    }

    public async Task<InventoryItem> AddItemAsync(string qrCode, Guid? catalogItemId = null, string? name = null)
    {
        if (await _context.InventoryItems.AnyAsync(x => x.QrCode == qrCode))
            throw new InvalidOperationException($"Artikel mit QR-Code '{qrCode}' ist bereits im Bestand.");

        var item = new InventoryItem
        {
            Id = Guid.NewGuid(),
            QrCode = qrCode,
            CatalogItemId = catalogItemId,
            Name = name,
            CreatedAt = DateTime.UtcNow
        };

        _context.InventoryItems.Add(item);
        await _context.SaveChangesAsync();

        return await GetByIdAsync(item.Id) ?? item;
    }

    public async Task<List<InventoryItem>> AddItemsAsync(List<string> qrCodes, Guid? catalogItemId = null)
    {
        var addedItems = new List<InventoryItem>();
        var now = DateTime.UtcNow;
        var distinctCodes = qrCodes.Distinct().ToList();

        var existingCodes = await _context.InventoryItems
            .Where(x => distinctCodes.Contains(x.QrCode))
            .Select(x => x.QrCode)
            .ToListAsync();
        var existingSet = existingCodes.ToHashSet();

        foreach (var qrCode in distinctCodes)
        {
            if (existingSet.Contains(qrCode))
                continue;

            var item = new InventoryItem
            {
                Id = Guid.NewGuid(),
                QrCode = qrCode,
                CatalogItemId = catalogItemId,
                CreatedAt = now
            };

            _context.InventoryItems.Add(item);
            addedItems.Add(item);
        }

        if (addedItems.Count > 0)
            await _context.SaveChangesAsync();

        return addedItems;
    }

    public async Task<bool> RemoveItemAsync(string qrCode)
    {
        var item = await _context.InventoryItems.FirstOrDefaultAsync(x => x.QrCode == qrCode);
        if (item == null)
            return false;

        _context.InventoryItems.Remove(item);
        await _context.SaveChangesAsync();
        return true;
    }

    public async Task<int> RemoveItemsAsync(List<string> qrCodes)
    {
        var count = 0;
        foreach (var qrCode in qrCodes.Distinct())
        {
            var item = await _context.InventoryItems.FirstOrDefaultAsync(x => x.QrCode == qrCode);
            if (item != null)
            {
                _context.InventoryItems.Remove(item);
                count++;
            }
        }

        if (count > 0)
            await _context.SaveChangesAsync();

        return count;
    }

    public async Task<InventoryItem> UpdateCategoryAsync(Guid id, Guid? catalogItemId)
    {
        var item = await _context.InventoryItems.FindAsync(id)
            ?? throw new InvalidOperationException("Artikel nicht gefunden");

        item.CatalogItemId = catalogItemId;
        item.UpdatedAt = DateTime.UtcNow;

        await _context.SaveChangesAsync();
        return item;
    }

    public async Task<int> UpdateCategoryForItemsAsync(List<Guid> itemIds, Guid? catalogItemId)
    {
        var now = DateTime.UtcNow;
        var count = 0;

        foreach (var id in itemIds)
        {
            var item = await _context.InventoryItems.FindAsync(id);
            if (item != null)
            {
                item.CatalogItemId = catalogItemId;
                item.UpdatedAt = now;
                count++;
            }
        }

        if (count > 0)
            await _context.SaveChangesAsync();

        return count;
    }

    public async Task DeleteAsync(Guid id)
    {
        var item = await _context.InventoryItems.FindAsync(id);
        if (item != null)
        {
            _context.InventoryItems.Remove(item);
            await _context.SaveChangesAsync();
        }
    }
}