Add daily study missions

api/QuestionsApi/Controllers/DailyMissionsController.cs

@@ -0,0 +1,36 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using QuestionsApi.Services;
+using System.Security.Claims;
+
+namespace QuestionsApi.Controllers;
+
+[ApiController]
+[Route("api/daily-missions")]
+[Authorize(Roles = "USER,SUPER")]
+public sealed class DailyMissionsController(
+    DailyMissionStore missions, DashboardStore dashboard, QuestionStore questions) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> Get()
+    {
+        var now = DateTime.UtcNow;
+        return Ok(await missions.GetOrCreateAsync(UserId(), await dashboard.GetAsync(UserId(), now),
+            await questions.GetPublishedAsync()));
+    }
+
+    [HttpPost("{missionId}/replace")]
+    public async Task<IActionResult> Replace(string missionId)
+    {
+        try
+        {
+            var result = await missions.ReplaceAsync(UserId(), missionId);
+            return result is null ? NotFound() : Ok(result);
+        }
+        catch (ArgumentException exception) { return NotFound(exception.Message); }
+        catch (InvalidOperationException exception) { return Conflict(exception.Message); }
+    }
+
+    private string UserId() => User.FindFirstValue(ClaimTypes.NameIdentifier)
+        ?? User.FindFirstValue(ClaimTypes.Name) ?? User.Identity?.Name ?? throw new UnauthorizedAccessException();
+}