feat(api): add news to /api/meta response

Catalogger.Backend/Services/NewsService.cs

@@ -0,0 +1,97 @@
+// Copyright (C) 2021-present sam (starshines.gay)
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+using Catalogger.Backend.Extensions;
+using NodaTime;
+using NodaTime.Extensions;
+using Remora.Discord.API;
+using Remora.Discord.API.Abstractions.Objects;
+using Remora.Discord.API.Abstractions.Rest;
+
+namespace Catalogger.Backend.Services;
+
+public class NewsService(
+    Config config,
+    ILogger logger,
+    IDiscordRestChannelAPI channelApi,
+    IClock clock
+)
+{
+    private static readonly Duration MaxNewsAge = Duration.FromDays(90); // 3 months
+    private static readonly Duration ExpiresAfter = Duration.FromHours(1);
+
+    private readonly ILogger _logger = logger.ForContext<NewsService>();
+    private List<IMessage>? _messages;
+    private readonly SemaphoreSlim _lock = new(1);
+    private bool _isExpired => clock.GetCurrentInstant() > clock.GetCurrentInstant() + ExpiresAfter;
+
+    public async Task<IEnumerable<NewsMessage>> GetNewsAsync()
+    {
+        if (_messages != null && !_isExpired)
+            return _messages.Select(FormatIMessage);
+
+        var messages = await GetRawNewsAsync();
+        return messages.Select(FormatIMessage);
+    }
+
+    public void AddMessage(IMessage message) =>
+        _messages = _messages?.Take(4).Prepend(message).ToList();
+
+    private async Task<List<IMessage>> GetRawNewsAsync()
+    {
+        await _lock.WaitAsync();
+        try
+        {
+            if (config.Web.NewsChannel == null)
+                return [];
+
+            _logger.Information("Fetching news from channel {ChannelId}", config.Web.NewsChannel);
+
+            var res = await channelApi.GetChannelMessagesAsync(
+                DiscordSnowflake.New(config.Web.NewsChannel.Value),
+                limit: 5
+            );
+            if (res.IsSuccess)
+                return _messages = res
+                    .Entity.Where(m =>
+                        m.ID.Timestamp.ToInstant() > clock.GetCurrentInstant() - MaxNewsAge
+                    )
+                    .ToList();
+
+            return [];
+        }
+        finally
+        {
+            _lock.Release();
+        }
+    }
+
+    public record NewsMessage(
+        string Author,
+        string Content,
+        IEnumerable<string> AttachmentUrls,
+        DateTimeOffset PostedAt,
+        DateTimeOffset? EditedAt
+    );
+
+    private NewsMessage FormatIMessage(IMessage msg) =>
+        new(
+            msg.Author.Tag(),
+            msg.Content,
+            msg.Attachments.Select(a => a.Url),
+            msg.ID.Timestamp,
+            msg.EditedTimestamp
+        );
+}