from __future__ import annotations

from decimal import Decimal, ROUND_HALF_UP
from typing import Any

TWOPLACES = Decimal("0.01")


def _money(value: Decimal) -> Decimal:
    return value.quantize(TWOPLACES, rounding=ROUND_HALF_UP)


def load_usage_records(data_dir) -> list[dict[str, Any]]:
    from pathlib import Path

    from .load import _read_json, default_data_dir

    root = data_dir or default_data_dir()
    path = Path(root) / "usage_records.json"
    if not path.exists():
        return []
    raw = _read_json(path)
    return list(raw.get("records", []))


def build_usage_summary(records: list[dict[str, Any]], period: str) -> dict:
    period_rows = [row for row in records if row.get("period") == period]
    by_member: dict[str, Decimal] = {}
    by_model: dict[str, Decimal] = {}
    total = Decimal("0")

    for row in period_rows:
        cost = Decimal(str(row.get("cost_eur", "0")))
        total += cost
        member_id = row.get("member_id") or "unknown"
        model = row.get("model") or "unknown"
        by_member[member_id] = by_member.get(member_id, Decimal("0")) + cost
        by_model[model] = by_model.get(model, Decimal("0")) + cost

    active_members = len(by_member) or 1
    return {
        "period": period,
        "total_ai_spend_eur": _money(total),
        "cost_per_active_user_eur": _money(total / active_members),
        "by_member": {key: _money(value) for key, value in sorted(by_member.items())},
        "by_model": {key: _money(value) for key, value in sorted(by_model.items())},
        "record_count": len(period_rows),
    }