"""Salvage value (scrap value) calculation helpers.

Most clients use straight % of cost; some use fixed dollar amounts.
"""

from dataclasses import dataclass
from typing import Literal


SalvageMethod = Literal['percentage', 'fixed', 'zero']


@dataclass
class SalvageConfig:
    method: SalvageMethod
    value: float = 0.0


def compute_salvage_value(*, cost: float, config: SalvageConfig) -> float:
    """Compute end-of-life salvage value."""
    if config.method == 'zero':
        return 0.0
    if config.method == 'percentage':
        return round(cost * config.value / 100, 2)
    if config.method == 'fixed':
        return round(config.value, 2)
    raise ValueError(f"Unknown salvage method: {config.method}")


def remaining_useful_life_value(*, current_book: float, salvage: float,
                                periods_used: int, total_periods: int) -> float:
    """Estimate remaining value if asset is sold/scrapped now."""
    if total_periods <= 0:
        return current_book
    if periods_used >= total_periods:
        return salvage
    remaining_pct = (total_periods - periods_used) / total_periods
    return round(salvage + (current_book - salvage) * remaining_pct, 2)