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+# Technical Specifications - Tech.Interviewer Web API
+
+## Table of Contents
+
+1. [Project Overview](#project-overview)
+2. [Architecture](#architecture)
+3. [Solution Structure](#solution-structure)
+4. [Technology Stack](#technology-stack)
+5. [Domain Model](#domain-model)
+6. [Database Architecture](#database-architecture)
+7. [Services and Features](#services-and-features)
+8. [Authentication & Authorization](#authentication--authorization)
+9. [External Integrations](#external-integrations)
+10. [API Design](#api-design)
+11. [Background Jobs & Scheduling](#background-jobs--scheduling)
+12. [Logging & Monitoring](#logging--monitoring)
+13. [Code Standards & Patterns](#code-standards--patterns)
+14. [Development Guide](#development-guide)
+15. [Deployment](#deployment)
+
+---
+
+## Project Overview
+
+Tech.Interviewer Web API is a monolithic backend API for [techinterview.space](https://techinterview.space), a platform for developer interview management, salary data collection and analysis, company reviews, and AI-powered insights.
+
+**Repository:** https://github.com/techinterview-space/web-api
+
+**Key Features:**
+- Interview management and PDF generation
+- Salary data collection, analysis, and visualization
+- Company reviews and ratings with AI analysis
+- Telegram bot integration for salary notifications
+- GitHub profile analysis
+- Currency conversion and historical data tracking
+- AI-powered company analysis (ChatGPT, Claude)
+
+---
+
+## Architecture
+
+### Architectural Pattern
+
+The application follows a **Clean Architecture / Domain-Driven Design (DDD)** approach with clear separation of concerns:
+
+```
+┌─────────────────────────────────────────────────────────┐
+│                   Web.Api Layer                        │
+│  (Controllers, Features, Middlewares, Setup)            │
+└─────────────────────┬───────────────────────────────────┘
+                      │
+                      ↓
+┌─────────────────────────────────────────────────────────┐
+│                Infrastructure Layer                    │
+│  (Database, External Services, AI, Email, Storage)    │
+└─────────────────────┬───────────────────────────────────┘
+                      │
+                      ↓
+┌─────────────────────────────────────────────────────────┐
+│                    Domain Layer                         │
+│  (Entities, Value Objects, Validation, Enums)          │
+└─────────────────────────────────────────────────────────┘
+```
+
+### Layer Responsibilities
+
+#### 1. Web.Api Layer (Presentation)
+- **Controllers**: API endpoints organized by feature
+- **Features**: Request/Command handlers (CQRS-like pattern)
+- **Middlewares**: Request/response processing
+- **Setup**: Dependency injection configuration
+
+#### 2. Infrastructure Layer (Application)
+- Database context and EF Core configurations
+- External service integrations (AI, Email, Storage)
+- Business logic services
+- Mediator pattern implementation
+
+#### 3. Domain Layer (Core Business Logic)
+- Entity models
+- Value objects
+- Business rules and validation
+- Domain events
+
+### Design Patterns
+
+1. **CQRS (Command Query Responsibility Segregation)**
+   - Separate handlers for commands and queries
+   - `IRequestHandler<TRequest, TResult>` interface
+
+2. **Repository Pattern**
+   - EF Core `DbContext` as aggregate root
+   - Custom extensions for complex queries
+
+3. **Specification Pattern**
+   - Fluent query builders for complex searches
+
+4. **Mediator Pattern**
+   - `IRequestHandler<TRequest, TResult>` for request/response handling
+
+5. **Dependency Injection**
+   - Constructor injection throughout
+   - Scoped, Transient, Singleton lifetimes as appropriate
+
+---
+
+## Solution Structure
+
+```
+src/
+├── Domain/                      # Core domain layer
+│   ├── Attributes/             # Custom validation attributes
+│   ├── Entities/               # Domain entities
+│   │   ├── Companies/          # Company-related entities
+│   │   ├── Interviews/         # Interview entities
+│   │   ├── Salaries/           # Salary data entities
+│   │   ├── Users/              # User entities
+│   │   ├── Github/             # GitHub profile entities
+│   │   ├── Telegram/           # Telegram bot entities
+│   │   ├── StatData/           # Statistics and subscriptions
+│   │   ├── Labels/             # Label entities
+│   │   ├── Prompts/            # AI prompt entities
+│   │   ├── CSV/                # CSV export entities
+│   │   ├── Currencies/         # Currency entities
+│   │   └── HistoricalRecords/  # Historical data entities
+│   ├── Enums/                  # Domain enumerations
+│   ├── Extensions/             # Domain extension methods
+│   ├── Totp/                   # TOTP (Two-Factor Auth) logic
+│   ├── Validation/             # Validation framework
+│   ├── ValueObjects/           # Value objects
+│   │   ├── Dates/             # Date-related value objects
+│   │   ├── Pagination/        # Pagination logic
+│   │   └── Ranges/            # Range value objects
+│   └── Domain.csproj
+│
+├── Infrastructure/              # Infrastructure layer
+│   ├── Ai/                    # AI service providers
+│   │   ├── ChatGpt/           # OpenAI ChatGPT integration
+│   │   └── Claude/            # Anthropic Claude integration
+│   ├── Authentication/         # Authentication services
+│   ├── Configs/               # Configuration classes
+│   ├── Currencies/            # Currency services
+│   ├── Database/              # EF Core database
+│   │   ├── Config/           # Entity configurations
