"""Snapshot diff logic."""
from typing import Any, Optional

from sqlalchemy.orm import Session

from app.models.snapshot import UpstreamRateSnapshot


def diff_snapshots(
    previous: Optional[dict[str, Any]],
    current: dict[str, Any],
) -> list[dict[str, Any]]:
    """Return list of rate changes between previous and current snapshots.
    Returns empty list if previous is None (first check)."""
    if not previous:
        return []
    old_groups: dict[str, Any] = previous.get("groups") or {}
    new_groups: dict[str, Any] = current.get("groups") or {}
    changes: list[dict[str, Any]] = []
    for gid, new_g in sorted(new_groups.items()):
        if not isinstance(new_g, dict):
            continue
        old_g = old_groups.get(gid)
        old_rate = old_g.get("rate") if isinstance(old_g, dict) else None
        new_rate = new_g.get("rate")
        if old_rate != new_rate:
            changes.append({
                "group_id": gid,
                "group_name": new_g.get("group_name", ""),
                "platform": new_g.get("platform", ""),
                "old_rate": old_rate,
                "new_rate": new_rate,
            })
    for gid, old_g in sorted(old_groups.items()):
        if gid not in new_groups and isinstance(old_g, dict):
            changes.append({
                "group_id": gid,
                "group_name": old_g.get("group_name", ""),
                "platform": old_g.get("platform", ""),
                "old_rate": old_g.get("rate"),
                "new_rate": None,
            })
    return changes


def prune_snapshots(db: Session, upstream_id: int, keep: int) -> None:
    if keep <= 0:
        return
    stale_ids = [
        row_id
        for (row_id,) in (
            db.query(UpstreamRateSnapshot.id)
            .filter(UpstreamRateSnapshot.upstream_id == upstream_id)
            .order_by(UpstreamRateSnapshot.captured_at.desc(), UpstreamRateSnapshot.id.desc())
            .offset(keep)
            .all()
        )
    ]
    if stale_ids:
        db.query(UpstreamRateSnapshot).filter(UpstreamRateSnapshot.id.in_(stale_ids)).delete(synchronize_session=False)