implemente pmoparadise

pmoparadise/IMPLEMENTATION.md

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+# Implementation Notes and Design Decisions
+
+## Overview
+
+`pmoparadise` is a Rust client library for Radio Paradise's streaming API, designed following idiomatic Rust patterns and inspired by the structure of `pmoqobuz`.
+
+## Architecture Decisions
+
+### 1. Module Structure
+
+The crate is organized into focused modules:
+- `client.rs` - HTTP client and API methods
+- `models.rs` - Data structures with serde serialization
+- `stream.rs` - Block streaming functionality
+- `track.rs` - Per-track extraction (feature-gated)
+- `error.rs` - Type-safe error handling
+
+This separation ensures clear boundaries and makes the code maintainable.
+
+### 2. Async/Await with Tokio
+
+**Decision**: Use async/await throughout the API with tokio runtime.
+
+**Rationale**:
+- Radio Paradise API calls are I/O bound
+- Streaming large FLAC blocks benefits from async I/O
+- Tokio is the de facto standard for async Rust
+- Enables efficient prefetching and concurrent operations
+
+### 3. Type Safety
+
+**Decision**: Use strong typing for all API concepts (EventId, DurationMs, Bitrate enum).
+
+**Rationale**:
+- Prevents mixing up event IDs with durations
+- Enum for Bitrate makes invalid states unrepresentable
+- Compile-time guarantees reduce runtime errors
+- Self-documenting code
+
+### 4. Error Handling
+
+**Decision**: Use `thiserror` for structured errors with specific variants.
+
+**Rationale**:
+- Users can match on specific error types
+- Better error messages than strings
+- Idiomatic Rust error handling
+- Easy to extend with new error types
+
+### 5. Feature Gates
+
+**Decision**: Gate the per-track functionality behind a feature flag.
+
+**Rationale**:
+- Most users don't need FLAC decoding
+- Reduces dependencies for common use cases
+- `claxon`, `hound`, `tempfile` add significant compile time
+- Keeps the default build lightweight
+
+## API Design Decisions
+
+### 1. Builder Pattern for Client
+
+**Decision**: Provide both `new()` and `builder()` methods.
+
+**Rationale**:
+- `new()` for simple cases (good defaults)
+- `builder()` for customization (bitrate, proxy, timeout)
+- Common Rust pattern (reqwest, etc.)
+- Extensible without breaking changes
+
+### 2. Block-Centric API
+
+**Decision**: Focus on blocks as the primary abstraction, not individual songs.
+
+**Rationale**:
+- Matches Radio Paradise's actual architecture
+- Blocks are the unit of streaming
+- Enables efficient prefetching
+- Transparent about implementation details
+
+### 3. Prefetching Support
+
+**Decision**: Provide explicit `prefetch_next()` method rather than automatic prefetching.
+
+**Rationale**:
+- Gives users control over when network calls happen
+- Allows batching metadata requests
+- Simpler to reason about
+- Users can implement custom prefetch strategies
+
+### 4. Stream Trait Implementation
+
+**Decision**: Return a custom `BlockStream` that implements `Stream<Item = Result<Bytes>>`.
+
+**Rationale**:
+- Standard Rust async iterator pattern
+- Compatible with futures combinators
+- Easy to consume with `while let Some(chunk) = stream.next().await`
+- Can be piped to any sink
+
+## Per-Track Feature Decisions
+
+### 1. Why It's Optional and Discouraged
+
+**Decision**: Document limitations and recommend player-based seeking.
+
+**Rationale**:
+- FLAC doesn't support random access
+- Must download entire block (50-100 MB)
+- CPU-intensive decoding
+- Players (mpv, ffmpeg) handle this better
+
+**Trade-offs**:
+- **Prefetch vs Per-Track**:
+  - Prefetch: Low latency, efficient, recommended
+  - Per-track: High latency, resource-intensive, only for special cases
+
+### 2. Implementation Approach
+
+**Decision**: Download to tempfile, decode with claxon, expose PCM/WAV.
+
+**Rationale**:
+- Claxon is pure Rust (no C dependencies)
+- Tempfile ensures cleanup
+- WAV export is a common use case
+- Simple implementation
+
+**Alternatives Considered**:
+- **Streaming decode**: Too complex, claxon doesn't support seeking
+- **HTTP range requests**: Radio Paradise blocks don't support it reliably
+- **Caching decoded blocks**: Too much memory
+
+### 3. Helper Method for Players
+
+**Decision**: Provide `track_position_seconds()` to get timing for external players.
+
+**Rationale**:
+- Gives users the information they need
+- Doesn't dictate how to use it
+- Works with any player
+- Zero overhead
+
+## Data Model Decisions
+
+### 1. HashMap for Songs
+
+**Decision**: Use `HashMap<String, Song>` matching the API response.
