"""Multi-currency conversion for financial reports.

Converts move-line amounts to the report's display currency at the
report end-date. Pure-Python - caller provides exchange rates as a
dict {(source_code, target_code, date): rate}."""

from dataclasses import dataclass
from datetime import date


@dataclass
class ConversionRate:
    source: str
    target: str
    rate: float
    rate_date: date


def convert_amount(amount: float, *, source_currency: str, target_currency: str,
                   rate_date: date, rates: dict) -> float:
    """Convert `amount` from source to target at the given date.

    `rates` is a dict keyed by (source, target, date) -> rate.
    If source == target, returns amount unchanged."""
    if source_currency == target_currency:
        return amount
    key = (source_currency, target_currency, rate_date)
    if key in rates:
        return amount * rates[key]
    inv_key = (target_currency, source_currency, rate_date)
    if inv_key in rates:
        inv = rates[inv_key]
        if inv != 0:
            return amount / inv
    candidates = [
        (d, r) for (s, t, d), r in rates.items()
        if s == source_currency and t == target_currency and d <= rate_date
    ]
    if candidates:
        candidates.sort(key=lambda x: x[0], reverse=True)
        return amount * candidates[0][1]
    raise ValueError(
        f"No exchange rate available for {source_currency}->{target_currency} on or before {rate_date}"
    )


def fetch_rates(env, *, target_currency_id: int, as_of: date,
                source_currency_ids: list[int] | None = None) -> dict:
    """Fetch all relevant rates from res.currency.rate as of a given date.

    Returns the dict-of-rates structure consumed by convert_amount.
    Pulls only rates where source != target and date <= as_of."""
    Rate = env['res.currency.rate'].sudo()
    target = env['res.currency'].browse(target_currency_id)
    domain = [
        ('name', '<=', as_of),
        ('currency_id', '!=', target.id),
    ]
    if source_currency_ids:
        domain.append(('currency_id', 'in', source_currency_ids))
    rates_recs = Rate.search(domain)

    out = {}
    for r in rates_recs:
        out[(r.currency_id.name, target.name, r.name)] = (1.0 / r.rate) if r.rate else 0.0
    return out