"""Shared dasha arithmetic used by the conditional-dasha modules.

This module must not import the API server or PyJHora. PyJHora stays a test
oracle only.
"""

from __future__ import annotations

NAKSHATRA_SPAN = 360.0 / 27.0

# Insertion order is the Vimshottari sequence. Callers compare items() before
# replacing a local table, and rely on this order staying stable.
VIMSHOTTARI_YEARS = {
    "Ketu": 7,
    "Venus": 20,
    "Sun": 6,
    "Moon": 10,
    "Mars": 7,
    "Rahu": 18,
    "Jupiter": 16,
    "Saturn": 19,
    "Mercury": 17,
}
VIMSHOTTARI_ORDER = list(VIMSHOTTARI_YEARS.keys())


def nakshatra_seeded_birth_balance(
    moon_longitude: float,
    *,
    anchor_index: int,
    sequence: tuple | list,
) -> tuple[str, float, int]:
    """Birth lord and remaining years for a nakshatra-seeded conditional dasha.

    The arithmetic matches the six copied helpers: offset from the anchor
    nakshatra, lord = sequence[offset % length], balance = years * (1 - fraction
    already elapsed inside the nakshatra). Operation order is fixed so the
    float matches the previous per-module copies.
    """
    moon = float(moon_longitude) % 360.0
    nakshatra_index = int(moon // NAKSHATRA_SPAN)
    offset = (nakshatra_index - int(anchor_index)) % 27
    lord, full_years = sequence[offset % len(sequence)]
    fraction_elapsed = (moon % NAKSHATRA_SPAN) / NAKSHATRA_SPAN
    remaining_years = full_years * (1.0 - fraction_elapsed)
    return lord, remaining_years, nakshatra_index