Add channel search and subscription

server/QMax.Api/Contracts/MaxContracts.cs

@@ -18,3 +18,13 @@ public sealed record MaxBrowserSnapshotDto(
     string BodyText,
     string ScreenshotPngBase64,
     DateTimeOffset CapturedAt);
+
+public sealed record MaxChannelSearchResultDto(
+    string ExternalId,
+    string Title,
+    string? AvatarUrl,
+    string? ChatUrl,
+    bool IsSubscribed,
+    string? Description);
+
+public sealed record SubscribeMaxChannelRequest(string Link);

server/QMax.Api/Controllers/MaxController.cs

@@ -21,6 +21,7 @@ public sealed class MaxController(
     MaxBridgeSyncService syncService,
     QMaxDbContext db,
     IHubContext<QMaxHub> hubContext,
+    ChatProjectionService projection,
     IOptions<QMaxOptions> options) : ControllerBase
 {
     private readonly QMaxOptions _options = options.Value;
@@ -69,6 +70,51 @@ public sealed class MaxController(
         return new { changed };
     }
 
+    [HttpGet("channels/search")]
+    public async Task<ActionResult<IReadOnlyList<MaxChannelSearchResultDto>>> SearchChannels(
+        string q,
+        CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(q))
+        {
+            return Array.Empty<MaxChannelSearchResultDto>();
+        }
+
+        var results = await maxBridge.SearchChannelsAsync(q.Trim(), cancellationToken);
+        return results.Select(ToDto).ToArray();
+    }
+
+    [HttpPost("channels/subscribe")]
+    public async Task<ActionResult<ChatDto>> SubscribeChannel(
+        SubscribeMaxChannelRequest request,
+        CancellationToken cancellationToken)
+    {
+        if (string.IsNullOrWhiteSpace(request.Link))
+        {
+            return BadRequest("Channel link is required.");
+        }
+
+        var update = await maxBridge.JoinChannelAsync(request.Link.Trim(), cancellationToken);
+        if (update is null)
+        {
+            return BadRequest("MAX did not return a channel for this link.");
+        }
+
+        await syncService.ApplyJoinedChannelAsync(update, cancellationToken);
+        var chat = await db.Chats.FirstOrDefaultAsync(
+            x => x.DeletedAt == null &&
+                (x.ExternalId == update.ExternalId ||
+                 (!string.IsNullOrWhiteSpace(update.ChatUrl) && x.WebUrl == update.ChatUrl)),
+            cancellationToken);
+        if (chat is null)
+        {
+            return BadRequest("Channel was joined but was not saved in QMAX.");
+        }
+
+        await hubContext.Clients.All.SendAsync("ChatListInvalidated", cancellationToken);
+        return projection.ToDto(chat);
+    }
+
     private async Task SaveStateAsync(MaxBridgeStatus status, CancellationToken cancellationToken)
     {
         var state = await db.MaxAccountStates.FirstOrDefaultAsync(x => x.Id == 1, cancellationToken);
@@ -92,4 +138,9 @@ public sealed class MaxController(
     {
         return new MaxBridgeStatusDto(status.Mode, status.IsAuthorized, status.LoginStage, status.Status, status.Url, status.Title, status.LastError, status.UpdatedAt);
     }
+
+    private static MaxChannelSearchResultDto ToDto(MaxChannelSearchResult channel)
+    {
+        return new MaxChannelSearchResultDto(channel.ExternalId, channel.Title, channel.AvatarUrl, channel.ChatUrl, channel.IsSubscribed, channel.Description);
+    }
 }

server/QMax.Api/Infrastructure/Max/IMaxBridgeClient.cs

@@ -19,4 +19,13 @@ public interface IMaxBridgeClient
     Task<MaxActionResult> SetReactionAsync(string externalChatId, string externalMessageId, string? currentText, string emoji, CancellationToken cancellationToken);
     Task<MaxActionResult> ClearReactionAsync(string externalChatId, string externalMessageId, string? currentText, string emoji, CancellationToken cancellationToken);
     Task<MaxMediaDownload?> DownloadMediaAsync(string remoteUrl, CancellationToken cancellationToken);
+    Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<IReadOnlyList<MaxChannelSearchResult>>(Array.Empty<MaxChannelSearchResult>());
+    }
+
+    Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<MaxChatUpdate?>(null);
+    }
 }

server/QMax.Api/Infrastructure/Max/MaxBridgeModels.cs

@@ -65,3 +65,11 @@ public sealed record MaxChatPresence(
     bool IsTyping,
     string? StatusText,
     DateTimeOffset UpdatedAt);
+
+public sealed record MaxChannelSearchResult(
+    string ExternalId,
+    string Title,
+    string? AvatarUrl,
+    string? ChatUrl,
+    bool IsSubscribed,
+    string? Description = null);

server/QMax.Api/Infrastructure/Max/MockMaxBridgeClient.cs

@@ -108,6 +108,30 @@ public sealed class MockMaxBridgeClient : IMaxBridgeClient
         return Task.FromResult<MaxMediaDownload?>(null);
     }
 
+    public Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        IReadOnlyList<MaxChannelSearchResult> result = string.IsNullOrWhiteSpace(query)
+            ? []
+            : [new MaxChannelSearchResult("mock-channel", "Mock channel", null, "mock-channel", false, "Mock MAX channel")];
+        return Task.FromResult(result);
+    }
+
+    public Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return Task.FromResult<MaxChatUpdate?>(new MaxChatUpdate(
+            "mock-channel",
+            "Mock channel",
+            null,
+            DateTimeOffset.UtcNow,
+            [],
+            "Mock channel subscribed",
+            false,
+            DateTimeOffset.UtcNow,
+            null,
+            MockChatUrl("mock-channel"),
+            "Channel"));
+    }
+
     private static string MockChatUrl(string externalChatId)
     {
         return $"pymax://mock/{Uri.EscapeDataString(externalChatId)}";

server/QMax.Api/Infrastructure/Max/WorkerMaxBridgeClient.cs

@@ -160,6 +160,25 @@ public sealed class WorkerMaxBridgeClient(
         }
     }
 
+    public async Task<IReadOnlyList<MaxChannelSearchResult>> SearchChannelsAsync(string query, CancellationToken cancellationToken)
+    {
+        return await SendAsync<IReadOnlyList<MaxChannelSearchResult>>(
+                HttpMethod.Post,
+                "/channels/search",
+                new { query },
+                cancellationToken)
+            ?? Array.Empty<MaxChannelSearchResult>();
+    }
+
+    public async Task<MaxChatUpdate?> JoinChannelAsync(string link, CancellationToken cancellationToken)
+    {
+        return await SendAsync<MaxChatUpdate>(
+            HttpMethod.Post,
+            "/channels/join",
+            new { link },
+            cancellationToken);
+    }
+
     private async Task<T?> SendAsync<T>(HttpMethod method, string path, object? body, CancellationToken cancellationToken)
     {
         try

server/QMax.Api/Services/MaxBridgeSyncService.cs

@@ -93,6 +93,16 @@ public sealed class MaxBridgeSyncService(
         }
     }
 
+    public async Task<int> ApplyJoinedChannelAsync(MaxChatUpdate update, CancellationToken cancellationToken)
+    {
+        return await ApplyUpdatesAsync(
+            [update],
+            incrementUnread: false,
+            sendPushNotifications: false,
+            cancellationToken,
+            allowGenericMediaHistoryFetch: false);
+    }
+
     private async Task<int> ApplyUpdatesAsync(
         IReadOnlyList<MaxChatUpdate> updates,
         bool incrementUnread,