CsvGuestbookStorage.cs

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using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Hosting;
using WeddingThankYou.Models;
 
namespace WeddingThankYou.Services
{
    public sealed class CsvGuestbookStorage : IGuestbookStorage
    {
        private readonly string _dataDir;
        private static readonly SemaphoreSlim _gate = new(1, 1);

        public CsvGuestbookStorage(IHostEnvironment env)
        {
            _dataDir = Path.Combine(env.ContentRootPath, "App_Data", "Guestbook");
            Directory.CreateDirectory(_dataDir);
        }

        private string CsvPath(string slug) =>
            Path.Combine(_dataDir, $"{Sanitize(slug)}.csv");

        private static string Sanitize(string slug) =>
            string.Concat((slug ?? string.Empty).ToLowerInvariant().Split(Path.GetInvalidFileNameChars()));

        public async Task<IReadOnlyList<GuestbookEntry>> LoadAsync(string slug, CancellationToken ct = default)
        {
            var csvPath = CsvPath(slug);
            await _gate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                var result = new List<GuestbookEntry>();
                if (!File.Exists(csvPath)) return result;
 
                using var fs = new FileStream(csvPath, FileMode.Open, FileAccess.Read, FileShare.Read);
                using var sr = new StreamReader(fs, Encoding.UTF8);
                string? line;
 
                // 헤더 지원: 첫 줄이 헤더 같으면 스킵
                bool first = true;
                while ((line = await sr.ReadLineAsync().ConfigureAwait(false)) != null)
                {
                    ct.ThrowIfCancellationRequested();
                    if (string.IsNullOrWhiteSpace(line)) continue;
 
                    if (first && IsHeader(line)) { first = false; continue; }
                    first = false;
 
                    var f = ParseCsvLine(line);
                    if (f.Count < 4) continue;
 
                    if (!DateTime.TryParseExact(f[3], "yyyy-MM-dd HH:mm:ss",
                            CultureInfo.InvariantCulture, DateTimeStyles.AssumeLocal, out var when))
                        when = DateTime.Now;
 
                    result.Add(new GuestbookEntry
                    {
                        Name = f[0],
                        Contact = f[1],
                        Message = f[2],
                        CreatedLocal = when
                    });
                }
                return result;
            }
            finally
            {
                _gate.Release();
            }
        }

        public async Task SaveAsync(string slug, IReadOnlyList<GuestbookEntry> entries, CancellationToken ct = default)
        {
            var csvPath = CsvPath(slug);
            await _gate.WaitAsync(ct).ConfigureAwait(false);
            try
            {
                var tmp = csvPath + ".tmp";
                using (var fs = new FileStream(tmp, FileMode.Create, FileAccess.Write, FileShare.None))
                using (var sw = new StreamWriter(fs, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false)))
                {
                    // 헤더 작성
                    await sw.WriteLineAsync("Name,Contact,Message,CreatedLocal").ConfigureAwait(false);
 
                    foreach (var e in entries)
                    {
                        ct.ThrowIfCancellationRequested();
                        var line = string.Join(",",
                            EscapeCsv(e.Name),
                            EscapeCsv(e.Contact),
                            EscapeCsv(e.Message),
                            EscapeCsv(e.CreatedLocal.ToString("yyyy-MM-dd HH:mm:ss")));
                        await sw.WriteLineAsync(line).ConfigureAwait(false);
                    }
                }
 
                File.Copy(tmp, csvPath, overwrite: true);
                File.Delete(tmp);
            }
            finally
            {
                _gate.Release();
            }
        }

        private static bool IsHeader(string line)
        {
            var l = line.Trim().ToLowerInvariant();
            return l.StartsWith("name,contact,message,createdlocal");
        }

        private static string EscapeCsv(string value)
        {
            value ??= string.Empty;
            bool needQuote = value.Contains(',') || value.Contains('"') || value.Contains('\n') || value.Contains('\r');
            if (!needQuote) return value;
            return $"\"{value.Replace("\"", "\"\"")}\"";
        }

        private static List<string> ParseCsvLine(string line)
        {
            var list = new List<string>();
            if (string.IsNullOrEmpty(line)) return list;
 
            var sb = new StringBuilder();
            bool inQuotes = false;
 
            for (int i = 0; i < line.Length; i++)
            {
                var ch = line[i];
                if (inQuotes)
                {
                    if (ch == '"')
                    {
                        if (i + 1 < line.Length && line[i + 1] == '"')
                        {
                            sb.Append('"'); i++; // "" -> "
                        }
                        else inQuotes = false;
                    }
                    else sb.Append(ch);
                }
                else
                {
                    if (ch == ',') { list.Add(sb.ToString()); sb.Clear(); }
                    else if (ch == '"') inQuotes = true;
                    else sb.Append(ch);
                }
            }
            list.Add(sb.ToString());
            return list;
        }
    }
}