fix: Pagination and Validation DTO and JWT

apps/api/Controllers/AdminQuestionsController.cs

@@ -1,4 +1,6 @@
 using DevDialogue.Api.Data;
+using DevDialogue.Api.Helpers;
+using DevDialogue.Api.Models;
 using DevDialogue.Api.Models.Dtos;
 using DevDialogue.Api.Models.Entities;
 using DevDialogue.Api.Security;
@@ -22,11 +24,13 @@ public AdminQuestionsController(AppDbContext context)
     }
 
     [HttpGet]
-    public async Task<ActionResult<List<QuestionBankDto>>> GetQuestions(
+    public async Task<ActionResult<PagedResult<QuestionBankDto>>> GetQuestions(
         [FromQuery] string? direction,
         [FromQuery] string? level,
         [FromQuery] string? stage,
-        [FromQuery] bool? isActive)
+        [FromQuery] bool? isActive,
+        [FromQuery] int page = 1,
+        [FromQuery] int pageSize = 20)
     {
         var query = _context.QuestionsBank.AsNoTracking().AsQueryable();
 
@@ -39,8 +43,9 @@ public async Task<ActionResult<List<QuestionBankDto>>> GetQuestions(
         if (isActive.HasValue)
             query = query.Where(q => q.IsActive == isActive.Value);
 
-        var items = await query
+        var pagedResult = await query
             .OrderByDescending(q => q.CreatedAt)
+            .ThenByDescending(q => q.Id)
             .Select(q => new QuestionBankDto(
                 q.Id,
                 q.Direction,
@@ -52,22 +57,37 @@ public async Task<ActionResult<List<QuestionBankDto>>> GetQuestions(
                 q.CreatedBy,
                 q.CreatedAt
             ))
-            .ToListAsync();
+            .ToPagedAsync(page, pageSize);
 
-        return Ok(items);
+        return Ok(pagedResult);
     }
 
     [HttpPost]
     public async Task<ActionResult<QuestionBankDto>> CreateQuestion([FromBody] CreateQuestionDto dto)
     {
+        if (!SupportedOptions.Directions.Contains(dto.Direction.ToLowerInvariant()))
+        {
+            return BadRequest(new { error = $"Invalid direction '{dto.Direction}'. Supported: {string.Join(", ", SupportedOptions.Directions)}", code = "INVALID_DIRECTION" });
+        }
+
+        if (!SupportedOptions.Levels.Contains(dto.Level.ToLowerInvariant()))
+        {
+            return BadRequest(new { error = $"Invalid level '{dto.Level}'. Supported: {string.Join(", ", SupportedOptions.Levels)}", code = "INVALID_LEVEL" });
+        }
+
+        if (!SupportedOptions.Stages.Contains(dto.Stage.ToLowerInvariant()))
+        {
+            return BadRequest(new { error = $"Invalid stage '{dto.Stage}'. Supported: {string.Join(", ", SupportedOptions.Stages)}", code = "INVALID_STAGE" });
+        }
+
         var userId = User.GetUserId();
 
         var item = new QuestionBank
         {
             Id = Guid.NewGuid(),
-            Direction = dto.Direction,
-            Stage = dto.Stage,
-            Level = dto.Level,
+            Direction = dto.Direction.ToLowerInvariant(),
+            Stage = dto.Stage.ToLowerInvariant(),
+            Level = dto.Level.ToLowerInvariant(),
             Topic = dto.Topic,
             QuestionText = dto.QuestionText,
             IsActive = true,