+│   │   └── Extensions/       # Database extensions
+│   ├── Emails/                # Email services
+│   ├── Extensions/            # Infrastructure extensions
+│   ├── Images/                # Image processing
+│   ├── Jwt/                   # JWT token generation
+│   ├── Migrations/            # Database migrations
+│   ├── Salaries/              # Salary data services
+│   ├── Services/              # Application services
+│   │   ├── AiServices/        # AI-related services
+│   │   ├── Companies/         # Company services
+│   │   ├── Correlation/       # Correlation ID tracking
+│   │   ├── Files/             # File storage (S3)
+│   │   ├── Github/            # GitHub API services
+│   │   ├── Html/              # HTML/Markdown generation
+│   │   ├── Mediator/          # Mediator pattern
+│   │   ├── PDF/               # PDF generation
+│   │   ├── Professions/       # Professions caching
+│   │   └── Telegram/          # Telegram bot services
+│   └── Infrastructure.csproj
+│
+├── Web.Api/                   # Presentation layer
+│   ├── Features/              # Feature modules (CQRS handlers)
+│   │   ├── Accounts/         # Account management
+│   │   ├── Admin/            # Admin features
+│   │   ├── Companies/        # Company endpoints
+│   │   ├── CompanyReviews/   # Company reviews
+│   │   ├── Emails/           # Email features
+│   │   ├── Github/           # GitHub features
+│   │   ├── Interviews/       # Interview endpoints
+│   │   ├── Salaries/         # Salary endpoints
+│   │   ├── Surveys/          # Survey features
+│   │   ├── Telegram/         # Telegram features
+│   │   └── Users/            # User endpoints
+│   ├── Middlewares/           # Custom middlewares
+│   ├── Services/              # Web.Api specific services
+│   ├── Setup/                 # DI and configuration
+│   ├── Views/                 # Razor views (emails)
+│   ├── Program.cs             # Application entry point
+│   ├── Startup.cs             # Startup configuration
+│   └── Web.Api.csproj
+│
+├── TestUtils/                 # Testing utilities
+│   ├── Auth/                  # Test auth utilities
+│   ├── Db/                    # In-memory database utilities
+│   ├── Fakes/                 # Entity factories
+│   ├── Mocks/                 # Service mocks
+│   └── TestUtils.csproj
+│
+├── Domain.Tests/               # Domain layer tests
+├── InfrastructureTests/        # Infrastructure layer tests
+└── Web.Api.Tests/            # Presentation layer tests
+```
+
+---
+
+## Technology Stack
+
+### Core Framework
+- **.NET 10** (Target Framework: `net10.0`)
+- **C# Latest** (Language version: latest)
+
+### Database
+- **PostgreSQL** 13 (via Docker)
+- **Entity Framework Core** 10.0.1
+- **Npgsql.EntityFrameworkCore.PostgreSQL** 10.0.0
+
+### Web Server
+- **ASP.NET Core** 10.0.0
+- **Kestrel** (default web server)
+
+### Infrastructure
+- **Docker & Docker Compose** (containerization)
+- **Elasticsearch** 8.0.0 (logging)
+- **Kibana** 8.0.0 (log visualization)
+- **LocalStack** (AWS services emulation)
+
+### Key Libraries
+
+| Category | Library | Version | Purpose |
+|----------|---------|---------|---------|
+| Authentication | Microsoft.AspNetCore.Authentication.JwtBearer | 10.0.0 | JWT authentication |
+| AI Integration | GraphQL.Client | 6.1.0 | GitHub GraphQL API |
+| PDF Generation | QuestPDF | 2025.12.0 | PDF generation |
+| Email | SendGrid | 9.29.3 | Email delivery |
+| Email | StrongGrid | 0.114.0 | Advanced SendGrid features |
+| Telegram | Telegram.Bot | 22.7.6 | Telegram bot |
+| Storage | AspNetCore.Aws.S3.Simple | 0.1.5 | AWS S3 integration |
+| CSV | CsvHelper | 33.1.0 | CSV parsing |
+| TOTP | Otp.NET | 1.4.1 | Two-factor authentication |
+| Environment | dotenv.net | 4.0.0 | .env file loading |
+| Logging | Serilog | 3.1.1 | Structured logging |
+| Elasticsearch Sink | Serilog.Sinks.Elasticsearch | 9.0.3 | Elasticsearch logging |
+| Scheduling | Coravel | 6.0.2 | Task scheduling |
+| Swagger | Swashbuckle.AspNetCore | 10.1.0 | API documentation |
+
+### AI Providers
+- **ChatGPT** (OpenAI) - AI analysis and chat
+- **Claude** (Anthropic) - Alternative AI provider
+
+---
+
+## Domain Model
+
+### Core Entities
+
+#### 1. User (src/Domain/Entities/Users/User.cs)
+Represents application users with multi-factor authentication support.
+
+**Properties:**
+- `Id` (long): Primary key
+- `Email` (string): User email (unique, max 150 chars)
+- `FirstName`, `LastName` (string): User names
+- `IdentityId` (string): External auth provider ID (Google/GitHub/Auth0)
+- `ProfilePicture` (string): Profile picture URL
+- `EmailConfirmed` (bool): Email verification status
+- `UniqueToken` (string): Unsubscribe token
+- `TotpSecret` (string): TOTP secret key for 2FA
+- `TotpVerifiedAt` (DateTimeOffset?): Last TOTP verification time
+- `DeletedAt` (DateTimeOffset?): Soft delete timestamp
+- `LastLoginAt` (DateTimeOffset?): Last login timestamp
+- `UserRoles` (List<UserRole>): User roles
+- `Salaries` (List<UserSalary>): User's salary records
+- `Reviews` (List<CompanyReview>): User's company reviews
+- `Votes` (List<CompanyReviewVote>): Review votes
+- `Emails` (List<UserEmail>): User email history
+
+**Key Methods:**
+- `HasOrFail(Role)`: Authorization check
+- `HasAnyOrFail(Role[])`: Multiple role check
+- `VerifyTotp(string)`: Verify 2FA code
+- `IsMfaEnabled()`: Check if 2FA is enabled
+- `GenerateTotpSecretKey()`: Generate TOTP secret
+- `ConfirmEmail()`: Mark email as confirmed
+- `Delete()`/`Restore()`: Soft delete/restore
+
+#### 2. Interview (src/Domain/Entities/Interviews/Interview.cs)
+Represents developer interviews.
