# Offline Queue Caching System Requirements

## Introduction

This spec addresses the need for offline playback continuity when network connections drop. The system will cache a rolling queue of 50 songs to ensure uninterrupted playback during network outages, with intelligent cache management and user-controlled refresh mechanisms.

## Requirements

### Requirement 1: Automatic Queue Caching

**User Story:** As a user, I want the app to automatically cache upcoming songs so playback continues when my connection drops

#### Acceptance Criteria

1. WHEN I start playing music THEN the system SHALL automatically cache the next 50 songs in the queue
2. WHEN a song finishes playing THEN the system SHALL cache the next song in sequence to maintain 50 cached songs
3. WHEN the cache reaches capacity THEN the system SHALL remove the oldest cached songs to make room for new ones
4. WHEN network is available THEN caching SHALL happen in the background without affecting playback
5. WHEN network is unavailable THEN the system SHALL continue playing from the cached queue

### Requirement 2: Connection Drop Handling

**User Story:** As a user, I want seamless playback continuation when my network connection drops

#### Acceptance Criteria

1. WHEN network connection is lost THEN playback SHALL continue from cached songs without interruption
2. WHEN skipping tracks offline THEN the system SHALL play the next cached song in sequence
3. WHEN going back to previous tracks THEN the system SHALL play cached songs if available
4. WHEN the cached queue is exhausted THEN the system SHALL display a clear message about network requirements
5. WHEN network connection is restored THEN the system SHALL resume normal operation and refresh the cache

### Requirement 3: Shuffle-Triggered Cache Refresh

**User Story:** As a user, I want to refresh the cached queue by toggling shuffle to get new songs for offline playback

#### Acceptance Criteria

1. WHEN I toggle shuffle on/off THEN the system SHALL clear the current cache and rebuild it with the new queue order
2. WHEN shuffle is enabled THEN the cache SHALL contain 50 randomly ordered songs from the current playlist
3. WHEN shuffle is disabled THEN the cache SHALL contain 50 songs in sequential order from the current position
4. WHEN toggling shuffle THEN the system SHALL show a loading indicator while rebuilding the cache
5. WHEN cache refresh completes THEN the system SHALL notify the user that new songs are available offline

### Requirement 4: Cache Management and Storage

**User Story:** As a user, I want efficient cache management that doesn't consume excessive device storage

#### Acceptance Criteria

1. WHEN caching songs THEN the system SHALL store audio data in temporary browser storage
2. WHEN cache size exceeds limits THEN the system SHALL automatically remove oldest entries
3. WHEN the app is closed THEN cached songs SHALL be cleared to free up storage
4. WHEN storage is low THEN the system SHALL reduce cache size and notify the user
5. WHEN manually clearing cache THEN all cached audio data SHALL be immediately removed

### Requirement 5: User Interface and Feedback

**User Story:** As a user, I want clear indicators of cache status and offline capabilities

#### Acceptance Criteria

1. WHEN songs are being cached THEN I SHALL see a progress indicator showing cache status
2. WHEN offline mode is active THEN I SHALL see a clear indicator that I'm playing from cache
3. WHEN cache is full THEN I SHALL see confirmation that 50 songs are available offline
4. WHEN network issues occur THEN I SHALL receive clear notifications about offline mode
5. WHEN cache refresh is triggered THEN I SHALL see progress and completion feedback

### Requirement 6: Performance and Reliability

**User Story:** As a user, I want the caching system to work efficiently without impacting app performance

#### Acceptance Criteria

1. WHEN caching is active THEN it SHALL not interfere with current playback quality or responsiveness
2. WHEN multiple songs are being cached THEN the system SHALL prioritize songs closer to the current position
3. WHEN device resources are limited THEN the system SHALL throttle caching to maintain performance
4. WHEN cache operations fail THEN the system SHALL retry with exponential backoff
5. WHEN switching between online and offline modes THEN transitions SHALL be seamless and fast