"""Offset / silence duration calculation."""

from midmid.beat_tracker import BeatData


def calculate_offset(
    beat_data: BeatData,
    bpm: float,
    beats_per_measure: int = 4,
    min_lead_in: float = 2.0,
) -> float:
    """Calculate silence duration to prepend to the audio."""
    if len(beat_data.downbeats) == 0:
        return min_lead_in

    first_downbeat = float(beat_data.downbeats[0])
    measure_duration = beats_per_measure * 60.0 / bpm

    n = 1
    while n * measure_duration < min_lead_in:
        n += 1

    silence = n * measure_duration - first_downbeat

    while silence < 0:
        n += 1
        silence = n * measure_duration - first_downbeat

    return silence