MoneyMap/MoneyMap/Pages/Upload.cshtml.cs

using System.Globalization;
using System.IO;
using System.Linq;
using System.Text.Json;
using System.Text.RegularExpressions;
using CsvHelper;
using CsvHelper.Configuration;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using MoneyMap.Data;
using MoneyMap.Models;
using MoneyMap.Models.Import;
using MoneyMap.Services;

namespace MoneyMap.Pages
{
    public class UploadModel : PageModel
    {
        private readonly MoneyMapContext _db;
        private readonly ITransactionImporter _importer;
        private readonly ITransactionCategorizer _categorizer;

        public UploadModel(MoneyMapContext db, ITransactionImporter importer, ITransactionCategorizer categorizer)
        {
            _db = db;
            _importer = importer;
            _categorizer = categorizer;
        }

        [BindProperty] public IFormFile? Csv { get; set; }
        [BindProperty] public PaymentSelectMode PaymentMode { get; set; } = PaymentSelectMode.Auto;
        [BindProperty] public int? SelectedCardId { get; set; }
        [BindProperty] public int? SelectedAccountId { get; set; }

        public List<Card> Cards { get; set; } = new();
        public List<Account> Accounts { get; set; } = new();
        public ImportResult? Result { get; set; }
        public List<TransactionPreview> PreviewTransactions { get; set; } = new();

        private const string PreviewSessionKey = "TransactionPreview";

        public async Task OnGetAsync()
        {
            Cards = await _db.Cards
                .Include(c => c.Account)
                .OrderBy(c => c.Owner)
                .ThenBy(c => c.Last4)
                .ToListAsync();

            Accounts = await _db.Accounts
                .OrderBy(a => a.Institution)
                .ThenBy(a => a.Last4)
                .ToListAsync();
        }

        public async Task<IActionResult> OnPostAsync()
        {
            if (!ValidateInput())
            {
                await OnGetAsync();
                return Page();
            }

            Cards = await _db.Cards
                .Include(c => c.Account)
                .OrderBy(c => c.Owner)
                .ThenBy(c => c.Last4)
                .ToListAsync();

            Accounts = await _db.Accounts
                .OrderBy(a => a.Institution)
                .ThenBy(a => a.Last4)
                .ToListAsync();

            var importContext = new ImportContext
            {
                PaymentMode = PaymentMode,
                SelectedCardId = SelectedCardId,
                SelectedAccountId = SelectedAccountId,
                AvailableCards = Cards,
                AvailableAccounts = Accounts,
                FileName = Csv!.FileName
            };

            var previewResult = await _importer.PreviewAsync(Csv!.OpenReadStream(), importContext);

            if (!previewResult.IsSuccess)
            {
                ModelState.AddModelError(string.Empty, previewResult.ErrorMessage!);
                await OnGetAsync();
                return Page();
            }

            // Apply categorization to preview
            foreach (var preview in previewResult.Data!)
            {
                if (string.IsNullOrWhiteSpace(preview.Transaction.Category))
                {
                    preview.SuggestedCategory = await _categorizer.CategorizeAsync(preview.Transaction.Name, preview.Transaction.Amount);
                    preview.Transaction.Category = preview.SuggestedCategory ?? "";
                }
            }

            PreviewTransactions = previewResult.Data!;

            // Store preview data in Session for confirm step
            HttpContext.Session.SetString(PreviewSessionKey,
                JsonSerializer.Serialize(PreviewTransactions.Select(p => p.Transaction).ToList()));

            return Page();
        }

        public async Task<IActionResult> OnPostConfirmAsync(string selectedIndices, string paymentData)
        {
            var previewDataJson = HttpContext.Session.GetString(PreviewSessionKey);
            if (string.IsNullOrWhiteSpace(previewDataJson))
            {
                ModelState.AddModelError(string.Empty, "Preview data expired. Please upload again.");
                await OnGetAsync();
                return Page();
            }

            var transactions = JsonSerializer.Deserialize<List<Transaction>>(previewDataJson);
            if (transactions == null || !transactions.Any())
            {
                ModelState.AddModelError(string.Empty, "No transactions to import.");
                await OnGetAsync();
                return Page();
            }