+
+**Properties:**
+- `Id` (Guid): Primary key (GUID-based)
+- `CandidateName` (string): Interview candidate name
+- `InterviewerId` (long): Foreign key to User
+- `Interviewer` (User): Interviewer entity
+- `OverallOpinion` (string): Overall interview opinion (max 50,000 chars)
+- `CandidateGrade` (DeveloperGrade?): Candidate grade
+- `ShareLink` (ShareLink): Shared link entity
+- `Subjects` (List<InterviewSubject>): Interview subjects
+
+#### 3. Company (src/Domain/Entities/Companies/Company.cs)
+Represents companies with review and rating system.
+
+**Properties:**
+- `Id` (Guid): Primary key
+- `Name` (string): Company name
+- `NormalizedName` (string): Uppercase name for searching
+- `Description` (string): Company description
+- `Links` (List<string>): Company links
+- `LogoUrl` (string): Logo URL
+- `Rating` (double): Average rating (0-5)
+- `ReviewsCount` (int): Number of reviews
+- `ViewsCount` (int): View counter
+- `Slug` (string): URL slug
+- `DeletedAt` (DateTime?): Soft delete timestamp
+- `RatingHistory` (List<CompanyRatingHistory>): Rating history
+- `Reviews` (List<CompanyReview>): Company reviews
+- `OpenAiAnalysisRecords` (List<CompanyOpenAiAnalysis>): AI analysis
+
+**Key Methods:**
+- `AddReview(CompanyReview)`: Add a review
+- `ApproveReview(Guid)`: Approve and recalculate rating
+- `RecalculateRating()`: Update average rating
+- `MarkReviewAsOutdated(Guid)`: Mark review as outdated
+
+#### 4. UserSalary (src/Domain/Entities/Salaries/UserSalary.cs)
+Represents salary data submissions.
+
+**Properties:**
+- `Id` (Guid): Primary key
+- `UserId` (long?): User ID
+- `User` (User): User entity
+- `Value` (double): Salary amount
+- `Quarter` (int): Quarter (1-4)
+- `Year` (int): Year (2000-3000)
+- `Currency` (Currency): Currency type
+- `Grade` (DeveloperGrade?): Developer grade
+- `Company` (CompanyType): Company type
+- `ProfessionEnum` (UserProfessionEnum): Profession enum
+- `City` (KazakhstanCity?): City
+- `Age` (int?): Age
+- `YearOfStartingWork` (int?): Work start year
+- `Gender` (Gender?): Gender
+- `UseInStats` (bool): Include in statistics
+- `SkillId` (long?): Skill ID
+- `WorkIndustryId` (long?): Work industry ID
+- `ProfessionId` (long?): Profession ID
+- `SourceType` (SalarySourceType?): Source type
+
+#### 5. CompanyReview (src/Domain/Entities/Companies/CompanyReview.cs)
+Company review with rating system.
+
+**Properties:**
+- `Id` (Guid): Primary key
+- `CompanyId` (Guid): Company ID
+- `Company` (Company): Company entity
+- `UserId` (long): User ID
+- `User` (User): User entity
+- `Title` (string): Review title
+- `Body` (string): Review body
+- `Ratings` (Dictionary<string, int>): Rating categories
+- `TotalRating` (double): Overall rating
+- `ApprovedAt` (DateTimeOffset?): Approval timestamp
+- `OutdatedAt` (DateTimeOffset?): Outdated timestamp
+
+### Enums
+
+#### Role (src/Domain/Enums/Role.cs)
+```csharp
+Undefined = 0,
+Interviewer = 1,
+Admin = 1024
+```
+
+#### DeveloperGrade (src/Domain/Entities/Enums/DeveloperGrade.cs)
+Standard developer grade levels (Junior, Middle, Senior, Tech Lead, etc.)
+
+#### Gender (src/Domain/Enums/Gender.cs)
+```csharp
+Undefined = 0,
+Female = 1,
+Male = 2,
+PreferNotToSay = 3,
+Other = 4
+```
+
+#### KazakhstanCity (src/Domain/Enums/KazakhstanCity.cs)
+Kazakhstan cities for location-based filtering
+
+#### CompanyType (src/Domain/Entities/Salaries/CompanyType.cs)
+Company types (Product, Outsource, Startup, etc.)
+
+#### UserProfessionEnum (src/Domain/Entities/Salaries/UserProfessionEnum.cs)
+Developer professions (Backend, Frontend, Fullstack, DevOps, etc.)
+
+### Value Objects
+
+#### CurrentUser (src/Domain/ValueObjects/CurrentUser.cs)
+Represents the authenticated user from HTTP context.
+
+**Properties:**
+- `UserId` (string): Auth provider user ID
+- `Email` (string): User email
+- `FirstName`, `LastName` (string): User names
+- `ProfilePicture` (string): Profile picture URL
+- `Roles` (List<Role>): User roles
+
+**Methods:**
+- `IsGoogleAuth()`: Check if Google OAuth
+- `IsGithubAuth()`: Check if GitHub OAuth
+- `IsAuth0Auth()`: Check if Auth0
+
+#### CompanySlug (src/Domain/ValueObjects/CompanySlug.cs)
+Company slug generation and validation.
