feat(apiv2): GET endpoints except guilds

- ResolveT methods in ControllerBase
- ContextFor methods in ControllerBase

PluralKit.API/Controllers/v2/MiscControllerV2.cs

@@ -5,6 +5,8 @@ using Microsoft.AspNetCore.Mvc;
 
 using Newtonsoft.Json.Linq;
 
+using NodaTime;
+
 using PluralKit.Core;
 
 namespace PluralKit.API
@@ -28,12 +30,25 @@ namespace PluralKit.API
             return Ok(o);
         }
 
-        [HttpGet("messages/{message_id}")]
-        public async Task<IActionResult> MessageGet(ulong message_id)
+        [HttpGet("messages/{messageId}")]
+        public async Task<ActionResult<MessageReturn>> MessageGet(ulong messageId)
         {
-            return new ObjectResult("Unimplemented")
+            var msg = await _db.Execute(c => _repo.GetMessage(c, messageId));
+            if (msg == null)
+                throw APIErrors.MessageNotFound;
+
+            var ctx = this.ContextFor(msg.System);
+
+            // todo: don't rely on v1 stuff
+            return new MessageReturn
             {
-                StatusCode = 501
+                Timestamp = Instant.FromUnixTimeMilliseconds((long)(msg.Message.Mid >> 22) + 1420070400000),
+                Id = msg.Message.Mid.ToString(),
+                Channel = msg.Message.Channel.ToString(),
+                Sender = msg.Message.Sender.ToString(),
+                System = msg.System.ToJson(ctx, v: APIVersion.V2),
+                Member = msg.Member.ToJson(ctx, v: APIVersion.V2),
+                Original = msg.Message.OriginalMid?.ToString()
             };
         }
     }