            // Parse selected indices
            var selectedIndexList = string.IsNullOrWhiteSpace(selectedIndices)
                ? new List<int>()
                : selectedIndices.Split(',').Select(int.Parse).ToList();

            // Parse payment data
            var paymentSelections = string.IsNullOrWhiteSpace(paymentData)
                ? new Dictionary<int, PaymentSelection>()
                : JsonSerializer.Deserialize<Dictionary<int, PaymentSelection>>(paymentData) ?? new();

            // Filter transactions based on user selection and update payment methods
            var transactionsToImport = new List<Transaction>();
            foreach (var index in selectedIndexList)
            {
                if (index >= 0 && index < transactions.Count)
                {
                    var txn = transactions[index];

                    // Update payment method based on user selection
                    if (paymentSelections.TryGetValue(index, out var payment))
                    {
                        // Account is required and set globally for all transactions
                        if (payment.AccountId.HasValue)
                        {
                            var account = await _db.Accounts.FindAsync(payment.AccountId.Value);
                            if (account != null)
                            {
                                txn.AccountId = payment.AccountId.Value;
                                txn.Last4 = account.Last4;
                            }
                        }

                        // Card is optional per transaction
                        if (payment.CardId.HasValue)
                        {
                            var card = await _db.Cards.FindAsync(payment.CardId.Value);
                            if (card != null)
                            {
                                txn.CardId = card.Id;
                            }
                        }
                        else
                        {
                            txn.CardId = null; // Direct account transaction, no card
                        }

                        // Category (user can edit in preview)
                        if (!string.IsNullOrWhiteSpace(payment.Category))
                        {
                            txn.Category = payment.Category.Trim();
                        }
                    }

                    // Check for duplicates
                    if (!await IsDuplicate(txn))
                    {
                        transactionsToImport.Add(txn);
                    }
                }
            }

            var result = await _importer.ImportAsync(transactionsToImport);

            if (!result.IsSuccess)
            {
                ModelState.AddModelError(string.Empty, result.ErrorMessage!);
                await OnGetAsync();
                return Page();
            }

            Result = result.Data;
            HttpContext.Session.Remove(PreviewSessionKey); // Clear preview data
            await OnGetAsync();
            return Page();
        }

        private async Task<bool> IsDuplicate(Transaction txn)
        {
            return await _db.Transactions.AnyAsync(t =>
                t.Date == txn.Date &&
                t.Amount == txn.Amount &&
                t.Name == txn.Name &&
                t.Memo == txn.Memo &&
                t.CardId == txn.CardId &&
                t.AccountId == txn.AccountId);
        }

        private bool ValidateInput()
        {
            if (Csv is null || Csv.Length == 0)
            {
                ModelState.AddModelError(nameof(Csv), "Please choose a CSV file.");
                return false;
            }
            return true;
        }

        public record ImportResult(int Total, int Inserted, int Skipped, string? Last4FromFile);
        public enum PaymentSelectMode { Auto, Card, Account }
    }

    // ===== Service Layer =====

    public interface ITransactionImporter
    {
        Task<PreviewOperationResult> PreviewAsync(Stream csvStream, ImportContext context);
        Task<ImportOperationResult> ImportAsync(List<Transaction> transactions);
    }

    public class TransactionImporter : ITransactionImporter
    {
        private readonly MoneyMapContext _db;
        private readonly ICardResolver _cardResolver;

        public TransactionImporter(MoneyMapContext db, ICardResolver cardResolver)
        {
            _db = db;
            _cardResolver = cardResolver;
        }

        public async Task<PreviewOperationResult> PreviewAsync(Stream csvStream, ImportContext context)
        {
            var previewItems = new List<TransactionPreview>();
            var addedInThisBatch = new HashSet<TransactionKey>();

