feat(apiv2): GET endpoints except guilds

- ResolveT methods in ControllerBase
- ContextFor methods in ControllerBase

PluralKit.API/Controllers/v2/GroupControllerV2.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 
 using Microsoft.AspNetCore.Mvc;
@@ -16,13 +17,23 @@ namespace PluralKit.API
     {
         public GroupControllerV2(IServiceProvider svc) : base(svc) { }
 
-        [HttpGet("systems/{system_id}/groups")]
-        public async Task<IActionResult> GetSystemGroups(string system_id)
+        [HttpGet("systems/{systemRef}/groups")]
+        public async Task<IActionResult> GetSystemGroups(string systemRef)
         {
-            return new ObjectResult("Unimplemented")
-            {
-                StatusCode = 501
-            };
+            var system = await ResolveSystem(systemRef);
+            if (system == null)
+                throw APIErrors.SystemNotFound;
+
+            var ctx = this.ContextFor(system);
+
+            if (!system.GroupListPrivacy.CanAccess(User.ContextFor(system)))
+                throw APIErrors.UnauthorizedGroupList;
+
+            var groups = _repo.GetSystemGroups(system.Id);
+            return Ok(await groups
+                .Where(g => g.Visibility.CanAccess(ctx))
+                .Select(g => g.ToJson(ctx))
+                .ToListAsync());
         }
 
         [HttpPost("groups")]
@@ -34,13 +45,16 @@ namespace PluralKit.API
             };
         }
 
-        [HttpGet("groups/{group_id}")]
-        public async Task<IActionResult> GroupGet(string group_id)
+        [HttpGet("groups/{groupRef}")]
+        public async Task<IActionResult> GroupGet(string groupRef)
         {
-            return new ObjectResult("Unimplemented")
-            {
-                StatusCode = 501
-            };
+            var group = await ResolveGroup(groupRef);
+            if (group == null)
+                throw APIErrors.GroupNotFound;
+
+            var system = await _repo.GetSystem(group.System);
+
+            return Ok(group.ToJson(this.ContextFor(group), systemStr: system.Hid));
         }
 
         [HttpPatch("groups/{group_id}")]