# Package Management Architecture

## Overview

This document describes the package management architecture for `apt-ostree`, covering how packages are installed, uninstalled, and managed within the OSTree system. The design follows the same principles as `rpm-ostree` but integrates with APT instead of RPM.

## Package Management Commands

### Core Commands

#### `apt-ostree install <packages>`
Installs packages by creating new OSTree layers containing the package files.

**Implementation Details:**
- Creates a new OSTree commit with package files
- Resolves dependencies using APT
- Downloads packages to temporary storage
- Extracts package contents to new OSTree layer
- Updates package database
- Commits changes atomically

**Example:**
```bash
apt-ostree install vim git
```

**Options:**
- `--reboot` - Reboot after installation
- `--preview` - Show what would be installed
- `--check` - Verify package integrity
- `--cache-only` - Use only cached packages

#### `apt-ostree uninstall <packages>`
Removes packages by creating a new OSTree commit without the package files.

**Implementation Details:**
- Creates new OSTree commit excluding package files
- Updates package database
- Removes package metadata
- Commits changes atomically

**Example:**
```bash
apt-ostree uninstall vim
```

#### `apt-ostree search <query>`
Searches for available packages using APT's search capabilities.

**Implementation Details:**
- Uses APT's search functionality
- Filters results based on current OSTree deployment
- Shows package availability and versions

**Example:**
```bash
apt-ostree search "web server"
```

## Package Layering Architecture

### OSTree Layer Management

Packages are managed through OSTree layers, where each package installation creates a new commit:

```
Base OSTree Commit
├── System packages (base image)
└── User-installed packages (layers)
    ├── Layer 1: vim, git
    ├── Layer 2: nginx
    └── Layer 3: postgresql
```

### Layer Creation Process

1. **Dependency Resolution**
   - Use APT to resolve package dependencies
   - Download all required packages
   - Verify package integrity

2. **OSTree Commit Preparation**
   - Create temporary working directory
   - Extract package contents
   - Apply package scripts and configuration

3. **Commit Creation**
   - Create new OSTree commit with changes
   - Update package database
   - Link to parent commit

4. **Deployment Update**
   - Update current deployment pointer
   - Prepare for next boot (if --reboot specified)

## APT Integration

### Package Sources

`apt-ostree` integrates with APT's package sources:

- **Debian/Ubuntu repositories** - Standard package sources
- **PPAs** - Personal Package Archives
- **Custom repositories** - Third-party package sources

### Package Database

Maintains APT package database within OSTree:

- Package metadata
- Dependency information
- Installation status
- Version history

### Dependency Resolution

Uses APT's dependency resolver:

- Automatic dependency installation
- Conflict resolution
- Version compatibility checking
- Repository priority handling

## Transaction Management

### Atomic Operations

All package operations are atomic:

- **Success**: Complete installation with new OSTree commit
- **Failure**: Rollback to previous state
- **Partial failure**: Not possible - all or nothing

### Rollback Support

Failed installations automatically rollback:

- Remove temporary files
- Restore previous OSTree commit
- Clean up package database
- Maintain system consistency

## Package Overrides

### Override System

Packages can be overridden at different levels:

- **System level** - Base image packages
- **User level** - User-installed packages
- **Temporary** - Runtime overrides

### Override Commands

```bash
# Replace system package
apt-ostree override replace <package>

# Remove override
apt-ostree override remove <package>

# Reset to default
apt-ostree override reset <package>
```

## Security Considerations

### Package Verification

- GPG signature verification
- Package integrity checks
- Repository authenticity validation
- Secure download protocols

### Privilege Management

- Polkit-based authorization
- Root privilege requirements
- User permission checking
- Audit logging

## Performance Optimization

### Caching Strategy

- Package download caching
- OSTree commit caching
- Dependency resolution caching
- Metadata caching

### Parallel Operations

- Concurrent package downloads
- Parallel dependency resolution
- Background OSTree operations
- Asynchronous processing

## Error Handling

### Common Error Scenarios

1. **Package Not Found**
   - Check repository configuration
   - Verify package names
   - Update package lists

2. **Dependency Conflicts**
   - Automatic conflict resolution
   - Manual conflict resolution
   - Rollback on unresolvable conflicts

3. **Network Issues**
   - Retry mechanisms
   - Offline package installation
   - Partial download recovery

4. **Disk Space Issues**
   - Space requirement checking
   - Automatic cleanup
   - User notification

## Integration with rpm-ostree

### Command Compatibility

`apt-ostree` maintains 1:1 CLI compatibility with `rpm-ostree`:

- Same command names and options
- Identical exit codes
- Compatible error messages
- Similar help output

### Feature Parity

Core package management features match `rpm-ostree`:

- Package installation/uninstallation
- Dependency resolution
- OSTree layering
- Transaction management
- Rollback support

## Future Enhancements

### Planned Features

1. **Package Groups**
   - Install package collections
   - Group-based management
   - Dependency optimization

2. **Advanced Caching**
   - Intelligent cache management
   - Predictive downloads
   - Bandwidth optimization

3. **Package Pinning**
   - Version pinning
   - Repository pinning
   - Update control

4. **Rollback History**
   - Extended rollback support
   - Rollback metadata
   - Rollback scheduling

## Implementation Notes

### Current Status

- Basic package management implemented
- APT integration functional
- OSTree layering working
- Transaction system operational

### Next Steps

1. **Performance Optimization**
   - Implement caching strategies
   - Optimize OSTree operations
   - Improve dependency resolution

2. **Advanced Features**
   - Package groups support
   - Advanced override system
   - Enhanced rollback capabilities

3. **Testing and Validation**
   - Comprehensive testing
   - Performance benchmarking
   - Security auditing