            // Load all existing transactions into memory for fast duplicate checking
            var existingTransactions = await _db.Transactions
                .Select(t => new TransactionKey(t.Date, t.Amount, t.Name, t.Memo, t.AccountId, t.CardId))
                .ToHashSetAsync();

            using var reader = new StreamReader(csvStream);
            using var csv = new CsvReader(reader, new CsvConfiguration(CultureInfo.InvariantCulture)
            {
                HasHeaderRecord = true,
                HeaderValidated = null,
                MissingFieldFound = null
            });

            csv.Read();
            csv.ReadHeader();
            var hasCategory = csv.HeaderRecord?.Any(h => h.Equals("Category", StringComparison.OrdinalIgnoreCase)) ?? false;
            csv.Context.RegisterClassMap(new TransactionCsvRowMap(hasCategory));

            while (csv.Read())
            {
                var row = csv.GetRecord<TransactionCsvRow>();

                var paymentResolution = await _cardResolver.ResolvePaymentAsync(row.Memo, context);
                if (!paymentResolution.IsSuccess)
                    return PreviewOperationResult.Failure(paymentResolution.ErrorMessage!);

                var transaction = MapToTransaction(row, paymentResolution);
                var key = new TransactionKey(transaction);

                // Fast in-memory duplicate checking
                bool isDuplicate = addedInThisBatch.Contains(key) || existingTransactions.Contains(key);

                previewItems.Add(new TransactionPreview
                {
                    Transaction = transaction,
                    IsDuplicate = isDuplicate,
                    PaymentMethodLabel = GetPaymentLabel(transaction, context)
                });

                addedInThisBatch.Add(key);
            }

            return PreviewOperationResult.Success(previewItems);
        }

        public async Task<ImportOperationResult> ImportAsync(List<Transaction> transactions)
        {
            int inserted = 0;
            int skipped = 0;

            foreach (var transaction in transactions)
            {
                _db.Transactions.Add(transaction);
                inserted++;
            }

            await _db.SaveChangesAsync();

            var result = new UploadModel.ImportResult(
                transactions.Count,
                inserted,
                skipped,
                null
            );

            return ImportOperationResult.Success(result);
        }

        private async Task<bool> IsDuplicate(Transaction txn)
        {
            return await _db.Transactions.AnyAsync(t =>
                t.Date == txn.Date &&
                t.Amount == txn.Amount &&
                t.Name == txn.Name &&
                t.Memo == txn.Memo &&
                t.CardId == txn.CardId &&
                t.AccountId == txn.AccountId);
        }

        private static Transaction MapToTransaction(TransactionCsvRow row, PaymentResolutionResult paymentResolution)
        {
            return new Transaction
            {
                Date = row.Date,
                TransactionType = row.Transaction?.Trim() ?? "",
                Name = row.Name?.Trim() ?? "",
                Memo = row.Memo?.Trim() ?? "",
                Amount = row.Amount,
                Category = (row.Category ?? "").Trim(),
                Last4 = paymentResolution.Last4,
                CardId = paymentResolution.CardId,
                AccountId = paymentResolution.AccountId!.Value // Required - must be present
            };
        }

        private string GetPaymentLabel(Transaction transaction, ImportContext context)
        {
            var account = context.AvailableAccounts.FirstOrDefault(a => a.Id == transaction.AccountId);
            var accountLabel = account?.DisplayLabel ?? $"Account ···· {transaction.Last4}";

            if (transaction.CardId.HasValue)
            {
                var card = context.AvailableCards.FirstOrDefault(c => c.Id == transaction.CardId);
                var cardLabel = card?.DisplayLabel ?? $"Card ···· {transaction.Last4}";
                return $"{cardLabel} → {accountLabel}";
            }

            return accountLabel;
        }
    }

    // ===== Card Resolution =====

    public interface ICardResolver
    {
        Task<PaymentResolutionResult> ResolvePaymentAsync(string? memo, ImportContext context);
    }

    public class CardResolver : ICardResolver
    {
        private readonly MoneyMapContext _db;