+
+#### KebabCaseSlug (src/Domain/ValueObjects/KebabCaseSlug.cs)
+Kebab-case slug generation.
+
+#### PageModel (src/Domain/ValueObjects/Pagination/PageModel.cs)
+Pagination parameters (page, pageSize).
+
+#### PercentileCollection (src/Domain/ValueObjects/PercentileCollection.cs)
+Statistical percentile calculations.
+
+---
+
+## Database Architecture
+
+### Database Context
+**Location:** `src/Infrastructure/Database/DatabaseContext.cs`
+
+**DbContext:** `DatabaseContext : DbContext`
+
+### DbSets (Tables)
+
+| Entity | DbSet Name | Primary Key Type |
+|--------|------------|------------------|
+| User | Users | long |
+| InterviewTemplate | InterviewTemplates | long |
+| Interview | Interviews | Guid |
+| ShareLink | ShareLinks | long |
+| UserLabel | UserLabels | long |
+| UserSalary | Salaries | Guid |
+| Skill | Skills | long |
+| WorkIndustry | WorkIndustries | long |
+| Profession | Professions | long |
+| SalariesBotMessage | SalariesBotMessages | long |
+| TelegramUserSettings | TelegramUserSettings | long |
+| UserCsvDownload | UserCsvDownloads | long |
+| SalariesSurveyReply | SalariesSurveyReplies | long |
+| StatDataChangeSubscription | SalariesSubscriptions | long |
+| Company | Companies | Guid |
+| CompanyRatingHistory | CompanyRatingHistoryRecords | long |
+| CompanyReview | CompanyReviews | Guid |
+| CompanyReviewVote | CompanyReviewVotes | long |
+| AiAnalysisRecord | AiAnalysisSubscriptionRecords | long |
+| TelegramInlineReply | TelegramInlineReplies | long |
+| SubscriptionTelegramMessage | SalariesSubscriptionTelegramMessages | long |
+| UserEmail | UserEmails | long |
+| GithubProfile | GithubProfiles | long |
+| GithubProfileBotChat | GithubProfileBotChats | long |
+| GithubProfileBotMessage | GithubProfileBotMessages | long |
+| GithubPersonalUserToken | GithubPersonalUserTokens | long |
+| GithubProfileProcessingJob | GithubProfileProcessingJobs | long |
+| OpenAiPrompt | OpenAiPrompts | long |
+| CompanyOpenAiAnalysis | CompanyOpenAiAnalysisRecords | long |
+| LastWeekCompanyReviewsSubscription | CompanyReviewsSubscriptions | long |
+| JobPostingMessageSubscription | JobPostingMessageSubscriptions | long |
+| SalariesHistoricalDataRecordTemplate | SalariesHistoricalDataRecordTemplates | long |
+| SalariesHistoricalDataRecord | SalariesHistoricalDataRecords | long |
+| CurrenciesCollection | CurrencyCollections | long |
+
+### Database Configuration
+
+**Location:** `src/Infrastructure/Database/Config/`
+
+Entity configurations use Fluent API:
+- Indexes (unique, composite)
+- Relationships (one-to-many, many-to-many)
+- Property constraints (max length, required, etc.)
+- Query filters (soft delete)
+
+**Key Configurations:**
+- `UserDbConfig.cs`: User entity indexes (Email, IdentityId, UniqueToken)
+- `CompanyEntityConfiguration.cs`: Company entity configuration
+- `InterviewConfig.cs`: Interview entity configuration
+- `UserSalaryConfig.cs`: Salary entity configuration
+
+### Migrations
+
+**Location:** `src/Infrastructure/Migrations/`
+
+⚠️ **IMPORTANT:** Migrations are manually generated and should NOT be modified directly.
+
+**Migration Generation:**
+```powershell
+./add-migration.ps1 <MigrationName>
+```
+
+Or using EF CLI:
+```bash
+dotnet ef migrations add <MigrationName> --project Infrastructure --startup-project Web.Api
+```
+
+### Database Methods
+
+**Save Operations:**
+```csharp
+await context.SaveAsync<TEntity>(entity)
+await context.SaveAsync(entities)
+await context.RemoveAsync(entity)
+```
+
+**Transaction Support:**
+```csharp
+await context.DoWithinTransactionAsync<TResult>(
+    action,
+    errorMessage,
+    cancellationToken)
+```
+
+---
+
+## Services and Features
+
+### Feature Pattern (CQRS)
+
+All features follow the CQRS pattern:
+- **Commands**: Write operations
+- **Queries**: Read operations
+- **Handlers**: `IRequestHandler<TRequest, TResult>` implementation
+
+**Example Handler Structure:**
+```csharp
+public class FeatureHandler : IRequestHandler<FeatureRequest, FeatureResponse>
+{
+    public async Task<FeatureResponse> Handle(
+        FeatureRequest request,
+        CancellationToken cancellationToken)
+    {
+        // Implementation
+    }
+}
+```
+
+### Key Features
+
+#### 1. Accounts (src/Web.Api/Features/Accounts/)
+- Account management
+- TOTP (2FA) setup and verification
+- User profile management
+
+**Controllers:**
+- `AccountController.cs`
+- `TotpController.cs`
+
+#### 2. Interviews (src/Web.Api/Features/Interviews/)
+- Interview creation and management
+- Interview templates
+- PDF generation
+- Share links
+
+**Controllers:**
+- `InterviewsController.cs`
+- `InterviewTemplateController.cs`
+
+**Services:**
+- `IInterviewPdfService` - PDF generation using QuestPDF
+
+#### 3. Companies (src/Web.Api/Features/Companies/)
+- Company CRUD operations
+- Company search
+- Company details
+
+**Controllers:**
+- `CompaniesController.cs`
+
+#### 4. Company Reviews (src/Web.Api/Features/CompanyReviews/)
+- Add company reviews
+- Approve/reject reviews
+- Vote on reviews (like/dislike)
+- RSS feed for recent reviews
+- Search reviews
+
+**Controllers:**
+- `CompanyReviewsController.cs`
+
+**RSS Endpoint:**
+```
+GET /api/companies/reviews/recent.rss
+```
+
+#### 5. Salaries (src/Web.Api/Features/Salaries/)
+- Salary data submission
+- Salary statistics and charts
+- Salary filtering and analysis
+- Historical data
+
+**Controllers:**
+- `SalariesController.cs`
+- `SalariesAdminController.cs`
+- `SalariesChartShare/ChartShareController.cs`
+
+**Features:**
+- Salary charts (by grade, experience, city, gender, etc.)
