using BudgetApp.Enums;
using BudgetApp.PublicModels;
using BudgetApp.Storage;
using Microsoft.AspNetCore.Http;
using Microsoft.EntityFrameworkCore;
using System.Globalization;
using System.Text;

namespace BudgetApp.Services
{
    public class UploadService(BudgetContext context) : IUploadService
    {
        private readonly BudgetContext _context = context ?? throw new ArgumentNullException(nameof(context));

        public async Task<BaseResponse> UploadCsv(IFormFile file, CancellationToken cancellationToken = default)
        {
            await SetUpdateStatusState(UpdateStatusState.Processing);

            var response = new BaseResponse();
            var errors = new List<string>();
            var transactionsToInsert = new List<Transaction>();

            var existingIds = await _context.Transactions
                .AsNoTracking()
                .Select(t => t.TransactionId)
                .ToListAsync(cancellationToken)
                .ConfigureAwait(false);

            var knownTransactionIds = new HashSet<string>(existingIds, StringComparer.OrdinalIgnoreCase);

            using (var stream = file.OpenReadStream())
            using (var reader = new StreamReader(stream, Encoding.UTF8, detectEncodingFromByteOrderMarks: true))
            {
                while (!reader.EndOfStream)
                {
                    cancellationToken.ThrowIfCancellationRequested();

                    var rawLine = await reader.ReadLineAsync().ConfigureAwait(false);
                    if (string.IsNullOrWhiteSpace(rawLine))
                    {
                        continue;
                    }

                    if (!rawLine.StartsWith("2168", StringComparison.Ordinal))
                    {
                        continue; // Non-transaction rows (e.g., headers) are ignored.
                    }

                    var cols = rawLine.Split(';');
                    if (cols.Length <= 23)
                    {
                        errors.Add("Skipping row with insufficient number of columns.");
                        continue;
                    }

                    var transactionId = cols[23].Trim('\"', ' ');
                    if (string.IsNullOrWhiteSpace(transactionId))
                    {
                        errors.Add("Skipping row without transaction identifier.");
                        continue;
                    }

                    if (!knownTransactionIds.Add(transactionId))
                    {
                        continue; // Already processed or exists in database.
                    }

                    if (!DateOnly.TryParseExact(cols[1].Trim('\"', ' '), "dd.MM.yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out var date))
                    {
                        errors.Add($"Skipping row with invalid date value: '{cols[1]}'.");
                        knownTransactionIds.Remove(transactionId);
                        continue;
                    }

                    if (!TryParseDecimal(cols[2], out var amount))
                    {
                        errors.Add($"Skipping row with invalid amount value: '{cols[2]}'.");
                        knownTransactionIds.Remove(transactionId);
                        continue;
                    }

                    if (!TryParseDecimal(cols[4], out var balance))
                    {
                        errors.Add($"Skipping row with invalid balance value: '{cols[4]}'.");
                        knownTransactionIds.Remove(transactionId);
                        continue;
                    }

                    var transaction = new Transaction
                    {
                        Amount = amount,
                        Balance = balance,
                        Category = cols[16].Trim('\"', ' '),
                        Date = date,
                        Note = cols[15].Trim('\"', ' '),
                        OperationDescription = string.Join(" | ",
                            SafeGetColumn(cols, 12),
                            SafeGetColumn(cols, 13),
                            SafeGetColumn(cols, 14)).Trim(' ', '|'),
                        TransactionId = transactionId
                    };

                    transactionsToInsert.Add(transaction);
                }
            }

            if (transactionsToInsert.Count > 0)
            {
                await _context.Transactions.AddRangeAsync(transactionsToInsert, cancellationToken).ConfigureAwait(false);
                await _context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
            }

            if (errors.Count > 0)
            {
                response.Success = false;
                response.Error = string.Join(" ", errors.Distinct());
            }

            await SetUpdateStatusState(UpdateStatusState.Done);

            return response;
        }

        private static string SafeGetColumn(string[] columns, int index)
        {
            return index >= 0 && index < columns.Length
                ? columns[index].Trim('\"', ' ')
                : string.Empty;
        }

        private static bool TryParseDecimal(string input, out decimal value)
        {
            value = 0m;
            if (string.IsNullOrWhiteSpace(input))
            {
                return false;
            }

            var sanitized = NormalizeDecimalValue(input);
            return decimal.TryParse(sanitized, NumberStyles.Number | NumberStyles.AllowLeadingSign, CultureInfo.InvariantCulture, out value);
        }

        private static string NormalizeDecimalValue(string input)
        {
            var normalized = input
                .Replace("\u00A0", string.Empty) // non-breaking space
                .Trim();

            var builder = new StringBuilder(normalized.Length);
            foreach (var ch in normalized)
            {
                if (char.IsDigit(ch) || ch is '-' or '+' || ch == ',' || ch == '.')
                {
                    builder.Append(ch);
                }
            }

            var cleaned = builder.ToString();
            var lastComma = cleaned.LastIndexOf(',');
            var lastDot = cleaned.LastIndexOf('.');

            if (lastComma >= 0 && lastDot >= 0)
            {
                if (lastComma > lastDot)
                {
                    cleaned = cleaned.Replace(".", string.Empty);
                    cleaned = cleaned.Replace(',', '.');
                }
                else
                {
                    cleaned = cleaned.Replace(",", string.Empty);
                }
            }
            else if (lastComma >= 0)
            {
                cleaned = cleaned.Replace(".", string.Empty);
                cleaned = cleaned.Replace(',', '.');
            }
            else
            {
                cleaned = cleaned.Replace(",", string.Empty);
            }

            return cleaned;
        }

        private async Task SetUpdateStatusState(UpdateStatusState state)
        {
            var updateStatus = await _context.UpdateStatuses
                .SingleAsync();

            updateStatus.State = state;
            await _context.SaveChangesAsync();
        }
    }

    public interface IUploadService
    {
        Task<BaseResponse> UploadCsv(IFormFile file, CancellationToken cancellationToken = default);
    }
}