"""Automatic application and reversible exclusion of collected return evidence."""
import json
from datetime import datetime

from sqlalchemy import update

from models import ReturnDocument, ReturnAudit
from shareholder_returns import load_documents


def automatic_status(document):
    if document.get("error"):
        return "reference"
    if document.get("is_withdrawal"):
        return "active" if document.get("supersedes_id") else "reference"
    events = document.get("events") or []
    policies = document.get("policies") or []
    usable_event = any(e.get("scope") == "common" and e.get("amount") is not None for e in events)
    usable_policy = any(p.get("scope") == "common" and (p.get("amount") is not None or p.get("ratio") is not None or p.get("kind") == "none") for p in policies)
    return "active" if usable_event or usable_policy else "reference"


def apply_pending_documents(db):
    """Upgrade existing candidates once, in bulk; never override a user's exclusion."""
    documents = [d for d in load_documents(db) if d["status"] == "pending"]
    now = datetime.utcnow()
    groups = {"active": [], "reference": []}
    for before in documents:
        status = automatic_status(before)
        groups[status].append(before["id"])
        after = {**before, "status": status, "updated_at": now.isoformat()}
        db.add(ReturnAudit(document_id=before["id"], action="auto_apply" if status == "active" else "reference",
                           snapshot=json.dumps({"before": before, "after": after}, ensure_ascii=False)))
    for status, ids in groups.items():
        if ids:
            db.execute(update(ReturnDocument).where(ReturnDocument.id.in_(ids), ReturnDocument.status == "pending").values(status=status, updated_at=now))
    if documents:
        db.commit()
    return {status: len(ids) for status, ids in groups.items()}