From b205967f1a0db577dee2ba1ba24b8ea8da39e878 Mon Sep 17 00:00:00 2001
From: Toutsu <hegin4@yandex.ru>
Date: Thu, 7 May 2026 10:15:06 +0300
Subject: [PATCH] feat(#13): add CalendarSubscriptionService with token
 generation and ICS rendering

---
 .../Services/CalendarSubscriptionService.cs   | 93 +++++++++++++++++++
 1 file changed, 93 insertions(+)
 create mode 100644 src/GmRelay.Web/Services/CalendarSubscriptionService.cs

diff --git a/src/GmRelay.Web/Services/CalendarSubscriptionService.cs b/src/GmRelay.Web/Services/CalendarSubscriptionService.cs
new file mode 100644
index 0000000..a3f72af
--- /dev/null
+++ b/src/GmRelay.Web/Services/CalendarSubscriptionService.cs
@@ -0,0 +1,93 @@
+using System.Text;
+using Dapper;
+using GmRelay.Shared.Domain;
+using Npgsql;
+
+namespace GmRelay.Web.Services;
+
+public sealed class CalendarSubscriptionService(NpgsqlDataSource dataSource)
+{
+    private const string IcsProdId = "-//GM-Relay//TTRPG Schedule//EN";
+
+    public string GenerateToken() => Guid.NewGuid().ToString("N");
+
+    public async Task<string> CreateSubscriptionAsync(
+        long userTelegramId,
+        Guid? groupId,
+        CalendarSubscriptionFilter filter,
+        CancellationToken ct = default)
+    {
+        var token = GenerateToken();
+        await using var connection = await dataSource.OpenConnectionAsync(ct);
+        await connection.ExecuteAsync(
+            @"INSERT INTO calendar_subscriptions (id, token, user_telegram_id, group_id, filter_type, created_at, expires_at)
+              VALUES (gen_random_uuid(), @token, @userTelegramId, @groupId, @filterType, now(), NULL)",
+            new { token, userTelegramId, groupId, filterType = (int)filter });
+        return token;
+    }
+
+    public async Task<string> GetIcsAsync(string token, CancellationToken ct = default)
+    {
+        await using var connection = await dataSource.OpenConnectionAsync(ct);
+
+        var subscription = await connection.QueryFirstOrDefaultAsync<SubscriptionRecord>(
+            @"SELECT id, user_telegram_id as UserTelegramId, group_id as GroupId, filter_type as FilterType
+              FROM calendar_subscriptions
+              WHERE token = @token
+                AND (expires_at IS NULL OR expires_at > now())",
+            new { token });
+
+        if (subscription is null)
+            throw new SubscriptionNotFoundException();
+
+        var sessions = await connection.QueryAsync<CalendarSessionDto>(
+            subscription.FilterType == (int)CalendarSubscriptionFilter.SpecificGroup && subscription.GroupId.HasValue
+                ? @"SELECT s.id as Id, s.title as Title, s.scheduled_at as ScheduledAt
+                    FROM sessions s
+                    WHERE s.group_id = @GroupId
+                      AND s.status = @Planned
+                      AND s.scheduled_at > NOW()
+                    ORDER BY s.scheduled_at ASC"
+                : @"SELECT s.id as Id, s.title as Title, s.scheduled_at as ScheduledAt
+                    FROM sessions s
+                    WHERE s.status = @Planned
+                      AND s.scheduled_at > NOW()
+                    ORDER BY s.scheduled_at ASC",
+            new { subscription.GroupId, Planned = SessionStatus.Planned });
+
+        var sb = new StringBuilder();
+        sb.AppendLine("BEGIN:VCALENDAR");
+        sb.AppendLine("VERSION:2.0");
+        sb.AppendLine($"PRODID:{IcsProdId}");
+        sb.AppendLine("CALSCALE:GREGORIAN");
+        sb.AppendLine("METHOD:PUBLISH");
+
+        foreach (var s in sessions)
+        {
+            var dtStart = FormatIcsDate(s.ScheduledAt);
+            var dtEnd = FormatIcsDate(s.ScheduledAt.AddHours(4));
+            sb.AppendLine("BEGIN:VEVENT");
+            sb.AppendLine($"UID:{s.Id}@gmrelay");
+            sb.AppendLine($"DTSTAMP:{FormatIcsDate(DateTime.UtcNow)}");
+            sb.AppendLine($"DTSTART:{dtStart}");
+            sb.AppendLine($"DTEND:{dtEnd}");
+            sb.AppendLine($"SUMMARY:{EscapeIcsText(s.Title)}");
+            sb.AppendLine("END:VEVENT");
+        }
+
+        sb.AppendLine("END:VCALENDAR");
+        return sb.ToString();
+    }
+
+    private static string FormatIcsDate(DateTime dt) => dt.ToUniversalTime().ToString("yyyyMMddTHHmmssZ");
+
+    private static string EscapeIcsText(string text) => text
+        .Replace("\\", "\\\\")
+        .Replace(";", "\\;")
+        .Replace(",", "\\,")
+        .Replace("\n", "\\n")
+        .Replace("\r", "");
+
+    private sealed record SubscriptionRecord(Guid Id, long UserTelegramId, Guid? GroupId, int FilterType);
+    private sealed record CalendarSessionDto(Guid Id, string Title, DateTime ScheduledAt);
+}