apps/api/Controllers/InterviewsController.cs

@@ -1,5 +1,7 @@
 using System.Text.Json;
 using DevDialogue.Api.Data;
+using DevDialogue.Api.Helpers;
+using DevDialogue.Api.Models;
 using DevDialogue.Api.Models.Dtos;
 using DevDialogue.Api.Models.Entities;
 using DevDialogue.Api.Security;
@@ -35,6 +37,36 @@ public InterviewsController(
     [HttpPost]
     public async Task<ActionResult<CreateInterviewResponseDto>> CreateInterview([FromBody] CreateInterviewDto dto)
     {
+        // Валідація мови: якщо мову не підтримується/не знайдено -> 404 Not Found
+        if (!SupportedOptions.Languages.Contains(dto.Language.ToLowerInvariant()))
+        {
+            return NotFound(new
+            {
+                error = $"Language '{dto.Language}' not found. Supported languages: {string.Join(", ", SupportedOptions.Languages)}",
+                code = "LANGUAGE_NOT_FOUND"
+            });
+        }
+
+        // Валідація напрямку
+        if (!SupportedOptions.Directions.Contains(dto.Direction.ToLowerInvariant()))
+        {
+            return BadRequest(new
+            {
+                error = $"Invalid direction '{dto.Direction}'. Supported: {string.Join(", ", SupportedOptions.Directions)}",
+                code = "INVALID_DIRECTION"
+            });
+        }
+
+        // Валідація рівня
+        if (!SupportedOptions.Levels.Contains(dto.Level.ToLowerInvariant()))
+        {
+            return BadRequest(new
+            {
+                error = $"Invalid level '{dto.Level}'. Supported: {string.Join(", ", SupportedOptions.Levels)}",
+                code = "INVALID_LEVEL"
+            });
+        }
+
         var userId = User.GetUserId();
         var dailyLimit = _config.GetValue<int>("DailyInterviewLimit", 10);
         var today = DateOnly.FromDateTime(DateTime.UtcNow);
@@ -74,7 +106,7 @@ public async Task<ActionResult<CreateInterviewResponseDto>> CreateInterview([Fro
         // Lookup starting topic from QuestionBank if available
         var seedQuestion = await _context.QuestionsBank
             .AsNoTracking()
-            .Where(q => q.Direction == dto.Direction && q.Level == dto.Level && q.IsActive)
+            .Where(q => q.Direction == dto.Direction.ToLowerInvariant() && q.Level == dto.Level.ToLowerInvariant() && q.IsActive)
             .OrderBy(_ => EF.Functions.Random())
             .FirstOrDefaultAsync();
 
@@ -89,9 +121,9 @@ public async Task<ActionResult<CreateInterviewResponseDto>> CreateInterview([Fro
         {
             Id = Guid.NewGuid(),
             UserId = userId,
-            Direction = dto.Direction,
-            Level = dto.Level,
-            Language = dto.Language,
+            Direction = dto.Direction.ToLowerInvariant(),
+            Level = dto.Level.ToLowerInvariant(),
+            Language = dto.Language.ToLowerInvariant(),
             Stage = "hard_skills",
             Status = "active",
             Transcript = JsonSerializer.Serialize(initialTranscript),
@@ -110,34 +142,24 @@ public async Task<ActionResult<CreateInterviewResponseDto>> CreateInterview([Fro
     }
 
     [HttpGet]
-    public async Task<ActionResult<List<InterviewSummaryDto>>> GetInterviews([FromQuery] int page = 1, [FromQuery] int pageSize = 20)
+    public async Task<ActionResult<PagedResult<InterviewSummaryDto>>> GetInterviews([FromQuery] int page = 1, [FromQuery] int pageSize = 20)
     {
         var userId = User.GetUserId();
 
         var query = _context.Interviews
             .AsNoTracking()
             .Where(i => i.UserId == userId)
-            .OrderByDescending(i => i.CreatedAt);
-
-        var items = await query
-            .Skip((page - 1) * pageSize)
-            .Take(pageSize)
+            .OrderByDescending(i => i.CreatedAt)
+            .ThenByDescending(i => i.Id)
             .Select(i => new InterviewSummaryDto(
-                i.Id,
-                i.UserId,
-                i.Direction,
-                i.Level,
-                i.Language,
-                i.Stage,
-                i.Status,
-                i.Score,
-                i.QuestionCount,
-                i.CreatedAt,
-                i.UpdatedAt
-            ))
-            .ToListAsync();
+                i.Id, i.UserId, i.Direction, i.Level, i.Language, 
+                i.Stage, i.Status, i.Score, i.QuestionCount, 
+                i.CreatedAt, i.UpdatedAt
+            ));
+
+        var pagedResult = await query.ToPagedAsync(page, pageSize);
 
-        return Ok(items);
+        return Ok(pagedResult);
     }
 
     [HttpGet("{id:guid}")]

apps/api/Controllers/OptionsController.cs

@@ -1,3 +1,4 @@
+using DevDialogue.Api.Models;
 using Microsoft.AspNetCore.Mvc;
 
 namespace DevDialogue.Api.Controllers;
@@ -11,9 +12,14 @@ public IActionResult GetOptions()
     {
         return Ok(new
         {
-            directions = new[] { "frontend", "backend", "devops", "qa", "pm" },
-            levels = new[] { "junior", "middle", "senior" },
-            languages = new[] { "uk", "en" }
+            directions = SupportedOptions.Directions,
+            levels = SupportedOptions.Levels,
+            stages = SupportedOptions.Stages,
+            languages = new[]
+            {
+                new { id = "uk", code = "uk", name = "Українська" },
+                new { id = "en", code = "en", name = "English" }
+            }
         });
     }
 }

