using Microsoft.EntityFrameworkCore;
using MoneyMap.Data;
using MoneyMap.Models;

namespace MoneyMap.Services
{
    public interface IMerchantService
    {
        Task<Merchant?> FindByNameAsync(string name);
        Task<Merchant> GetOrCreateAsync(string name);
        Task<int?> GetOrCreateIdAsync(string? name);
        Task<Merchant?> GetMerchantByIdAsync(int id, bool includeRelated = false);
        Task<List<MerchantWithStats>> GetAllMerchantsWithStatsAsync();
        Task<MerchantUpdateResult> UpdateMerchantAsync(int id, string newName);
        Task<MerchantDeleteResult> DeleteMerchantAsync(int id);
    }

    public class MerchantService : IMerchantService
    {
        private readonly MoneyMapContext _db;

        public MerchantService(MoneyMapContext db)
        {
            _db = db;
        }

        public async Task<Merchant?> FindByNameAsync(string name)
        {
            if (string.IsNullOrWhiteSpace(name))
                return null;

            return await _db.Merchants
                .FirstOrDefaultAsync(m => m.Name == name.Trim());
        }

        public async Task<Merchant> GetOrCreateAsync(string name)
        {
            var trimmedName = name.Trim();

            var existing = await _db.Merchants
                .FirstOrDefaultAsync(m => m.Name == trimmedName);

            if (existing != null)
                return existing;

            var merchant = new Merchant { Name = trimmedName };
            _db.Merchants.Add(merchant);
            await _db.SaveChangesAsync();

            return merchant;
        }

        public async Task<int?> GetOrCreateIdAsync(string? name)
        {
            if (string.IsNullOrWhiteSpace(name))
                return null;

            var merchant = await GetOrCreateAsync(name);
            return merchant.Id;
        }

        public async Task<Merchant?> GetMerchantByIdAsync(int id, bool includeRelated = false)
        {
            var query = _db.Merchants.AsQueryable();

            if (includeRelated)
            {
                query = query
                    .Include(m => m.Transactions)
                    .Include(m => m.CategoryMappings);
            }

            return await query.FirstOrDefaultAsync(m => m.Id == id);
        }

        public async Task<List<MerchantWithStats>> GetAllMerchantsWithStatsAsync()
        {
            var merchants = await _db.Merchants
                .Include(m => m.Transactions)
                .Include(m => m.CategoryMappings)
                .OrderBy(m => m.Name)
                .ToListAsync();

            return merchants.Select(m => new MerchantWithStats
            {
                Id = m.Id,
                Name = m.Name,
                TransactionCount = m.Transactions.Count,
                MappingCount = m.CategoryMappings.Count
            }).ToList();
        }

        public async Task<MerchantUpdateResult> UpdateMerchantAsync(int id, string newName)
        {
            var merchant = await _db.Merchants.FindAsync(id);
            if (merchant == null)
            {
                return new MerchantUpdateResult
                {
                    Success = false,
                    Message = "Merchant not found."
                };
            }

            var trimmedName = newName.Trim();

            // Check if another merchant with the same name exists
            var existing = await _db.Merchants
                .FirstOrDefaultAsync(m => m.Name == trimmedName && m.Id != id);

            if (existing != null)
            {
                return new MerchantUpdateResult
                {
                    Success = false,
                    Message = $"Merchant '{trimmedName}' already exists."
                };
            }

            merchant.Name = trimmedName;
            await _db.SaveChangesAsync();

            return new MerchantUpdateResult
            {
                Success = true,
                Message = "Merchant updated successfully."
            };
        }

        public async Task<MerchantDeleteResult> DeleteMerchantAsync(int id)
        {
            var merchant = await _db.Merchants
                .Include(m => m.Transactions)
                .Include(m => m.CategoryMappings)
                .FirstOrDefaultAsync(m => m.Id == id);

            if (merchant == null)
            {
                return new MerchantDeleteResult
                {
                    Success = false,
                    Message = "Merchant not found."
                };
            }

            var transactionCount = merchant.Transactions.Count;
            var mappingCount = merchant.CategoryMappings.Count;

            _db.Merchants.Remove(merchant);
            await _db.SaveChangesAsync();

            return new MerchantDeleteResult
            {
                Success = true,
                Message = $"Deleted merchant '{merchant.Name}'. {transactionCount} transactions and {mappingCount} category mappings are now unlinked.",
                TransactionCount = transactionCount,
                MappingCount = mappingCount
            };
        }
    }

    // DTOs
    public class MerchantWithStats
    {
        public int Id { get; set; }
        public string Name { get; set; } = "";
        public int TransactionCount { get; set; }
        public int MappingCount { get; set; }
    }

    public class MerchantUpdateResult
    {
        public bool Success { get; set; }
        public string Message { get; set; } = "";
    }

    public class MerchantDeleteResult
    {
        public bool Success { get; set; }
        public string Message { get; set; } = "";
        public int TransactionCount { get; set; }
        public int MappingCount { get; set; }
    }
}