SPMS.API/Controllers/StatsController.cs

@@ -73,6 +73,15 @@ public class StatsController : ControllerBase
         return File(fileBytes, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet", fileName);
     }
 
+    [HttpPost("failure")]
+    [SwaggerOperation(Summary = "실패원인 통계 조회", Description = "실패 원인별 집계를 상위 N개로 조회합니다.")]
+    public async Task<IActionResult> GetFailureStatAsync([FromBody] FailureStatRequestDto request)
+    {
+        var serviceId = GetServiceId();
+        var result = await _statsService.GetFailureStatAsync(serviceId, request);
+        return Ok(ApiResponse<FailureStatResponseDto>.Success(result, "조회 성공"));
+    }
+
     [HttpPost("send-log")]
     [SwaggerOperation(Summary = "발송 상세 로그 조회", Description = "특정 메시지의 개별 디바이스별 발송 상세 로그를 조회합니다.")]
     public async Task<IActionResult> GetSendLogDetailAsync([FromBody] SendLogDetailRequestDto request)

SPMS.Application/DTOs/Stats/FailureStatRequestDto.cs

@@ -0,0 +1,19 @@
+using System.ComponentModel.DataAnnotations;
+using System.Text.Json.Serialization;
+
+namespace SPMS.Application.DTOs.Stats;
+
+public class FailureStatRequestDto
+{
+    [Required]
+    [JsonPropertyName("start_date")]
+    public string StartDate { get; set; } = string.Empty;
+
+    [Required]
+    [JsonPropertyName("end_date")]
+    public string EndDate { get; set; } = string.Empty;
+
+    [JsonPropertyName("limit")]
+    [Range(1, 20)]
+    public int Limit { get; set; } = 5;
+}

SPMS.Application/DTOs/Stats/FailureStatResponseDto.cs

@@ -0,0 +1,39 @@
+using System.Text.Json.Serialization;
+
+namespace SPMS.Application.DTOs.Stats;
+
+public class FailureStatResponseDto
+{
+    [JsonPropertyName("total_fail")]
+    public int TotalFail { get; set; }
+
+    [JsonPropertyName("period")]
+    public FailureStatPeriodDto Period { get; set; } = new();
+
+    [JsonPropertyName("items")]
+    public List<FailureStatItemDto> Items { get; set; } = new();
+}
+
+public class FailureStatPeriodDto
+{
+    [JsonPropertyName("start_date")]
+    public string StartDate { get; set; } = string.Empty;
+
+    [JsonPropertyName("end_date")]
+    public string EndDate { get; set; } = string.Empty;
+}
+
+public class FailureStatItemDto
+{
+    [JsonPropertyName("fail_reason")]
+    public string FailReason { get; set; } = string.Empty;
+
+    [JsonPropertyName("count")]
+    public int Count { get; set; }
+
+    [JsonPropertyName("ratio")]
+    public double Ratio { get; set; }
+
+    [JsonPropertyName("description")]
+    public string Description { get; set; } = string.Empty;
+}

SPMS.Application/Interfaces/IStatsService.cs

@@ -11,4 +11,5 @@ public interface IStatsService
     Task<DeviceStatResponseDto> GetDeviceStatAsync(long serviceId);
     Task<SendLogDetailResponseDto> GetSendLogDetailAsync(long serviceId, SendLogDetailRequestDto request);
     Task<byte[]> ExportReportAsync(long serviceId, StatsExportRequestDto request);
+    Task<FailureStatResponseDto> GetFailureStatAsync(long serviceId, FailureStatRequestDto request);
 }

SPMS.Application/Services/StatsService.cs

@@ -373,6 +373,52 @@ public class StatsService : IStatsService
         return stream.ToArray();
     }
 
+    public async Task<FailureStatResponseDto> GetFailureStatAsync(long serviceId, FailureStatRequestDto request)
+    {
+        var (startDate, endDate) = ParseDateRange(request.StartDate, request.EndDate);
+
+        var startDateTime = startDate.ToDateTime(TimeOnly.MinValue);
+        var endDateTime = endDate.ToDateTime(TimeOnly.MinValue).AddDays(1);
+
+        var failureStats = await _pushSendLogRepository.GetFailureStatsAsync(serviceId, startDateTime, endDateTime, request.Limit);
+
+        var totalFail = failureStats.Sum(f => f.Count);
+
+        var items = failureStats.Select(f => new FailureStatItemDto
+        {
+            FailReason = f.FailReason,
+            Count = f.Count,
+            Ratio = totalFail > 0 ? Math.Round((double)f.Count / totalFail * 100, 2) : 0,
+            Description = GetFailReasonDescription(f.FailReason)
+        }).ToList();
+
+        return new FailureStatResponseDto
+        {
+            TotalFail = totalFail,
+            Period = new FailureStatPeriodDto
+            {
+                StartDate = request.StartDate,
+                EndDate = request.EndDate
+            },
+            Items = items
+        };
+    }
+
+    private static string GetFailReasonDescription(string failReason)
+    {
+        return failReason switch
+        {
+            "InvalidToken" => "만료/잘못된 디바이스 토큰",
+            "NotRegistered" => "FCM/APNs에 미등록",
+            "MessageTooBig" => "페이로드 크기 초과 (4KB)",
+            "RateLimit" => "FCM/APNs 발송 제한 초과",
+            "ServerError" => "FCM/APNs 서버 오류",
+            "NetworkError" => "네트워크 연결 실패",
+            "Unknown" => "분류 불가",
+            _ => failReason
+        };
+    }
+
     private static double CalcCtr(int openCount, int successCount)
     {
         return successCount > 0 ? Math.Round((double)openCount / successCount * 100, 2) : 0;