+- Percentile calculations
+- Currency conversion
+- Historical data templates
+
+#### 6. Salary Subscriptions (src/Web.Api/Features/SalarySubscribtions/)
+- Telegram subscriptions for salary updates
+- Subscription management (activate/deactivate)
+- AI-powered salary reports
+
+**Controllers:**
+- `SalaryTelegramSubscriptionsController.cs`
+
+**Services:**
+- `SalariesSubscriptionService`
+
+#### 7. GitHub Integration (src/Web.Api/Features/Github/)
+- GitHub profile analysis
+- GitHub personal tokens
+- Profile processing jobs
+
+**Controllers:**
+- `GithubController.cs`
+
+**Services:**
+- `IGithubGraphQLService` - GitHub API integration
+- `IGithubPersonalUserTokenService` - Token management
+
+#### 8. Telegram Bots (src/Web.Api/Features/Telegram/)
+- Salary notification bot
+- GitHub profile bot
+- Inline replies
+- User settings
+
+**Controllers:**
+- `TelegramBotController.cs`
+
+**Hosted Services:**
+- `SalariesTelegramBotHostedService`
+- `GithubProfileBotHostedService`
+
+**Services:**
+- `ISalariesTelegramBotClientProvider`
+- `IGithubProfileBotProvider`
+- `ITelegramAdminNotificationService`
+
+#### 9. Admin Features (src/Web.Api/Features/Admin/)
+- Admin dashboard
+- Debug tools
+- AI prompt management
+- System administration
+
+**Controllers:**
+- `AdminDashboardController.cs`
+- `AdminToolsController.cs`
+- `DebugController.cs`
+- `AiPromptController.cs`
+
+#### 10. Dictionaries (src/Web.Api/Features/Dictionaries/)
+- Skills management
+- Professions management
+- Work industries management
+
+**Controllers:**
+- `SkillsController.cs`
+- `ProfessionsController.cs`
+- `WorkIndustriesController.cs`
+
+**Services:**
+- `IProfessionsCacheService` - Cached professions data
+
+#### 11. Surveys (src/Web.Api/Features/Surveys/)
+- Salary surveys
+- Survey statistics
+- Survey responses
+
+**Controllers:**
+- `SurveyController.cs`
+
+#### 12. Import/Export (src/Web.Api/Features/Import/)
+- CSV data export
+- Data import utilities
+
+**Controllers:**
+- `ImportController.cs`
+
+#### 13. Webhooks (src/Web.Api/Features/Webhooks/)
+- External webhook handling
+
+**Controllers:**
+- `WebhooksController.cs`
+
+---
+
+## Authentication & Authorization
+
+### Authentication Flow
+
+The application supports multiple authentication providers:
+1. **Google OAuth2**
+2. **GitHub OAuth**
+3. **Auth0**
+
+### Authentication Service
+
+**Location:** `src/Infrastructure/Authentication/AuthorizationService.cs`
+
+**Key Methods:**
+```csharp
+Task<User> GetCurrentUserOrFailAsync()
+Task<User> GetCurrentUserOrNullAsync()
+Task HasRoleOrFailAsync(Role role)
+Task HasAnyRoleOrFailAsync(Role[] roles)
+```
+
+### Current User Detection
+
+Based on `IdentityId` prefix:
+- **Google**: `google-oauth2|` prefix
+- **GitHub**: `github|` prefix
+- **Auth0**: `auth0|` prefix
+
+### Authorization
+
+**Attribute-based Authorization:**
+```csharp
+[HasAnyRole]          // Require any authenticated user
+[HasAnyRole(Role.Admin)]  // Require specific role
+```
+
+**Location:** `src/Web.Api/Setup/Attributes/HasAnyRoleAttribute.cs`
+
+### Role-Based Access Control (RBAC)
+
+**Roles:**
+- `Undefined = 0` - No role
+- `Interviewer = 1` - Standard interviewer role
+- `Admin = 1024` - Administrator role
+
+### Two-Factor Authentication (2FA)
+
+Using TOTP (Time-based One-Time Password):
+- Library: **Otp.NET** 1.4.1
+- Implementation: `src/Domain/Totp/`
+
+**Key Methods:**
+- `GenerateTotpSecretKey()`: Generate TOTP secret
+- `VerifyTotp(string code)`: Verify 6-digit code
+- `TotpVerificationExpired()`: Check if verification expired (6-hour window)
+
+### JWT Token Generation
+
+**Location:** `src/Infrastructure/Jwt/TechinterviewJwtTokenGenerator.cs`
+
+---
+
+## External Integrations
+
+### 1. AI Services
+
+#### OpenAI ChatGPT
+**Location:** `src/Infrastructure/Ai/ChatGpt/`
+
+**Interface:** `IAiProvider`
+```csharp
+Task<AiChatResult> AnalyzeChatAsync(
+    string input,
+    string systemPrompt,
+    string model = null,
+    string correlationId = null,
+    CancellationToken cancellationToken)
+```
+
+**Features:**
+- Company review analysis
+- Salary data analysis
+- General AI chat
+
+#### Anthropic Claude
+**Location:** `src/Infrastructure/Ai/Claude/`
+
+**Features:**
+- Alternative AI provider
+- Same interface as ChatGPT
+
