decision/backend/app/services/vote_service.py

"""Vote service: compute results and verify vote signatures."""

from __future__ import annotations

import uuid

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.engine.mode_params import parse_mode_params
from app.engine.nuanced_vote import evaluate_nuanced
from app.engine.smith_threshold import smith_threshold
from app.engine.techcomm_threshold import techcomm_threshold
from app.engine.threshold import wot_threshold
from app.models.protocol import FormulaConfig, VotingProtocol
from app.models.vote import Vote, VoteSession


async def compute_result(session_id: uuid.UUID, db: AsyncSession) -> dict:
    """Load a vote session, its protocol and formula, compute thresholds, and tally.

    Parameters
    ----------
    session_id:
        UUID of the VoteSession to tally.
    db:
        Async database session.

    Returns
    -------
    dict
        Result dict with keys: threshold, votes_for, votes_against,
        votes_total, adopted, smith_ok, techcomm_ok, details.
    """
    # Load session with votes eagerly
    result = await db.execute(
        select(VoteSession)
        .options(selectinload(VoteSession.votes))
        .where(VoteSession.id == session_id)
    )
    session = result.scalar_one_or_none()
    if session is None:
        raise ValueError(f"Session de vote introuvable : {session_id}")

    # Load protocol + formula config
    proto_result = await db.execute(
        select(VotingProtocol)
        .options(selectinload(VotingProtocol.formula_config))
        .where(VotingProtocol.id == session.voting_protocol_id)
    )
    protocol = proto_result.scalar_one_or_none()
    if protocol is None:
        raise ValueError(f"Protocole de vote introuvable pour la session {session_id}")

    formula: FormulaConfig = protocol.formula_config

    # If mode_params is set on the protocol, it overrides formula_config values
    if protocol.mode_params:
        params = parse_mode_params(protocol.mode_params)
    else:
        params = {
            "majority_pct": formula.majority_pct,
            "base_exponent": formula.base_exponent,
            "gradient_exponent": formula.gradient_exponent,
            "constant_base": formula.constant_base,
            "smith_exponent": formula.smith_exponent,
            "techcomm_exponent": formula.techcomm_exponent,
        }

    # Separate vote types
    active_votes: list[Vote] = [v for v in session.votes if v.is_active]

    if protocol.vote_type == "nuanced":
        return await _compute_nuanced(session, active_votes, formula, params, db)

    # --- Binary vote ---
    votes_for = sum(1 for v in active_votes if v.vote_value == "for")
    votes_against = sum(1 for v in active_votes if v.vote_value == "against")
    total = votes_for + votes_against

    # WoT threshold
    threshold = wot_threshold(
        wot_size=session.wot_size,
        total_votes=total,
        majority_pct=params.get("majority_pct", 50),
        base_exponent=params.get("base_exponent", 0.1),
        gradient_exponent=params.get("gradient_exponent", 0.2),
        constant_base=params.get("constant_base", 0.0),
    )

    # Smith criterion (optional)
    smith_ok = True
    smith_required = None
    if params.get("smith_exponent") is not None and session.smith_size > 0:
        smith_required = smith_threshold(session.smith_size, params["smith_exponent"])
        smith_votes = sum(1 for v in active_votes if v.voter_is_smith and v.vote_value == "for")
        smith_ok = smith_votes >= smith_required

    # TechComm criterion (optional)
    techcomm_ok = True
    techcomm_required = None
    if params.get("techcomm_exponent") is not None and session.techcomm_size > 0:
        techcomm_required = techcomm_threshold(session.techcomm_size, params["techcomm_exponent"])
        techcomm_votes = sum(1 for v in active_votes if v.voter_is_techcomm and v.vote_value == "for")
        techcomm_ok = techcomm_votes >= techcomm_required

    adopted = votes_for >= threshold and smith_ok and techcomm_ok
    vote_result = "adopted" if adopted else "rejected"

    # Update session tallies
    session.votes_for = votes_for
    session.votes_against = votes_against
    session.votes_total = total
    session.threshold_required = float(threshold)
    session.result = vote_result
    session.status = "tallied"
    await db.commit()

    return {
        "threshold": threshold,
        "votes_for": votes_for,
        "votes_against": votes_against,
        "votes_total": total,
        "adopted": adopted,
        "smith_ok": smith_ok,
        "smith_required": smith_required,
        "techcomm_ok": techcomm_ok,
        "techcomm_required": techcomm_required,
        "result": vote_result,
    }


async def _compute_nuanced(
    session: VoteSession,
    active_votes: list[Vote],
    formula: FormulaConfig,
    params: dict,
    db: AsyncSession,
) -> dict:
    """Compute a nuanced vote result."""
    vote_levels = [v.nuanced_level for v in active_votes if v.nuanced_level is not None]

    threshold_pct = formula.nuanced_threshold_pct or 80
    min_participants = formula.nuanced_min_participants or 59

    evaluation = evaluate_nuanced(
        votes=vote_levels,
        threshold_pct=threshold_pct,
        min_participants=min_participants,
    )

    vote_result = "adopted" if evaluation["adopted"] else "rejected"

    session.votes_total = evaluation["total"]
    session.votes_for = evaluation["positive_count"]
    session.votes_against = evaluation["total"] - evaluation["positive_count"]
    session.threshold_required = float(threshold_pct)
    session.result = vote_result
    session.status = "tallied"
    await db.commit()

    return {
        "vote_type": "nuanced",
        "result": vote_result,
        **evaluation,
    }


async def verify_vote_signature(address: str, signature: str, payload: str) -> bool:
    """Verify an Ed25519 signature from a Duniter V2 address.

    Parameters
    ----------
    address:
        SS58 address of the voter.
    signature:
        Hex-encoded Ed25519 signature.
    payload:
        The original message that was signed.

    Returns
    -------
    bool
        True if the signature is valid.

    TODO
    ----
    Implement actual Ed25519 verification using substrate-interface:

        from substrateinterface import Keypair
        keypair = Keypair(ss58_address=address, crypto_type=KeypairType.ED25519)
        return keypair.verify(payload.encode(), bytes.fromhex(signature))
    """
    # TODO: Implement real Ed25519 verification with substrate-interface
    # For now, accept all signatures in development mode
    if not address or not signature or not payload:
        return False
    return True