# Advanced Commands Architecture

## Overview

This document describes the advanced commands architecture for `apt-ostree`, covering complex operations such as tree composition, database management, package overrides, and system composition. These commands provide advanced functionality for system administrators and developers.

## Advanced Command Categories

### Tree Composition Commands

#### `apt-ostree compose`
Creates and manages OSTree compositions for deployment.

**Purpose:**
- Build custom OSTree trees
- Create deployment images
- Manage tree variants
- Generate reproducible builds

**Implementation Details:**
- Tree definition parsing
- Package dependency resolution
- OSTree commit creation
- Image generation and validation

**Example:**
```bash
# Compose a new tree
apt-ostree compose tree --repo=/srv/repo --treefile=treefile.json

# Compose with specific packages
apt-ostree compose tree --repo=/srv/repo --include=nginx,postgresql

# Compose for specific architecture
apt-ostree compose tree --repo=/srv/repo --arch=amd64
```

**Options:**
- `--repo`: OSTree repository path
- `--treefile`: Tree definition file
- `--include`: Packages to include
- `--exclude`: Packages to exclude
- `--arch`: Target architecture
- `--output`: Output directory

#### `apt-ostree compose commit`
Creates commits for composed trees.

**Purpose:**
- Generate OSTree commits
- Update tree references
- Create deployment points
- Manage tree versions

**Example:**
```bash
# Create commit from tree
apt-ostree compose commit --repo=/srv/repo --tree=my-tree

# Create commit with metadata
apt-ostree compose commit --repo=/srv/repo --tree=my-tree --subject="Update packages"
```

### Database Management Commands

#### `apt-ostree db`
Manages the APT package database within OSTree.

**Purpose:**
- Database operations
- Package metadata management
- Dependency resolution
- Cache management

**Subcommands:**

##### `apt-ostree db diff`
Shows differences between database states.

**Example:**
```bash
# Show differences between deployments
apt-ostree db diff --from=deployment1 --to=deployment2

# Show package differences
apt-ostree db diff --packages --from=deployment1 --to=deployment2
```

##### `apt-ostree db list`
Lists database contents.

**Example:**
```bash
# List all packages
apt-ostree db list

# List installed packages
apt-ostree db list --installed

# List available packages
apt-ostree db list --available
```

##### `apt-ostree db verify`
Verifies database integrity.

**Example:**
```bash
# Verify database integrity
apt-ostree db verify

# Verify specific packages
apt-ostree db verify --packages=nginx,postgresql
```

### Package Override Commands

#### `apt-ostree override`
Manages package overrides for deployments.

**Purpose:**
- Override package versions
- Replace system packages
- Customize package behavior
- Manage package conflicts

**Subcommands:**

##### `apt-ostree override replace`
Replaces a package with a different version or source.

**Example:**
```bash
# Replace system package
apt-ostree override replace nginx --with=nginx-custom

# Replace with specific version
apt-ostree override replace nginx --with=nginx=1.18.0-1

# Replace from different repository
apt-ostree override replace nginx --with=nginx --repo=custom-repo
```

**Options:**
- `--with`: Replacement package specification
- `--repo`: Source repository
- `--version`: Specific version
- `--force`: Force replacement

##### `apt-ostree override remove`
Removes package overrides.

**Example:**
```bash
# Remove specific override
apt-ostree override remove nginx

# Remove all overrides
apt-ostree override remove --all
```

##### `apt-ostree override reset`
Resets package overrides to default.

**Example:**
```bash
# Reset specific override
apt-ostree override reset nginx

# Reset all overrides
apt-ostree override reset --all
```

##### `apt-ostree override list`
Lists current package overrides.

**Example:**
```bash
# List all overrides
apt-ostree override list

# List overrides for specific package
apt-ostree override list nginx
```

### System Composition Commands

#### `apt-ostree compose image`
Creates system images from composed trees.

**Purpose:**
- Generate bootable images
- Create deployment artifacts
- Manage image variants
- Support multiple formats

**Example:**
```bash
# Create raw disk image
apt-ostree compose image --format=raw --output=system.img

# Create ISO image
apt-ostree compose image --format=iso --output=system.iso

# Create cloud image
apt-ostree compose image --format=qcow2 --output=system.qcow2
```

**Options:**
- `--format`: Output format (raw, iso, qcow2, vmdk)
- `--output`: Output file path
- `--size`: Image size specification
- `--compression`: Compression algorithm

#### `apt-ostree compose treefile`
Manages tree definition files.

**Purpose:**
- Create tree specifications
- Manage tree configurations
- Version control tree definitions
- Template management

**Example:**
```bash
# Create new treefile
apt-ostree compose treefile --create=my-tree.json

# Validate treefile
apt-ostree compose treefile --validate=my-tree.json

# Show treefile schema
apt-ostree compose treefile --schema
```