+**Factory:** `IAiProviderFactory` selects provider based on configuration
+
+### 2. Email Services
+
+**Providers:**
+- **SendGrid** (Production)
+- **Local** (Development)
+
+**Location:** `src/Infrastructure/Emails/`
+
+**Interfaces:**
+```csharp
+IEmailApiSender
+ITechinterviewEmailService
+IViewRenderer (Razor views for email templates)
+```
+
+**Services:**
+- `SendgridEmailApiSender`
+- `LocalEmailApiSender`
+- `TechInterviewerEmailService`
+
+**Email Templates:** `src/Web.Api/Views/EmailTemplates/`
+
+### 3. Storage Services
+
+**AWS S3 Integration**
+**Library:** `AspNetCore.Aws.S3.Simple` 0.1.5
+**Location:** `src/Infrastructure/Services/Files/`
+
+**Services:**
+```csharp
+IPublicStorage    // Public file storage
+ICvStorage        // CV storage
+```
+
+**Implementations:**
+- `PublicStorage` - S3 public storage
+- `CvStorageS3Service` - S3 CV storage
+
+### 4. Telegram Bots
+
+**Library:** `Telegram.Bot` 22.7.6
+
+**Services:**
+- `SalariesTelegramBotClientProvider` - Salary notifications
+- `GithubProfileBotProvider` - GitHub profile bot
+
+**Features:**
+- Salary update notifications
+- Chart sharing via Telegram
+- Inline replies
+- User settings management
+
+### 5. GitHub Integration
+
+**Library:** `GraphQL.Client` 6.1.0
+
+**Services:**
+```csharp
+IGithubGraphQLService         - GraphQL API
+IGithubPersonalUserTokenService - Personal token management
+```
+
+**Features:**
+- Profile data retrieval
+- Repository analysis
+- Bot interactions
+
+### 6. Currency Services
+
+**Location:** `src/Infrastructure/Currencies/`
+
+**Interfaces:**
+```csharp
+ICurrencyService       - Currency operations
+ICurrenciesHttpService - HTTP-based currency data
+```
+
+**Features:**
+- Currency conversion
+- Exchange rate caching
+- Historical currency data
+
+### 7. PDF Generation
+
+**Library:** `QuestPDF` 2025.12.0
+
+**Services:**
+```csharp
+IPdf                    - Base PDF service
+IInterviewPdfService    - Interview-specific PDF generation
+```
+
+**Features:**
+- Interview reports
+- Markdown to PDF conversion
+- Custom layouts
+
+---
+
+## API Design
+
+### RESTful API Design
+
+**Base URL:** `https://api.techinterview.space`
+
+### Routing Conventions
+
+```
+/api/{resource}
+/api/{resource}/{id}
+/api/{resource}/{id}/{sub-resource}
+```
+
+**Examples:**
+- `/api/companies` - List companies
+- `/api/companies/{id}` - Get company details
+- `/api/companies/{id}/reviews` - Get company reviews
+
+### Controller Pattern
+
+**Feature-based controllers:**
+```csharp
+[ApiController]
+[Route("api/companies")]
+public class CompaniesController : ControllerBase
+{
+    // Actions
+}
+```
+
+### Request/Response Pattern
+
+**Commands (Write):**
+```csharp
+public class CreateCompanyCommand { }
+public class CreateCompanyHandler : IRequestHandler<CreateCompanyCommand, Guid> { }
+```
+
+**Queries (Read):**
+```csharp
+public class GetCompanyQuery { }
+public class GetCompanyHandler : IRequestHandler<GetCompanyQuery, CompanyDto> { }
+```
+
+### Mediator Pattern
+
+**Usage in Controllers:**
+```csharp
+return Ok(await _serviceProvider.HandleBy<Handler, Request, Response>(
+    request,
+    cancellationToken));
+```
+
+**Location:** `src/Infrastructure/Services/Mediator/ServiceProviderExtensions.cs`
+
+### Pagination
+
+**Model:** `PageModel` (src/Domain/ValueObjects/Pagination/PageModel.cs)
+
+**Properties:**
+- `Page` (int): Page number
+- `PageSize` (int): Items per page
+
+**Response:** `Pageable<T>` (src/Domain/ValueObjects/Pagination/PaginatedListBase.cs)
+
+### Validation
+
+**Request Validation:**
+- Fluent validation through data annotations
+- `EntityValidator<T>` for entity validation
+- `ThrowIfInvalid()` method
+
+**Custom Attributes:**
+- `NotDefaultValueAttribute` - Validate not default value
+- `CollectionNotEmptyBaseAttribute` - Validate non-empty collections
+
+### Error Handling
+
+**Middleware:** `ExceptionHttpMiddleware`
+
+**Exception Types:**
+- `NotFoundException` - 404
+- `BadRequestException` - 400
+- `NoPermissionsException` - 403
+- `EntityInvalidException` - 400
+- `DatabaseException` - 500
+
+**Location:** `src/Domain/Validation/Exceptions/`
+
+### Correlation ID
+
+**Header:** `X-Correlation-Id`
+
+**Middleware:** `CorrelationIdMiddleware`
+
+**Service:** `ICorrelationIdAccessor`
+
+Every request/response includes a correlation ID for tracing.