SPMS.Domain/Interfaces/IPushSendLogRepository.cs

@@ -21,6 +21,7 @@ public interface IPushSendLogRepository : IRepository<PushSendLog>
         long serviceId, DateTime startDate, DateTime endDate,
         long? messageId = null, long? deviceId = null,
         PushResult? status = null, int maxCount = 100000);
+    Task<List<FailureStatRaw>> GetFailureStatsAsync(long serviceId, DateTime startDate, DateTime endDate, int limit);
 }
 
 public class HourlyStatRaw
@@ -46,3 +47,9 @@ public class MessageDailyStatRaw
     public int SendCount { get; set; }
     public int SuccessCount { get; set; }
 }
+
+public class FailureStatRaw
+{
+    public string FailReason { get; set; } = string.Empty;
+    public int Count { get; set; }
+}

SPMS.Infrastructure/Persistence/Repositories/PushSendLogRepository.cs

@@ -156,4 +156,23 @@ public class PushSendLogRepository : Repository<PushSendLog>, IPushSendLogReposi
             .OrderByDescending(d => d.StatDate)
             .ToListAsync();
     }
+
+    public async Task<List<FailureStatRaw>> GetFailureStatsAsync(long serviceId, DateTime startDate, DateTime endDate, int limit)
+    {
+        return await _dbSet
+            .Where(l => l.ServiceId == serviceId
+                && l.Status == PushResult.Failed
+                && l.SentAt >= startDate
+                && l.SentAt < endDate
+                && l.FailReason != null)
+            .GroupBy(l => l.FailReason!)
+            .Select(g => new FailureStatRaw
+            {
+                FailReason = g.Key,
+                Count = g.Count()
+            })
+            .OrderByDescending(f => f.Count)
+            .Take(limit)
+            .ToListAsync();
+    }
 }

TASKS.md

@@ -18,14 +18,14 @@
 |--------|:------:|:---------:|:------:|-------|
 | **Public** | 10 | 10 | 0 | Phase 2-2 ✅ |
 | **Auth** | 6 | 6 | 0 | Phase 2-1 ✅ |
-| **Account** | 5 | 5 | 0 | Phase 2-1 ✅ |
+| **Account** | 9 | 9 | 0 | Phase 2-1 + 3-2 ✅ |
 | **Service** | 13 | 13 | 0 | Phase 2-1 ✅ |
 | **Device** | 7 | 7 | 0 | Phase 2-2 ✅ |
 | **Message** | 5 | 1 | 4 | Phase 3 ← 다음 |
 | **Push** | 8 | 5 | 3 | Phase 3 |
 | **Stats** | 5 | 0 | 5 | Phase 3-2 |
 | **File** | 6 | 6 | 0 | Phase 2-2 ✅ |
-| **총계** | **65** | **53** | **12** | - |
+| **총계** | **65** | **57** | **8** | - |
 
 ---
 
@@ -1649,9 +1649,9 @@ Milestone: Phase 3: 메시지 & Push Core
 | 3 | [Feature] 플랫폼별 비중 조회 API | Feature | Medium | DSH-03 | ✅ |
 | 4 | [Feature] 메시지별 전환율 조회 API | Feature | Medium | DSH-04 | ✅ |
 | 5 | [Feature] 발송 이력 조회 API | Feature | High | DDN-01 | ✅ |
-| 6 | [Feature] 발송 상세 로그 조회 API | Feature | High | DDL-02 | ⬜ |
-| 7 | [Feature] 통계 리포트 다운로드 API | Feature | Medium | EXP-01 | ⬜ |
-| 8 | [Feature] 상세 로그 다운로드 API | Feature | Medium | EXP-02 | ⬜ |
+| 6 | [Feature] 발송 상세 로그 조회 API | Feature | High | DDL-02 | ✅ |
+| 7 | [Feature] 통계 리포트 다운로드 API | Feature | Medium | EXP-01 | ✅ |
+| 8 | [Feature] 상세 로그 다운로드 API | Feature | Medium | EXP-02 | ✅ |
 | 9 | [Feature] 실패원인 순위 API | Feature | Medium | ANA-01 | ⬜ |
 | 10 | [Feature] 웹훅 설정 API | Feature | High | WHK-01 | ⬜ |
 | 11 | [Feature] **웹훅 발송 서비스** | Feature | High | WHK-02 | ⬜ |