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

        public async Task<PaymentResolutionResult> ResolvePaymentAsync(string? memo, ImportContext context)
        {
            if (context.PaymentMode == UploadModel.PaymentSelectMode.Card)
                return ResolveCard(context);

            if (context.PaymentMode == UploadModel.PaymentSelectMode.Account)
                return ResolveAccount(context);

            return await ResolveAutomaticallyAsync(memo, context);
        }

        private PaymentResolutionResult ResolveCard(ImportContext context)
        {
            if (context.SelectedCardId is null)
                return PaymentResolutionResult.Failure("Pick a card or switch to Auto.");

            var card = context.AvailableCards.FirstOrDefault(c => c.Id == context.SelectedCardId);
            if (card is null)
                return PaymentResolutionResult.Failure("Selected card not found.");

            // Card must have a linked account
            if (!card.AccountId.HasValue)
                return PaymentResolutionResult.Failure($"Card {card.DisplayLabel} is not linked to an account. Please link it to an account first.");

            return PaymentResolutionResult.SuccessCard(card.Id, card.AccountId.Value, card.Last4);
        }

        private PaymentResolutionResult ResolveAccount(ImportContext context)
        {
            if (context.SelectedAccountId is null)
                return PaymentResolutionResult.Failure("Pick an account or switch to Auto/Card mode.");

            var account = context.AvailableAccounts.FirstOrDefault(a => a.Id == context.SelectedAccountId);
            if (account is null)
                return PaymentResolutionResult.Failure("Selected account not found.");

            return PaymentResolutionResult.SuccessAccount(account.Id, account.Last4);
        }

        private Task<PaymentResolutionResult> ResolveAutomaticallyAsync(string? memo, ImportContext context)
        {
            // Extract last4 from both memo and filename
            var last4FromFile = CardIdentifierExtractor.FromFileName(context.FileName);
            var last4FromMemo = CardIdentifierExtractor.FromMemo(memo);

            // PRIORITY 1: Try memo first (for per-transaction card detection like "usbank.com.2765")
            if (!string.IsNullOrWhiteSpace(last4FromMemo))
            {
                var result = TryResolveByLast4(last4FromMemo, context);
                if (result != null) return Task.FromResult(result);
            }

            // PRIORITY 2: Fall back to filename (for account-level CSVs or when memo has no card)
            if (!string.IsNullOrWhiteSpace(last4FromFile))
            {
                var result = TryResolveByLast4(last4FromFile, context);
                if (result != null) return Task.FromResult(result);
            }

            // Nothing found - error
            var searchedLast4 = last4FromMemo ?? last4FromFile;
            if (string.IsNullOrWhiteSpace(searchedLast4))
            {
                return Task.FromResult(PaymentResolutionResult.Failure(
                    "Couldn't determine card or account from memo or file name. Choose an account manually."));
            }

            return Task.FromResult(PaymentResolutionResult.Failure(
                $"Couldn't find account or card with last4 '{searchedLast4}'. Choose an account manually."));
        }

        private PaymentResolutionResult? TryResolveByLast4(string last4, ImportContext context)
        {
            // Look for both card and account matches
            var matchingCard = context.AvailableCards.FirstOrDefault(c => c.Last4 == last4);
            var matchingAccount = context.AvailableAccounts.FirstOrDefault(a => a.Last4 == last4);

            // Prioritize card matches (for credit card CSVs or memo-based card detection)
            if (matchingCard != null)
            {
                // Card found - it must have an account
                if (!matchingCard.AccountId.HasValue)
                    return PaymentResolutionResult.Failure($"Card {matchingCard.DisplayLabel} is not linked to an account. Please link it first or choose an account manually.");

                return PaymentResolutionResult.SuccessCard(matchingCard.Id, matchingCard.AccountId.Value, matchingCard.Last4);
            }

            // Fall back to account match (for direct account transactions)
            if (matchingAccount != null)
            {
                return PaymentResolutionResult.SuccessAccount(matchingAccount.Id, matchingAccount.Last4);
            }

            return null; // No match found
        }
    }

    // ===== Helper Classes =====

    public static class CardIdentifierExtractor
    {
        // Match patterns: "usbank.com.2765" or "usbank.com.0479" or similar formats
        private static readonly Regex MemoLast4Pattern = new(@"\.(\d{4})(?:\D|$)", RegexOptions.Compiled);
        private const int Last4Length = 4;

        public static string? FromMemo(string? memo)
        {
            if (string.IsNullOrWhiteSpace(memo))
                return null;

