✨ Accumulate tally endpoint (#62)

* New endpoint for tally accumulation

* Update the Postman collection with sample tally accumulation requests

Author: rkorsak

app/api/v1/api.py

@@ -1,9 +1,10 @@
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import ballot, election, key, ping
+from app.api.v1.endpoints import ballot, election, key, ping, tally
 
 api_router = APIRouter()
 api_router.include_router(ping.router, prefix="/ping", tags=["ping"])
 api_router.include_router(election.router, prefix="/election", tags=["election"])
 api_router.include_router(ballot.router, prefix="/ballot", tags=["ballot"])
 api_router.include_router(key.router, prefix="/key", tags=["key"])
+api_router.include_router(tally.router, prefix="/tally", tags=["tally"])

app/api/v1/endpoints/tally.py

@@ -0,0 +1,68 @@
+from electionguard.ballot import CiphertextAcceptedBallot
+from electionguard.election import (
+    CiphertextElectionContext,
+    ElectionDescription,
+    InternalElectionDescription,
+)
+from electionguard.tally import (
+    publish_ciphertext_tally,
+    CiphertextTally,
+    PublishedCiphertextTally,
+)
+from fastapi import APIRouter, Body, HTTPException
+from pydantic import BaseModel
+from typing import Any, List, Optional
+
+router = APIRouter()
+
+
+class AccumulateTallyRequest(BaseModel):
+    ballots: List[Any]
+    encrypted_tally: Optional[Any] = None
+    description: Any
+    context: Any
+
+
+@router.post("/accumulate")
+def accumulate_tally(request: AccumulateTallyRequest = Body(...)) -> Any:
+    """
+    Accumulate ballots into a new or existing tally
+    """
+
+    ballots = [
+        CiphertextAcceptedBallot.from_json_object(ballot) for ballot in request.ballots
+    ]
+    description = ElectionDescription.from_json_object(request.description)
+    internal_description = InternalElectionDescription(description)
+    context = CiphertextElectionContext.from_json_object(request.context)
+    published_tally: Optional[PublishedCiphertextTally] = (
+        PublishedCiphertextTally.from_json_object(request.encrypted_tally)
+        if request.encrypted_tally
+        else None
+    )
+
+    tally = _get_new_or_existing_tally(internal_description, context, published_tally)
+
+    tally_succeeded = tally.batch_append(ballots)
+
+    if tally_succeeded:
+        published_tally = publish_ciphertext_tally(tally)
+        return published_tally.to_json_object()
+    else:
+        raise HTTPException(
+            status_code=500, detail="Tally accumulation was unsuccessful"
+        )
+
+
+def _get_new_or_existing_tally(
+    description: ElectionDescription,
+    context: CiphertextElectionContext,
+    published_tally: PublishedCiphertextTally,
+) -> CiphertextTally:
+    if not published_tally:
+        return CiphertextTally("election-results", description, context)
+
+    full_tally = CiphertextTally(published_tally.object_id, description, context)
+    full_tally.cast = published_tally.cast
+
+    return full_tally