+
+---
+
+## Background Jobs & Scheduling
+
+### Scheduling
+
+**Library:** `Coravel` 6.0.2
+
+**Configuration:** `src/Web.Api/Setup/ScheduleConfig.cs`
+
+### Hosted Services
+
+**Base Class:** `BackgroundServiceBase`
+**Location:** `src/Web.Api/Setup/HostedServices/`
+
+### Telegram Bot Hosted Services
+
+1. **SalariesTelegramBotHostedService**
+   - Processes salary update notifications
+   - Handles bot commands
+   - Sends scheduled messages
+
+2. **GithubProfileBotHostedService**
+   - Processes GitHub profile requests
+   - Handles profile analysis
+   - Sends results via Telegram
+
+### Initialization Service
+
+**AppInitializeService**
+- Runs on application startup
+- Initializes required data
+- Validates configuration
+
+---
+
+## Logging & Monitoring
+
+### Logging Framework
+
+**Library:** `Serilog` 3.1.1
+
+**Sinks:**
+- Console (development)
+- Elasticsearch (production)
+
+### Configuration
+
+**Location:** `src/Infrastructure/Services/Logging/ElkSerilog.cs`
+
+**Setup in Startup:**
+```csharp
+new ElkSerilog(
+    config: _configuration,
+    appName: "TechInterview.API",
+    connectionString: _configuration.GetConnectionString("Elasticsearch"),
+    environmentName: _environment.EnvironmentName).Setup();
+```
+
+### Structured Logging
+
+**Correlation ID:** Added to all log entries via `CorrelationIdEnricher`
+
+**Log Levels:**
+- Debug (development)
+- Information (general)
+- Warning (issues)
+- Error (exceptions)
+- Fatal (critical failures)
+
+### Health Checks
+
+**Location:** `src/Web.Api/Setup/Healthcheck/`
+
+**Endpoints:**
+- `/health` - Basic health check
+- `/health/db` - Database health check
+
+**Custom Response:** `HealthCheckCustomResponse.Setup(app)`
+
+---
+
+## Code Standards & Patterns
+
+### Coding Standards
+
+**Ruleset:** `src/standard.ruleset`
+
+**StyleCop Analyzers:**
+- SA (StyleCop) rules for code style
+- CA (Code Analysis) rules for code quality
+
+**Key Rules:**
+- PascalCase for public members
+- camelCase for private fields (with underscore prefix)
+- Proper spacing and formatting
+- XML documentation comments (optional)
+
+### Naming Conventions
+
+| Element | Style | Example |
+|---------|-------|---------|
+| Namespaces | PascalCase | `TechInterviewer.Features.Interviews` |
+| Classes | PascalCase | `InterviewService` |
+| Interfaces | PascalCase with "I" prefix | `IInterviewRepository` |
+| Methods | PascalCase | `GetInterviewByIdAsync` |
+| Properties | PascalCase | `CreatedAt` |
+| Private fields | camelCase with underscore | `_dbContext` |
+| Local variables | camelCase | `interviewId` |
+| Parameters | camelCase | `cancellationToken` |
+| Async methods | PascalCase with "Async" suffix | `CreateInterviewAsync` |
+
+### File Organization
+
+**Feature-based structure:**
+```
+Features/
+├── FeatureName/
+│   ├── FeatureNameController.cs
+│   ├── CreateFeature/
+│   │   ├── CreateFeatureCommand.cs
+│   │   ├── CreateFeatureHandler.cs
+│   │   └── CreateFeatureResponse.cs
+│   └── GetFeature/
+│       ├── GetFeatureQuery.cs
+│       ├── GetFeatureHandler.cs
+│       └── GetFeatureResponse.cs
+```
+
+### Validation Pattern
+
+**Entity Validation:**
+```csharp
+entity.ThrowIfInvalid();
+```
+
+**Request Validation:**
+```csharp
+request.ThrowIfInvalid();
+```
+
+### Null Checking
+
+**Extension Methods:** `src/Domain/Extensions/`
+```csharp
+entity.ThrowIfNull(nameof(entity));
+collection.ThrowIfNullOrEmpty(nameof(collection));
+```
+
+### Async/Await
+
+All async operations use `async`/`await` pattern:
+```csharp
+public async Task<Result> MethodAsync(CancellationToken cancellationToken)
+{
+    var result = await _service.DoSomethingAsync(cancellationToken);
+    return result;
+}
+```
+
+### Transaction Management
+
+```csharp
+await _context.DoWithinTransactionAsync<TResult>(
+    async () =>
+    {
+        // Operations
+        return result;
+    },
+    errorMessage,
+    cancellationToken);
+```
+
+---
+
+## Development Guide
+
+### Prerequisites
+
+1. **Docker Desktop** - Required for running infrastructure
+2. **.NET 10 SDK** - Development framework
+3. **IDE** - Visual Studio, Rider, or VS Code
+4. **PostgreSQL Client** - For database management (optional)
+
+### Getting Started
+
+1. **Clone Repository:**
+```bash
+git clone https://github.com/techinterview-space/web-api.git
+cd web-api
+```
+
+2. **Restore Dependencies:**
+```bash
+cd src
+dotnet restore
+```
+
+3. **Start Infrastructure:**
+```bash
+cd ..