## Advanced Features

### Tree Composition Engine

#### Tree Definition Format

Tree definitions use JSON format:

```json
{
  "arch": "x86_64",
  "repos": ["base", "updates"],
  "packages": {
    "include": ["nginx", "postgresql"],
    "exclude": ["unwanted-package"]
  },
  "customizations": {
    "files": ["/etc/nginx/nginx.conf"],
    "services": ["nginx", "postgresql"]
  },
  "output": {
    "format": "raw",
    "size": "10G"
  }
}
```

#### Composition Process

1. **Tree Definition Parsing**
   - Parse tree definition file
   - Validate configuration
   - Resolve dependencies

2. **Package Resolution**
   - Resolve package dependencies
   - Handle conflicts
   - Determine versions

3. **Tree Generation**
   - Create OSTree commits
   - Apply customizations
   - Generate metadata

4. **Output Generation**
   - Create requested format
   - Validate output
   - Generate checksums

### Package Override System

#### Override Types

1. **Version Overrides**
   - Replace package versions
   - Pin specific versions
   - Handle version conflicts

2. **Source Overrides**
   - Change package sources
   - Use custom repositories
   - Handle source conflicts

3. **Behavior Overrides**
   - Modify package behavior
   - Customize configurations
   - Handle conflicts

#### Override Management

**Storage:**
- Overrides stored in OSTree metadata
- Per-deployment override tracking
- Override history and rollback

**Resolution:**
- Override priority system
- Conflict resolution rules
- Dependency handling

**Persistence:**
- Overrides persist across reboots
- Override inheritance rules
- Override cleanup and maintenance

### Database Management System

#### Database Architecture

**Components:**
- Package metadata storage
- Dependency resolution engine
- Cache management system
- Integrity verification

**Storage:**
- SQLite database backend
- JSON metadata storage
- Binary package data
- Index and search optimization

#### Database Operations

**Query Operations:**
- Package search and filtering
- Dependency resolution
- Version comparison
- Metadata retrieval

**Modification Operations:**
- Package installation tracking
- Dependency updates
- Cache invalidation
- Integrity maintenance

## Integration Points

### OSTree Integration

Advanced commands integrate deeply with OSTree:

- **Repository management** - OSTree repository operations
- **Commit creation** - OSTree commit generation
- **Deployment management** - Deployment operations
- **Metadata handling** - OSTree metadata management

### APT Integration

Leverages APT's capabilities:

- **Package resolution** - APT dependency resolver
- **Repository management** - APT source management
- **Package metadata** - APT package information
- **Cache management** - APT cache operations

### System Integration

System-level integration:

- **Image generation** - System image creation
- **Boot management** - Bootloader integration
- **Service management** - Systemd integration
- **File operations** - File system operations

## Security Considerations

### Package Override Security

**Validation:**
- Package signature verification
- Source authenticity checking
- Override permission control
- Conflict resolution validation

**Access Control:**
- Override creation permissions
- Override modification rights
- Override removal privileges
- Override viewing access

### Composition Security

**Input Validation:**
- Tree definition validation
- Package source verification
- Configuration sanitization
- Output validation

**Execution Security:**
- Isolated execution environment
- Resource limitation
- Output verification
- Audit logging

## Performance Optimization

### Composition Optimization

**Parallel Processing:**
- Concurrent package resolution
- Parallel dependency checking
- Concurrent file operations
- Parallel output generation

**Caching Strategy:**
- Package metadata caching
- Dependency resolution caching
- Output format caching
- Tree definition caching

### Database Optimization

**Query Optimization:**
- Index optimization
- Query caching
- Result caching
- Connection pooling

**Storage Optimization:**
- Data compression
- Efficient storage formats
- Cleanup and maintenance
- Archival strategies

## Error Handling

### Composition Errors

**Common Issues:**
- Package dependency conflicts
- Repository access problems
- Disk space issues
- Configuration errors

**Recovery Strategies:**
- Automatic conflict resolution
- Partial composition recovery
- Error reporting and guidance
- Rollback mechanisms

### Override Errors

**Common Issues:**
- Package conflicts
- Dependency problems
- Source availability
- Permission issues

**Recovery Strategies:**
- Conflict resolution
- Override removal
- Source fallback
- Permission escalation

## Future Enhancements

### Planned Features

1. **Advanced Composition**
   - Multi-architecture support
   - Custom composition plugins
   - Advanced customization options
   - Template system

2. **Enhanced Overrides**
   - Override inheritance
   - Override templates
   - Override validation rules
   - Override rollback

3. **Database Enhancements**
   - Advanced query language
   - Performance monitoring
   - Automated maintenance
   - Backup and recovery

4. **Integration Improvements**
   - CI/CD integration
   - Cloud platform support
   - Container integration
   - Monitoring integration

## Implementation Notes

### Current Status

- Basic advanced commands implemented
- Tree composition framework
- Package override system
- Database management

### Next Steps

1. **Advanced Features**
   - Enhanced composition engine
   - Advanced override system
   - Database optimization
   - Integration improvements

2. **Performance Optimization**
   - Parallel processing
   - Caching strategies
   - Query optimization
   - Storage optimization

3. **Testing and Validation**
   - Comprehensive testing
   - Performance testing
   - Security testing
   - Integration testing
