Translation Service Layer

The Translation Service Layer sits between the document format handlers and the external TMT API. Its job is to take large, unstructured text extracted from a document and produce translated text efficiently — without hammering the API or doing redundant work.

Responsibilities

• Text segmentation — split raw strings into sentences using linguistic delimiters (., !, ?, and the Devanagari danda ।).
• Concurrency management — an async Semaphore limits the number of simultaneous API requests.
• Deduplication & caching — identical sentences within or across documents are translated only once.
• In-flight merging — if two tasks request the same sentence at the same time, only one network call is made; the second waits on a tokio::sync::oneshot channel for the result.

Service Constraints

Pipeline Flow

Document Handler
      │
      │  raw text block
      ▼
TranslationService::translate_text()
      │
      ├─ split_sentences()          # split on . ! ? ।
      │
      ├─ for each sentence:
      │     ├─ cache hit?  ──▶  return cached result
      │     ├─ in-flight?  ──▶  wait on oneshot channel
      │     └─ new request ──▶  acquire Semaphore permit
      │                              │
      │                        TmtClient::translate()
      │                              │
      │                         (rate limiting / retry)
      │                              │
      │                         translated sentence
      │
      └─ rejoin sentences ──▶  translated text block

Sub-pages

• TranslationService & Sentence Splitting
• TMT API Client
• Rate Limiting & Backoff