# Epic 1: Foundation & Core YouTube Integration

## Epic Overview

**Goal**: Establish the foundational infrastructure and core YouTube integration capabilities that all subsequent features will build upon. This epic delivers a functional system that can accept YouTube URLs, extract transcripts, and display them through a basic but polished web interface.

**Priority**: Critical - Must be completed before Epic 2  
**Epic Dependencies**: None (foundational epic)  
**Estimated Complexity**: High (foundational setup)  

## Epic Success Criteria

Upon completion of this epic, the YouTube Summarizer will:

1. **Fully Operational Development Environment**
   - Single-command Docker setup
   - Hot-reload for both frontend and backend
   - Automated code quality enforcement

2. **Core YouTube Processing Capability**
   - Accept all standard YouTube URL formats
   - Extract transcripts with fallback mechanisms
   - Handle error cases gracefully with user guidance

3. **Basic User Interface**
   - Clean, responsive web interface
   - Real-time processing feedback
   - Mobile-friendly design

4. **Production-Ready Foundation**
   - Comprehensive testing framework
   - CI/CD pipeline
   - Documentation and setup guides

## Stories in Epic 1

### Story 1.1: Project Setup and Infrastructure ✅ COMPLETED

**As a** developer  
**I want** a fully configured project with all necessary dependencies and development tooling  
**So that** the team can begin development with consistent environments and automated quality checks

#### Acceptance Criteria
1. FastAPI application structure created with proper package organization (api/, services/, models/, utils/)
2. Development environment configured with hot-reload, debugging, and environment variable management
3. Docker configuration enables single-command local development startup
4. Pre-commit hooks enforce code formatting (Black), linting (Ruff), and type checking (mypy)
5. GitHub Actions workflow runs tests and quality checks on every push
6. README includes clear setup instructions and architecture overview

**Status**: Story created and validated  
**File**: `docs/stories/1.1.project-setup-infrastructure.md`

### Story 1.2: YouTube URL Validation and Parsing

**As a** user  
**I want** the system to accept any valid YouTube URL format  
**So that** I can paste URLs directly from my browser without modification

#### Acceptance Criteria
1. System correctly parses video IDs from youtube.com/watch?v=, youtu.be/, and embed URL formats
2. Invalid URLs return clear error messages specifying the expected format
3. System extracts and validates video IDs are exactly 11 characters
4. Playlist URLs are detected and user is informed they're not yet supported
5. URL validation happens client-side for instant feedback and server-side for security

**Status**: ✅ Story created and ready for development  
**Story File**: [`1.2.youtube-url-validation-parsing.md`](../stories/1.2.youtube-url-validation-parsing.md)  
**Dependencies**: Story 1.1 (Project Setup)

### Story 1.3: Transcript Extraction Service

**As a** user  
**I want** the system to automatically retrieve video transcripts  
**So that** I can get summaries without manual transcription

#### Acceptance Criteria
1. Successfully retrieves transcripts using youtube-transcript-api for videos with captions
2. Falls back to auto-generated captions when manual captions unavailable
3. Returns clear error message for videos without any captions
4. Extracts metadata including video title, duration, channel name, and publish date
5. Handles multiple languages with preference for English when available
6. Implements retry logic with exponential backoff for transient API failures

**Status**: ✅ Story created and ready for development  
**Story File**: [`1.3.transcript-extraction-service.md`](../stories/1.3.transcript-extraction-service.md)  
**Dependencies**: Story 1.2 (URL Validation)

### Story 1.4: Basic Web Interface

**As a** user  
**I want** a clean web interface to input URLs and view transcripts  
**So that** I can interact with the system through my browser

#### Acceptance Criteria
1. Landing page displays prominent URL input field with placeholder text
2. Submit button is disabled until valid URL is entered
3. Loading spinner appears during transcript extraction with elapsed time counter
4. Extracted transcript displays in scrollable, readable format with timestamps
5. Error messages appear inline with suggestions for resolution
6. Interface is responsive and works on mobile devices (320px minimum width)