            // Try to find all matches and return the last one (most likely to be card/account number)
            var matches = MemoLast4Pattern.Matches(memo);
            if (matches.Count == 0)
                return null;

            // Return the last match (typically the card number at the end)
            return matches[^1].Groups[1].Value;
        }

        public static string? FromFileName(string fileName)
        {
            var name = Path.GetFileNameWithoutExtension(fileName);
            var parts = name.Split(new[] { '-', '_', ' ' }, StringSplitOptions.RemoveEmptyEntries);

            foreach (var part in parts.Select(p => p.Trim()))
            {
                if (part.Length == Last4Length && int.TryParse(part, out _))
                    return part;
            }

            return null;
        }
    }

    // ===== Data Transfer Objects =====

    public record TransactionKey(DateTime Date, decimal Amount, string Name, string Memo, int AccountId, int? CardId)
    {
        public TransactionKey(Transaction txn)
            : this(txn.Date, txn.Amount, txn.Name, txn.Memo, txn.AccountId, txn.CardId) { }
    }

    public class ImportContext
    {
        public required UploadModel.PaymentSelectMode PaymentMode { get; init; }
        public int? SelectedCardId { get; init; }
        public int? SelectedAccountId { get; init; }
        public required List<Card> AvailableCards { get; init; }
        public required List<Account> AvailableAccounts { get; init; }
        public required string FileName { get; init; }
    }

    public class ImportStats
    {
        public int Total { get; set; }
        public int Inserted { get; set; }
        public int Skipped { get; set; }
    }

    public class PaymentResolutionResult
    {
        public bool IsSuccess { get; init; }
        public int? CardId { get; init; }
        public int? AccountId { get; init; } // Required for all transactions
        public string? Last4 { get; init; }
        public string? ErrorMessage { get; init; }

        // When a card is used: accountId is the account the card is linked to (or a default account)
        public static PaymentResolutionResult SuccessCard(int cardId, int accountId, string last4) =>
            new() { IsSuccess = true, CardId = cardId, AccountId = accountId, Last4 = last4 };

        // When no card: accountId is the primary account for the transaction
        public static PaymentResolutionResult SuccessAccount(int accountId, string last4) =>
            new() { IsSuccess = true, AccountId = accountId, Last4 = last4 };

        public static PaymentResolutionResult Failure(string error) =>
            new() { IsSuccess = false, ErrorMessage = error };
    }

    public class ImportOperationResult
    {
        public bool IsSuccess { get; init; }
        public UploadModel.ImportResult? Data { get; init; }
        public string? ErrorMessage { get; init; }

        public static ImportOperationResult Success(UploadModel.ImportResult data) =>
            new() { IsSuccess = true, Data = data };

        public static ImportOperationResult Failure(string error) =>
            new() { IsSuccess = false, ErrorMessage = error };
    }

    public class PreviewOperationResult
    {
        public bool IsSuccess { get; init; }
        public List<TransactionPreview>? Data { get; init; }
        public string? ErrorMessage { get; init; }

        public static PreviewOperationResult Success(List<TransactionPreview> data) =>
            new() { IsSuccess = true, Data = data };

        public static PreviewOperationResult Failure(string error) =>
            new() { IsSuccess = false, ErrorMessage = error };
    }

    public class TransactionPreview
    {
        public required Transaction Transaction { get; init; }
        public bool IsDuplicate { get; init; }
        public required string PaymentMethodLabel { get; init; }
        public string? SuggestedCategory { get; set; }
    }

    public class PaymentSelection
    {
        public int? AccountId { get; set; } // Set globally for all transactions
        public int? CardId { get; set; }    // Optional per transaction
        public string? Category { get; set; } // User can edit in preview
    }
}