From 4c22cfaf19fe3d8143298bb467400919c992873f Mon Sep 17 00:00:00 2001
From: Chris Chen <yuanson.ch@gmail.com>
Date: Tue, 23 Jun 2026 19:18:50 -0700
Subject: [PATCH] Add Line webhook controller with signature verification and
 dispatch

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 .../Controllers/LineWebhookController.cs      | 88 +++++++++++++++++++
 .../DTOs/Notifications/LineWebhookDtos.cs     | 28 ++++++
 2 files changed, 116 insertions(+)
 create mode 100644 API/ROLAC.API/Controllers/LineWebhookController.cs
 create mode 100644 API/ROLAC.API/DTOs/Notifications/LineWebhookDtos.cs

diff --git a/API/ROLAC.API/Controllers/LineWebhookController.cs b/API/ROLAC.API/Controllers/LineWebhookController.cs
new file mode 100644
index 0000000..42e9a70
--- /dev/null
+++ b/API/ROLAC.API/Controllers/LineWebhookController.cs
@@ -0,0 +1,88 @@
+using System.Text;
+using System.Text.Json;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Options;
+using ROLAC.API.DTOs.Notifications;
+using ROLAC.API.Services.Notifications;
+
+namespace ROLAC.API.Controllers;
+
+/// <summary>
+/// Anonymous Line webhook. Verifies the X-Line-Signature over the raw body, then dispatches
+/// follow/message/join/leave events. Always returns 200 for valid payloads so Line does not retry;
+/// returns 400 only on signature failure.
+/// </summary>
+[ApiController]
+[Route("api/line")]
+[AllowAnonymous]
+public sealed class LineWebhookController : ControllerBase
+{
+    private static readonly JsonSerializerOptions JsonOpts = new() { PropertyNameCaseInsensitive = true };
+
+    private readonly ILineNotificationService _line;
+    private readonly IMessageChannel _channel;
+    private readonly LineOptions _options;
+
+    public LineWebhookController(
+        ILineNotificationService line, IMessageChannel channel, IOptions<LineOptions> options)
+    {
+        _line = line;
+        _channel = channel;
+        _options = options.Value;
+    }
+
+    [HttpPost("webhook")]
+    public async Task<IActionResult> Webhook(CancellationToken ct)
+    {
+        using var reader = new StreamReader(Request.Body, Encoding.UTF8);
+        var rawBody = await reader.ReadToEndAsync(ct);
+        var signature = Request.Headers["X-Line-Signature"].FirstOrDefault();
+
+        if (!LineSignature.IsValid(_options.ChannelSecret, Encoding.UTF8.GetBytes(rawBody), signature))
+            return BadRequest();
+
+        var payload = JsonSerializer.Deserialize<LineWebhookPayload>(rawBody, JsonOpts);
+        if (payload?.Events is not null)
+            foreach (var evt in payload.Events)
+                await DispatchAsync(evt, ct);
+
+        return Ok();
+    }
+
+    private async Task DispatchAsync(LineWebhookEvent evt, CancellationToken ct)
+    {
+        switch (evt.Type)
+        {
+            case "follow":
+                if (evt.ReplyToken is not null)
+                    await _channel.ReplyAsync(evt.ReplyToken, "歡迎！請輸入您的綁定碼以連結教會帳號。", ct);
+                break;
+
+            case "message":
+                if (evt.Message?.Type == "text"
+                    && evt.Source?.UserId is { } userId
+                    && evt.Message.Text is { } text)
+                {
+                    var result = await _line.TryBindMemberAsync(userId, text, ct);
+                    if (evt.ReplyToken is not null)
+                        await _channel.ReplyAsync(evt.ReplyToken, result.Message, ct);
+                }
+                break;
+
+            case "join":
+                if (evt.Source?.GroupId is { } joinGroupId)
+                {
+                    await _line.RegisterGroupAsync(joinGroupId, ct);
+                    if (evt.ReplyToken is not null)
+                        await _channel.ReplyAsync(evt.ReplyToken, "已加入群組，請至後台命名此群組。", ct);
+                }
+                break;
+
+            case "leave":
+                if (evt.Source?.GroupId is { } leaveGroupId)
+                    await _line.DeactivateGroupAsync(leaveGroupId, ct);
+                break;
+        }
+    }
+}
diff --git a/API/ROLAC.API/DTOs/Notifications/LineWebhookDtos.cs b/API/ROLAC.API/DTOs/Notifications/LineWebhookDtos.cs
new file mode 100644
index 0000000..6d9b441
--- /dev/null
+++ b/API/ROLAC.API/DTOs/Notifications/LineWebhookDtos.cs
@@ -0,0 +1,28 @@
+namespace ROLAC.API.DTOs.Notifications;
+
+/// <summary>Top-level Line webhook payload (deserialized case-insensitively).</summary>
+public sealed class LineWebhookPayload
+{
+    public List<LineWebhookEvent>? Events { get; set; }
+}
+
+public sealed class LineWebhookEvent
+{
+    public string?            Type       { get; set; }   // follow | message | join | leave | ...
+    public string?            ReplyToken { get; set; }
+    public LineWebhookSource? Source     { get; set; }
+    public LineWebhookMessage? Message   { get; set; }
+}
+
+public sealed class LineWebhookSource
+{
+    public string? Type    { get; set; }   // user | group | room
+    public string? UserId  { get; set; }
+    public string? GroupId { get; set; }
+}
+
+public sealed class LineWebhookMessage
+{
+    public string? Type { get; set; }       // text | image | ...
+    public string? Text { get; set; }
+}