+docker-compose up -d --build database.api elasticsearch localstack
+```
+
+4. **Configure Environment:**
+```bash
+cp .env.example .env
+# Edit .env with your settings
+```
+
+5. **Run Application:**
+```bash
+cd src
+dotnet run
+```
+
+**Application URL:** `https://localhost:5001`
+
+### Development Tools
+
+**Swagger UI:** `https://localhost:5001/swagger`
+
+**Kibana:** `http://localhost:5601` (Log visualization)
+
+**PostgreSQL:** `localhost:5432`
+
+### Building
+
+```bash
+cd src
+dotnet build
+```
+
+### Testing
+
+**Run All Tests:**
+```bash
+dotnet test
+```
+
+**Run Specific Project:**
+```bash
+dotnet test Domain.Tests
+dotnet test InfrastructureTests
+dotnet test Web.Api.Tests
+```
+
+### Database Migrations
+
+**Create Migration:**
+```powershell
+./add-migration.ps1 <MigrationName>
+```
+
+**Or using EF CLI:**
+```bash
+dotnet ef migrations add <MigrationName> \
+  --project Infrastructure \
+  --startup-project Web.Api
+```
+
+⚠️ **IMPORTANT:** Do not modify migration files or DbContext snapshots manually.
+
+### Code Quality
+
+**Run Build (includes analysis):**
+```bash
+dotnet build
+```
+
+**Check Ruleset:** Follow rules in `src/standard.ruleset`
+
+### Debugging
+
+**Development Mode:**
+- `ASPNETCORE_ENVIRONMENT=Development`
+- Detailed error pages
+- PII logging enabled
+- Swagger UI enabled
+
+---
+
+## Deployment
+
+### Docker Deployment
+
+**Docker Compose:** `docker-compose.yml`
+
+**Services:**
+- `database.api` - PostgreSQL 13
+- `elasticsearch` - Elasticsearch 8.0.0
+- `kibana` - Kibana 8.0.0
+- `localstack` - AWS services emulation
+- `api` - Web API application
+
+### Deployment Compose
+
+**File:** `docker-compose.deploy.yml`
+
+**Production Deployment:**
+```bash
+docker-compose -f docker-compose.deploy.yml up -d --build
+```
+
+### Environment Variables
+
+**Required Variables:**
+- `ASPNETCORE_ENVIRONMENT`
+- `ConnectionStrings__Database`
+- `ConnectionStrings__Elasticsearch`
+- `ASPNETCORE_Kestrel__Certificates__Default__Path`
+- `ASPNETCORE_Kestrel__Certificates__Default__Password`
+
+### Kubernetes Deployment
+
+**Manifests:** `manifests/`
+
+**Files:**
+- `deployment.yml` - API deployment
+- `service.yml` - Service definition
+- `ingress.yml` - Ingress configuration
+- `cert.yml` - Certificate configuration
+
+**Stage Manifests:**
+- `deployment-stage.yml`
+- `service-stage.yml`
+
+### CI/CD
+
+**GitHub Actions:** `.github/workflows/`
+
+**Workflows:**
+- `deploy.yml` - Deployment workflow
+- `test.yml` - Testing workflow
+
+### Health Checks
+
+**Endpoints:**
+- `/health` - Application health
+- `/health/db` - Database health
+
+### Monitoring
+
+**Elasticsearch & Kibana:**
+- Structured logging
+- Log aggregation
+- Visualization dashboards
+
+---
+
+## Appendix
+
+### Key File Locations
+
+| File/Component | Location |
+|----------------|----------|
+| Startup Configuration | `src/Web.Api/Startup.cs` |
+| Program Entry Point | `src/Web.Api/Program.cs` |
+| Database Context | `src/Infrastructure/Database/DatabaseContext.cs` |
+| Entity Configurations | `src/Infrastructure/Database/Config/` |
+| Service Registration | `src/Web.Api/Setup/ServiceRegistration.cs` |
+| Ruleset | `src/standard.ruleset` |
+| Docker Compose | `docker-compose.yml` |
+| Environment Example | `.env.example` |
+
+### Configuration Files
+
+| File | Purpose |
+|------|---------|
+| `appsettings.json` | Base configuration |
+| `appsettings.Development.json` | Development settings |
+| `appsettings.Production.json` | Production settings |
+| `.env` | Environment variables (not committed) |
+
+### Important Notes
+
+1. **No Microservices:** This is a monolithic application
+2. **Migration Restrictions:** Do not generate or modify migrations manually
+3. **Code Style:** Always follow `standard.ruleset`
+4. **Build Verification:** Run `dotnet build` after all changes
+5. **Testing:** Use xUnit framework
+6. **Test Utilities:** Leverage existing test infrastructure in `TestUtils/`
+
+### External Documentation
+
+- **Contribution Guidelines:** `CONTRIBUTING.md`
+- **Code of Conduct:** `CODE_OF_CONDUCT.md`
+- **AI Agent Guidelines:** `CLAUDE.md`
+- **GitHub API Optimization:** `docs/github-api-optimization.md`
+
+---
+
+## Contact & Support
+
+- **Repository:** https://github.com/techinterview-space/web-api
+- **Issues:** https://github.com/techinterview-space/web-api/issues
+- **Website:** https://techinterview.space
+- **API:** https://api.techinterview.space
+
+---
+
+*Document Version: 1.0*
+*Last Updated: January 2026*
+*Framework: .NET 10*
diff --git a/src/Web.Api/Features/Salaries/GetSalariesChart/GetSalariesChartHandler.cs b/src/Web.Api/Features/Salaries/GetSalariesChart/GetSalariesChartHandler.cs
index edcd0898..b6dae39a 100644
--- a/src/Web.Api/Features/Salaries/GetSalariesChart/GetSalariesChartHandler.cs
+++ b/src/Web.Api/Features/Salaries/GetSalariesChart/GetSalariesChartHandler.cs
@@ -8,7 +8,6 @@
 using Domain.Entities.Salaries;
 using Domain.Extensions;
 using Domain.ValueObjects;
-using Domain.ValueObjects.Dates;
 using Infrastructure.Authentication.Contracts;
 using Infrastructure.Currencies.Contracts;
 using Infrastructure.Database;