apps/api/Helpers/PaginationExtensions.cs

@@ -0,0 +1,23 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace DevDialogue.Api.Helpers;
+
+public record PagedResult<T>(List<T> Items, int Page, int PageSize, int TotalCount)
+{
+    public int TotalPages => (int)Math.Ceiling(TotalCount / (double)PageSize);
+}
+
+public static class PaginationExtensions
+{
+    public static async Task<PagedResult<T>> ToPagedAsync<T>(
+        this IQueryable<T> query, int page, int pageSize)
+    {
+        page = Math.Max(page, 1);
+        pageSize = Math.Clamp(pageSize, 1, 100);
+
+        var total = await query.CountAsync();
+        var items = await query.Skip((page - 1) * pageSize).Take(pageSize).ToListAsync();
+
+        return new PagedResult<T>(items, page, pageSize, total);
+    }
+}

apps/api/Models/Dtos/AdminDtos.cs

@@ -1,3 +1,5 @@
+using System.ComponentModel.DataAnnotations;
+
 namespace DevDialogue.Api.Models.Dtos;
 
 public record QuestionBankDto(
@@ -13,18 +15,42 @@ DateTime CreatedAt
 );
 
 public record CreateQuestionDto(
+    [Required(ErrorMessage = "Напрямок (Direction) є обов'язковим")]
+    [MaxLength(50, ErrorMessage = "Напрямок не може перевищувати 50 символів")]
     string Direction,
+
+    [Required(ErrorMessage = "Етап (Stage) є обов'язковим")]
+    [MaxLength(50, ErrorMessage = "Етап не може перевищувати 50 символів")]
     string Stage,
+
+    [Required(ErrorMessage = "Рівень (Level) є обов'язковим")]
+    [MaxLength(50, ErrorMessage = "Рівень не може перевищувати 50 символів")]
     string Level,
+
+    [Required(ErrorMessage = "Тема (Topic) є обов'язковою")]
+    [MaxLength(200, ErrorMessage = "Тема не може перевищувати 200 символів")]
     string Topic,
+
+    [Required(ErrorMessage = "Текст питання (QuestionText) є обов'язковим")]
+    [MaxLength(3000, ErrorMessage = "Текст питання не може перевищувати 3000 символів")]
     string QuestionText
 );
 
 public record UpdateQuestionDto(
+    [MaxLength(50, ErrorMessage = "Напрямок не може перевищувати 50 символів")]
     string? Direction,
+
+    [MaxLength(50, ErrorMessage = "Етап не може перевищувати 50 символів")]
     string? Stage,
+
+    [MaxLength(50, ErrorMessage = "Рівень не може перевищувати 50 символів")]
     string? Level,
+
+    [MaxLength(200, ErrorMessage = "Тема не може перевищувати 200 символів")]
     string? Topic,
+
+    [MaxLength(3000, ErrorMessage = "Текст питання не може перевищувати 3000 символів")]
     string? QuestionText,
+
     bool? IsActive
 );

apps/api/Models/Dtos/AnswerRequestDto.cs

@@ -0,0 +1,15 @@
+using System.ComponentModel.DataAnnotations;
+using Microsoft.EntityFrameworkCore;
+
+namespace DevDialogue.Api.Models.Dtos
+{
+    public class AnswerRequestDto
+    {
+        [Required(ErrorMessage = "Відповідь не може бути порожньою")]
+        [MaxLength(3000, ErrorMessage = "Відповідь перевищує ліміт у 3000 символів")]
+        public string UserAnswer { get; set; } = string.Empty;
+
+        [Required]
+        public Guid QuestionId { get; set; }
+    }
+}

apps/api/Models/Dtos/InterviewDtos.cs

@@ -1,10 +1,15 @@
 using System.Text.Json.Serialization;
-
+using System.ComponentModel.DataAnnotations;
 namespace DevDialogue.Api.Models.Dtos;
 
 public record CreateInterviewDto(
+    [Required(ErrorMessage = "Напрямок (Direction) є обов'язковим")]
     string Direction,
+
+    [Required(ErrorMessage = "Рівень (Level) є обов'язковим")]
     string Level,
+
+    [Required(ErrorMessage = "Мова (Language) є обов'язковою")]
     string Language
 );
 
@@ -14,6 +19,8 @@ string FirstQuestion
 );
 
 public record SendMessageDto(
+    [Required(ErrorMessage = "Повідомлення не може бути порожнім")]
+    [MaxLength(3000, ErrorMessage = "Відповідь перевищує ліміт у 3000 символів")]
     string Content
 );
 

apps/api/Models/SupportedOptions.cs

@@ -0,0 +1,9 @@
+namespace DevDialogue.Api.Models;
+
+public static class SupportedOptions
+{
+    public static readonly string[] Directions = ["frontend", "backend", "devops", "qa", "pm"];
+    public static readonly string[] Levels = ["junior", "middle", "senior"];
+    public static readonly string[] Stages = ["hard_skills", "soft_skills", "english"];
+    public static readonly string[] Languages = ["uk", "en"];
+}