**Status**: ✅ Story created and ready for development  
**Story File**: [`1.4.basic-web-interface.md`](../stories/1.4.basic-web-interface.md)  
**Dependencies**: Story 1.3 (Transcript Extraction)

### Story 1.5: Video Download and Storage Service

**As a** user  
**I want** the system to download and store YouTube videos locally  
**So that** I can process videos offline, build a personal archive, and get better transcription quality

#### Acceptance Criteria
1. System downloads videos using yt-dlp with configurable quality settings
2. Audio is automatically extracted from videos for transcription
3. Videos are stored in organized directory structure by video ID  
4. Download progress is tracked and displayed in real-time
5. Duplicate downloads are prevented through cache checking
6. Storage management enforces size limits and cleanup options
7. Service integrates seamlessly with transcript extraction

**Status**: 📋 Story created and ready for development  
**Story File**: [`1.5.video-download-storage-service.md`](../stories/1.5.video-download-storage-service.md)  
**Dependencies**: Story 1.1 (Project Setup), Story 1.2 (URL Validation)

## Technical Architecture Context

### Technology Stack for Epic 1
- **Backend**: FastAPI + Python 3.11+ with async support
- **Frontend**: React 18 + TypeScript + shadcn/ui + Tailwind CSS  
- **Database**: SQLite for development (simple setup)
- **Deployment**: Docker Compose for self-hosted deployment
- **Testing**: pytest (backend) + Vitest (frontend)
- **Code Quality**: Black, Ruff, mypy, ESLint, Prettier

### Key Architecture Components
1. **Project Structure**: Modular monolith with clear service boundaries
2. **API Design**: RESTful endpoints with OpenAPI documentation
3. **Error Handling**: Comprehensive error types with recovery guidance
4. **Development Workflow**: Hot-reload, automated testing, pre-commit hooks

## Non-Functional Requirements for Epic 1

### Performance
- Development environment starts in under 60 seconds
- Hot-reload responds to changes within 2 seconds
- URL validation provides instant client-side feedback

### Security
- Input sanitization for all user inputs
- CORS configuration for development environment
- Environment variable management for sensitive data

### Reliability
- Comprehensive error handling with user-friendly messages
- Fallback mechanisms for transcript extraction
- Health checks for all services

### Usability
- Self-documenting setup process
- Clear error messages with actionable suggestions
- Responsive design from 320px to desktop

## Definition of Done for Epic 1

- [ ] All 5 stories completed and validated
- [ ] Docker Compose starts entire development environment
- [ ] User can input YouTube URL and see extracted transcript
- [ ] All tests passing with >80% coverage
- [ ] CI/CD pipeline running successfully
- [ ] Documentation complete with troubleshooting guide
- [ ] Architecture validated by developer implementation

## Risks and Mitigation

### Technical Risks
1. **YouTube API Changes**: Use multiple transcript sources (youtube-transcript-api + yt-dlp)
2. **Development Complexity**: Comprehensive documentation and automated setup
3. **Performance Issues**: Early optimization and monitoring

### Project Risks
1. **Scope Creep**: Strict acceptance criteria and story validation
2. **Technical Debt**: Automated code quality enforcement
3. **Documentation Lag**: Documentation as part of Definition of Done

## Success Metrics

### Technical Metrics
- **Setup Time**: < 5 minutes from clone to running application
- **Test Coverage**: > 80% backend, > 70% frontend
- **Code Quality**: All automated checks passing
- **Performance**: Transcript extraction < 10 seconds for typical video

### User Experience Metrics
- **URL Validation**: Instant feedback for invalid URLs
- **Error Handling**: Clear recovery guidance for all error states
- **Mobile Support**: Full functionality on mobile devices
- **Developer Experience**: Hot-reload and debugging working smoothly

---

**Epic Status**: In Progress (Story 1.1 created and validated)  
**Next Action**: Create Story 1.2 (URL Validation and Parsing)  
**Epic Owner**: Bob (Scrum Master)  
**Last Updated**: 2025-01-25