Refactor: ASR Engine Abstraction and Service Layer Cleanup

🚀 Refactor: Engine Logic Abstraction

📌 Overview

This MR refactors the ASR engine architecture to improve modularity, remove circular dependencies, and enforce a clean separation of concerns. The changes align the system with scalable design principles, making it easier to maintain and extend with new ASR engines.

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❗ Problem

The previous architecture had several issues:

• Circular Dependency

  • SwechaGonthukaEngine depended on asr_service.py, while asr_service.py also depended on engines.

• God Object

  • asr_service.py handled multiple responsibilities:

    • Transcription logic
    • Audio conversion
    • Punctuation
    • Subtitle generation

• Inconsistent Engine Design

  • Swecha engine was not self-contained
  • Whisper engine followed a cleaner structure

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✅ Solution

This MR introduces a structured refactor:

• Engine Self-Containment

  • Moved all Swecha-specific logic into SwechaGonthukaEngine
  • Removed dependency on asr_service.py

• Abstract Engine Interface

  • Introduced AsrEngine base class (app/asr/types.py)

  • Standardized engine contract:

    • transcribe
    • transcribe_pcm16
    • name
    • supported_languages

• Service Layer Cleanup

  • Removed engine-specific logic from asr_service.py
  • Retained only cross-cutting responsibilities

• Router Simplification

  • Router now directly calls engine methods
  • Removed dynamic mutation of engine configuration

• Whisper Engine Refactor

  • Supports constructor-based configuration
  • Improved consistency with Swecha engine

• Service Extraction

  • Introduced:

    • JobManager → handles async job lifecycle
    • StreamingService → handles WebSocket streaming

  • Reduced responsibility of main.py

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🔧 Key Changes

Modified Files

• app/asr/engines/swecha_gonthuka.py
• app/asr/engines/whisper.py
• app/asr/router.py
• app/asr/types.py
• app/asr_service.py
• app/main.py

New Files

• app/services/job_manager.py
• app/services/streaming_service.py

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🧪 Testing

• Existing test suite reviewed and executed

• Verified:

  • Engine routing behavior
  • Batch transcription flow (/transcribe)
  • Streaming functionality (/stream)

• No regression in API responses

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🎯 Impact

• Eliminates circular dependencies
• Enforces Single Responsibility Principle
• Enables easy addition of new ASR engines
• Improves code readability and maintainability
• Aligns architecture with scalable backend design

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🚫 Out of Scope

• No changes to ASR models
• No changes to API contracts
• No changes to deployment setup

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🧠 Summary

This refactor transforms the ASR system into a clean, modular, and extensible architecture by introducing a unified engine interface and decoupling responsibilities across layers.

*Closes #17 (closed)