+
+**Rationale**:
+- Matches JSON structure exactly
+- Easy serde deserialization
+- Provides `songs_ordered()` helper for iteration
+- Preserves all data from API
+
+### 2. Optional Fields
+
+**Decision**: Make many fields `Option<T>` (year, rating, cover, etc.).
+
+**Rationale**:
+- API doesn't always provide all fields
+- Future-proof against API changes
+- Explicit about what's guaranteed
+
+### 3. Extra Fields
+
+**Decision**: Use `#[serde(flatten)]` for unknown fields.
+
+**Rationale**:
+- Forwards compatibility
+- Don't break on new API fields
+- Can inspect raw data if needed
+
+## Testing Strategy
+
+### 1. Unit Tests
+
+- Inline tests for data model parsing
+- Tests for timing calculations
+- Builder pattern validation
+
+### 2. Integration Tests with Mocks
+
+**Decision**: Use `wiremock` for HTTP mocking.
+
+**Rationale**:
+- Don't hit real API in CI
+- Reproducible tests
+- Fast execution
+- Can test error conditions
+
+### 3. Example Programs
+
+**Decision**: Provide runnable examples for all major features.
+
+**Rationale**:
+- Examples serve as documentation
+- Users can copy-paste working code
+- Tested in CI (via `cargo test --doc`)
+
+## Documentation Strategy
+
+### 1. Extensive Rustdoc
+
+**Decision**: Document every public function, struct, and enum.
+
+**Rationale**:
+- Discoverability via docs.rs
+- IDE autocomplete shows docs
+- Examples in docs are tested
+- Professional appearance
+
+### 2. README with Use Cases
+
+**Decision**: Detailed README covering common scenarios.
+
+**Rationale**:
+- First thing users see
+- Explains design decisions
+- Guides users to best practices
+- Warns about per-track limitations
+
+### 3. Module-Level Documentation
+
+**Decision**: Each module has overview documentation.
+
+**Rationale**:
+- Explains purpose of module
+- Links to related modules
+- Top-down understanding
+
+## Performance Considerations
+
+### 1. Streaming vs Downloading
+
+- **Streaming** (`stream_block`): Low latency, constant memory
+- **Downloading** (`download_block`): Required for per-track, high memory
+
+### 2. Prefetching
+
+- Metadata prefetch is cheap (~1KB JSON)
+- Block prefetch is expensive (~50-100MB)
+- Leave block caching to users
+
+### 3. Connection Pooling
+
+**Decision**: Allow sharing `reqwest::Client`.
+
+**Rationale**:
+- Reuse connections
+- User controls connection pool size
+- Works with existing infrastructure
+
+## Future Extensions
+
+### Possible Additions (Not Implemented)
+
+1. **Channel Support**: Main mix, mellow, rock, world (API supports this)
+2. **Historical Blocks**: Fetch blocks by date/time
+3. **Playlist API**: If Radio Paradise adds it
+4. **WebSocket Live Updates**: Real-time now-playing updates
+5. **Caching Layer**: Optional disk cache for blocks
+
+### Why Not Included Now
+
+- Keep initial release focused
+- No user demand yet
+- Can add without breaking changes
+- Some features may require API changes
+
+## Lessons Learned
+
+### What Worked Well
+
+1. **Builder pattern**: Easy to extend
+2. **Feature gates**: Keeps default build fast
+3. **Strong typing**: Caught many bugs at compile time
+4. **Integration tests**: Gave confidence in refactoring
+
+### What Could Be Improved
+
+1. **FLAC seeking**: Claxon limitations make per-track expensive
+2. **Error messages**: Could be more actionable
+3. **Examples**: Could add more advanced patterns
+
+## Comparison with pmoqobuz
+
+### Similarities
+
+- Builder pattern for client
+- Serde models
+- Async/await
+- Integration with PMOMusic ecosystem
+
+### Differences
+
+- **No caching layer**: Radio Paradise API is simpler, less need
+- **Streaming focus**: Qobuz is track-based, Paradise is block-based
+- **No authentication**: Paradise API is public (for metadata)
+- **Feature gates**: Paradise has optional FLAC decoding
+
+## Conclusion
+
+This implementation prioritizes:
+1. **Ergonomics**: Easy for common cases, flexible for advanced
+2. **Performance**: Async, streaming, minimal allocations
+3. **Safety**: Type-safe, comprehensive error handling
+4. **Documentation**: Extensive docs and examples
+5. **Honesty**: Clear about limitations (per-track)
+
+The result is a production-ready library that's pleasant to use and maintains high code quality standards.